JP2016047900A - Film forming material for electrowetting, and evaluation method of contact angle of film forming material for electrowetting, and optical element using the film forming material for electrowetting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film forming material for electrowetting, with which transparency of an insulating film is ensured and a dielectric constant is increased.SOLUTION: A film forming material for electrowetting is formed by mixing polyvinylidene fluoride as a thermoplastic fluorine-containing polymer with an ionic liquid. In relation to the film forming material for electrowetting, insulating films 5, 6 are formed on surfaces of transparent electrodes 3, 4, water and oil repellent films 7, 8 are formed on surfaces of the insulating films 5, 6, a polar liquid is dropped on the water and oil repellent films 7, 8, and a contact angle θ is measured by applying potential difference V between the polar liquid and the transparent electrodes 3, 4. The film forming material for electrowetting is evaluated by variation of the contact angle with respect to potential difference of 0, using difference from the contact angle θ at the potential difference of 0.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a film forming material for electrowetting, a method for evaluating a contact angle of the film forming material for electrowetting, and an optical element using the film forming material for electrowetting.

  Conventionally, a film forming material for electrowetting used for driving a conductive liquid (polar liquid) of an optical element such as a liquid lens is known (for example, see Patent Document 1).

  In this material, as a highly dielectric inorganic particle in a vinylidene fluoride polymer, for example, barium titanate is contained as a metal oxide, and an applied voltage is changed to use a film forming material for electrowetting. The contact angle of the conductive liquid with respect to the formed hydrophobic dielectric film as the insulating film is changed.

  The contact angle can be increased as the film thickness of the hydrophobic dielectric film is reduced with a constant driving voltage. Further, the larger the dielectric constant, the larger the dielectric constant.

JP 2012-181513 A

By the way, it is desirable from the viewpoint of optical performance that the insulating film formed on the liquid lens using the electrowetting film forming material is transparent.
When high dielectric inorganic particles such as barium titanate are used, the dielectric constant can be increased, but white turbidity tends to occur when an insulating film is formed.
Even if the white turbid insulating film is used, it is conceivable to reduce the film thickness of the insulating film so that the optical performance of the liquid lens is not hindered. However, if the film thickness is reduced, pinholes are generated when the insulating film is formed, and dielectric breakdown is likely to occur. Further, the faster the driving speed of the optical element, the better.

  The present invention has been made in view of the above circumstances, and a film forming material for electrowetting capable of ensuring the transparency of an insulating film and increasing the driving speed of an optical element, and the electrowetting. It is an object of the present invention to provide a method for evaluating a contact angle of a film forming material for coating and an optical element using the film forming material for electrowetting.

  The film forming material for electrowetting according to the present invention is formed by mixing polyvinylidene fluoride as a thermoplastic fluoropolymer with an ionic liquid (also referred to as an ionic liquid).

  According to the present invention, the insulating film formed using this electrowetting film forming material can be made as transparent as possible, and the driving speed of the optical element can be increased.

FIG. 1 is a sectional view showing the configuration of liquid glass as an optical element using the electrowetting film forming material of the present invention as an insulating film. FIG. 2 is a schematic diagram for explaining a method for evaluating a contact angle of a film forming material for electrowetting. FIG. 3 is a graph showing the measured values of the contact angle corresponding to Table 2. FIG. 4 is a graph showing the amount of change in contact angle corresponding to Table 3.

  FIG. 1 is an explanatory diagram showing a cross-sectional structure of a liquid lens as an optical element according to an embodiment of the present invention. In FIG. 1, reference numerals 1 and 2 denote glass substrates. Transparent electrodes (ITO) 3 and 4 are formed on the upper surfaces of the glass substrates 1 and 2 by patterning.

Insulating films 5 and 6 are formed on the surfaces of the transparent electrodes 3 and 4. Water and oil repellent films 7 and 8 are formed on the surfaces of the insulating films 5 and 6. The glass substrates 1 and 2 are disposed to face each other with the glass ring member 9 interposed therebetween.
A durable adhesive 9 a is provided on the outer peripheral surface of the glass ring member 9. Note that an AF coat is used for the water and oil repellent films 7 and 8. Polyparaxylylene, polytetrafluoroethane, a fluorine-based polymer, a silicone resin, or the like is used as a material for the water / oil repellent films 7 and 8.

  The enclosure space formed by the glass substrates 1 and 2 and the glass ring member 9 is filled with a conductive liquid (polar liquid) 10 and a nonpolar liquid 11, and the inlet of the enclosure space is sealed. It is sealed with a UV curable resin (ultraviolet curable adhesive) as the agent 12.

