JP6219781B2 - Polarizing film, polarizing plate and liquid crystal panel - Google Patents

Description

  The present invention relates to a polarizing film, a polarizing plate and a liquid crystal panel which are suitably used for a liquid crystal display device.

  A polarizing plate is widely used as a polarized light supplying element in an image display device such as a liquid crystal display device. As a polarizing plate, the thing of the structure which bonded the protective film to the polarizing film using the adhesive agent is common (for example, patent document 1).

  Various mobile devices using liquid crystal display devices, thin liquid crystal televisions, etc. are already widely used, and accordingly, in recent years, there has been an increasing demand for thinner polarizing plates and liquid crystal cells that constitute liquid crystal panels of liquid crystal display devices. Yes.

JP 2013-148806 A

  Generally, a polarizing plate, particularly a thin polarizing plate, is usually manufactured through a stretching process. Therefore, the polarizing film has an absorption axis direction (MD) and further a transmission axis direction (absorption). Warpage is likely to occur in a direction (TD) perpendicular to the axial direction, for example, in a high temperature environment or a high humidity environment. When such a polarizing plate is bonded to a liquid crystal cell to produce a liquid crystal panel, the resulting liquid crystal panel is warped particularly when the liquid crystal cell is thin and has low rigidity. The warpage of the liquid crystal panel may adversely affect the visibility of the liquid crystal display device.

  Accordingly, an object of the present invention is to provide a polarizing film capable of providing a polarizing plate with improved warping to such an extent that warpage of the liquid crystal panel can be sufficiently suppressed, and a polarizing plate and a liquid crystal panel using the polarizing film.

The present invention provides the following polarizing film, polarizing plate and liquid crystal panel.
[1] A polarizing film having a shrinkage force of 1.5 N or less per 2 mm width in the absorption axis direction when held at 80 ° C. for 4 hours.

[2] The polarizing film according to [1], which is a stretched film.
[3] The polarizing film according to [1] or [2], wherein the thickness is 20 μm or less.

  [4] The polarizing film according to any one of [1] to [3], wherein the boron content is in the range of 0.5 to 2.0% by weight.

  [5] The polarizing film according to any one of [1] to [4], wherein the transmittance correction single transmittance is 40% or more and the visibility correction polarization degree is 90% or more.

[6] A polarizing film having a shrinkage force per width of 2 mm in the absorption axis direction when held at 80 ° C. for 4 hours is 1.5 N or less,
A protective film disposed on at least one surface of the polarizing film;
A polarizing plate including

[7] The polarizing plate according to [6], wherein the protective film has a thickness of 50 μm or less.
[8] including a protective film disposed on both sides of the polarizing film;
The polarizing plate as described in [6] or [7] whose thickness ratio of the other protective film with respect to one protective film is 1.5 or more.

  [9] The polarizing plate according to any one of [6] to [8], which has a rectangular shape having a long side of 8 cm or more and a short side of 5 cm or more.

  [10] A liquid crystal panel comprising a liquid crystal cell and the polarizing plate according to any one of [6] to [9] disposed on at least one surface thereof.

  [11] The liquid crystal panel according to [10], wherein the thickness of the substrate constituting the liquid crystal cell is 0.5 mm or less.

  According to the polarizing film of the present invention, it is possible to provide a polarizing plate with improved warpage to such an extent that warpage of the liquid crystal panel can be sufficiently suppressed. The liquid crystal panel using the polarizing plate of the present invention is suppressed in warpage and can be suitably applied to a thin liquid crystal display device.

<Polarizing film>
A polarizing film is an optical film having the property of absorbing linearly polarized light having a vibration plane parallel to the absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). The polarizing film of the invention is characterized in that the shrinkage force per 2 mm width in the absorption axis direction is 1.5 N or less. Hereinafter, the absorption axis direction is also referred to as “MD”, and the transmission axis direction (direction orthogonal to the absorption axis) is also referred to as “TD”.

(1) Shrinkage force of polarizing film The present inventor performs various studies on the warpage of a polarizing plate formed by laminating a protective film on one or both sides of a polarizing film, and uses a cut sample of the polarizing plate [Example]. The ratio of the warpage amount in MD (the warpage amount in the absorption axis direction) and the warpage amount in TD (the warpage amount in the transmission axis direction) of the polarizing plate determined in accordance with the measurement method described in detail in the section (hereinafter referred to as “MD / It was also found that when the TD warpage ratio is adjusted to 1.0 or the vicinity thereof, the warpage of a liquid crystal panel produced using this polarizing plate can be effectively suppressed.

