JP5071149B2 - Liquid optical element - Google Patents

Description

  The present invention relates to a liquid optical element utilizing a phenomenon in which a liquid is deformed and displaced by electrowetting for electrostatically controlling paintability.

  2. Description of the Related Art Conventionally, a phenomenon in which a liquid is deformed and displaced by electrowetting that electrostatically controls paintability is known. This phenomenon is caused, for example, when the conductive droplet 213 is disposed between the insulating film 211 formed on the surface of the electrode 210 and the electrode 212 as shown in FIG. Further, when a voltage is applied between the electrode 212 and the electrode 212, the paintability of the insulating film 211 changes according to the voltage. That is, as the wettability of the insulating film 211 changes, the contact angle θ of the droplet 213 with respect to the insulating film 211 changes, and the droplet 213 is deformed and displaced. In this case, the relationship between the wettability of the insulating film 211 and the contact angle θ of the droplet 213 with respect to the insulating film 211 is explained by the equation shown in Equation 1.

(Equation 1)
γ _LV cos θ = γ _SV −γ _SL + γ _EW (1)
γ _EW = (d × σ _L ² ) / (2 × ε ₀ × ε _r ) (2)
σ _L = ε ₀ × ε _r × V / d (3)
(Γ _LV represents the interfacial tension between liquid and gas, γ _SV represents the interfacial tension between solid and gas, γ _SL represents the interfacial tension between solid and liquid, and γ _EW represents the interfacial tension due to the strength of the electric field. Ε ₀ represents the dielectric constant of the vacuum, ε _r represents the dielectric constant of the insulating film 111, V represents the magnitude of the applied voltage, and d represents the distance between the electrodes 110 and 112. )

  It is known that such a phenomenon using electrowetting occurs even when two types of liquids having different conductivity and not mixed are used. In the case of using these two kinds of liquids, a water repellent film is generally used as the insulating film, and the two kinds of liquids having a polarity including water and a nonpolar electrode including silicon oil or a hydrocarbon-based material. Liquid is used. The technique using the water repellent film and two kinds of liquids having different polarities is attracting attention because it can be applied in various fields.

Specifically, a technique is known that uses a difference in refractive index between two types of liquids as a microlens provided in a zoom lens or a display device (see, for example, Patent Documents 1 and 2). In addition, a technique is known in which a dye or the like is dissolved or dispersed in one of two types of liquid and used for a display device using a difference in light transmittance between the two types of liquid (for example, Patent Documents). 3 and 4).
JP-T-2006-504132 JP 2006-267386 A JP 2000-356750 A Special table 2007-500876 gazette

  In the techniques of Patent Documents 1 to 4 described above, an inorganic salt is contained in a polar liquid in order to enable use even in a low temperature environment. For this reason, when a voltage is applied to the electrodes, the inorganic salt is ionized and becomes impurity ions that are accumulated or adsorbed on the surface of the water-repellent film. It was.

  The present invention has been made in view of such problems, and an object thereof is to provide a liquid optical element capable of ensuring low temperature characteristics and improving voltage holding performance.

  The liquid optical element of the present invention includes a first electrode having an insulating film formed on the surface, a second electrode disposed opposite to the insulating film side of the first electrode, the first electrode, and the second electrode It is provided with a transparent polar liquid and an opaque nonpolar liquid that are sealed between the electrodes and kept separated from each other. The polar liquid is a mixed liquid of water and alcohol, and the impurity ion concentration in the mixed liquid is set to be equal to or lower than the concentration at which the voltage holding ratio between the first electrode and the second electrode is 90%. . This “voltage holding ratio” is the ratio of the amount of charge held after a predetermined time has elapsed with respect to the amount of charge charged when a voltage is applied between the electrodes. Furthermore, “impurity ions” are inorganic or organic ions that cause a decrease in voltage holding ratio, for example, lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, chloride ions. , Nitrate ions, sulfate ions, phosphate ions, acetate ions, or those obtained by decomposing and ionizing constituent materials such as partition walls or dyes. For example, the insulating film preferably has a higher affinity with the nonpolar liquid than the polar liquid described above in the absence of an electric field.