  The polar liquid 10 includes, for example, water as a main component and an antifreeze liquid. Nonpolar liquid 11 is, for example, a hydrocarbon material such as hexane, octane, decane, dodecane, hexadecane, undecane, benzel, toluene, xylene, mesitylene, butylbenzene, 1,1-diphenylethylene, or transparent silicone oil. (Organic agent) is used.

As the film forming material for electrowetting used for forming the insulating films 5 and 6, a mixture of polyvinylidene fluoride (PVDF) as a thermoplastic fluoropolymer and an ionic liquid is used.
The film forming material for electrowetting is prepared by adding 5 to 20 parts by weight of an ionic liquid to 100 parts by weight of polyvinylidene fluoride (solid), melting them, and stirring and mixing them. The
Here, the transparency of the film forming material for electrowetting is enhanced by performing nano-dispersion treatment of molecules of the ionic liquid in polyvinylidene fluoride.

The ionic liquid includes any one of imidazole ionic liquid, pyrrolidinium ionic liquid, piperidinium ionic liquid, pyridinium ionic liquid, ammonium ionic liquid, and phosphonium liquid, or a mixture thereof. Can be used.
That is, the ionic liquid may be configured to be composed of at least one of a pyridine system as a cation, an aliphatic amine system, and an alicyclic amine system.
In particular, an ionic liquid that is liquid at room temperature and has a high dielectric constant and ionic conductivity is desirable.

  In this embodiment, the insulating films 5 and 6 are coated with the electrowetting film-forming material on the surfaces of the transparent electrodes (ITO) 3 and 4 and are subjected to spin coating for 20 seconds at a rotational speed of 3000 rpm. Was formed.

The film thickness of the insulating films 5 and 6 is 3 μm to 4 μm here, but if it is in the range of 1 μm to 20 μm, the transparency can be maintained within the range that does not hinder the use as a liquid lens.
By the way, the driving speed of the optical element can be increased as the change amount of the contact angle with respect to the driving voltage increases.

The contact angle of the insulating films 5 and 6 is generally evaluated by measuring the change in the contact angle θ of the insulating films 5 and 6 with respect to the polar liquid 10 by changing the driving voltage (applied voltage or potential difference) V. is there.
FIG. 2 is a schematic diagram showing an example of measurement of the change in the contact angle θ. In FIG. 2, the same reference numerals as those shown in FIG. 1 denote the same components.
Here, the polar liquid 10 is dropped on the surface of the AF coat as the water / oil repellent film 7, the electrode 10 a is inserted into the droplet 10 ′ of the polar liquid 10, and the transparent electrodes 3, 4 as the ITO films are connected. A change in the contact angle θ was measured by applying a driving voltage (potential difference) V therebetween.

  For comparison, the insulating films 5 and 6 are formed of a mixture of polyvinylidene fluoride (PVDF) and 100 parts by weight of polyvinylidene fluoride (PVDF) with 5 parts by weight of an ionic liquid added thereto (sample) 2 for the insulating films 5 and 6 (referred to as sample name 1031) formed by a mixture obtained by adding 10 parts by weight of ionic liquid to 100 parts by weight of polyvinylidene fluoride (PVDF). θ was measured.

Table 1 shows the insulating films 5 and 6 used for the measurement of the contact angle θ, and Table 2 shows the contact angle θ measured by changing the drive voltage (potential difference) V for each sample. The relationship between the contact angle θ and the potential difference V is shown in FIG. 3 as a graph.

  Even if it is attempted to evaluate the change of the contact angle θ of the insulating films 5 and 6 with respect to the change of the potential difference with reference to FIG. Since the line segments indicating the change in the contact angle θ of the mixture of ionic liquids intersect, the complexity increases, and it is difficult to determine whether the change amount Vθ in the contact angle θ is large at first glance.

Therefore, for each sample, Table 3 is created by taking the difference of the contact angle θ0 when the drive voltage (potential difference) V = 0 volts with respect to the contact angle θ of the drive voltage (potential difference) V = Vr volts. The relationship between the contact angle θ and the drive voltage (potential difference) V is shown in FIG.

  According to FIG. 4, since the line segment indicating the change in the contact angle θ of the ionic liquid does not intersect the line segment indicating the change in the contact angle θ of the polyvinylidene fluoride (PVDF) itself, the complexity is reduced. It can be judged whether or not the change amount Vθ of the contact angle θ is large.

  In this embodiment, two prototypes having the insulating films 5 and 6 with the sample name 1030 are created and measured, and two prototypes having the insulating films 5 and 6 with the sample name 1031 are also created. Each measurement is performed to measure the change amount Vθ of the contact angle θ. In Table 2, Table 3, FIG. 3, and FIG. 4, these two measurements are shown as sample names 1030-1, 1030-2, 1031-1, and 1031-2 for convenience.

