JP2002226616A - Hydrophilizing method for surface of hydrophobic resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrophilizing method for the surface of a hydrophobic resin film, which highly hydrophilizes the surface and does not damage to the film. SOLUTION: Under approximately atmospheric pressure, some solid dielectrics are placed on at least one of counter electrodes, the hydrophobic resin film is placed between the countering electrode and the solid dielectrics or the solid dielectrics mutually, and plasma discharge is generated by impressing between the countering electrodes. In this hydrophilizing method for the hydrophobic resin film, the plasma discharge is generated under an atmosphere containing at least O2. A surface of particularly norbornene resin film used as a protective film for a polarizing plate of a liquid crystal display is hydrophilized by plasma discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for hydrophilizing the surface of a hydrophobic resin film, particularly a norbornene resin film used as a protective film for a polarizing plate of a liquid crystal display by a plasma discharge treatment.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays (LCDs) are often used for vehicles and mobile phones.
There is a strong demand for the reliability of a CD in a high-temperature or high-temperature and high-humidity environment.

Conventionally, a polarizing plate used in an LCD is used by attaching it to one or both sides of a liquid crystal cell in which liquid crystal is sealed between two electrode substrates on which a transparent electrode is formed. As a polarizing plate of this type, triacetyl cellulose (TAC) was adhered as a protective film to both surfaces of a polarizer produced by adsorbing iodine or a dichroic dye on polyvinyl alcohol (PVA) and stretching the same. Things are commonly used.

Since the above TAC has poor adhesiveness to a polarizer as it is, alkali-treated TAC (saponified TA) is used.
C) is used. However, since the saponified TAC has too high water absorption, the degree of polarization decreases in a high-temperature and high-humidity environment, and the transmittance increases due to fading.
The saponification TA is caused by the force of the VA polarizer to relax the orientation.
Birefringence occurs in C and the degree of polarization is reduced, and the like has become apparent as a problem.

In order to solve the above problems, various resin films have been proposed as the protective film. However, most of the resin films proposed so far are hydrophobic, and it is extremely difficult to adhere to the polarizer due to a difference in polarity from PVA constituting the polarizer.

The adhesion is improved by making the surface of the hydrophobic resin film hydrophilic. As a method for hydrophilizing the surface of a hydrophobic resin film, a hydrophilization method by corona discharge treatment is widely used. For example, JP-A-4-347
Japanese Patent Publication No. 802 proposes a retardation plate for a liquid crystal display using a corona discharge treatment on one surface of a hydrophobic plastic film such as a stretched polycarbonate film.

[0007]

However, in the method of hydrophilizing the surface of the hydrophobic resin film by corona discharge treatment, the degree and the life of the hydrophilization treatment are short, and the degree and the life of the hydrophilization treatment are reduced to a small extent. When the processing strength is increased to extend the film, there is a problem that wrinkles and the like are generated in the hydrophobic resin film due to pinholes, temperature rise, and the like, and the hydrophobic resin film is damaged.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides a method for hydrophilizing a hydrophobic resin film surface in which the surface of the film is highly hydrophilized and does not damage the film. The purpose is to provide.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that in a normal-pressure plasma discharge process, a plasma process is performed in an atmosphere containing at least oxygen gas. It has been found that the surface of the hydrophobic resin film is highly hydrophilized and that a hydrophilization treatment that does not damage the film can be performed.

That is, according to the present invention, a solid dielectric is provided on at least one opposing surface of a counter electrode under a pressure atmosphere near atmospheric pressure, and a solid dielectric is provided between the counter electrode and the solid dielectric or between the solid dielectrics. Place a hydrophobic resin film on the
The method of generating a plasma discharge by applying a voltage between the opposed electrodes to hydrophilize the hydrophobic resin film surface, wherein the plasma discharge is performed in an atmosphere containing at least oxygen gas. This is a method for hydrophilizing the surface of a resin film.

Here, the pressure near the atmospheric pressure is 100
~ 800 Torr (about 1.33 × 10^Four~ 10.6 × 1
0^FourPa). Especially easy pressure adjustment
700 to 780 Torr (approximately 9.
31 × 10^Four~ 10.4 × 10 ^FourPa) range is preferred
No.