  In the liquid optical element of the present invention, when a driving voltage is applied between the first electrode and the second electrode, the wettability of the insulating film formed on the surface of the first electrode changes electrostatically. As a result, the polar liquid and the nonpolar liquid are deformed and displaced so that the light transmittance is increased. Therefore, since the polar liquid is a mixed liquid of water and alcohol, it becomes difficult for the polar liquid to solidify when exposed to a low-temperature environment. When returning to the state, the polar liquid and the nonpolar liquid are rapidly deformed and displaced. In addition, when the impurity ion concentration in the polar liquid is equal to or lower than the concentration at which the voltage holding ratio between the first electrode and the second electrode is 90%, when a driving voltage is applied between both electrodes, Since the amount of impurity ions accumulated or adsorbed on the surface of the insulating film is small, a decrease in voltage holding ratio is suppressed.

  According to the liquid optical element of the present invention, the polar liquid is a mixed liquid of water and alcohol, and the impurity ion concentration in the mixed liquid is 90% between the first electrode and the second electrode. Since the concentration is equal to or less than%, the low temperature characteristics can be secured and the voltage holding property can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional configuration of a liquid optical element according to an embodiment of the present invention. 2 shows an enlarged view of one cell included in the liquid optical element shown in FIG. 1, and FIG. 3 shows a planar configuration of the cell of the liquid optical element shown in FIG. 2A and 3A show a state in which the driving voltage is not applied, and FIGS. 2B and 3B show a state in which the driving voltage is applied. As shown in FIG. 1, the liquid optical element includes a cell electrode substrate 10 and a counter electrode substrate 20 which are arranged to face each other, and a transparent polar liquid 30 sealed between the cell electrode substrate 10 and the counter electrode substrate 20. And an opaque nonpolar liquid 40. This liquid optical element is a so-called transmission-type liquid optical element that includes a plurality of cells shown in FIG. 2 and controls the amount of transmitted light, and is used for a display device, a shutter of a camera, a diaphragm, or the like.

  The cell electrode substrate 10 includes a plurality of cell electrodes 12 that are divided into a matrix and formed on the surface of the transparent substrate 11 on the counter electrode substrate 20 side, and a water repellent formed so as to cover the surface of each cell electrode 12. The film 13 and the partition wall 14 formed on the water-repellent film 13 so as to surround each cell are configured. The cell electrode 12 corresponds to a specific example of “first electrode” of the present invention, and the water repellent film 13 corresponds to a specific example of “insulating film” formed on the surface of the first electrode of the present invention. Correspond.

  The cell electrode substrate 10 is preferably washed with pure water having an impurity ion concentration of 50 ppm or less. This is because the impurity ion concentration in the polar liquid 40 can be kept low.

  The transparent substrate 11 is made of a transparent (light transmissive) material such as glass, silicon, or plastic.

  The cell electrode 12 is one electrode for applying a driving voltage between the cell electrode substrate 10 and the counter electrode substrate 20 to control the paintability of the water repellent film 13. The cell electrode 12 is a transparent electrode having optical transparency, for example, and is made of a transparent electrode material such as indium tin oxide (ITO) or zinc oxide.

  The water repellent film 13 is an insulating film whose paintability is changed electrostatically by a driving voltage applied between the cell electrode substrate 10 and the counter electrode substrate 20. The contact area of the water repellent film 13 with the polar liquid 30 and the nonpolar liquid 40 varies depending on the wettability of the water repellent film 13 that is an insulating film. The water repellent film 13 preferably has a higher affinity with the nonpolar liquid 40 than the polar liquid 30 under no electric field, and preferably has a higher surface hydrophobicity than the polar liquid 30 and the nonpolar liquid 40. Examples of the material of the water repellent film 13 include a fluorine-based polymer such as polyvinylidene fluoride or polytetrafluoroethylene, and specifically, a Teflon AF (AF1601S system having a relative dielectric constant of about 2; manufactured by DuPont). (Teflon is a registered trademark)) and Cytop (Asahi Glass Co., Ltd.). The water repellent film 13 may have a structure in which a water repellent layer is laminated on an insulating layer in order to enhance insulation. Examples of the material for the insulating layer used in this case include silica-based materials.

