JP2000319428A - Production of functionally gradient material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thin film having a refractive index continuously varying along the direction of its thickness by disposing a substrate between a pair of opposed electrodes under a pressure near atmospheric pressure, applying a specified pulsed voltage between the electrodes to effect the discharge plasma treatment of the substrate, and forcibly drying the treated substrate. SOLUTION: The pulsed voltage is limited to one having a voltage rise time of at longest 100 μs and an electrical field strength of 1-100 kV/cm. The pressure is desirably in the range of 700-780 Torr. The electrodes are exemplified by simple metals such as copper and aluminum, alloys such as stainless steel and brass, and intermetailic compounds. The substrate is exemplified by a plastic, glass, ceramic, or metallic one and is not particularly limited on shape. The treatment gas used to generate a plasma is desirably e.g. a metal alkoxide when an inorganic thin film is to be formed, while it is desirably e.g. an unsaturated hydrocarbon or an unsaturated halogen compound when an organic thin film is to be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a functionally gradient material.

[0002]

2. Description of the Related Art A functionally graded material is a material based on a new concept. Functionally graded materials manufactured by using a gas phase synthesis method such as PVD or CVD include electric / magnetic, optical, chemical, biological / medical. Applications are desired in a wide range of fields such as aviation and space. It is known that the functionally graded material is effective as a means for preventing cracks and improving the adhesion to a substrate. Therefore, in recent years, applications to new optical materials by continuously changing the refractive index have been reported.

[0003] With the spread of color displays,
A high resolution is required, and a multi-layer deposited film utilizing interference of light or a film coated with a CVD film and provided with an antireflection function has been put to practical use. However, the antireflection coatings made of these multi-layer coatings are currently applied only to a limited number of high-grade varieties because of their high formation costs.
It is an issue to obtain a high-performance antireflection film at low cost. In addition, since the refractive index of the antireflection film formed by the multilayer coating film changes stepwise in the film thickness direction, the loss of the optical waveguide is large, and the antireflection performance in a wide band is deteriorated. In addition, there has been a problem that the adhesion between the films deteriorates.

[0004] Therefore, plasma C is applied on a plastic substrate.
In forming the hard coat layer by the VD method, the refractive index of the portion in contact with the plastic substrate is substantially equal to the refractive index of the substrate, and the reflectance is reduced over a wide area by continuously decreasing in the thickness direction. Method (Japanese Unexamined Patent Publication No. 7-5)
No. 6002) has been proposed.

[0005]

However, the above method requires a high degree of vacuum when forming a hard coat layer by the plasma CVD method, which not only hinders mass production, but also reduces the length of the product. There is a drawback that it cannot be handled, and the processing speed is slow.

Further, when plasma discharge is performed near the atmospheric pressure, the substrate is greatly damaged, so that it cannot be applied to the formation of a thin film on a substrate having low heat resistance.

[0007] The present invention solves the above-mentioned problems, and a thin film can be formed at a high speed by performing plasma discharge near the atmospheric pressure without requiring a high degree of vacuum, and the refractive index is continuously increased in the thickness direction. It is an object of the present invention to provide a method for producing a functionally graded material that can be dynamically changed.

[0008]

According to a method of manufacturing a functionally gradient material of the present invention, a substrate is placed between a pair of opposed electrodes under a pressure near atmospheric pressure, and a voltage rise time between the opposed electrodes is 100 μs. Hereinafter, a pulsed voltage having an electric field strength of 1 to 100 kV / cm is applied to perform a discharge plasma treatment, and then the treated substrate is forcibly dried.

In the present invention, "under a pressure near the atmospheric pressure" means
Refers to a pressure of 100 to 800 Torr. In particular, the pressure can be easily adjusted and the apparatus can be simplified 700 to 780 Torr
Is preferable.

In the present invention, examples of the pair of counter electrodes include those composed of a single metal such as copper and aluminum, alloys such as stainless steel and brass, and intermetallic compounds.
It is preferable that the counter electrode has a structure in which the distance between the counter electrodes is substantially constant in order to avoid occurrence of arc discharge due to electric field concentration. Examples of an electrode structure that satisfies this condition include a parallel plate type, a cylindrical opposed plate type, a spherical opposed plate type, a hyperboloid opposed plate type, and a coaxial cylindrical structure.

