JPH0862419A - Protective film for polarizer and polarizing film - Google Patents

Abstract

PURPOSE: To provide a protective film for polarizer which can suppress hygroscopic property and makes it possible to select a highly stable material by using a specific polycarbonate film. CONSTITUTION: A polycarbonate film which is composed of polymer of bisphenol A and has average molecular weight of 30000 or more and glass-transition temperature of 150 deg.C or more is used as a protective film of polarizer. Preferably, the polycarbonate film has retardation value of 10 nm or less, irregularity of a lag axis of ±10 degrees or less, and haze value of 0.5 % or less. Moreover, it is preferable that the thickness of the polycarbonate film is 50-250μm and unevenness of its thickness is within ±5%. A polarizing film is composed such that the protective films for polarizer are accumulated at least on a face of polarizer by a film composed of polyvinyl alcohol.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polarizing film used in a liquid crystal display. Furthermore, the present invention relates to a protective film for a polarizing film, which is excellent in reliability and durability and is suitable for use in liquid crystal displays for in-vehicle applications, general OA applications and mobile devices, which require durability in the future.

[0002]

2. Description of the Related Art A polarizing film used in a liquid crystal display has a structure in which a polarizer and a protective film are laminated. As the polarizer, a film obtained by drawing a solution film of polyvinyl alcohol in a boric acid solution and adsorbing iodine or a dichroic dye is used. In order to protect this polarizer, what laminated | stacked the solution-formed triacetylcellulose film on both surfaces of a polarizer as a protective film is used as a polarizing film.

The polarizing film is required to have a non-glare treatment, an antireflection treatment, a hard coat treatment, an ultraviolet absorbing treatment, etc. for controlling the reflection on the surface as the required characteristics such as light transmittance and polarization degree and reliability and additional required characteristics. There is. Among them, the degree of polarization and the transmittance are PVA used as a polarizer.
It is a factor that is governed by the characteristics of the film and the iodine or dichroic dye.

Although various proposals have been made as polarizers, those having a track record of use in liquid crystal display applications include dyeing PVA (polyvinyl alcohol) with iodine or a water-soluble acid dye or direct dye, or It is obtained by stretching a colored film. The reason is that the polarizing property is excellent, that is, the degree of polarization and the transmittance are excellent. A polarizer made of this polyvinyl alcohol in which both sides are protected by a triacetyl cellulose film is generally used for liquid crystal applications.

However, both the polyvinyl alcohol film used as the polarizer and the triacetyl cellulose film used as the protective film show hydrophilicity and insufficient moisture resistance and heat resistance. When it is used for a long time in a high temperature or high humidity atmosphere, the transparency is significantly reduced and the transparency is lowered due to the separation of the polarizer and the protective film or the hydrolysis of the triacetyl cellulose film, which may cause various restrictions on the application. Was coming.

[0006] Many proposals have been made to improve these problems. For example, a conventional type polyvinyl alcohol film with a transparent film laminated with good moisture resistance on both sides of the polarizer, a hydrophobic polymer having a polyethylene structure is used, and a hydrophobic polymer such as polyester or polyamide is used for liquid crystals. Examples thereof include dichroic dyes or iodine compounds to which a polarizing property is imparted.

[0007]

Thus, the polarizing films that have been put into practical use thus far lack remarkably stable reliability such as humidity resistance, heat resistance, and light resistance. The cause is the problem of the polyvinyl alcohol film itself,
This is a problem of the triacetyl cellulose film used as a protective film. Originally, the protective film should have the function of completely protecting the polarizer from the external environment, but it cannot be said that the current triacetyl cellulose film completely fulfills the function.
Further, acetic acid generated by the hydrolysis is a material which adversely promotes deterioration of the polarizer.

No proposal has been made to surpass a polyvinyl alcohol film material as a polarizer, and in the liquid crystal display field for the time being, the polyvinyl alcohol film material must be used as a polarizer. The polarizer is deteriorated due to the high hygroscopicity due to the hydrophilicity of the polyvinyl alcohol-based material.

The present invention solves the above problems, and a protective film for a polarizer and a polarizing film capable of suppressing the hygroscopicity of the protective film of the polarizer and selecting a material having high stability per se. Aim to get.