  In this embodiment, since at most five measurement values are evaluated, it may not look complicated without obtaining the difference, but the complexity increases dramatically as the number of samples increases.

Therefore, it is desirable to determine the contact angle when the drive voltage (potential difference) V is a predetermined potential difference (other than 0 volts) as the amount of change Vθ with respect to the contact angle θ0 when the potential difference V = 0 volts.
In Table 1, the dielectric constant εr was measured with a known dielectric constant measuring device, and the film thickness d was measured with a known film thickness measuring device.

  According to this liquid lens, when a predetermined drive voltage (potential difference) V is applied to the transparent electrodes 3 and 4, the contact angle θ of the polar liquid 10 with respect to the nonpolar liquid 11 shown in FIG. 11 is deformed as indicated by a broken line, and the curvature and thickness of the interface 10c between the polar liquid 10 and the nonpolar liquid 11 change.

  As a result, the result is equivalent to the change in the curvature and thickness of the glass lens, the refraction angle of the light beam incident on the liquid lens is changed, and the optical characteristics of the liquid lens can be changed.

  Further, according to this embodiment, the electrowetting film forming material is evaluated not by the dielectric constant but by the change in the contact angle θ directly related to the high-speed response. The forming material can be accurately evaluated.

  For example, when a colorant such as a black pigment or dye is added to the nonpolar liquid 11, the ratio of the amount of transmitted light is changed by changing the maximum thickness of the interface 10 c between the polar liquid 10 and the nonpolar liquid 11. Can be changed. Therefore, by adding a colorant to the nonpolar liquid 11, the function of an ND filter as an optical element can be provided.

  In this way, the water / oil repellent film 7 of a pair of assemblies in which the transparent electrodes 3, 4, the insulating films 5, 6 and the water / oil repellent films 7, 8 are formed in this order on the glass substrates 1, 2 as transparent substrates. , 8 are opposed to each other, and an enclosed space is formed by interposing a glass ring 9 as a spacer member between the opposed surfaces of the assembly, and a polar liquid 10 and a nonpolar liquid 11 are formed in the enclosed space. And an electrowetting film forming material made of polyvinylidene fluoride in which an ionic liquid is added to the insulating films 5 and 6, the drive voltage V is applied to the polar liquid 10 to An optical element that can drive the nonpolar liquid 11 at high speed by changing the contact angle θ of the polar liquid 10 can be provided.

  The film forming material for electrowetting according to the embodiment of the present invention can be applied to optical elements such as shutter members and encoders in addition to optical elements of liquid lenses and ND filters.

3, 4 ... Transparent electrodes 5, 6 ... Insulating film θ ... Contact angle

Claims (6)

An electrowetting film-forming material formed by mixing polyvinylidene fluoride as a thermoplastic fluoropolymer with an ionic liquid. The ionic liquid is any one of imidazole ionic liquid, pyrrolidinium ionic liquid, piperidinium ionic liquid, pyridinium ionic liquid, ammonium ionic liquid, and phosphonium liquid, or a mixture thereof. The film forming material for electrowetting according to claim 1. 2. The electrowetting film formation according to claim 1, wherein the ionic liquid is composed of at least one of a pyridine series, an aliphatic amine series, and an alicyclic amine series as a cation. material. An insulating film is formed on the surface of the transparent electrode using the electrowetting film forming material according to any one of claims 1 to 3, and a water and oil repellent film is formed on the surface of the insulating film. A polar liquid is dropped on the water / oil repellent film, a potential difference is given to the polar liquid and the transparent electrode to measure a contact angle with the polar liquid, and a difference with respect to the contact angle when the potential difference is 0 is obtained. A contact angle evaluation method for evaluating a contact angle with respect to a polar liquid of a film forming material for electrowetting based on a change amount of a contact angle with respect to a potential difference of 0. An optical element using the film forming material for electrowetting according to any one of claims 1 to 3. An assembly in which a transparent electrode, an insulating film, and a water / oil repellent film are formed in this order on a transparent substrate are opposed to each other so that the water / oil repellent film faces each other, and a spacer member is interposed between the opposed surfaces of the assembly. The polar liquid and the nonpolar liquid are sealed in the enclosed space, and the contact angle of the polar liquid with respect to the nonpolar liquid is changed by applying a driving voltage to the polar liquid to change the nonpolar liquid. In the optical element that drives
An optical element, wherein the insulating film is formed using the film forming material for electrowetting according to any one of claims 1 to 3.