JP2002148436A - Polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate excellent in adhesiveness to a polarizer and in water and wet heat resistances and having high reliability. SOLUTION: A protective film is stuck to one face or both faces of a polyvinyl alcohol polarizing film with a moisture curable one-component silicone adhesive to obtain the objective polarizing plate. In order to improve adhesiveness, a protective film whose face to be stuck has been subjected to at least one treatment selected from corona treatment, plasma treatment, flame treatment, primer coating treatment and saponification treatment is used and a polyvinyl alcohol polarizing film having >=1 mass% water content is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a polarizing plate used for a liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) are used in desktop electronic calculators, electronic watches, personal computers, word processors, and the like, and in recent years, the demand for these devices has been rapidly increasing.

A polarizing plate used for an LCD is generally formed by forming an aqueous solution of polyvinyl alcohol (PVA), adsorbing iodine or a dichroic dye, uniaxially stretching the film, and cross-linking the film with a boron compound. It is manufactured by bonding a protective film such as triacetyl cellulose on at least one surface of the film via an adhesive layer formed using a polyvinyl alcohol-based resin aqueous solution. When the polyvinyl alcohol-based adhesive is used, if left under high temperature and high humidity for a long time, the film absorbs moisture and the adhesive strength is reduced, so that the film is easily peeled or the dimensional stability of the polarizing plate is reduced. Therefore, there is a problem that a hue change of the liquid crystal display occurs.

To solve this problem, Japanese Patent Laid-Open Publication No.
No. 17 proposes a polarizing plate having improved adhesiveness and wet heat resistance by using a urethane prepolymer as an adhesive. Also, Japanese Patent Application Laid-Open No. 9-258023
Japanese Patent Application Laid-Open Publication No. H11-15064 proposes a method of using a polyvinyl alcohol-based adhesive containing a water-soluble epoxy compound as an adhesive and saponifying the surface of triacetyl cellulose to improve the adhesive strength. Further, JP-A-8-10130
7, JP-A-8-216315, JP-A-8-216315
Japanese Patent Publication No. 254669 proposes a polarizing plate in which a polarizer and a protective film are bonded with a thermosetting adhesive to improve the adhesiveness and the wet heat resistance. Further, Japanese Unexamined Patent Publication No.
No. 240716 proposes a polarizing plate having improved adhesiveness and heat resistance by using a polycarbonate film as a protective film instead of triacetyl cellulose having poor heat resistance.

[0005]

However, when a urethane prepolymer or PVA to which a crosslinking agent is added is used as the adhesive, the adhesive strength is strong but the water resistance is insufficient, and the polarizing plate is used in a wet heat environment. There is a problem that the film is peeled off when the film is placed in water or immersed in water. Also,
When the polarizer and the protective film are bonded with a thermosetting adhesive, the adhesive property and the wet heat resistance are sufficient, but it is not economical because a heating step of the adhesive is required in the manufacturing process of the polarizing plate. Furthermore, if a protective film other than triacetylcellulose such as a polyacrylic film, a polycarbonate film, a polyester film, and a polynorbornene film is used, the adhesive property with various adhesives such as an epoxy-based, acrylic-based, urethane-based, and phenol-based film can be obtained. Are good, but these adhesives are inferior in adhesion to the polarizer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate which is excellent in both adhesiveness to a polarizer, water resistance and wet heat resistance and has high reliability.

[0007]

In order to achieve the above object, a polarizing plate of the present invention is a polarizing plate comprising a polyvinyl alcohol-based polarizing film and a protective film laminated on at least one surface of the polarizing film. Are bonded with a one-component silicone-based moisture-curable adhesive. Since the adhesive constituting the present invention is of a one-component type, it does not require the labor of pre-mixing such as a two-component type adhesive at the time of lamination, and is also pre- or laminating such as a solvent-based or water-based adhesive. Since there is no need to dry later, there is an advantage that the working process can be shortened. Further, since the adhesive has good adhesiveness to a polarizer, and the formed adhesive layer has high transparency and no optical anisotropy, it is possible to provide an optically high-performance polarizing plate. it can.

In order to improve the adhesiveness, it is preferable to use a protective film whose adhesive surface has been subjected to at least one treatment selected from corona treatment, plasma treatment, flame treatment, primer coating treatment and saponification treatment.

Further, since the adhesive of the present invention is cured at room temperature by moisture, it is cured by moisture in polyvinyl alcohol even if it is sealed with a protective film. In order to improve the adhesiveness, it is preferable to use a polyvinyl alcohol-based polarizing film having a water content of 1% by mass or more.