  The partition wall 14 is opaque, and is for limiting a region where the nonpolar liquid 40 moves on the surface of the water repellent film 13. The partition wall 14 is provided on the water-repellent film 13 between the cells, that is, between the cell electrodes 12 so as to surround each cell. The partition wall 14 is formed, for example, by a photolithography method, and examples of the material include an opaque resist material such as a black resist. The barrier ribs 14 are arbitrary as long as they block light transmission between the cell electrodes 12, and may have a structure in which a transparent layer is laminated on an opaque layer. Examples of the transparent layer material used in this case include a transparent resist material such as SU8 (manufactured by Kayaku Microchem).

  The counter electrode substrate 20 has a configuration in which a counter electrode 22 is formed on the surface of the transparent substrate 21 on the cell electrode substrate 10 side. As with the cell electrode substrate 10, the counter electrode substrate 20 is preferably cleaned with pure water having an impurity ion concentration of 50 ppm or less. This is because the impurity ion concentration in the polar liquid 40 can be kept low. The counter electrode substrate 20 may be formed by forming an insulating film having a lower hydrophobicity than the water repellent film 13 on the surface of the counter electrode 22. The transparent substrate 21 is made of the same material as that of the transparent substrate 11, for example. The counter electrode 22 is another electrode for applying a voltage between the cell electrode substrate 10 and the counter electrode substrate 20, and is made of, for example, the same material as that of the cell electrode 12.

  The polar liquid 30 is a transparent liquid that does not mix with the nonpolar liquid 40 (ie, keeps separated from each other). The polar liquid 30 is a mixed liquid of water and alcohol, and the impurity ion concentration in the mixed liquid is not higher than the concentration at which the voltage holding ratio between the cell electrode 12 and the counter electrode 22 is 90%. is there. Thereby, since alcohol is included in addition to water, coagulation is suppressed even when exposed to a low temperature environment. Further, since the impurity ion concentration is low, the amount of impurity ions accumulated or adsorbed on the surface of the water repellent film 13 can be made small, and a driving voltage is repeatedly applied between the cell electrode 12 and the counter electrode 22. Even in this case, a decrease in the voltage holding ratio is suppressed. Therefore, low temperature characteristics are ensured and voltage retention is improved.

  The mixing ratio of water and alcohol in the polar liquid 30 is arbitrary as long as a dye or pigment contained in the nonpolar liquid 40 described later does not elute into the polar liquid 30. However, when the proportion of the alcohol in the polar liquid 30 is increased, solidification of the polar liquid 30 and a decrease in the voltage holding ratio are further suppressed, and a driving voltage is not applied as described later (FIG. 2 ( Since the contact angle of the nonpolar liquid 40 with respect to the water-repellent film 13 in the state A) and the state shown in FIG. On the other hand, if the proportion of the alcohol in the polar liquid 30 is too large, the dye or pigment contained in the nonpolar liquid 40 may be eluted into the polar liquid 30. Therefore, the proportion of alcohol in the polar liquid 30 is preferably 10% by weight to 60% by weight, that is, the proportion of water in the polar liquid 30 is preferably 40% by weight to 90% by weight. .

  The polar liquid 30 is preferably a mixed liquid of pure water having an impurity ion concentration of 50 ppm or less and an alcohol having a purity of 99.5% or more. This is because a decrease in voltage holding ratio is suppressed. Examples of the pure water include those having a specific resistance value of 18 MΩ · cm or more, and specifically, pure water for precision equipment cleaning produced by an ultrapure water production system manufactured by Millipore. In addition, the alcohol preferably has a very small content of impurity ions, and since it has high polarity, it is preferably a lower alcohol. Examples of the lower alcohol include methanol (MeOH), ethanol (EtOH), isopropyl alcohol (iPrOH), and ethylene glycol. These may be used alone or in combination of two or more. Of these, methanol, ethanol, or a mixture of methanol and ethanol is preferable. This is because the polarity can be increased when methanol is used, and the safety can be increased when ethanol is used.

The nonpolar liquid 40 is an opaque liquid that does not mix with the polar liquid 30 (that is, maintains a state separated from each other), and includes, for example, a nonpolar solvent or dispersion medium and a dye or pigment. Examples of the nonpolar solvent or dispersion medium include octane (C ₈ H ₁₈ ), decane (C ₁₀ H ₂₂ ), undecane (C ₁₁ H ₂₄ ), dodecane (C ₁₂ H ₂₆ ), and hexadecane (C ₁₆ H _34). ) And the like, and silicon oil. These may be used alone or in combination of two or more. Examples of pigments or dyes include carbon black and sudan black.