  Further, as a specific means for adjusting the MD / TD warpage ratio of the polarizing plate to 1.0 or the vicinity thereof by further study, the shrinkage force per 2 mm width in the absorption axis direction of the polarizing film (hereinafter referred to as “MD shrinkage”). It has also been found that it is extremely effective to set the force to 1.5 N or less.

  As described above, the polarizing film is usually produced through a stretching process, and the stretching axis in this case is usually MD (the absorption axis is also MD). Therefore, the conventional polarizing plate has a MD / TD warp ratio of 1.0 or larger than the vicinity thereof. On the other hand, if the polarizing film of this invention whose MD shrinkage force is 1.5 N or less is used, the MD / TD warpage ratio of the polarizing plate can be set to 1.0 or the vicinity thereof.

  MD contraction force here means MD contraction force of the polarizing film before sticking a protective film to make a polarizing plate, and per 2 mm width in the absorption axis direction when held at 80 ° C. for 4 hours. The contraction force. The MD shrinkage force is measured using a cut sample of the polarizing film, and the details of the measuring method are as described in the [Example] section. Since it is effective to bring the MD / TD warpage ratio of the polarizing plate close to 1.0, the MD shrinkage force is preferably 0.1 to 1.3 N, more preferably 0.3 to 1.1 N. is there.

  On the other hand, in the polarizing film of the present invention, the shrinkage force per 2 mm width in the transmission axis direction (hereinafter also referred to as “TD shrinkage force”) when kept at 80 ° C. for 4 hours is usually 0.1 to 1.0 N. It is. The details of the method for measuring the TD contraction force are as described in the [Example] section. The TD contraction force here also means the TD contraction force of the polarizing film before the protective film is bonded to form a polarizing plate.

(2) Material, Thickness, etc. of Polarizing Film The polarizing film of the present invention can be a single (single layer) film made of a stretched thermoplastic resin film, typically a uniaxially stretched polyvinyl alcohol system. A dichroic dye is adsorbed and oriented on a resin film.

  As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, a saponified polyvinyl acetate resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group. The degree of saponification of the polyvinyl alcohol-based resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 99.5 mol%, more preferably 94.0. It is in the range of ˜99.0 mol%.

  The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10,000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol resin can be determined according to JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain preferable polarization performance, and if it exceeds 10,000, film processability may be inferior.

  The dichroic dye adsorbed and oriented on the polarizing film can be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include: Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Includes Sky Blue, Direct First Orange S and First Black. A dichroic dye may be used individually by 1 type, and may use 2 or more types together.

  Although the thickness of a polarizing film is about 5-40 micrometers normally, from the viewpoint of thickness reduction of a polarizing plate and a liquid crystal panel, it is so preferable that thickness is thin in the range which can ensure sufficient handleability and durability. Therefore, the thickness of the polarizing film is preferably 20 μm or less, and more preferably 15 μm or less. However, since the MD / TD warp ratio tends to be larger than 1 as the thickness is thinner, the MD contraction force needs to be lowered in order to bring the MD / TD warp ratio closer to 1.

(3) Polarization characteristics of polarizing film The polarizing performance of the polarizing film can be mainly expressed by numerical values called single transmittance and degree of polarization.
Single transmittance (λ) = 0.5 × (Tp (λ) + Tc (λ))
Polarization degree (λ) = 100 × (Tp (λ) −Tc (λ)) / (Tp (λ) + Tc (λ))
Defined by

  Here, Tp (λ) is the transmittance (%) of the polarizing film measured in the relationship between the linearly polarized light having the incident wavelength λnm and the parallel Nicol, and Tc (λ) is crossed with the linearly polarized light having the incident wavelength λnm. It is the transmittance | permeability (%) of the polarizing film measured by the relationship of Nicol, and is a measured value obtained by the polarized ultraviolet visible absorption spectrum measurement by a spectrophotometer. In addition, the single transmittance (λ) and the degree of polarization (λ) obtained for each wavelength are subjected to sensitivity correction called visibility correction, respectively, and the visibility correction single transmittance (Ty) and the visibility correction polarization, respectively. Called degrees (Py). These Ty and Py values can be measured using, for example, a spectrophotometer.

  In order to ensure good clarity of an image when applied to a liquid crystal display device, the polarizing film preferably has a visibility corrected single transmittance (Ty) of 40% or more, and a visibility corrected polarization degree. (Py) is preferably 90% or more. Ty is more preferably 42% or more, and Py is more preferably 99% or more. More preferably, Ty is 42.8% or more, and Py is 99.99% or more.

