JP2007139447A - Thin film moisture permeability measuring apparatus and moisture permeability measuring method - Google Patents

Abstract

An apparatus capable of measuring the moisture permeability of a thin film with high accuracy and a method for measuring the same are provided.
A moisture permeation measuring apparatus (1) includes a lower electrode film (3) on an insulating substrate (5), a hygroscopic film (2) so as to cover at least a part of the lower electrode film (3), and at least a part of the lower electrode film (3) and a hygroscopic property. There is an upper electrode film 4 that is face-to-face across the film 2 and insulated from the lower electrode film 3, and a capacitance meter 7 is connected between the lower electrode film 3 and the upper electrode film 4 to absorb moisture. The moisture permeability of the sample film 6 to be measured covering the conductive film 2 is measured with a capacitance meter 7.
[Selection] Figure 1

Description

  The present invention relates to an apparatus for measuring the moisture permeability of a thin film from a change in capacitance due to moisture absorption, and a moisture permeability measuring method.

  Electrical and electronic parts and electrical appliances are surface-coated to prevent moisture and oxygen from entering. The waterproof and moistureproof performance of the coating film can be evaluated by measuring the moisture permeability of the coating film. As an example of means for measuring the moisture permeability, a capacitive humidity sensor can be used.

  Patent Document 1 discloses a capacitance type humidity sensor using polyimide resin. On the other hand, Patent Document 2 discloses a capacitance type humidity sensor using a fluorine-based organic compound as a moisture sensitive film, and Patent Document 3 discloses a fluorinated polyimide material.

JP 2002-005867 A JP 2001-249099 A JP 2000-026380 A

  However, the conventional humidity sensor has a sensitivity that is too low to accurately measure the moisture permeability of the coating film.

  An object of this invention is to provide the apparatus which can measure the water vapor transmission rate of a thin film accurately, and its measuring method.

  In order to achieve the above object, the invention described in claim 1 includes a lower electrode film on an insulating substrate, a hygroscopic film so as to cover at least a part of the lower electrode film, And an upper electrode film that is at least partly opposed to the lower electrode film across the hygroscopic film and is insulated from the lower electrode film, the lower electrode film, the upper electrode film, A moisture meter is connected to each other, and the moisture permeability of the sample film to be measured covering the hygroscopic membrane is measured with a capacitance meter.

  The invention described in claim 2 is the moisture permeability measuring apparatus described in claim 1, characterized in that the upper electrode film is a water-permeable electrode film.

  The invention described in claim 3 is the moisture permeability measuring apparatus described in claim 1, wherein the hygroscopic film is a polyimide film.

  The invention described in claim 4 is the moisture permeability measuring apparatus described in claim 1, wherein the hygroscopic film is a fluorinated polyimide film.

  According to a fifth aspect of the invention, there is provided a lower electrode film on an insulating substrate, a hygroscopic film so as to cover at least a part of the lower electrode film, and at least a part of the lower electrode film and the hygroscopic film interposed therebetween A humidity sensor having an upper electrode film that is face-to-face and insulated from the lower electrode film, the hygroscopic film is covered with a sample film to be measured, and the gap between the lower electrode film and the upper electrode film is Is measured by converting the moisture permeability of the sample film to be measured from the capacity, and calculating the moisture permeability.

  The invention described in claim 6 is the moisture permeability measurement method described in claim 5, wherein an equation for calculating the moisture permeability of the sample film to be measured from the capacity is calculated.

(In a few 1, D _w moisture permeability, Delta] t is the time measured, d is the film thickness, epsilon _w is the relative permittivity of water, epsilon _p is the relative dielectric constant of the thin film during drying, epsilon _s is the thin film at the time of moisture absorption Dielectric constant, C is the capacitance of the thin film when absorbing moisture, and C _p is the capacitance of the thin film when drying)
It is characterized by being.

  The invention described in claim 7 is the moisture permeability measuring method described in claim 5, wherein at least two of the humidity sensors are provided on the sample film to be measured, one of which is a hygroscopic material having a known moisture permeability. Calibration is performed using a standard sensor using a film.

The moisture permeability measuring apparatus of the present invention can measure the moisture permeability of a thin film with high sensitivity of 10 ⁻³ to 10 ⁻⁵ g / m ² · day. Since the moisture permeation measuring apparatus accurately measures even a small amount of moisture permeating the thin film, the waterproof and moisture proof effect of the thin film can be easily evaluated.

  According to the moisture permeability measuring method of the present invention, it is possible to accurately measure the moisture permeability of a thin film by a simple operation without requiring an expensive device.