  In this liquid optical element, the contact angle of the nonpolar liquid 40 with respect to the water repellent film 13 in a state where no driving voltage is applied (the state shown in FIGS. 2A and 3A) is the water repellent film 13. The contact angle is preferably small (the cosine value of the contact angle is close to 1), although it varies depending on the hydrophobicity and the composition of the polar liquid 30 and the nonpolar liquid 40. Even when the driving voltage is low, the response time until the polar liquid 30 and the nonpolar liquid 40 reach the state shown in FIGS. 2 (B) and 3 (B) from FIG. 2 (A) and FIG. 3 (A). This is because the response speed is increased.

  In addition, the contact angle of the nonpolar liquid 40 with respect to the above-mentioned water-repellent film 13 can be calculated | required with the measuring method shown, for example in FIG. That is, as shown in FIG. 4, the container 100 filled with the polar liquid 30A and the substrate 101 on which the water repellent film 13A is formed are placed in the container 100 so that the surface of the water repellent film 13A faces downward. The nonpolar liquid 40A is placed on the surface of the water repellent film 13A by the saddle type syringe 102. In this case, the contact angle θ can be obtained by measuring the angle of the nonpolar liquid 40A with respect to the water repellent film 13A. However, the polar liquid 30A in the case shown in FIG. 4 is a liquid having polarity, and the nonpolar liquid 40A is a liquid that does not mix with the polar liquid 30A. FIG. 4 is an example of a measurement method for obtaining the contact angle θ when the specific gravity of the nonpolar liquid 40A is smaller than the specific gravity of the polar liquid 30A.

  Further, the contact angle of the nonpolar liquid 40 with respect to the water repellent film 13 can be estimated by reference data to be described later, for example. Next, details of this reference data will be described.

(Reference data 1-1 to 1-8)
The contact angle θ was determined by the measurement method shown in FIG. At that time, the polar liquid 30A is composed of a mixture of water and methanol (MeOH) mixed at a ratio shown in Table 1, the nonpolar liquid 40A is composed of dodecane (C ₁₂ H ₂₆ ), and Cytop (manufactured by Asahi Glass Co., Ltd.). The contact angle θ was determined using the substrate 101 on which the water repellent film 13A was formed. In this reference data, a nonpolar liquid 40A that does not contain a dye or pigment is used.

(Reference data 1-9 to 1-13, 1-14 to 1-18)
Except that decane (C ₁₀ H ₂₂ ; reference data 1-9 to 1-13) or octane (C ₈ H ₁₈ ; reference data 1-14 to 1-18) was used instead of dodecane as the nonpolar liquid, The contact angle θ was determined in the same manner as the reference data 1-1, 1-2, 1-4, 1-6, or 1-8.

(Reference data 2-1, 2-2)
Contact as in Reference Data 1-6, except that a mixed liquid of water and ethanol (EtOH; Reference Data 2-1) or isopropyl alcohol (iPrOH; Reference Data 2-2) was used as the polar liquid 30A. The angle θ was determined.

  When the cosine value (cos θ) of the contact angle θ was calculated for these reference data 1-1 to 1-18, the results shown in Table 1 and FIG. 5 were obtained. Further, when the cosine value of the contact angle θ was obtained for the reference data 2-1 and 2-2, the results shown in Table 1 were obtained. FIG. 5 shows the relationship between the proportion (% by weight) of water in the polar liquid and the cosine value (cos θ) of the contact angle θ of the nonpolar liquid. In FIG. 5, reference data 1-1 to 1-8, reference data 1-9 to 1-13, and reference data 1-14 to 1-18 are shown as one data series.

  As shown in Table 1 and FIG. 5, from the results of the reference data 1-1 to 1-8, when dodecane is used as the nonpolar liquid 40A, the proportion of water in the polar liquid 30A is 40% by weight. In the range of 90% by weight or less, it was confirmed that the cosine value is about 0.8 or more and tends to have a good contact angle θ. Further, from the results of the reference data 1-9 to 1-13 and the reference data 1-14 to 1-18, even when decane or octane is used as the nonpolar liquid 40A, the reference data 1-1 to 1-8 It was confirmed that the same tendency was exhibited. That is, regardless of the type of nonpolar liquid, the cosine value is about 0.8 or more when the proportion of water in the polar liquid 30A is in the range of 40% by weight to 90% by weight, and a good contact angle θ. Turned out to be.