  In order to increase Ty and Py, it is usually necessary to increase the draw ratio, but in this case, the MD contraction force tends to increase. Therefore, when obtaining a polarizing film having high Ty and Py, it is necessary to sufficiently reduce the MD shrinkage force by the method described later.

(4) Boron content in polarizing film In order to reduce the MD shrinkage of the polarizing film, it is effective to lower the boron content in the polarizing film. For example, the boron content in the polarizing film is reduced. It is preferable to set it as 0.5 to 2.0 weight%. The boron content in the polarizing film can be calculated as follows. First, the weight of the polarizing film is measured, and then the polarizing film is immersed in hot water at 95 ° C. for 60 minutes to completely dissolve it. Subsequently, the aqueous solution in which the polarizing film is dissolved is subjected to neutralization titration, and the boron content in the polarizing film is calculated from the weight and titration amount of the polarizing film.

<Polarizing plate>
The polarizing plate of the present invention includes a polarizing film and a protective film disposed on at least one surface thereof.

(1) Polarizing film In order to adjust the MD / TD warpage ratio of the polarizing plate to 1.0 or the vicinity thereof, the MD shrinkage force of the polarizing film is preferably 0.1 to 1.3 N as described above. More preferably, it is 0.3-1.1N. Moreover, the TD shrinkage force of the polarizing film with which the polarizing plate of this invention is provided is 0.1-1.0N normally.

  The MD and TD contraction force herein has the same meaning as the contraction force described in the above section <Polarization film> except that it is the contraction force of the polarizing film obtained by removing the protective film from the polarizing plate. The details of the measurement method are as described in the [Example] section. Since the heat history may be different before and after the protective film is bonded, the value of the shrinkage force in the above section <Polarizing film> may be slightly different from the value of the shrinkage force here.

  Regarding the material, thickness, polarization characteristics, boron content and the like of the polarizing film provided in the polarizing plate of the present invention, the description in the above section <Polarizing film> is cited.

(2) Protective film The protective film that is bonded and disposed on one or both sides of the polarizing film is a thermoplastic resin, for example, a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin (norbornene resin, etc.). Polyolefin resin such as cellulose triacetate, cellulose ester resin such as cellulose diacetate; polyester resin such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate; polycarbonate resin; polymethyl methacrylate resin (Meth) acrylic resin; or a transparent resin film made of a mixture or copolymer thereof. A protective film is normally laminated | stacked on a polarizing film through an adhesive bond layer.

  The protective film can also be a protective film having an optical function such as a retardation film and a brightness enhancement film. For example, a retardation film provided with an arbitrary retardation value by stretching a transparent resin film made of the above material (uniaxial stretching or biaxial stretching) or forming a liquid crystal layer or the like on the film. It can be.

  A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, or an antifouling layer can be formed on the surface of the protective film opposite to the polarizing film. The method for forming the surface treatment layer on the surface of the protective film is not particularly limited, and a known method can be used.

  In the case where protective films are bonded to both surfaces of the polarizing film, these protective films may be the same type of resin film or a different type of resin film. From the viewpoint of more effectively bringing the MD / TD warpage ratio of the polarizing plate closer to 1.0, the protective films on both sides are preferably films made of the same kind of resin, but even when made of different kinds of resins. According to the present invention, the MD / TD warp ratio can be made sufficiently close to 1.0.

  The thickness of the protective film is preferably thin from the viewpoint of reducing the thickness of the polarizing plate, but if it is too thin, the strength is lowered and the processability is poor. Therefore, it is preferable that the thickness of the 1st protective film 20 is 5-150 micrometers, More preferably, it is 5-100 micrometers, More preferably, it is 10-50 micrometers. As another means for bringing the MD / TD warp ratio close to 1.0, it is conceivable to increase the reinforcing effect of the protective film, for example, to increase the thickness of the protective film. However, this means is disadvantageous for making the polarizing plate thinner. According to the present invention, even if the thickness of the protective film is reduced to 50 μm or less, the MD / TD warpage ratio can be brought close to 1.0.

  When bonding a protective film on both surfaces of a polarizing film, these protective films may have the same thickness and may have mutually different thickness. As another means for bringing the MD / TD warpage ratio closer to 1.0, it is conceivable to bond protective films on both surfaces of the polarizing film and utilize the reinforcing effect of these protective films. However, in the case of this means, there arises a restriction that the thicknesses of the protective films on both sides must be equal or nearly equal. According to the present invention, even when the thickness ratio of the protective films on both sides is 1.5 or more, and even 2.0 or more, the MD / TD warpage ratio can be close to 1.0.