[0011] Further, usually, it is performed in an apparatus in which a solid dielectric is provided on at least one of the opposing surfaces of the electrodes. In this case, the discharge space in which plasma is generated is between the solid dielectric and the electrode when a solid dielectric is provided on one of the electrodes, and between the solid dielectrics when the solid dielectric is provided on both of the electrodes. Is the space between

Examples of the material of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. And the like.

The distance between the electrodes is determined by the thickness of the solid dielectric,
It is determined in consideration of the magnitude of the applied voltage, the purpose of utilizing the plasma, and the like, and is preferably 1 to 50 mm.
If it is less than 1 mm, it is not enough to place the electrodes at intervals. If it exceeds 50 mm, it is difficult to generate uniform discharge plasma.

The substrate used in the present invention includes:
Examples thereof include plastics such as polyethylene, polypropylene, polystyrene, polycarbonate, polyethylene terephthalate, polytetrafluoroethylene, and acrylic resin, glass, ceramic, and metal. Examples of the shape of the substrate include a plate shape and a film shape, but are not particularly limited thereto. According to the surface treatment method of the present invention, it is possible to easily cope with the treatment of substrates having various shapes.

In the present invention, the electric field applied between the electrodes is pulsed (hereinafter referred to as "pulse voltage" or "pulse electric field").

The shorter the rise time of the pulse voltage in the present invention, the more efficiently the ionization of the processing gas when generating plasma is performed. Rise time 100μs
When the discharge current exceeds the threshold value, the discharge state easily shifts to an arc and becomes unstable, so that a high-density plasma state due to a pulsed electric field cannot be expected. Further, it is better that the rise time is fast. However, there is a limit to a device that has an electric field intensity large enough to generate plasma at normal pressure and generates an electric field with a fast rise time. It is difficult to achieve a pulsed electric field with a rise time of less than. Therefore, the rise time of the pulse voltage is limited to 100 μs or less, preferably 40 ns to 100 μs, and more preferably 50 ns to 5 μs. Here, the rise time refers to a time during which the voltage change is continuously positive.

The electric field intensity is limited to 1 to 100 kV / cm, because if the electric field intensity is too weak, the processing takes too much time, and if the electric field intensity is too strong, an arc discharge easily occurs.

It is preferable that the fall time of the pulse electric field is also steep.
It is preferable that the time scale is less than μs. For example, in the power supply device used in the embodiment of the present invention, the rise time and the fall time can be set to the same time, although it differs depending on the pulse electric field generation technique.

The waveform and pulse duration of the pulse electric field applied between the electrodes include an impulse type, a square wave type, and a modulation type, as described in JP-A No. 10-154598. A so-called one-sided waveform in which a voltage is applied to either the positive or negative polarity side may be used. Similarly, the pulse duration time is 1 to 1000 μs
It is preferred that

Further, within a range not exceeding the breakdown voltage,
Modulation or bias may be superimposed using pulses having different pulse waveforms, rise times, and frequencies.

The frequency of the pulse electric field is 0.5 kHz to 1
It is preferably 00 kHz. If the frequency is less than 0.5 kHz, the plasma density is low, so that it takes too much time for the treatment. If the frequency exceeds 100 kHz, arc discharge is likely to occur. More preferably, it is 1 kHz or more. By applying such a high-frequency pulsed electric field, the processing speed can be greatly improved.

A power source for applying the pulse electric field is also a device described in Japanese Patent Application Laid-Open No. H10-154598 (for example,
Semiconductor device: manufactured by Heiden Laboratories, Inc., model number “TO-247AD” manufactured by IXYS) can be used.

The processing gas for generating the plasma is not particularly limited as long as it excites and decomposes in the discharge space to form a thin film on the substrate, and any treatment can be performed by this selection. .

When it is desired to form an inorganic thin film, a metal-containing gas such as a metal organic compound, a metal-halogen compound, a metal-hydrogen compound, a metal-halogen compound, or a metal alkoxide is preferably used as the processing gas. it can.
These may be used alone or in combination of two or more.