  Further, from the results of the reference data 1-6, 2-1, and 2-2, if the alcohol mixed in the polar liquid 30A is a lower alcohol, a good contact angle θ is obtained. If the alcohol includes methanol, a better contact is obtained. It was confirmed that the angle θ was obtained.

(Reference data 3-1 to 3-5)
The contact angle θ was determined in the same manner as in Reference Data 1-4, except that a liquid in which sudan black was dissolved in dodecane was used as the nonpolar liquid 40A. At this time, in Reference Data 3-1, sudan black was dissolved in dodecane so that the transmittance of the 10 μm-thick nonpolar liquid 40A was 10%. Further, in the reference data 3-2 to 3-5, the concentration of sudan black in the nonpolar liquid 40A is 50% (reference data 3-2) and 33.3% (reference data 3) with respect to the reference data 3-1. -3), 14% (reference data 3-4) or 2% (reference data 3-5).

  When the cosine value of the contact angle θ was calculated for these reference data 3-1 to 3-5, the results shown in Table 2 and FIG. 6 were obtained. FIG. 6 shows the relationship between the relative concentration of sudan black in the nonpolar liquid (reference data 3-1 is 100%) and the cosine value (cos θ) of the contact angle θ.

  As shown in Table 2 and FIG. 6, the contact angle θ varies depending on the content of the dye or the like in the nonpolar liquid, but the amount of change is small and is the same as when the nonpolar liquid does not contain the dye or the like. It was confirmed that there was.

  From the results shown in Tables 1 and 2 and FIGS. 5 and 6, in the liquid optical element in the present embodiment, the contact angle of the nonpolar liquid 40 with respect to the water repellent film 13 is nonpolar in the state where the drive voltage is not applied. Regardless of the composition of the liquid 40, it is considered that the proportion of alcohol in the polar liquid 30 is affected. That is, it was confirmed that the contact angle of the nonpolar liquid 40 with respect to the water repellent film 13 can be estimated by the above reference data.

  Next, a method for manufacturing the above-described liquid optical element will be described. This liquid optical element is manufactured, for example, by the following procedure.

  First, the cell electrode substrate 10 is produced. That is, after a film made of a transparent electrode material is formed on the surface of the transparent substrate 11, a photosensitive resist material is applied on the film, and a predetermined pattern is formed by photolithography. After that, the matrix cell electrode 12 is formed by etching the film made of the transparent electrode material by immersing in a mixed acid. Subsequently, the transparent substrate 11 on which the cell electrode 12 is formed is ultrasonically cleaned using a detergent or the like that is also used in a cleaning process of a glass substrate such as an LCD (Liquid Crystal Display), and the impurity ion concentration is 50 ppm or less. Thoroughly remove the detergent with pure water. After that, dry cleaning is performed by ultraviolet ozone treatment. Subsequently, a water repellent film 13 is formed so as to cover the cell electrode 12 on the transparent substrate 11 by spin coating or the like. Subsequently, after the surface of the water-repellent film 13 is treated by an ultraviolet ozone treatment method or an oxygen plasma ashing method, a photosensitive resist material is applied on the water-repellent film 13, and the partition walls 14 having a predetermined pattern are formed by a photolithography method. Form. Subsequently, the impurity ions on the surfaces of the water repellent film 13 and the partition wall 14 are removed with pure water having an impurity ion concentration of 50 ppm or less. Finally, the surface of the water repellent film 13 and the partition wall 14 is treated by an ultraviolet ozone treatment method or an oxygen plasma ashing method to adjust the water repellency of those surfaces.

  Further, after the counter electrode 22 made of a transparent electrode material is formed on the surface of the transparent substrate 21, the surface of the counter electrode 22 is cleaned in the same manner as the cleaning method performed after the cell electrode 12 is formed. The substrate 20 is produced.

  Next, a gap forming material (not shown) for keeping the cell electrode substrate 10 and the counter electrode substrate 20 at a predetermined interval is disposed on the outer periphery of the cell electrode substrate 10. Examples of the gap forming material include a seal adhesive and an adhesive in which silica spheres are mixed.