  Further, as another means for bringing the MD / TD warp ratio closer to 1.0, it is conceivable to bond a protective film only on one side of the polarizing film and utilize the reinforcing effect of the protective film. There are significant restrictions on the protective film that can be used, such as the thickness to obtain sufficient effects and the rigidity of the material. According to the present invention, the MD / TD warpage ratio can be made close to 1.0 regardless of whether the protective film is laminated on one side or on both sides. As described above, the polarizing plate of the present invention is advantageous in that the MD / TD warpage ratio can be brought close to 1.0 while maintaining a wide degree of freedom such as the number, material, and thickness of the protective film to be bonded. It is.

(3) Configuration of Polarizing Plate The polarizing plate (polarizing film) can have an appropriate shape and size required for the applied liquid crystal display device. For example, a rectangular shape having a long side of 8 cm or more and a short side of 5 cm or more (for example, Rectangular, square). When the MD / TD warpage ratio is large as in the case of a conventional polarizing plate, the warpage of the liquid crystal panel tends to become more prominent as the size of the polarizing plate is larger. Even if the side is increased to 100 cm or more, warping of the liquid crystal panel can be satisfactorily suppressed.

  As described above, the MD / TD warpage ratio in the polarizing plate of the present invention is 1.0 or in the vicinity thereof, more specifically 1.0 ± 0.4, and preferably 1.0 ± 0. .3, more preferably 1.0 ± 0.2. If it is this range, the curvature of a liquid crystal panel can be suppressed effectively.

  A polarizing plate can have an adhesive layer for bonding to a liquid crystal cell. The pressure-sensitive adhesive layer is laminated on the outer surface of the protective film (for example, when a protective film is laminated on both sides of the polarizing film) or on the polarizing film surface (for example, when the protective film is laminated on one side of the polarizing film). Can do.

  The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually based on a (meth) acrylic resin, styrene resin, silicone resin or the like, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. It consists of an adhesive composition. The thickness of the pressure-sensitive adhesive layer can be about 1 to 40 μm.

<Production method of polarizing film and polarizing plate>
A polarizing film formed by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film is a step of uniaxially stretching the polyvinyl alcohol resin film; by dyeing the polyvinyl alcohol resin film with a dichroic dye A step of adsorbing a dichroic dye; a step of treating a polyvinyl alcohol-based resin film adsorbed with a dichroic dye with an aqueous boric acid solution; and a step of washing after the treatment with an aqueous boric acid solution. it can. The thickness of the polyvinyl alcohol-type resin film used as a raw material is about 10-150 micrometers, for example. Since the polarizing film having a thickness of 20 μm or less can be easily produced, the thickness of the polyvinyl alcohol-based resin film is preferably 40 μm or less.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before, simultaneously with, or after dyeing the dichroic dye. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Moreover, you may uniaxially stretch in these several steps.

  In uniaxial stretching, it may be uniaxially stretched between rolls having different peripheral speeds, or may be uniaxially stretched using a hot roll. Further, the uniaxial stretching may be dry stretching in which stretching is performed in the air, or may be wet stretching in which stretching is performed in a state where a solvent is used and the polyvinyl alcohol-based resin film is swollen. The draw ratio is usually about 3 to 8 times. In order to impart good polarization characteristics, the draw ratio is preferably 4 times or more, more preferably 5 times or more.

  In order to reduce the MD shrinkage force of the polarizing film, it is preferable to carry out uniaxial stretching separately before boric acid treatment and during boric acid treatment. In this case, the total draw ratio before the boric acid treatment is more than 1.0 times, preferably 1.01 to 2.5 times. The total draw ratio is more preferably 1.01 to 2.1 times, and still more preferably 1.01 to 1.7 times.

  As a method of dyeing the polyvinyl alcohol resin film with the dichroic dye, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution (dye solution) containing the dichroic dye is employed. The polyvinyl alcohol-based resin film is preferably subjected to an immersion treatment (swelling treatment) in water before the dyeing treatment.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol resin film by dipping in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this dyeing aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing aqueous solution is usually about 20 to 40 ° C.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in a dyeing aqueous solution containing the dichroic organic dye is usually employed. The content of the dichroic organic dye in the dyeing aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight and preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This dyeing aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dyeing aqueous solution is usually about 20 to 80 ° C.