The treatment method of the present invention is performed in an apparatus having a pair of opposed electrodes, and a solid dielectric placed on at least one of the opposed surfaces of the electrodes. The portion where plasma is generated is between the solid dielectric and the electrode when a solid dielectric is installed on one of the electrodes, and between the solid dielectrics when the solid dielectric is installed on both of the electrodes. Space. The treatment is performed by disposing a hydrophobic resin film which is a target object of the hydrophilic treatment between the solid dielectric and the electrode or between the solid dielectrics.

Examples of the electrode include those made of a simple metal such as copper and aluminum, alloys such as stainless steel and brass, and metal 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 the electrode structure satisfying this condition include a parallel plate type, a cylindrical opposed plate type, a spherical opposed plate type, a hyperboloid, an opposed plate type, and a coaxial cylindrical type structure.

The solid dielectric is provided on one or both of the opposing surfaces of the electrode. At this time, the electrode on the side on which the solid dielectric is placed is in close contact with the electrode, and the opposing surface of the contacting electrode is completely covered. This is because if there is a part where the electrodes directly oppose each other without being covered by the solid dielectric, an arc discharge will occur from there.

The shape of the solid dielectric may be a sheet or a film, but preferably has a thickness of 0.01 to 4 mm. If the thickness is too large, a high voltage is required to generate discharge plasma. If the thickness is too small, dielectric breakdown occurs when a voltage is applied, and arc discharge occurs.

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 solid dielectric has a relative dielectric constant of 25.
It is preferably 2 or more in an environment of ° C. Dielectric constant is 2
Specific examples of the above dielectric include polytetrafluoroethylene, glass, and a metal oxide film.
Further, in order to stably generate high-density discharge plasma, it is preferable to use a solid dielectric having a relative dielectric constant of 10 or more.

The upper limit of the relative dielectric constant is not particularly limited, but about 18500 is known as a real material. As a solid dielectric having a relative dielectric constant of 10 or more, titanium oxide is 5 to 50% by weight, and aluminum oxide is 50 to 95%.
It is preferable to use a metal oxide film mixed at a weight% or a metal oxide film containing zirconium oxide and having a thickness of 10 to 1000 μm.

The distance between the electrodes is determined by the pressure of the atmospheric gas,
It is determined in consideration of the oxygen concentration, the thickness of the solid dielectric, the magnitude of the applied voltage, the purpose of using the film subjected to the plasma discharge treatment, and the like. The smaller the distance between the electrodes is, the more stable discharge plasma tends to be obtained, but it is preferably 0.5 to 50 mm. If it is less than 0.5 mm, the variation in oxygen concentration in the atmosphere gas between the electrodes is large, and the hydrophilic treatment tends to be uneven. In addition, the thickness of the object to be processed provided between the electrodes is limited. On the other hand, if it exceeds 50 mm, it is difficult to generate uniform discharge plasma.

The voltage to be applied is preferably a pulse voltage. The pulse waveform may be any of an impulse waveform, a square waveform waveform, and a modulation waveform, and even if the applied voltage is a positive / negative repetition, a one-sided waveform in which a voltage is applied to either the positive or negative polarity side. May be.

The voltage rise time of the pulse voltage is 100
μs or less is preferable. Application of such a high-speed pulse voltage leads to generation of high-density plasma, and is important for achieving high-speed continuous processing. Here, the voltage rise time of the pulse voltage means a time during which the voltage change is continuously positive.

The shorter the rise time of the pulse voltage is, the more efficiently the gas is ionized at the time of plasma generation, and if the rise time of the pulse voltage exceeds 100 μs, the discharge state is likely to shift to an arc and is unstable. Therefore, a high-density plasma state due to the pulse voltage cannot be expected. Also, it is better that the pulse voltage rise time is short, but there are restrictions on the device that has an electric field strength enough to generate plasma at normal pressure and generates an electric field with a fast pulse voltage rise time. In practice, it is difficult to realize a pulse voltage having a voltage rise time of less than 40 ns. More preferably, the voltage rise time of the pulse voltage is 50 ns to 5 μs.