The polarizing plate of the present invention is characterized in that the protective film is a norbornene-based thermoplastic resin film. When a norbornene-based resin film is used as the protective film, the film provides a good barrier from heat and moisture, greatly improving the durability of the polarizing plate and significantly reducing dimensional stability due to the low moisture absorption of the polarizing plate. To improve.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a polarizing plate having excellent adhesion between a polyvinyl alcohol-based polarizing film and a protective film and excellent heat and moisture resistance.

That is, the structure of the polarizing plate of the present invention is such that a polarizer made of a polyvinyl alcohol-based polarizing film containing a dichroic substance is protected on one side or both sides via a one-part silicone moisture-curable adhesive layer. It consists of laminated transparent protective films to be layers.

As a polarizer (polarizing film), a film made of a polyvinyl alcohol-based polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol is subjected to a swelling treatment and a dyeing treatment with a dichroic substance such as iodine or a dichroic dye. , A cross-linking treatment and a stretching treatment, which can transmit a linearly polarized light when natural light is incident thereon, can be used. In particular, those having excellent light transmittance and degree of polarization are preferable. The steps of dyeing, crosslinking, and stretching do not need to be performed separately but may be performed simultaneously, and the order of the steps may be arbitrary. In general, a film obtained by uniaxially stretching the film at a stretching ratio of 3 to 7 times and then drying is used. The thickness of the polarizing film is generally from 5 to 80 μm, but is not limited thereto.

The polyvinyl alcohol polymer used as the polarizing film may be a polymer obtained by polymerizing vinyl acetate and then saponifying, or a copolymer of vinyl acetate with a small amount of unsaturated carboxylic acid, unsaturated sulfonic acid, cationic monomer, or the like. Those obtained by copolymerizing monomers are exemplified. The average degree of polymerization of the polyvinyl alcohol-based polymer is not particularly limited, and any one can be used.
0 or more is preferable, and 3000 to 5000 is more preferable.
It is. The saponification degree of the polyvinyl alcohol-based polymer is preferably at least 85 mol%, more preferably 98 mol%.
１００100 mol%.

The one-part silicone moisture-curable adhesive has the property of curing at room temperature due to moisture. Therefore, even if the adhesive is sealed with a protective film, the polyvinyl alcohol-based polymer can be used as a protective film. If used, it is cured by moisture in the protective film. Therefore, there is no particular limitation as long as the polyvinyl alcohol-based polymer substantially contains water. In order to enhance the adhesiveness, the water content is preferably 1 to 25% by mass, more preferably 1 to 12% by mass.

As the protective film provided on one side or both sides of the polarizing film (polarizer), an appropriate transparent film can be used. Among them, a film made of a polymer which has low birefringence and is excellent in transparency, mechanical strength, heat stability, moisture shielding property and the like is preferably used. Examples of the polymer include acetate resins such as triacetyl cellulose, polycarbonate resins, polyester resins such as polyarylate and polyethylene terephthalate, polyimide resins, polysulfone resins, polyethersulfone resins, polystyrene resins, polyethylene, and polypropylene. And the like, polyolefin resins, polyvinyl alcohol resins, polyvinyl chloride resins, polynorbornene resins, polymethyl methacrylate resins, liquid crystal polymers, and the like. The film may be manufactured by any of a casting method, a calendar method, and an extrusion method.

Transparent protective films that can be preferably used from the viewpoint of polarization characteristics and durability are a triacetyl cellulose film or a norbornene-based thermoplastic resin film whose surface is saponified with an alkali or the like. The norbornene-based thermoplastic resin film greatly improves the durability of the polarizing plate because the film becomes a good barrier from heat and wet heat, and greatly improves the dimensional stability due to the low moisture absorption of the polarizing plate. Are particularly preferred.

The thickness of the protective film is arbitrary, but is generally 500 μm or less, preferably 5 to 300 μm, particularly preferably 5 to 150 μm, for the purpose of reducing the thickness of the polarizing plate.
m. When transparent protective films are provided on both sides of the polarizing film, the transparent protective films may be made of different polymers on the front and back.

In order to improve the adhesiveness to the protective film, it is preferable to use a protective film whose adhesive surface has been subjected to at least one treatment selected from corona treatment, plasma treatment, flame treatment, primer coating treatment and saponification treatment. preferable. The corona treatment can be formed by, for example, a method of discharging in a normal pressure air by a corona treatment machine. The plasma treatment can be formed by, for example, a method of discharging in normal pressure air by a plasma discharge machine. The frame treatment can be formed by, for example, a method of bringing a flame into direct contact with the film surface. The primer coating treatment can be formed by, for example, diluting an isocyanate compound, a silane coupling agent, or the like with a solvent, and applying a thin coating. The saponification treatment can be formed by, for example, a method of immersing in a sodium hydroxide aqueous solution.