When the metal is Si, for example, tetramethylsilane [Si (CH ₃ ) ₄ ], dimethylsilane [S
i (CH ₃ ) ₂ H ₂ ], tetraethylsilane [Si (C ₂ H ₅ )
₄ ] and the like; metal halide compounds such as silicon tetrafluoride (SiF ₄ ), silicon chloride (SiCl ₄ ) and silicon chloride (SiH ₂ Cl ₂ ); monosilane (SiH ₄ ), disilane (SiH ₃ ) SiH ₃ ), trisilane (SiH ₃ SiH ₂ Si)
H ₃ ) and other metal hydrogen compounds; tetramethoxysilane [Si
(OCH ₃ ) ₄ ], tetraethoxysilane [Si (OC
₂ H ₅ ) ₄ ], triethoxymethylsilane [SiCH ₃ (OC ₂
H ₅ )] and the like. These may be used alone or in combination of two or more.

When the metal is Ti, for example, tetramethyl titanium [Ti (CH ₃ ) ₄ ], dimethyl titanium [T
i (CH ₃ ) ₂ H ₂ ], tetraethyl titanium [Ti (C ₂ H ₅ )
_4] an organometallic compound such as; 4 silicon fluoride (TiF _4), 4 silicon tetrachloride (TiCl _4), metal halide compounds such as 2 silicon tetrachloride (TiH ₂ Cl _2); Mono titanium (TiH _4), Jichitan (TiH ₃ TiH ₃ ), trititanium (TiH ₃ TiH ₂ Ti)
H ₃₎ metal hydride such as; tetramethoxy titanium [Ti
(OCH ₃ ) ₄ ], tetraisopropoxy titanium [Ti (O
CH ₃ CHCH ₃ ) ₄ ]. These may be used alone or in combination of two or more.

In the above-mentioned metal-containing gas, in consideration of safety, it is preferable that there is no danger of ignition or explosion at room temperature and in the atmosphere, such as metal alkoxide and metal halide, in consideration of safety. From the point of generation, metal alkoxides are preferably used.

If the metal-containing gas is a gas, it can be introduced into the discharge space as it is. If it is liquid or solid, it can be introduced into the discharge space via a vaporizer.
By using such a processing gas, SiO ₂ , T
By forming a metal oxide thin film such as iO ₂ or SnO ₂ , electrical and optical functions can be given to the substrate surface.

Further, by using a fluorine-containing compound gas as the above-mentioned processing gas, a fluorine-containing polymer thin film can be formed on the surface of the base material to lower the surface energy and obtain a water-repellent surface.

On the other hand, when it is desired to form an organic thin film, unsaturated hydrocarbons, unsaturated halogen compounds and the like can be suitably used. Further, by performing the treatment in an atmosphere of a monomer having a hydrophilic group and a polymerizable unsaturated bond in the molecule, a hydrophilic polymer thin film can be deposited. These may be used alone or in combination of two or more.

When the functionally graded material obtained in the present invention is used for optical applications, the above-mentioned processing gas is used as a processing gas for forming a thin film having a high refractive index such as TiO _{2 or} ZrO _2. A processing gas for forming a low-refractive-index thin film such as SiO _2, Al ₂ O _{3, or a} fluorine-based thin film may be appropriately selected from the above-described processing gases.

On the other hand, when applied to electronic materials, the dielectric constant (low dielectric constant SiO _2, Al ₂ O, etc .; high dielectric constant TiO _2, barium titanate, strontium titanate) or conductivity (low dielectric constant) A reaction gas that can synthesize thin films having different SiO _2, high dielectric constant ITO, and ZnO) is selected.

From the viewpoint of economy and safety, it is preferable to carry out the treatment in an atmosphere diluted with a diluent gas rather than in the atmosphere of the treatment gas alone. Examples of the diluting gas include rare gases such as helium, neon, argon, and xenon, and nitrogen gas. These may be used alone or in combination of two or more. When the processing gas is a liquid and has a high boiling point, it is preferable to use it after heating or vaporizing it with a vaporizer using ultrasonic waves and diluting it with a large amount of diluting gas.

As a diluent gas, a compound having more electrons is more advantageous in increasing the plasma density and performing high-speed processing. However, argon or nitrogen is preferred in that it is easily available and inexpensive. When a diluent gas is used, the concentration of the processing gas is preferably 0.01 to 10% by volume. When a metal alkoxide is used as a processing gas, an oxygen gas may be added in order to form a dense metal oxide thin film having a small amount of organic components.