[0010]

The protective film for a polarizer of the present invention comprises a polymer of bisphenol A, has an average molecular weight of 30,000 or more, and has a glass transition temperature of 1 or less.
It is characterized in that a polycarbonate film having a temperature of 50 ° C. or higher is used as a protective film for a polarizer.

An important characteristic required for the protective film of the polarizer is the optical characteristic of the protective film. Optical properties include high transparency and no coloring in the visible range, but the polarizer has the important property of giving linearly polarized light. Optical characteristics that do not give are required. Generally speaking, they are compared on the scale of optical isotropy. The optical isotropy of a film is represented by retardation. The retardation is represented by the product of the birefringence of the film and the film thickness of the film. In order not to reduce the polarization degree of the polarizer, it is desirable that the retardation is 20 nm or less, and the degree of freedom of the attachment angle of the protective film is increased, and the retardation-induced coloring is prevented. Is 10 nm
The following is desired.

Further, the molecular orientation axis direction in which the in-plane refractive index of the protective film shows the maximum value, and the slow axis direction in the case of a resin having a positive refractive index anisotropy, the slow axis direction. The variation in the axis of is preferably within ± 15 degrees, and more preferably within ± 10 degrees for the same reason as the above retardation.

The visible light transmittance of the protective film is determined by the refractive index of the resin constituting the film and the refractive index of air, but the total light transmittance in the visible light region is 90% or more. It must be a transparent film that does not degrade. As a cause of lowering the transmittance of such a film, the haze of the film, that is, haze becomes a problem, but the haze also needs to be 1% or less, and in this application, 0.5% or less. It is necessary to be.

Films satisfying such characteristics include polycarbonate film, polyarylate film, polysulfone film, polyester carbonate film, polyether sulfone film and amorphous polyolefin film, and the possibility of solution film formation and optical characteristics and A polycarbonate film is preferably used from the viewpoint of price, and also in the polycarbonate film, a polycarbonate film containing bisphenol A as a bisphenol component is preferably used, and as an average film satisfying both stability and reliability as a protective film, A film having a molecular weight of 30,000 or more and a glass transition temperature of 150 ° C. or more is preferably used. The higher the average degree of polymerization is, the more the mechanical properties and reliability of the film are improved, but from the viewpoint of cost increase due to the trouble in polymerization and the film formability, a film having an average degree of polymerization of 75,000 or less is preferable.

As a method for forming a film satisfying the above required characteristics, there are used a melt extrusion method and a solution film forming method. However, from the viewpoint of visual defects contained in the film, the viewpoint of film thickness uniformity, and the retardation film. The liquid film forming method is preferably used when it is used for a fine display device such as a liquid crystal application as the viewpoint of controllability and uniformity of the application and the application, but in other applications such as sunglasses and sports goggles. A melt extrusion method can also be preferably used.

In the case of the solution film-forming method, the resin is dissolved in a solvent that dissolves polycarbonate resin such as methylene chloride and dioxolane in a suitable concentration, and the solution is cast on a substrate such as a film or a stainless belt and then dried and peeled. By doing so, the target film can be obtained. Since the tension and temperature during drying have a great influence on the optical characteristics of the obtained film, it is necessary to appropriately combine a tenter dryer and a hanging dryer to set the optimum film forming conditions.

In the case of solution casting, residual solvent may impair the mechanical properties and stability of the obtained film,
It is preferable to perform sufficient drying to obtain at least 0.2% or less residual solvent, and it is particularly preferable for the residual solvent to be 0.1% or less. Reducing the residual solvent is desirable not only from the viewpoint of improving the glass transition temperature and Young's modulus but also from the viewpoint of dimensional stability and stability of those characteristics with time.

In the case of the melt extrusion film forming method, a film can be obtained by forming a film on a casting drum with a usual combination of a ruder and a T die and cooling it.

Affects the reliability of the protective film and
In order to prevent warpage due to shrinkage when attached to both sides of the polarizer, it is desired that the heat shrinkage rate when heated is low. When used in a harsh environment such as for automobiles, it is expected that the ambient temperature will be 100 ° C, so that the heat shrinkage rate after heat treatment at 120 ° C for 1 hour is 0. 05%
It is preferable that the heat shrinkage is less than or equal to 0.1% in both the width direction and the flow direction of the film after the heat treatment at 150 ° C. for 30 minutes. Further, from the viewpoint of the uniformity of the film, it is preferable that the ratio of the heat shrinkage ratios in the width direction and the flow direction is 0.5 or more.