  The boric acid treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution. The amount of boric acid in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight per 100 parts by weight of water. As described above, in order to reduce the MD shrinkage force of the polarizing film, it is effective to reduce the boron content in the polarizing film. For example, the boron content in the polarizing film is 0.5-2. It is preferable to set it to 0.0% by weight. Therefore, in order to reduce the MD shrinkage force of the polarizing film, the amount of boric acid in the boric acid-containing aqueous solution is preferably 0.1 to 3 parts by weight per 100 parts by weight of water. More preferred are parts by weight. In order to reduce the MD shrinkage force of the polarizing film more effectively, it is preferable to apply the boric acid concentration and adopt the preferred stretching mode described above.

  When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight and preferably about 5 to 12 parts by weight per 100 parts by weight of water. The temperature of the boric acid-containing aqueous solution is usually about 50 to 85 ° C.

  The polyvinyl alcohol-based resin film after the boric acid treatment is usually washed by immersing it in water or an aqueous potassium iodide solution. The temperature of the water or the potassium iodide aqueous solution in the washing treatment is usually about 5 to 40 ° C.

  After washing, a drying process is performed to obtain a polarizing film. The drying treatment can be performed using a hot air dryer, a far infrared heater, a hot roll, or the like. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 50 to 80 ° C. It is preferable that the film moisture content before a drying process is 25 to 55 weight% from a viewpoint of drying efficiency. Moreover, although the film moisture content after a drying process is 5-35 weight% normally, it is preferable that it is 6-33 weight% from a transportable viewpoint.

  A polarizing plate can be obtained by bonding a protective film via an adhesive layer on one side or both sides of a polarizing film (single film) obtained as described above. As an adhesive for forming the adhesive layer, a water-based adhesive or a photocurable adhesive can be used. When bonding a protective film on both surfaces, the adhesive agent which forms two adhesive bond layers may be the same, and a different kind may be sufficient as it. For example, when a protective film is bonded to both sides, one side may be bonded using a water-based adhesive, and the other side may be bonded using a photocurable adhesive.

  Examples of the water-based adhesive include an adhesive made of a polyvinyl alcohol-based resin aqueous solution, an aqueous two-component urethane emulsion adhesive, and the like. Among these, a water-based adhesive composed of a polyvinyl alcohol-based resin aqueous solution is preferably used.

  Polyvinyl alcohol resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. A polyvinyl alcohol copolymer obtained by saponifying a polymer, or a modified polyvinyl alcohol polymer obtained by partially modifying the hydroxyl group thereof can be used. The water-based adhesive can include additives such as polyvalent aldehydes, water-soluble epoxy compounds, melamine compounds, zirconia compounds, and zinc compounds.

  When using an aqueous adhesive, it is preferable to carry out a drying step for removing water contained in the aqueous adhesive after bonding. The drying temperature is preferably 30 to 100 ° C. When it is lower than 30 ° C., the protective film is easily peeled off from the polarizing film. If the drying temperature exceeds 100 ° C., the polarizing performance of the polarizing film may be deteriorated by heat. After the drying step, a curing step of curing at room temperature or slightly higher temperature, for example, at a temperature of about 20 to 45 ° C. for about 12 to 600 hours may be provided.

  The photocurable adhesive refers to an adhesive that is cured by irradiating active energy rays such as ultraviolet rays, for example, an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, and a binder. The thing containing resin and a photoreactive crosslinking agent can be mentioned. Examples of the polymerizable compound include photopolymerizable monomers such as a photocurable epoxy monomer, a photocurable acrylic monomer, and a photocurable urethane monomer, and oligomers derived from the photopolymerizable monomer. As a photoinitiator, what contains the substance which generate | occur | produces active species like neutral radical, anion radical, and a cation radical by irradiation of active energy rays, such as an ultraviolet-ray, can be mentioned. As the photocurable adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photocurable epoxy monomer and a photocationic polymerization initiator can be preferably used.

  When using a photocurable adhesive, after bonding, a photocurable adhesive is hardened by irradiating an active energy ray. The light source of the active energy ray is not particularly limited, but an active energy ray having a light emission distribution at a wavelength of 400 nm or less is preferable. Specifically, the low-pressure mercury lamp, the medium-pressure mercury lamp, the high-pressure mercury lamp, the ultrahigh-pressure mercury lamp, the chemical lamp, and the black light lamp A microwave excitation mercury lamp, a metal halide lamp and the like are preferably used.