Further, the voltage fall time of the pulse voltage is preferably steep, and the time scale is preferably 100 μs or less, which is the same as the voltage rise time of the pulse voltage. Although it differs depending on the pulse electric field generation technology, for example, in the power supply device used in the embodiment of the present invention,
The voltage rise time and the voltage fall time of the pulse voltage can be set to the same time.

The frequency of the pulse voltage is 0.5 to 100 k
Hz is preferable. If the frequency is less than 0.5 kHz, the processing takes too much time due to the low plasma density.
If it exceeds 0 kHz, arc discharge is likely to occur. More preferably, the frequency is 1 kHz or more. By applying such a high-frequency pulse voltage, the processing speed can be greatly improved.

The pulse duration of the pulse voltage is preferably 1 to 1000 μs. 1 μs
When the discharge time is less than 1,000 μs, the discharge becomes unstable.
When it exceeds, it is easy to shift to arc discharge. More preferably, it is 3 to 200 μs. Here, the pulse continuation time means the time during which a pulse is continuous in a pulse voltage consisting of repetition of ON and OFF.

Further, in order to stabilize the discharge, it is preferable to have an OFF time lasting at least 1 μs within a discharge time of 1 ms. In applying the pulse voltage, a direct current may be superimposed.

The atmosphere gas generating the plasma discharge is a gas containing at least oxygen gas. Examples of the mixed gas other than the oxygen gas include a nitrogen gas and an argon gas, and the volume ratio of the oxygen gas to the gas other than oxygen is 1:99 to
The mixture can be mixed at an almost arbitrary ratio in the range of 99: 1. However, if the oxygen gas concentration in the mixed gas is less than 1% by volume, the treatment speed of the hydrophilization treatment is lowered, which is not suitable.

The plasma discharge can be performed even when the atmospheric gas is oxygen alone. However, when the oxygen gas is used alone, the hydrophobic resin film, which is the object to be processed, is liable to be damaged (for example, there is a risk of ignition). Therefore, the oxygen gas concentration in the mixed gas is preferably 80% by volume or less, and more preferably 50% by volume or less. The improvement of the hydrophilization treatment speed by mixing oxygen is achieved by increasing the oxygen concentration to 10% by volume
Even with the above, there is no significant improvement, and when the mixing ratio is 50% by volume or more, damage to the base material tends to increase.

The hydrophobic resin film in the present invention is:
It means a resin film whose surface has a contact angle of 50 degrees or more with water. Among them, various films for liquid crystal display applications (for example, protective films for polarizing plates, etc.) require high transparency, and such resins are not particularly limited. For example, olefin resins, Examples include acrylic resins, engineering plastics such as polycarbonate and polysulfone.

Examples of the olefin resin include cycloolefin polymers such as norbornene resins, and copolymers of olefins with maleic anhydride or N-alkylmaleimide. Examples of the acrylic resin include those obtained by homopolymerizing or copolymerizing an acrylic acid ester obtained by esterifying acrylic acid with an alcohol component having a norbornane skeleton and a polymer of methyl methacrylate or a copolymer thereof. .

In particular, a cycloolefin resin film is excellent in optical properties such as transparency, heat resistance and durability, and is suitable for a protective film for a polarizing plate of a liquid crystal display.

The cycloolefin-based resin is, for example, a norbornene-based resin or a dicyclopentadiene-based resin, preferably a hydrogenated unsaturated bond. Hydrogenated product, hydrogenated product of a copolymer of two or more norbornene-based monomers, hydrogenated product of a copolymer of norbornene-based monomer and olefin-based monomer (ethylene, α-olefin, etc.), norbornene-based monomer and cyclic olefin System monomers (cyclopentene, cyclooctene,
5,6-dihydrodicyclopentadiene) and modified products thereof. Specific examples are trade names of ZEONEX and ZEO manufactured by Zeon Corporation.
NOR, Product name: A made by JSR (JSR) Ltd.
RTON, trade name: OPTOREZ manufactured by Hitachi Chemical Co., Ltd., APEL manufactured by Mitsui Chemicals, Inc. are commercially available.