The thickness of the film preferably used for the protective film is preferably 50 to 250 μm. In the case of a triacetyl cellulose film, a film having a film thickness of 80 μm is used as a protective film for a polarizing film for liquid crystal applications. In other applications, for example, in sports goggles, a film having a thick film thickness of 250 μm is preferably used. The thickness of the protective film can be appropriately selected according to the requirements such as optical characteristics and reliability in the intended use. Generally, in a film using an aromatic compound resin using a petrochemical-derived raw material, retardation has a property of easily increasing in proportion to the film thickness of the film. It is necessary to control retardation by optimizing film forming conditions such as heat conditions and drying conditions. In terms of controlling retardation and easily obtaining a value of 20 nm or less, the solution film-forming method is preferable because the solution film-forming method is easier to control than the melt-extrusion film-forming method.

Even if a film having a large retardation is obtained at the time of film formation, the tension in the flow direction is set to a small value, which is usually carried out by heat treatment of the film, and the temperature is kept near the glass transition point. It is also possible to adjust the retardation to 10 nm or less, which is the object of the present invention, by continuously performing the longitudinal relaxation heat treatment in. In the case of the film obtained by solution casting, the residual solvent can be adjusted at the same time by this longitudinal relaxation heat treatment.

Since the protective film of the present invention is used by being attached to a polarizer, it needs to be attached to a polyvinyl alcohol film with an adhesive. As a material that adheres to both polyvinyl alcohol film and polycarbonate film, polyester-based, acrylic-based, polyolefin-based, polyamide-based heat-sensitive adhesive resin: acrylic-based, polyester-based, urethane-based, polyether-based, rubber-based, etc. Pressure-sensitive adhesive resin: A film obtained by mixing a resin having a functional group such as a saturated polyester resin, a polyurethane resin, a polybutadiene polyol, and a functional group-containing acrylic copolymer with a curing agent to form a film, and partially or partially crosslinking the resin. : Polyvinyl chloride with plasticizer eg 2
Soft polyvinyl chloride film blended with 0% by weight or more: Saturated polyester resin film: Acrylic copolymer film: Butyl rubber, urethane rubber, butadiene rubber (polybutadiene rubber, styrene-butadiene rubber, styrene-butadiene-styrene block copolymer) etc),
Film obtained by forming a synthetic rubber such as styrene-isoprene-styrene rubber: a film obtained by forming a polyolefin resin such as low molecular weight polyethylene, atactic polypropylene, chlorinated polypropylene: ethylene-vinyl acetate Optically isotropic pressure-sensitive adhesives or adhesives such as films obtained by forming ethylene copolymers such as polymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers are preferably used. To be

The film thickness of these adhesives or adhesives is 1 to
It is preferably set to 50 μm. The pressure-sensitive adhesive or the adhesive can be attached by a usual coating method or a method of transferring the release film onto the polyvinyl alcohol film or the protective film and then laminating the two films.

According to the demands for the protective film, the surface of the protective film can be subjected to various treatments before being bonded to the polarizer to improve its characteristics.
For example, anti-glare treatment, anti-glare treatment, anti-reflection treatment, etc. as a treatment to prevent surface reflection and improve the visibility of the liquid crystal panel: anti-static treatment and anti-contamination treatment to reduce the adhesion of dirt on the surface: mechanical properties Hard coat treatment to improve and harden the surface hardness and solvent resistance and chemical resistance: Moisture-proof treatment to lower moisture permeability and improve reliability, etc .: Reduce ultraviolet transmission amount and improve reliability Ultraviolet absorption treatment: Coloring treatment for imparting a desired hue and the like can be mentioned. These treatments can be performed by known methods depending on the purpose. Further, it is also possible to combine several types of functions and execute them.

The addition of these functions can also serve the purpose not only by surface treatment but also by mixing with a resin / solvent system at the time of forming the protective film. The method of giving a function can be appropriately selected according to the required characteristics.