  Next, after applying the nonpolar liquid 40 on the water repellent film 13 of the cell electrode substrate 10, the polar liquid 30 is poured at a predetermined speed.

  Finally, after the cell electrode substrate 10 and the counter electrode substrate 20 are bonded together via a gap forming material, the peripheral portions of the cell electrode substrate 10 and the counter electrode substrate 20 are sealed using a sealant. Thereby, the liquid optical element shown in FIGS. 1 to 3 is completed.

  Next, the operation of the above-described liquid optical element will be described with reference to FIGS.

  In the liquid optical element described above, first, when no drive voltage is applied, the nonpolar liquid 40 covers the entire water-repellent film 13 as shown in FIGS. 2 (A) and 3 (A). It has become. For this reason, for example, when light is irradiated from the cell electrode substrate 10 side, the incident non-polar liquid 40 blocks the incident light. On the other hand, when a driving voltage is applied between the cell electrode 12 and the counter electrode 22, the wettability of the water repellent film 13 changes according to the potential difference between the cell electrode 12 and the counter electrode 22 (the hydrophobicity decreases). The polar liquid 30 and the nonpolar liquid 40 move so that the contact angle of the nonpolar liquid 40 with respect to the surface of the water repellent film 13 is increased. As a result, as shown in FIGS. 2B and 3B, the nonpolar liquid 40 is deformed into a raised shape. Therefore, for example, when light is irradiated from the cell electrode substrate 10 side, the incident light passes between the partition wall 14 and the nonpolar liquid 40 and is emitted to the counter electrode substrate 20 side. That is, the amount of transmitted light is adjusted by changing the area where the water repellent film 13 is covered with the nonpolar liquid 40 according to the driving voltage.

  In the liquid optical element according to the present embodiment, as described above, the polar liquid 30 is a mixture of water and alcohol, and the impurity ion concentration in the polar liquid 30 is between the cell electrode 12 and the counter electrode 22. When the voltage holding ratio is 90% or less, the polar liquid 30 is difficult to solidify when exposed to a low temperature environment, and the water repellent film 13 is applied when a driving voltage is applied. Since the amount of impurity ions accumulated or adsorbed on the surface is small, a significant decrease in voltage holding ratio is suppressed. That is, according to this liquid optical element, it is possible to secure low temperature characteristics and improve voltage holding performance.

  Examples of the present invention will be described in detail.

Example 1
The liquid optical element shown in FIGS. 1 to 3 was produced by the following procedure.

  First, the cell electrode substrate 10 was produced. That is, after forming an indium tin oxide (ITO) film on the surface of the transparent substrate 11 made of glass, a photosensitive resist material was applied on the ITO film, and a predetermined pattern was formed by photolithography. After that, the ITO cell was etched by immersing it in a mixed acid to form a matrix cell electrode 12. Subsequently, the transparent substrate 11 on which the cell electrodes 12 were formed using a detergent was subjected to ultrasonic cleaning, and then the detergent was sufficiently removed with pure water (impurity ion concentration was 50 ppm or less). After that, dry cleaning was performed by ultraviolet ozone treatment. Subsequently, a water repellent film 13 made of CYTOP (Asahi Glass Co., Ltd.) was formed by spin coating. Subsequently, after the surface of the water-repellent film 13 is treated by an ultraviolet ozone treatment method, a photosensitive black resist material containing a surfactant is applied on the water-repellent film 13, and a partition 14 having a predetermined pattern is formed by a photolithography method. Formed. Subsequently, impurity ions on the surfaces of the water-repellent film 13 and the partition wall 14 were removed with pure water (impurity ion concentration was 50 ppm or less). Finally, the surface of the water repellent film 13 and the partition wall 14 was treated by an ultraviolet ozone treatment method to adjust the water repellency of those surfaces.

  Next, the counter electrode substrate 20 was produced. That is, after the counter electrode 22 made of ITO was formed on the surface of the transparent substrate 21, ultrasonic cleaning was performed using a detergent, and then the detergent was sufficiently removed with pure water (impurity ion concentration was 50 ppm or less). After that, dry cleaning was performed by ultraviolet ozone treatment.