  Prior to the bonding of the polarizing film and the protective film, the bonding surface of the polarizing film and / or the protective film has a plasma treatment, a corona treatment, an ultraviolet irradiation treatment, a frame (flame) treatment, in order to improve adhesion. Easy adhesion treatment such as saponification treatment may be performed.

  The polarizing plate of the present invention is not limited to the above method, and a polyvinyl alcohol-based resin layer is formed on a base film as described in, for example, JP-A-2009-98653, and this resin layer is formed into a polarizer layer ( It can also be produced by a method that corresponds to a polarizing film. This method is advantageous for obtaining a thin polarizer layer.

Specifically, the method is
After applying a coating liquid containing a polyvinyl alcohol-based resin on at least one surface of the base film, a resin layer forming step of forming a polyvinyl alcohol-based resin layer by drying to obtain a laminated film,
A stretching step of stretching a laminated film to obtain a stretched film;
A dyeing step of obtaining a polarizing laminated film by dyeing a polyvinyl alcohol resin layer of a stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizing film);
The 1st bonding process of bonding a protective film using the adhesive agent on the polarizer layer of a light-polarizing laminated film, and obtaining a bonding film,
Peeling process of peeling and removing the base film from the bonding film to obtain a polarizing plate with a single-sided protective film,
Can be included in this order.

When laminating a protective film on both surfaces of the polarizer layer, it further includes a second laminating step of laminating the protective film on the polarizer surface of the polarizing plate with a single-side protective film using an adhesive.

<LCD panel>
The liquid crystal panel of the present invention includes a liquid crystal cell and the polarizing plate according to the present invention which is bonded and disposed on at least one surface thereof. Usually, the polarizing plate is bonded to the liquid crystal cell via an adhesive layer. The liquid crystal panel may include the polarizing plate according to the present invention only on one side or on both sides. From the viewpoint of suppressing warpage of the liquid crystal panel, the polarizing plate according to the present invention is preferably disposed on both surfaces of the liquid crystal cell.

  The liquid crystal cell includes a pair of substrates (for example, a transparent substrate such as a glass substrate) arranged to face each other at a predetermined distance by a spacer, and a liquid crystal layer formed by enclosing a liquid crystal between the pair of substrates. Yes, it may be an arbitrary driving method such as a TN (Twisted Nematic) type, a STN (Super-Twisted Nematic) type, a VA (Vertical Alignment) type, or an IPS (In-Plane Switching) type.

  The thickness of the substrate constituting the liquid crystal cell is arbitrary, but when the MD / TD warpage ratio is large as in the case of a conventional polarizing plate, the warp of the liquid crystal panel tends to become more prominent as the substrate is thinner. According to the present invention, even if the thickness of the substrate is reduced to, for example, 0.5 mm or less, and further to 0.3 mm or less, the warp of the liquid crystal panel can be satisfactorily suppressed.

  The liquid crystal panel can have an appropriate shape and size required for the applied liquid crystal display device, and can be, for example, a rectangular shape (for example, a rectangle or a square) having a long side of 8 cm or more and a short side of 5 cm or more. When the MD / TD warpage ratio is large as in the conventional polarizing plate, the warpage of the liquid crystal panel tends to become more prominent as the size of the liquid crystal panel (and hence the polarizing plate) increases. Even when the size is increased to, for example, a long side of 200 cm or more and a short side of 100 cm or more, warping of the liquid crystal panel can be satisfactorily suppressed.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the following examples and comparative examples, the boron content in the polarizing film, the polarizing properties of the polarizing film, the MD and TD shrinkage (before and after bonding of the protective film), and the MD / TD warpage ratio are as follows: Measured according to the method.

[A] Boron content in polarizing film The weight of the obtained polarizing film was measured, and then the polarizing film was immersed in hot water at 95 ° C. for 60 minutes to completely dissolve it. Subsequently, the aqueous solution in which the polarizing film was dissolved was subjected to neutralization titration, and the boron content in the polarizing film was calculated from the weight and titration amount of the polarizing film.

[B] Polarization characteristics of polarizing film About the obtained polarizing film, using a spectrophotometer ("V-7100" manufactured by JASCO Corporation), the visibility corrected single transmittance (Ty) and the visibility corrected polarization The degree (Py) was measured.