Generally, a triacetyl cellulose film has low heat resistance and insufficient mechanical properties, has a large coefficient of hygroscopic expansion and is poor in dimensional stability, and has low solvent resistance. There is a drawback in that the processing conditions for the implementation cannot be set and sufficient functionality cannot be provided. On the other hand, when the polycarbonate film of the present invention is used, heat resistance, mechanical properties and dimensional stability are at a very high level, so that the setting of processing conditions for imparting such functionality is sufficient. It is possible to set satisfactorily strict conditions, and even in this respect it is extremely advantageous in that it is possible to realize multiple functions of the polarizing film.

The method of measuring the parameters relating to the polarizing film used in the description of the present invention will be described below. Polarization degree: Y is the single transmittance of the polarizing film. The transmittance Y0 of two sheets with the polarization axes of the polarizing film aligned in parallel. Transmittance Y90 of two sheets when the polarization axes of the polarizing film are orthogonalized. The degree of polarization P = {(Y0-Y90) / (Y0 + Y90)},
It is determined by measuring Y0 and Y90 respectively with a spectrophotometer. Transmittance: Spectral transmittance is measured with an integrating sphere of a spectrophotometer, and is defined as the spectral transmittance of a specific wavelength. The total light transmittance is defined as the total light transmittance measured by a haze meter. Haze: Defined as the haze measurement value with a haze meter. Retardation: Chromatic dispersion is measured by a retardation measuring device, and a value of 590 nm is defined as retardation. The shaft angle can also be measured with the same measuring machine, and the fluctuation range with respect to the center value of the variation is expressed as ±. The axis here is a slow axis.
Measuring machine example M-150 manufactured by JASCO Corporation. Birefringence: Three-dimensional refractive index is measured with a retardation measuring device. The difference (nx-ny) in the in-plane refractive index is defined as the in-plane birefringence index. nx = refractive index in the film flow direction, ny = refractive index in the film width direction. Measuring machine example M-150 manufactured by JASCO Corporation. Film thickness: Measure with a dial gauge or continuous thickness gauge. Thickness unevenness: The value obtained by dividing the difference between the maximum and minimum values measured by a continuous thickness meter by the average thickness. Average molecular weight: measured by GPC method. Glass transition temperature: Measured by a DSC method at a heating rate of 20 ° C./min. Amount of residual solvent: After accurately weighing a film sample, after heating for 2 hours at 120 ° C., which is a temperature sufficiently higher than the boiling point of the solvent used for solution casting, it was further heated at a temperature 5 ° C. lower than the glass transition temperature of the film resin. The film sample after heating for a certain period of time is precisely weighed and the difference is expressed as a residual solvent amount in% by weight. Dimensional stability: A film sample having a width of 1 cm and a length of 10 cm is cut out in the flow direction and the width direction of the film, and the length is precisely measured with an electronic micrometer.
The length is precisely measured by treating at a predetermined temperature and time, and the value obtained by dividing the change in length by the length before treatment is expressed as% to obtain dimensional stability.

[0028]

Example A polyvinyl alcohol film (trade name "VF9P-75R" manufactured by Kuraray) was uniaxially stretched vertically at 105 ° C (stretching ratio 3.3 times). Then add 0.2 iodine
weight%. It was immersed in a solution containing 10% by weight of potassium iodide to adsorb iodine. Boric acid 12 for immobilization
60% by weight in a solution containing 10% by weight of potassium iodide
After being dipped in, the film was stretched 1.3 times, washed with water and dried to obtain a polyvinyl alcohol-iodine type polarizer.

A solution of a polycarbonate resin (trade name "C-1400" manufactured by Teijin Chemicals Co., Ltd., "C-1400") dissolved in methylene chloride in an amount of 20% by weight was cast from a die onto a stainless steel belt to form a film, which was successively dried to obtain 0.12% residual solvent Thickness of 80μ
An m polycarbonate film was obtained.

The thickness unevenness of the obtained polycarbonate film was ± 2.5 μm, the retardation at 590 nm was 8 ± 2 nm, and the variation in the axial angle was ± 8 degrees. The glass transition temperature of the film is 158 ° C.
The heat shrinkage ratio after heat treatment at 0 ° C. for 1 hour was 0.03%.