(Function) In the normal-pressure plasma discharge treatment of the present invention, by performing the plasma treatment in an atmosphere containing at least oxygen gas, the surface of the hydrophobic resin film becomes highly hydrophilic and the film is damaged. Without this, it is possible to improve the adhesiveness.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention and comparative examples are shown below, but the present invention is not limited to these examples.

(Example 1) As a cycloolefin resin film, a norbornene resin (ARTON) manufactured by JSR Corporation was used.
G grade) obtained by solution casting was used. The contact angle of this untreated norbornene-based resin film with water was measured by a contact angle measuring device (contact angle meter CA-X150, manufactured by FACE), and the contact angle was 79 degrees. .

FIG. 1 shows a plasma discharge processing apparatus. An upper electrode 2 (stainless steel (SUS
304), size: 150 mm × 100 mm) and lower electrode 3 (stainless steel (SUS304), size: 1)
(50 mm × 100 mm) are arranged in a state insulated from the metal chamber 1. The distance between the electrodes is 2 mm.
The electrode facing surfaces of the upper electrode 2 and the lower electrode 3 are 1.5 mm
It is covered with a thick Al ₂ O ₃ spray coating 4.

After the norbornene-based resin film 7 is disposed between the upper electrode 2 and the lower electrode 3, the inside of the apparatus is reduced to 1T.
The pump was evacuated with an oil rotary pump until the pressure reached orr (about 133 Pa). After evacuation, argon gas: oxygen gas 70: 3
A gas mixed at a volume ratio of 0 was introduced from the gas introduction pipe 5 until the inside of the apparatus reached 760 Torr (about 1.01 × 10 ⁵ Pa).

An AC pulse voltage having a rise time of 5 μs, a pulse width of 100 μs, a frequency of 10 kHz, and a voltage of ± 5 kV is applied between the electrodes from the pulse power source 6 to generate plasma discharge, and the plasma is applied to both sides of the norbornene resin film 7. Discharge treatment was performed. The norbornene-based resin film 7 has a distance of 4 m between the upper electrode 2 and the lower electrode 3.
The plasma discharge treatment was performed while moving at a speed of / min.

Example 2 A plasma discharge treatment was performed on a norbornene-based resin film 7 in the same manner as in Example 1 except that the volume ratio of nitrogen gas: oxygen gas was 70:30.

(Comparative Example 1) Corona discharge treatment was performed on both surfaces of the norbornene resin film 7 at a treatment intensity of 0.4 kW and a speed of 3.0 m / min. The corona discharge treatment is performed using a corona discharge treatment device (high-frequency power supply AGI-0) manufactured by Kasuga Electric Co., Ltd.
20) was used.

The appearance of the norbornene-based resin film subjected to the hydrophilization treatment in Examples 1 and 2 and Comparative Example 1 was visually evaluated. The contact angle of the surface of the norbornene-based resin film with water was measured by a contact angle measuring device. Table 1 shows the results.

[0043]

[Table 1]

Further, the above Examples 1 and 2 and Comparative Example 1
Using a norbornene-based resin film hydrophilized by the above method, a polarizing plate produced by the following method was subjected to a durability test by the following method to evaluate a change in transmittance and a change in degree of polarization. Table 2 shows the results.

(Preparation of Polarizing Plate) An unstretched polyvinyl alcohol (PVA) film having a thickness of 75 μm and a saponification degree of 99% was washed with water at room temperature, and then stretched 5 times in the longitudinal uniaxial direction. The stretched film was immersed in an aqueous solution containing 0.5% by weight of iodine and 5% by weight of potassium iodide while maintaining the tension state to adsorb the dichroic dye. Furthermore, 5% of boric acid and 10% by weight of potassium iodide are used.
Cross-linking treatment was performed for 5 minutes with an aqueous solution at 0 ° C. to obtain three types of polarizers (Examples 1 and 2 and Comparative Example 1).

A norbornene-based resin film hydrophilized on the both sides of the obtained polarizer (Examples 1 and 2 and Comparative Example 1) by wet lamination using an aqueous urethane adhesive according to the above Examples and Comparative Examples As a protective film. This was put into a 45 ° C. gear oven for 60 hours to perform drying and curing of the adhesive, thereby producing three types of polarizing plates (Examples 1, 2 and Comparative Example 1).