The transparent protective film may be subjected to a hard coat treatment, an antireflection treatment, a treatment for preventing sticking, a diffusion or an antiglare, or the like, as long as the object of the present invention is not impaired. The hard coat treatment is performed for the purpose of preventing the surface of the polarizing plate from being scratched, and for example, transparently protects a cured film excellent in hardness and slipperiness by an appropriate ultraviolet curable resin such as a silicone or acrylic resin. It can be formed by a method of adding to the surface of the film.

On the other hand, the anti-reflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an anti-reflection film or the like according to the related art.
In addition, anti-sticking is performed to prevent adhesion between adjacent layers, and anti-glare treatment is performed to prevent external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate. For example, it can be formed by providing a fine uneven structure on the surface of the transparent protective film by an appropriate method such as a roughening method such as a sand blast method or an embossing method or a method of blending transparent fine particles.

Examples of the transparent fine particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 20 μm. Organic fine particles may be used, and organic fine particles made of crosslinked or uncrosslinked polymer particles or the like may be used. The amount of the transparent fine particles to be used is generally 2 to 70 parts by mass, particularly 5 to 50 parts by mass per 100 parts by mass of the transparent resin.

Further, the antiglare layer containing the transparent fine particles can be provided as the transparent protective layer itself or as a coating layer on the surface of the transparent protective layer. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle compensation function) for diffusing light transmitted through the polarizing plate to increase the viewing angle. The above-described anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided as an optical layer made of a sheet or the like provided with such a layer, separately from the transparent protective layer.

In the present invention, a one-component silicone-based moisture-curable adhesive is used for the bonding between the polarizing film and the protective film. The adhesive is obtained by adding various silicone compounds as a curing agent to an organopolysiloxane, and depending on the type of curing agent used, an acetic acid type, an oxime type, an alcohol type, an acetone type, an amine type, an amide type, There are types such as aminoxy type, dehydrogenated type and dehydrated type.
Specific examples thereof include, for example, acetic acid type to which methyltriacetoxysilane, vinyltriacetoxysilane and the like are added, oxime type to which methyltris (ethylmethyloxime) silane and the like are added, methyltrimethoxysilane Dimethyl bis (N-ethylacetoamino) silane, amide type to which vinylmethylbis (N-ethylacetamino) silane, etc. are added, alcohol type to which vinyltrimethoxysilane or the like is added, methyltris (1-methylvinyl) oxy Acetone type to which {silane, vinyltris} (1-methylvinyl) oxy} silane or the like is added is exemplified. Among them,
From the viewpoint of adhesiveness and wet heat resistance, acetic acid type, alcohol type, acetone type, and oxime type one-component silicone moisture-curable adhesives are preferable. A silane coupling agent may be appropriately added for the purpose of improving the adhesiveness or the like. Commercial products include, for example, Silex “White” (Konishi Co., Ltd.) and Silex “Clear”
(Konishi Co., Ltd.), one-component RTV rubber "KE-41-
T ”(Shin-Etsu Chemical Co., Ltd.), one-component RTV rubber“ K
E-3475-T "(Shin-Etsu Chemical Co., Ltd.), Cemedine" Super X "(Cemedine Corporation) and the like.

The adhesive layer is formed as a layer for applying and drying an adhesive, and may be blended with other additives and a catalyst such as an acid as needed. The thickness of the adhesive layer is generally 0.05 to 20 μm, preferably 0.1 to 10 μm.

The polarizing plate of the present invention can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, a reflector, a transflector, a retardation plate (including a λ plate such as a 波長 wavelength plate and a 板 wavelength plate), a viewing angle compensation film, and a brightness enhancement film For example, one or more appropriate optical layers that may be used for forming a liquid crystal display device or the like can be used. In particular, a polarizing plate comprising the polarizer of the present invention and the protective layer described above, a reflective plate, or a reflective polarizer or a semi-transmissive reflective polarizer obtained by laminating a transflective reflector, the polarizer described above. A polarizing plate comprising a protective layer, an elliptically polarizing plate or a circularly polarizing plate wherein a retardation plate is further laminated, a polarizing plate comprising a polarizer and a protective layer described above, and a polarizing plate further comprising a viewing angle compensation film, Alternatively, a polarizing plate in which a brightness enhancement film is further laminated on the above-described polarizing plate comprising a polarizer and a protective layer is preferable.

The polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers, such as a polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate and retardation plate may be used. An optical member in which two or three or more optical layers are laminated can be formed by a method in which the optical members are sequentially laminated separately in a manufacturing process of a liquid crystal display device or the like. This has the advantage that the stability of quality and the workability of assembling are excellent and the manufacturing efficiency of a liquid crystal display device or the like can be improved. Note that an appropriate bonding means such as an adhesive layer can be used for lamination.

The above-mentioned polarizing plate or optical member may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed with an appropriate pressure-sensitive adhesive, such as an acrylic resin, according to the related art. In particular, from the viewpoint of preventing foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to differences in thermal expansion and the like, prevention of warpage of liquid crystal cells, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is low. It is preferable that the pressure-sensitive adhesive layer is low and has excellent heat resistance. Further, an adhesive layer or the like which contains fine particles and exhibits light diffusibility can be used. The adhesive layer may be provided on a necessary surface if necessary.For example, if mention is made of a protective layer of a polarizing plate comprising a polarizer and a protective layer, if necessary, an adhesive layer may be provided on one or both sides of the protective layer. May be provided.

When the adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until the adhesive layer is put to practical use for the purpose of preventing contamination and the like. The separator is formed by a method of providing a release coat with a suitable release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide as necessary, on a suitable thin leaf according to the transparent protective film or the like. be able to.

The layers such as the polarizing film and the transparent protective film, the optical layer and the adhesive layer forming the polarizing plate and the optical member are made of, for example, salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds and cyanoacrylate compounds. Compounds having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorbent such as a compound or a nickel complex compound may be used.

The polarizing plate can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed as a device having an appropriate structure according to the related art, such as a transmission type or a reflection type in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell, or a transmission / reflection type. Therefore, the liquid crystal cell forming the liquid crystal display device is optional, and for example, an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twisted nematic type or a super twisted nematic type, etc. A liquid crystal cell of any type may be used.

When polarizing plates and optical members are provided on both sides of the liquid crystal cell, they may be the same or different. Further, in forming the liquid crystal display device, one or more layers of appropriate components such as a prism array sheet, a lens array sheet, a light diffusing plate, and a backlight can be arranged at appropriate positions.

Next, the present invention will be described specifically with reference to examples.

[0034]

EXAMPLES Example 1 A commercially available 75 μm thick PVA film was swollen in pure water and dyed with a mixed aqueous solution of iodine and potassium iodide. After that, cross-linking with boric acid and 4-fold stretching are performed, and dried at 50 ° C. to a thickness of 25 μm.
m polarizing film was produced. The water content of the polarizing film is 8
% By mass. The water content is a value measured by Karl Fischer titration. On both sides of the produced polarizer,
As a protective film, a saponification-treated 80 μm-thick triacetylcellulose film is used as an acrylic-modified one-pack moisture-curable adhesive (manufactured by Konishi Co., Ltd., trade name:
Bond Silex “Clear”). The thickness of the adhesive layer was 2 μm.

(Embodiment 2) The same thickness as that of Embodiment 1 (25 μm)
A thickness of 38 as a protective film on both sides of the polarizing film
μm norbornene-based thermoplastic resin film (JSR
(Trade name: ARTON film), which were subjected to corona treatment, and bonded together using an acetic acid-based one-component moisture-curable adhesive (trade name: KE-41-T, manufactured by Shin-Etsu Chemical Co., Ltd.). The thickness of the adhesive layer was 3 μm.

(Comparative Example 1) The same thickness as in Example 1 (25 μm)
A thickness of 80 as a protective film on both sides of the polarizing film
The saponified saponified triacetyl cellulose film having a thickness of μm was bonded using an adhesive obtained by adding glyoxal to polyvinyl alcohol. The thickness of the adhesive layer was 0.5 μm.

(Comparative Example 2) The same thickness of 25 μm as in Example 1.
A thickness of 38 as a protective film on both sides of the polarizing film
μm norbornene-based thermoplastic resin film (JSR
Manufactured by Arton Film Co., Ltd.), and bonded with an acrylic adhesive (manufactured by Konishi Co., Ltd., trade name: Kony Bond). The thickness of the adhesive layer was 2 μm.

With respect to the polarizing plates prepared in Examples and Comparative Examples, adhesion, water resistance, wet heat resistance, durability,
A dimensional stability test was performed. The results are shown in Tables 1 to 3.

(Adhesive force) According to JIS K6854,
The polarizing plate produced by the above method was cut into a size having a width of 25 mm, and a T-peel test was performed under the conditions of a pulling speed of 100 mm / min.

(Hot water immersion test) The polarizing plate produced by the above method was cut into a size of 50 mm x 50 mm,
, And the time until one of the surfaces was completely peeled off was measured.