Next, the polar liquid 30 and the nonpolar liquid 40 were adjusted to have the compositions shown in Table 3 to be described later. That is, pure water (impurity ion concentration of 50 ppm or less) and methanol (purity of 99.9% or more) were mixed at a weight ratio of 75:25 to obtain a polar liquid 30. In addition, Sudan black was dissolved in dodecane (C ₁₂ H ₂₆ ) so that the transmittance of the 10 μm-thick nonpolar liquid 40 was 10%, whereby the nonpolar liquid 40 was obtained.

  Next, after a gap forming material made of a seal adhesive is arranged on the outer periphery of the cell electrode substrate 10, the nonpolar liquid 40 is applied on the water repellent film 13, and then the polar liquid 30 is poured at a predetermined speed. .

  Finally, after pasting the cell electrode substrate 10 and the counter electrode substrate 20 through the gap forming material, the peripheral portions of the cell electrode substrate 10 and the counter electrode substrate 20 are sealed using a sealant, The liquid optical element shown in FIGS. 1 to 3 was completed.

(Comparative Example 1)
A procedure similar to that in Example 1 was performed except that the cell electrode substrate 10 and the counter electrode substrate 20 that were not washed with pure water and pure water as the polar liquid 30 were used.

(Comparative Example 2)
A procedure similar to that in Example 1 was performed except that pure water was used as the polar liquid 30.

(Comparative Example 3)
A procedure similar to that in Example 1 was performed except that an aqueous lithium chloride (LiCl) solution (0.5 mol / dm ³ ) was used as the polar liquid 30.

For the liquid optical elements of Example 1 and Comparative Example 1 manufactured as described above, the temperature dependence of the response time was examined. Specifically, in Example 1, the response time in an atmosphere in which the temperature was changed at 10 ° C. intervals in the range of −40 ° C. to 60 ° C. and in Comparative Example 1 in the range of 0 ° C. to 60 ° C. It evaluated by measuring by the following procedures. First, in each temperature atmosphere, a response time (T _on ) until the light transmittance is changed from 10% to 90% by applying the cell electrode substrate 10 as a reference potential and applying a positive DC voltage of 20 V as a driving voltage. Was measured. Subsequently, the drive voltage was returned to the non-application state, and the response time (T _off ) until the light transmittance was changed from 90% to 10% was measured.

  Moreover, the voltage holding ratio was investigated about the liquid optical element of Example 1 and Comparative Examples 1-3. Specifically, the voltage applied between the cell electrode 12 and the counter electrode 22 was monitored in the following manner with the repetition of application and non-application (ON and OFF) of the drive voltage being 60 Hz, and the voltage holding ratio was obtained. First, in the state where the drive voltage is applied for about 8.3 msec (ON state), the positive DC voltage of 20V with the cell electrode substrate 10 as the reference potential for 20% of the time (about 1.66 msec). And the remaining 80% of the time (approximately 6.64 ms) was made open circuit, and the voltage was monitored. Subsequently, in a state where the drive voltage is not applied (OFF state) for about 8.3 msec, the cell electrode substrate 10 is set to 0 V as the reference potential for 20% of the time (about 1.66 msec). A DC voltage was applied, and the remaining 80% of the time (about 6.64 ms) was made to be an open circuit, and the voltage was monitored. Finally, in the ON state, when the voltage applied in the first 20% of time is open circuit, the integration value when the voltage is kept as it is is taken as 100%, and the time in which the voltage is open in the ON state. The voltage holding ratio (%) was calculated from the integrated value of the voltage held at.

The response times (T _ON and T _OFF ) measured in each temperature atmosphere of Example 1 and Comparative Example 1 are collectively shown in FIG. The results of monitoring the voltage applied between the cell electrode 12 and the counter electrode 22 of Example 1 and Comparative Examples 1 to 3 are shown in FIG. 8, and the voltage holding ratio at that time is shown in Table 3.

As shown in FIG. 7, in Example 1, short both T _on and T _off than Comparative Example 1, the difference between Example 1 and Comparative Example 1 In a particularly 10 ° C. or less was remarkable. In Example 1, both T _on and T _off tended to become longer as the temperature decreased at 0 ° C. or lower, but it was good despite being in a low temperature environment. That is, in this liquid optical element, it was confirmed that the low temperature characteristics can be ensured when the polar liquid 30 is a mixed liquid of water and methanol. Moreover, from the results of FIG. 7 and FIG. 6 shown as reference data, the contact angle of the nonpolar liquid 40 with respect to the water-repellent film 13 is smaller than that when methanol is not included because the polar liquid 30 contains methanol. It was confirmed that the response time was shortened.