As an anchor coat layer on the polycarbonate film (trade name "PC-7 manufactured by Shin-Etsu Chemical Co., Ltd."
A)) is diluted with methyl isobutyl ketone and applied to form an easy-adhesion layer having a thickness of 1 μm on both surfaces, and then butyl acrylate / 2-ethylhexyl acrylate / acrylic acid cast on a peelable sheet. Copolymerization ratio 30/67
A 20 μm-thick adhesive layer obtained by drying a solution consisting of 35 parts of a 3/3 acrylic copolymer, 2 parts of tolylene diisocyanate-trimethylolpropane adduct and 63 parts of ethyl acetate for 3 minutes at 80 ° C. At the very least, a polycarbonate film provided with an adhesive was prepared.

A polycarbonate film provided with such an adhesive was laminated on both sides of a polarizer to obtain a polarizing film. The obtained polarizing film had a transmittance of 42% and a polarization degree of 99.2%.

The polarizing film was placed in a high temperature dryer at 80 ° C. and a high temperature and high humidity tester set at 60 ° C. and 80% RH, and the characteristic change after 500 hours was confirmed. No significant change was observed in the appearance after 500 hours, and both the transmittance and the polarization degree showed a retention rate of 95% or more of the initial value.

[0034]

[Comparative Example 1] A protective film for a polarizer was used as a triacetyl cellulose film having a thickness of 80 μm (manufactured by Fuji Photo Film
Trade name "Fujitac") A polarizing film was prepared in exactly the same manner as in the example except that a polyvinyl alcohol-based material was used as an adhesive for bonding with a polarizer.

The resulting polarizing film had a transmittance of 43% and a degree of polarization of 99.3%. As a result of carrying out a reliability test similar to that of the above polarizing film, whitening due to hydrolysis of the triacetate film was observed in the high temperature test, and in the high temperature test, shrinkage from the end surface due to shrinkage of the triacetate film was observed and durability was insufficient. It was confirmed.

[0036]

[Comparative Example 2] A protective film of a polarizer is a polycarbonate film having a thickness of 100 μm (trade name “OK-10” manufactured by Teijin Ltd.
0 ”) was used, and a polarizing film was prepared in the same manner as in Example 1. The average molecular weight of the polycarbonate film is 23000, and the glass transition temperature is 145 ° C.
The retardation value was 25 ± 5 nm, and the variation in the axial angle was ± 20 degrees.

The obtained polarizing film was subjected to the same reliability test as in Example, but the curl after the test became tight,
Peeling of the protective film was observed in 1 part, which was not sufficient for reliability.

[0038]

Industrial Applicability As described above, the present invention relates to a polycarbonate film protective film having specified properties which gives a polarizing film excellent in reliability and durability. By using the protective film of the present invention,
The reliability of the liquid crystal display panel for in-vehicle use, outdoor use and general OA use can be improved.

Claims (8)

[Claims] 1. A protective film for a polarizer, which comprises using a polycarbonate film made of a polymer of bisphenol A and having an average molecular weight of 30,000 or more and a glass transition temperature of 150 ° C. or more as a protective film for the polarizer. the film. 2. The polycarbonate film has a retardation value of 10 nm or less, a slow axis variation of ± 10 degrees or less, and a haze value of 0.5% or less. The protective film for a polarizer according to 1. 3. The polycarbonate film is formed by a solution casting method.
The protective film for a polarizer according to any one of 2. 4. The protective film for a polarizer according to claim 1, wherein the polycarbonate film has a residual solvent concentration of 0.2% by weight or less. 5. The polycarbonate film has a dimensional stability of 0.05% or less in the machine direction and the width direction of the film after heat treatment at 120 ° C. for 1 hour, and after heat treatment at 150 ° C. for 30 minutes. The protective film for a polarizer according to any one of claims 1 to 4, wherein the flow direction and the width direction of the film are respectively 0.1% or less. 6. The polycarbonate film has a thickness of 5
It is 0-250 micrometers and thickness unevenness is within +/- 5%, The protective film for polarizers in any one of Claims 1-5 characterized by the above-mentioned. 7. The method according to claim 1, wherein at least one surface of the polarizer formed of a film made of polyvinyl alcohol is provided.
A polarizing film comprising the protective film for a polarizer according to any one of 1. 8. A processing layer for improving optical characteristics or a processing layer for improving mechanical characteristics and solvent resistance is provided on the surface of the protective film for a polarizer opposite to the surface to be attached to the polarizer. The polarizing film according to claim 7, which is characterized in that.