(Durability of Polarizing Plate) The polarizing plate manufactured by the above method was subjected to a heat and humidity condition of 60 ° C. and 95% RH for 1000 hours.
After heating for a time, the transmittance and the degree of polarization of the polarizing plate before and after heating were measured, and the state of the change was observed. The transmittance is the transmittance (%) at 546.1 nm of one polarizing plate.
The degree of polarization is represented by the following equation, where Tp is the transmittance (%) measured when two polarizing plates are stacked in parallel, and Tc is the transmittance (%) measured when two polarizing plates are stacked orthogonally. It is.

[0042]

(Equation 1)

(Dimensional Change of Polarizing Plate) The polarizing plate produced by the above method was cut into a size of 100 mm × 100 mm, and allowed to stand at 60 ° C. and 95% RH for 120 hours. The dimensions (initial dimensions) before and after the heat test (dimensions after the test) are measured in the direction (absorption axis direction of the polarizing plate) and the TD direction (direction perpendicular to the absorption axis), and the dimensions change according to the following formula. The rate (%) was determined. In addition, the dimension in the MD direction was measured by measuring the distance between the upper and lower ends of the test piece in the MD direction at a midpoint 5 cm inside, and the dimension in the TD direction was measured 5 cm inward from the left and right ends in the TD direction. The distance was measured. Dimensional change rate (%) = [(dimension after test-initial dimension) / initial dimension] x 100

[Table 1] Experiment No. Adhesion Hot water immersion test (N) (min) Example 1 90 120 or more Example 2 80 or more (protective film break) 120 or more Comparative example 1 150 or more (protective film break) 29 Comparative example 2 7 120 or more

As is clear from the results shown in Table 1, it is understood that the polarizing plate of the present invention has excellent adhesive strength, water resistance and heat and humidity resistance.

[Table 2] (Durability of Polarizing Plate) Transmittance (%) Polarization Polarization Heating 0 hr Heating 1000 hr Difference Heating 0 hr Heating 1000 hr Difference Example 1 43.39 46.12 2.73 99.93 94.10 -5.83 Example 2 42.61 43.07 0.46 99.90 98.84 -1.06

As is evident from the results in Table 2, the polarizing plate using the norbornene-based thermoplastic resin film of the present invention as a protective film has a smaller change in transmittance and degree of polarization than a triacetyl cellulose film. Understand.

[0048] [Table 3] (dimensional change of the polarizing plate) experiment No. MD direction TD direction Example 1 -0.585 0.924 Example 2 -0.294 0.544

As is evident from the results in Table 3, the polarizing plate using the polynorbornene-based thermoplastic resin film of the present invention as a protective film has a smaller dimensional change after heat treatment than the triacetyl cellulose film. I understand.

[0050]

As described above, in the polarizing plate of the present invention, since the polyvinyl alcohol-based polarizing film and the protective film are adhered to each other with the one-component type silicone-based moisture-curable adhesive, water resistance, moisture-heat resistance and water resistance are improved. The resulting polarizing plate has excellent adhesiveness, and has the effect that the performance of the polarizing plate does not deteriorate even when left at high temperature and high humidity for a long time. Further, the adhesive layer formed of the one-part silicone moisture-curable adhesive of the present invention has high transparency and no optical anisotropy. Therefore, the polarizing plate has a high optical performance. Furthermore, since the adhesive of the present invention is a one-component type, it does not require the labor of pre-mixing such as a two-component type adhesive at the time of bonding, and is dried before or after bonding like a solvent-based or water-based adhesive. Since there is no need to perform, there is an advantage that the working process can be shortened.Also, since it is a moisture-curing type, even if it is sealed with a protective film, curing is promoted by moisture in polyvinyl alcohol, and it is cured at room temperature, so that it is cured after application. This has the effect that the step of drying the adhesive becomes unnecessary.

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Claims (4)

[Claims] 1. A polarizing plate comprising a protective film laminated on at least one surface of a polyvinyl alcohol-based polarizing film, wherein the polarizing film and the protective film are adhered to each other with a one-component silicone-based moisture-curable adhesive. Polarizing plate. 2. The polarizing plate according to claim 1, wherein a protective film whose adhesive surface has been subjected to at least one treatment selected from corona treatment, plasma treatment, flame treatment, primer coating treatment and saponification treatment is used. 3. The polarizing plate according to claim 1, wherein a polyvinyl alcohol-based polarizing film having a water content of 1% by mass or more is used. 4. The polarizing plate according to claim 1, wherein the protective film is a norbornene-based thermoplastic resin film.