The water-based urethane adhesive is a main component of the water-based urethane adhesive (product number: EL- manufactured by Toyo Morton Co., Ltd.).
436A) 10 parts by weight and 3 parts by weight of a curing agent (product number: EL-436B manufactured by Toyo Morton Co., Ltd.) are mixed and diluted to 100% by weight with ion-exchanged water to obtain a two-part aqueous urethane. An adhesive was used. I have.

(Durability test) The above three types (Examples 1 and 2)
From the polarizing plate of Comparative Example 1), a square test piece of 50 mm × 50 mm was punched out so that one side thereof was parallel to the absorption axis of the polarizer, and three types of tests (Examples 1, 2 and Comparative Example 1) were performed. A test piece was prepared, and a change in transmittance and a change in polarization degree were measured for each test piece. The measurement conditions were as follows: each test piece was dried at 90 ° C. in an atmosphere of
After leaving for 0 hours, the change in transmittance and the change in polarization degree before the test and after leaving for 500 hours were measured.

The transmittance change was measured by a Y-value using a spectrophotometer (TC-1800 manufactured by Tokyo Denshoku Co., Ltd.).

The change in the degree of polarization was measured by measuring the parallel and orthogonal transmittance using two polarizing plates, and the degree of polarization = [(H
Was measured using a 1-H2) / (H1 + H2) ] ^1/2 becomes equation. Here, H1 is a parallel transmittance, which is a transmittance measured by overlapping two polarizers so that their absorption axes are parallel. H2 is the orthogonal transmittance, which is the transmittance measured by stacking two polarizers so that the absorption axes of the polarizers are at right angles.

[0051]

[Table 2]

[0052]

As described above, according to the method for hydrophilizing the surface of a hydrophobic resin film of the present invention, the surface of the hydrophobic resin film is highly hydrophilized and the surface of the hydrophobic resin film is not damaged, and the adhesive property is improved. Can be improved

In particular, a cycloolefin-based resin film, particularly a norbornene-based resin film, whose surface has been hydrophilized by the hydrophilization treatment method of the present invention has a high affinity with an adhesive, and is particularly useful for protecting a polarizing plate for a liquid crystal display. When used as a film, the adhesive strength to a polarizer is high, and the film can be suitably used without a decrease in the degree of polarization even in a high temperature or high temperature and high humidity environment.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

[Description of Signs] 1 Metal chamber 2 Upper electrode 3 Lower electrode 4 Thermal spray film 5 Gas introduction tube 6 Pulse power supply 7 Hydrophobic resin film (norbornene resin film)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // C08L 65:00 G02B 1/10 Z F term (reference) 2H049 BA02 BA27 BB22 BB43 BB51 BC01 BC03 BC22 2K009 BB12 DD17 EE00 4F073 AA01 BA06 BB01 DA01 HA01 HA12

Claims (6)

[Claims] A solid dielectric is provided on at least one opposing surface of a counter electrode under a pressure atmosphere near atmospheric pressure, and a hydrophobic resin is provided between the counter electrode and the solid dielectric or between the solid dielectrics. In the method of arranging a film and generating a plasma discharge by applying a voltage between the opposed electrodes to hydrophilize the hydrophobic resin film surface, the plasma discharge is performed in an atmosphere containing at least oxygen gas. A method for hydrophilizing the surface of a hydrophobic resin film. 2. The oxygen gas in the atmosphere has a volume fraction of 1 to 99.
%. The method for hydrophilizing the surface of a hydrophobic resin film according to claim 1, wherein 3. The method for hydrophilizing the surface of a hydrophobic resin film according to claim 1, wherein the voltage applied between the opposed electrodes is a pulse voltage. 4. A pulse voltage having a voltage rise time of 10
The method for hydrophilizing the surface of a hydrophobic resin film according to claim 3, wherein the frequency is 0.5 μs or less and the frequency is 0.5 to 100 kHz. 5. The method according to claim 1, wherein the hydrophobic resin film is a cycloolefin-based resin film. 6. The method for hydrophilizing the surface of a hydrophobic resin film according to claim 5, wherein the hydrophobic resin film is a protective film for a polarizing plate comprising a cycloolefin resin film.