[C] MD and TD shrinkage force of polarizing film before bonding protective film From the obtained polarizing film, for measuring MD shrinkage force having a width of 2 mm and a length of 10 mm with the absorption axis direction (MD, stretching direction) as the long side. A sample was cut out. The long side generated when this sample is set in the thermomechanical analyzer (TMA) “EXSTAR-6000” manufactured by SII Nanotechnology, Inc. and kept at 80 ° C. for 4 hours while keeping the dimensions constant. The contraction force (MD contraction force) in the direction (absorption axis direction, MD) was measured. Further, TD contraction force was measured in the same manner as described above except that a sample having a width of 2 mm and a length of 10 mm having a long side in the transmission axis direction (direction orthogonal to the absorption axis direction, TD) was used.

[D] MD and TD shrinkage force of polarizing film after bonding protective film The obtained polarizing plate was cut into small pieces of 10 cm × 5 cm, immersed in 600 mL of methylene dichloride, and subjected to ultrasonic treatment at room temperature for 30 minutes. Then, the bonded protective film was dissolved and removed. A sample for measuring MD contraction force having a width of 2 mm and a length of 10 mm having a long side in the absorption axis direction (MD, stretching direction) was cut out from the polarizing film from which the protective film was removed. The MD contraction force was measured in the same manner as in the above [c] except that this sample was used. Moreover, it is the same as MD contraction force except that a polarizing plate piece having a width of 2 mm and a length of 10 mm having a long side in the transmission axis direction (direction perpendicular to the absorption axis direction, TD) is cut out from the polarizing film from which the protective film has been removed. Then, the TD contraction force was measured.

[E] MD / TD Warpage Ratio of Polarizing Plate A sample for measuring MD warpage with a width of 40 mm and a length of 150 mm having a long side in the absorption axis direction (MD, stretching direction) was cut out from the obtained polarizing plate. This sample was bonded to the center of the surface of a flat glass substrate (width 51 mm, length 156 mm, thickness 0.5 mm) using an acrylic adhesive. In this state, the amount of warpage in the absorption axis direction was measured by the following procedure. Two-dimensional dimensional measuring instrument is used to measure the height at 5 points (5, 40, 75, 110, and 145 mm along the long side direction, all located at the center in the short side direction), with one of the short sides of the sample as 0 mm The amount of MD warpage (mm) before heating was determined as the difference between the maximum height and the minimum height. The sample was then heated at 85 ° C. for 250 hours. With respect to the sample after heating, one of the short sides of the sample is defined as a point 0 mm, and the height at five points (points 5 mm, 40 mm, 75 mm, 110 mm, and 145 mm) along the long side direction (all located at the center in the short side direction) The thickness was measured with a two-dimensional dimension measuring device, and the MD warpage amount (mm) after heating was determined as the difference between the maximum height and the minimum height. The value obtained by subtracting the MD warp amount before heating from the MD warp amount after heating was defined as the MD warp amount. Further, the amount of warpage in the transmission axis direction (TD warpage amount) is the same as the above except that a sample having a width of 40 mm and a length of 150 mm with the long side in the transmission axis direction (direction orthogonal to the absorption axis direction, TD) is used. , Mm), and the following formula:
MD / TD warp ratio = MD warp ratio was determined according to MD warp amount / TD warp amount.

<Example 1>
(A) Production of Polarizing Film While continuously transporting a long polyvinyl alcohol original film (width 450 cm, thickness 30 μm, average polymerization degree of polyvinyl alcohol about 2400, saponification degree 99.9 mol% or more), 30 After swelled by immersing in pure water of 0 ° C. for 97 seconds, dyeing was performed by immersing in an aqueous solution containing iodine of 30 ° C. having a weight ratio of potassium iodide / water of 2/100 for 123 seconds. Thereafter, boric acid treatment was performed by immersing in an aqueous solution of 56 ° C. having a weight ratio of potassium iodide / boric acid / water of 12 / 1.0 / 100 for 81 seconds. Thereafter, the film was washed by immersing the film in a washing tank filled with 5 ° C. pure water for 2 seconds, followed by drying at 60 ° C. for 160 seconds by passing the film through a hot-air drying furnace to obtain polyvinyl alcohol. A long polarizing film in which iodine was adsorbed and oriented was obtained. During this time, the longitudinal uniaxial stretching process is mainly performed in the dyeing process and the boric acid treatment process, the total stretch ratio before the boric acid treatment process is 2.1 times, and the total stretch ratio from the raw film is 5.5 times. there were. The thickness of the polarizing film was 12.5 μm, and the boron content in the polarizing film was 1.5% by weight.