  Further, as shown in FIG. 8 and Table 3, in Example 1, the voltage in the open circuit was higher in Example 1 than in Comparative Examples 1 to 3, and the voltage holding ratio was 95%. In particular, in Comparative Examples 1 and 3, the voltage holding ratio was significantly lower than that in Comparative Example 2. On the other hand, in the OFF state, in Example 1, the voltage during the open circuit was lower than those in Comparative Examples 1 to 3. In Comparative Examples 1 to 3, in particular, a voltage of about 3 V was applied at the time of the open circuit although no drive voltage was applied. As a result, when the polar liquid 30 contains inorganic ions, the inorganic ions are accumulated or adsorbed on the water-repellent film 13, so that it is difficult to maintain the voltage even when a driving voltage is applied. Represents. That is, it is considered that the voltage holding ratio increases as the impurity ion concentration in the polar liquid 30 decreases.

  Therefore, in the liquid optical element described above, the polar liquid 30 is a mixture of water and alcohol, and the impurity ion concentration in the polar liquid 30 is 90% between the cell electrode 12 and the counter electrode 22. It was confirmed that the low-temperature characteristics were ensured and the voltage retention was improved when the concentration was not more than%.

  The liquid optical element of the present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the modes described in the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the transmissive liquid optical element has been described. However, the present invention is not necessarily limited thereto, and may be, for example, a reflective type. In the case of the reflection type, the cell electrode is made of an electrode material having light reflectivity such as aluminum.

  Further, in the above-described embodiments and examples, a display device, a shutter of a camera, or a diaphragm is cited as a use application. However, the use application of the liquid optical element of the present invention is not necessarily limited to those uses, and other uses. It may be.

It is sectional drawing showing the structure of the liquid optical element which concerns on one embodiment of this invention. It is sectional drawing which expands and represents the cell part of the liquid optical element shown in FIG. It is a top view of the cell part of the liquid optical element shown in FIG. It is a figure showing the method of measuring the contact angle of the nonpolar liquid with respect to a water repellent film. It is a figure showing the correlation between the ratio for which the water in the polar liquid accounts in reference data, and a contact angle. It is a figure showing the correlation between the density | concentration of the dye in a nonpolar liquid in reference data, and a contact angle. It is a figure showing the correlation of the temperature and response time in the liquid optical element produced in the Example. It is a figure showing the change of the voltage with respect to time in the liquid optical element produced in the Example. It is a figure for demonstrating an electrowetting phenomenon.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Cell electrode substrate, 11, 21 ... Transparent substrate, 12 ... Cell electrode, 13, 13A ... Water-repellent film, 14 ... Partition, 20 ... Counter electrode substrate, 22 ... Counter electrode, 30, 30A ... Polar liquid, 40, 40A ... nonpolar liquid, 100 ... container, 110 ... substrate, 120 ... saddle type syringe.

Claims (6)

A first electrode having an insulating film formed on the surface;
A second electrode disposed opposite to the insulating film side of the first electrode;
A transparent polar liquid and an opaque nonpolar liquid enclosed between the first electrode and the second electrode and kept separated from each other;
The polar liquid is a mixture of water and alcohol, and
The liquid optical element, wherein the impurity ion concentration in the mixed solution is equal to or less than a concentration at which a voltage holding ratio between the first electrode and the second electrode is 90%. The first electrode and the second electrode in a state where the insulating film is formed are washed with pure water having an impurity ion concentration of 50 ppm or less,
The liquid optical element according to claim 1, wherein the polar liquid is a mixture of pure water having an impurity ion concentration of 50 ppm or less and alcohol having a purity of 99.5% or more. The liquid optical element according to claim 1, wherein the alcohol includes ethanol. The liquid optical element according to claim 1, wherein the alcohol is a mixture of ethanol and methanol. 2. The liquid optical element according to claim 1, wherein the proportion of the alcohol in the polar liquid is 10% by weight or more and 60% by weight or less. The liquid optical element according to claim 1, wherein the insulating film has a higher affinity with the nonpolar liquid than the polar liquid under no electric field.

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