In the present invention, a substrate may be placed between the opposing electrodes, and after plasma treatment, a new substrate may be placed between the opposing electrodes. You may. By doing so, the functionally gradient thin film can be continuously coated even on a long base material, and the processing speed is improved.

In the present invention, after subjecting the substrate to discharge plasma treatment, the treated substrate is forcibly dried. The drying method is not particularly limited, a method of directly contacting the treated substrate with a heating roll and drying, a method of drying in a non-contact manner by infrared rays, a dryer, a method of drying using a supercritical fluid, and the like. Is mentioned. Drying conditions such as drying temperature and drying time are appropriately determined depending on the film to be formed on the surface of the base material. Since drying at a high temperature can be performed in a short time, it is recommended that the drying be performed at a temperature as high as possible below the heat resistant temperature of the base material used. preferable.

When drying using the above supercritical fluid,
As the fluid, inorganic materials such as carbon dioxide and water; and alcohols such as methanol and ethanol are preferably used.
The method of drying using a supercritical fluid, compared to the method of drying by heating, even if unreacted substances remain in a porous state of the film formed on the substrate surface, it is easy to degrease and dry, This is preferable because cracks due to contraction of the film can be prevented.

After the discharge plasma treatment, the drying time of the treated substrate depends on the quality of the film obtained by the treatment. However, when the film reacts with the outside air in the atmosphere and naturally dries, Since there is a possibility that the refractive index in the film may become uncontrollable due to the gradient in the thickness direction, it is preferable to dry the treated substrate within 3 days after performing the discharge plasma treatment. When processing is performed by continuously moving between the opposing electrodes, it is more preferable to dry in-line.

(Function) In the method for producing a functionally graded material of the present invention, a substrate is placed between a pair of opposed electrodes under a pressure near atmospheric pressure, and a voltage rise time between the opposed electrodes is 100 μm.
s or less, a pulse-like voltage having an electric field intensity of 1 to 100 kV / cm is applied to perform a discharge plasma treatment, and then the treated substrate is forcibly dried. In order to perform discharge plasma processing by applying a pulsed voltage at, it is considered that a cycle of stopping discharge before starting arc discharge and restarting discharge has been realized, and under a pressure near atmospheric pressure. Therefore, even in an atmosphere that does not contain a component having a long time from a plasma discharge state such as helium to an arc discharge state, it is possible to stably generate a discharge plasma regardless of the type of gas present in the discharge space. Become. Therefore, a thin film can be formed at a high speed by performing plasma discharge near the atmospheric pressure without requiring a high degree of vacuum.

On the other hand, by forcibly drying the treated substrate, the organic matter in the thin film being formed is decomposed, so that the forcibly dried portion substantially accelerates the reaction of the plasma treatment. A dense thin film is formed. As a result, it is possible to obtain a functionally graded material in which the refractive index is continuously changed in the thickness direction and the thin film itself does not have a clear interface.

[0041]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of an apparatus for producing a functionally gradient material according to the present invention.

As shown in FIG. 1, the apparatus for producing a functionally graded material of the present invention is provided with a pair of opposing electrodes 3 and 4 in a container 2. Electrically connected, the lower electrode 4 is grounded, a pulse voltage is applied between the upper electrode 3 and the lower electrode 4, and plasma is generated. The base material 5 is supplied from the feeding roll 9 into the container 2 having the sealing mechanism 91, runs while being in close contact with the lower electrode 4 by the support roll 92, and is wound by the winding roll 93.

On the other hand, the processing gas whose flow rate is controlled by the flow rate control section 71 from the processing gas supply section 7 is introduced between the upper electrode 3 and the base material 5 through the gas introduction section 6, A discharge space is formed.

The substrate 51 subjected to the discharge plasma treatment in the discharge space is heated and dried by the heating roll 8 while
The film is wound by the winding roll 93, the refractive index changes continuously in the thickness direction, and the functionally graded material in which the thin film itself does not have a clear interface is obtained.

[0045]

EXAMPLES The present invention will be described in more detail with reference to Examples. In the following examples, a pulse generating power source (manufactured by Heiden Laboratories, semiconductor element: manufactured by IXYS, model number TO-247AD) was used as a power source.