  The moisture permeability measuring apparatus and measuring method of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view of an embodiment of a moisture permeability measuring apparatus 1 of the present invention, and FIG. 2 is a sectional view thereof. The lower electrode film 3 is formed in a strip shape on the insulating substrate 5, and the hygroscopic film 2 is coated thereon so that at least a part of the lower electrode film 3 is covered. Next, the upper electrode film 4 is formed in a strip shape so as to face at least part of the lower electrode film 3 across the hygroscopic film 2. The lower electrode film 3 and the upper electrode film 4 are connected to a capacitance meter 7.

  The sample film 6 to be measured is coated on the surface of the moisture permeability measuring device 1 thus obtained so that at least a part of the portion where the lower electrode film 3 and the upper electrode film 4 face each other is covered. .

  When the hygroscopic film 2 absorbs moisture, the capacitance of the hygroscopic film 2 changes. This capacitance change is measured with a capacitance meter, and the moisture permeability is calculated using the above formula.

  The thinner the hygroscopic film, the higher the sensitivity of moisture detection, and a smaller amount of moisture can be detected. However, if it is too thin, the film strength will decrease. The film thickness of the hygroscopic film is preferably 50 nm to 5 μm. The hygroscopic film is produced by a spin coating method when the film thickness is about several hundred nanometers to several microns. On the other hand, when the film thickness is several hundred nanometers or less, it is preferable to produce it by a vacuum deposition method.

  A fluorinated polyimide film is preferably used as the hygroscopic film. The fluorinated polyimide has both the characteristics of hydrophilicity of polyimide and hydrophobicity of fluorine. Since moisture can be quickly absorbed and released according to the ambient humidity, the moisture permeability of the sample film to be measured can be accurately measured even if the humidity environment changes rapidly. In order to appropriately measure moisture permeability, the fluorine content in the fluorinated polyimide film is preferably 5 to 50% by weight. Specific examples of such a fluorinated polyimide include polyimides containing a trifluoromethyl group or a hexafluoropropane group.

The lower electrode film 3 may have a film thickness of 10 nm to 1 μm, and the upper electrode 4 may have a thickness of 5 nm to 100 nm. Both the upper and lower electrodes 4 are formed by vacuum deposition or sputtering. The upper electrode 4 must be conductive and have a thickness that allows moisture to pass therethrough. The upper electrode 4 is preferably gold, but may be aluminum or silver. The area where the upper electrode and the lower electrode overlap is preferably 0.01 mm ^{2 to} 10 cm ² in the lower electrode.

  The insulating substrate is preferably a glass substrate, and may be a plastic film such as polyethylene terephthalate or polyethylene naphthalate whose back surface is waterproofed.

  Specific examples of the sample film to be measured include a polyethylene terephthalate film, a polypropylene film, other polyethylene, and a silicon oxide or nitride film formed on the film.

  The moisture permeability of the thin film is affected by the film thickness and temperature. Therefore, a standard sensor using a hygroscopic film with a known moisture permeability may be prepared, and calibration may be performed by providing one standard sensor and one or more humidity sensors on one surface of the sample film to be measured. .

  FIG. 3 is a view showing another embodiment of the moisture permeability measuring apparatus of the present invention. The moisture permeability measuring device 1 is installed in a metal cylindrical head 8 provided with a window at the top. The lower electrode film 3 and the upper electrode film 4 of the apparatus are connected to a capacitance meter 7 (shown in FIG. 3) outside the head.

  The sample film 6 to be measured is tightly fixed to the window portion above the moisture permeability measuring head 11. Moisture that permeates the thin film 6 and enters the head is measured by a moisture permeability measuring device in the head, and the moisture permeability is determined in the same manner as described above. The inside of the head is evacuated in advance to remove moisture in the head.

Examples of the present invention will be described in detail below, but the scope of the present invention is not limited to these examples.
An example in which a moisture permeability measuring apparatus to which the present invention is applied is shown in Example 1.

Example 1
A glass substrate having a length of 25 mm, a width of 25 mm, and a thickness of 1 mm was washed with water and acetone. It can be washed with alcohol. Gold was vapor-deposited on this glass substrate so as to have a width of 5 mm and a film thickness of 100 nm to form a lower electrode film. On top of that, a polyimide thin film containing trifluoromethyl or hexafluoropropane group was formed as a moisture sensitive film by spin coating so as to have a film thickness of 1000 nm. Since polyimide is insoluble in a solvent, a polyimide was prepared by spin coating a solution of polyamic acid which is a precursor of polyimide. Next, gold was vapor-deposited thereon so as to have a width of 5 mm and a film thickness of 100 nm in a direction facing the lower electrode film, thereby forming an upper electrode film. The lower gold electrode film and the upper gold electrode film were deposited by vacuum deposition. The upper electrode film and the lower electrode film were connected to a capacitance meter, and the moisture permeability measuring device of Example 1 was obtained.