(Embodiment 1) In the apparatus shown in FIG.
Upper electrode 3 and lower electrode 4 (made of SUS304, depth 35)
0 mm, a width of 100 mm, and a thickness of 20 mm) are sprayed with a sprayed film of zirconium containing 8% by weight of yttrium oxide as a solid dielectric (relative dielectric constant 16, film thickness 50).
0 μm) is used. The upper electrode 3 has a quartz window 31 (depth 30) that transmits ultraviolet light.
0 mm, width 20 mm, thickness 20 mm) from the outlet side
It is the same as the lower electrode 4 except that it is provided at a position of 0 to 40 mm.

The distance between the upper electrode 3 and the lower electrode 4 was 2 mm, and the base material 5 was coated with a 5 μm polyfunctional acrylic hard coat agent (manufactured by Dainichi Seika Co., Ltd., product number “EXF-37”) and had a thickness of 80 μm. Triacetylcellulose was supplied from the feeding roll 9 into the container 2 having the sealing mechanism 91, and was run while being in close contact with the lower electrode 4 by the support roll 92.

Next, the inside of the container 2 was evacuated to 1 Torr by an oil rotary roll (not shown), and argon gas was introduced until the pressure reached 760 Torr. Then, tetraisopropoxy titanium was supplied to the processing gas supply unit 7. From the 3SL so as to be 0.5% by volume by the flow controller 71.
The mixture was diluted with M argon gas and introduced between the upper electrode 3 and the base material 5 via the gas introduction unit 6.

Next, a pulse voltage having a voltage rise time of 1 μs, a frequency of 8 kHz, and an applied voltage of ± 3 kV was applied between the upper electrode 3 and the lower electrode 4 from the pulse power supply 1 to generate a discharge plasma. Substrate 5 subjected to discharge plasma treatment
1 is a heating roll 8 (300 m in diameter) heated to 90 ° C.
m), the substrate 51 is heated and dried from the non-treatment side, and transported by the winding roll 93 so that the transport speed is 1 m / min (substantial contact time between the heating roller 8 and the substrate 51 is 30 seconds). did.

As a result, a functionally graded material having a thin film of over 1000 ° formed on the polyfunctional acrylic hard coat film was obtained.

Example 2 A functionally gradient material was obtained in the same manner as in Example 1 except that the substrate subjected to the discharge plasma treatment was supplied into a supercritical carbon dioxide fluid.

(Comparative Example) A thin film of a little over 1000 ° was formed on a substrate in the same manner as in Example 1 except that the heating and drying were not performed. As shown in Table 1, the refractive index of the thin film was constant in the depth direction.

While the thin films formed on the substrate in Examples 1 and 2 and Comparative Example 1 were etched by discharging in an argon atmosphere, the change in the refractive index in the depth direction was measured using an ellipsometer (manufactured by Mizojiri Co., Ltd.). ). The results are summarized in Table 1.

[0054]

[Table 1]

[0055]

The method for producing a functionally graded material of the present invention is constructed as described above, so that a thin film can be formed at a high speed by performing a plasma discharge near the atmospheric pressure without requiring a high degree of vacuum. Thus, the refractive index can be continuously changed in the thickness direction.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an apparatus for producing a functionally gradient material according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pulse power supply 2 Container 3 Upper electrode 4 Lower electrode 5 Base material 6 Processing gas introduction part 8 Heating roll

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2K009 AA02 AA15 BB01 BB02 BB12 BB24 CC03 DD03 DD04 EE00 4F073 AA01 AA02 AA07 AA14 AA32 BA03 BA07 BA08 BA16 BA18 BA19 BA24 BB01 BB09 CA01 HA01 HA12 4F100 AJ00 BA25 E EJ612 EJ862 JL02 JM02B JN18B 4G075 AA29 BB02 CA14 CA47 EB42 EC21 ED04 ED11 FB01 FB02 FB04 FB06 FB12 FC15

Claims (1)

[Claims] 1. A pulse-like voltage having a voltage rising time of 100 μs or less and an electric field intensity of 1 to 100 kV / cm between a pair of opposed electrodes under a pressure near atmospheric pressure. And applying a discharge plasma treatment, followed by forcibly drying the treated base material.