(Calibration test)
A calibration test was performed on the manufactured moisture permeability measuring device. Nitrogen gas containing a certain amount of water vapor was poured into a container that had been previously evacuated. Water vapor was adsorbed to the polyimide film on the quartz oscillator, and the adsorbed amount was read from the film thickness meter. At the same time, the moisture permeability measuring device obtained in Example 1 was installed in the same place, and the change in capacitance when moisture was absorbed was measured with a capacitance meter. The measurement results are shown in FIG.

As is clear from FIG. 4, the relationship between the amount of adsorption per unit area and the increase in capacitance due to adsorption showed a linear relationship. This means that although measurement stability affects measurement accuracy, it can measure up to 0.01% capacitance change, that is, accuracy of 10 ng / cm ² in a short time of about several minutes. .

  Next, Example 2 in which the moisture permeability of the thin film was measured using the moisture permeability measuring apparatus of Example 1 is shown in Example 2.

(Example 2)
A 60 μm-thick polyethylene terephthalate (PET) thin film was thermocompression bonded to the surface of the upper electrode film side of the moisture permeability measuring device obtained in Example 1 to obtain a sample for measuring moisture permeability.

(Capacitance measurement)
Using the sample prepared in Example 2, the capacitance was measured.
Using a commercially available impedance analyzer model number 4284A or 4294A (manufactured by Agilent Technologies) for the capacitance meter, the change with time of the capacitance was measured while changing the humidity from 0% to 80% at a temperature of 30 ° C and a frequency of 10kHz. . For comparison, the same measurement was performed for the apparatus of Example 1 in which the thin film to be measured was not provided. The measurement results are shown in FIG.

  As is apparent from FIG. 5, the apparatus of Example 1 responded immediately after the start of measurement, and the capacitance changed greatly. On the other hand, the apparatus of Example 2 provided with the PET thin film showed little change in capacitance, but was able to measure with high accuracy.

  The moisture permeability measuring device of the present invention can be used as a moisture permeability monitor for a coating film applied to an electronic component, a flat display, an organic electroluminescent material, or the like. It also contributes to the development of excellent coating films.

It is a perspective view of a moisture permeability measuring device to which the present invention is applied.

It is sectional drawing of the water vapor permeability measuring apparatus to which this invention is applied.

It is sectional drawing of one Example of the moisture permeability measuring apparatus to which this invention is applied.

It is a graph which shows the capacity | capacitance change per unit area in the moisture permeability measuring apparatus of Example 1. FIG.

It is a graph which shows the time-dependent change of the electrostatic capacitance in the water vapor transmission rate measuring apparatus of Example 1 and Example 2.

Explanation of symbols

  1 is a moisture permeability measuring device, 2 is a moisture sensitive film, 3 is a lower electrode film, 4 is an upper electrode film, 5 is an insulating substrate, 6 is a sample film to be measured, 7 is a capacitance meter, 8 is a cylindrical head, 11 is This is a moisture permeability measuring head.

Claims (7)

  A lower electrode film on an insulating substrate, a hygroscopic film so as to cover at least a part of the lower electrode film, and at least a part of the lower electrode film and the surface opposite to each other with the hygroscopic film interposed therebetween, and the lower part The electrode film has an insulated upper electrode film, a capacitance meter is connected between the lower electrode film and the upper electrode film, and the moisture permeability of the sample film to be measured covering the hygroscopic film is measured by the capacitance meter. A moisture permeation measuring device characterized by measuring with   The moisture permeability measuring device according to claim 1, wherein the upper electrode film is a moisture permeable electrode film.   The moisture permeability measuring device according to claim 1, wherein the hygroscopic film is a polyimide film.   The moisture permeability measuring device according to claim 1, wherein the hygroscopic film is a fluorinated polyimide film.   A lower electrode film on an insulating substrate, a hygroscopic film so as to cover at least a part of the lower electrode film, and at least a part of the lower electrode film and the surface opposite to each other with the hygroscopic film interposed therebetween, and the lower part Cover the hygroscopic film of the humidity sensor having the upper electrode film insulated from the electrode film with the sample film to be measured, measure the capacitance between the lower electrode film and the upper electrode film, and measure the capacitance from the capacitance. A method of measuring moisture permeability, wherein the moisture permeability of a measurement sample film is converted and calculated. An equation for calculating the moisture permeability of the sample film to be measured from the capacity is

(In a few 1, D _w moisture permeability, Delta] t is the time measured, d is the film thickness, epsilon _w is the relative permittivity of water, epsilon _p is the relative dielectric constant of the thin film during drying, epsilon _s is the thin film at the time of moisture absorption Dielectric constant, C is the capacitance of the thin film when absorbing moisture, and C _p is the capacitance of the thin film when drying)
The moisture permeability measuring method according to claim 5, wherein:   6. The measurement sample film is provided with at least two humidity sensors, one of which is calibrated by using a standard sensor using a hygroscopic film having a known moisture permeability. Moisture permeability measurement method.

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