(B) Production of Polarizing Plate While continuously transporting the long polarizing film obtained in (A) above, a protective film (thickness 40 μm) made of triacetyl cellulose is passed through an aqueous adhesive with a bonding roll. After being bonded to both sides of the polarizing film, it was passed through a hot air drying oven for 98 seconds at 60 ° C. to obtain a long polarizing plate in which protective films were bonded to both sides of the polarizing film. For the water-based adhesive, an acetoacetyl group-modified polyvinyl alcohol resin (trade name “Gosefimer Z-200”, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) is dissolved in pure water to prepare a 10% aqueous solution. To this, sodium glyoxylate as a cross-linking agent was mixed so that the weight ratio of the former: the latter solid content was 1: 0.1, and 1 polyvinylacetate resin modified with acetoacetyl group was added to 100 parts by weight of water. What was diluted with pure water so that it might become a weight part was used.

<Examples 2 to 4>
Example, except that the thickness of the raw film made of polyvinyl alcohol, the drying temperature in the drying process at the time of polarizing plate preparation (after bonding of the protective film), and the thickness of the obtained polarizing film are as shown in Table 1. In the same manner as in Example 1, a polarizing film and a polarizing plate were produced.

<Comparative Example 1>
(A) Production of Polarizing Film While continuously transporting a long polyvinyl alcohol original film (width 450 cm, thickness 30 μm, average polymerization degree of polyvinyl alcohol about 2400, saponification degree 99.9 mol% or more), 20 After swelled by immersing in pure water at 24 ° C. for 24 seconds, dyeing was carried out by immersing in an aqueous solution containing 30 ° C. iodine having a weight ratio of potassium iodide / water of 2/100 for 74 seconds. Then, the boric acid treatment was performed by dipping in a 56 ° C. aqueous solution having a weight ratio of potassium iodide / boric acid / water of 12 / 1.5 / 100 for 64 seconds. Thereafter, the film was washed with water by immersing the film in a washing tank filled with 5 ° C. pure water for 2 seconds. Subsequently, the film was passed through a hot air drying oven and dried at 60 ° C. for 160 seconds to obtain a long polarizing film in which iodine was adsorbed and oriented on polyvinyl alcohol. During this time, the longitudinal uniaxial stretching process is mainly performed in the dyeing process and the boric acid treatment process. The total draw ratio before the boric acid treatment process is 3.7 times, and the total draw ratio from the raw film is 5.5 times. there were. The thickness of the polarizing film was 13.2 μm, and the boron content in the polarizing film was 2.4% by weight.

(B) Production of Polarizing Plate A polarizing plate was produced in the same manner as in Example 1 using the long polarizing film obtained in (A) above.

<Comparative example 2>
A polarizing film and a polarizing plate were prepared in the same manner as in Comparative Example 1 except that the drying temperature in the drying treatment step at the time of preparing the polarizing plate (after bonding of the protective film) was 90 ° C.

  Boron content in the polarizing film obtained in each Example and Comparative Example, polarizing property of the polarizing film, MD and TD shrinkage force of the polarizing film before and after bonding of the protective film, MD warpage amount of the polarizing plate, The amount of TD warpage and the MD / TD warpage ratio are shown together in Table 1.

Claims (9)

Shrinkage force per width 2mm the absorption axis direction of when held for 4 hours at 80 ° C. is Ri der than 1.5N or less 0.3 N, boron content area by near 0.5 to 2.0 wt% A polarizing film;
A protective film disposed on both sides of the polarizing film via an adhesive layer;
Including
The amount of MD warpage obtained for a polarizing plate sample having a width of 40 mm and a length of 150 mm with the absorption axis direction as the long side, and a polarizing plate sample with a width of 40 mm and a length of 150 mm having the direction orthogonal to the absorption axis direction as the long side From the amount of TD warpage obtained for the following formula:
MD / TD warp ratio = MD polarizing plate whose MD / TD warp ratio calculated according to MD warp amount / TD warp amount is 0.6 to 1.4.   The polarizing plate according to claim 1, wherein the polarizing film is a stretched film.   The polarizing plate according to claim 1, wherein the polarizing film has a thickness of 20 μm or less. The polarizing film, visibility correction single transmittance is not less than 40%, visibility correction polarization degree is 90% or more, the polarizing plate according to any one of claims 1-3. Wherein at least one of the protective film disposed on both sides of the polarizing film has a thickness is 50μm or less, the polarizing plate according to any one of claims 1-4. The polarizing plate of any one of Claims 1-5 whose thickness ratio of the other protective film with respect to one protective film arrange | positioned on both surfaces of the said polarizing film is 1.5 or more. Having long sides 8cm or short side 5cm or more rectangular shape, the polarizing plate according to any one of claims 1-6. Comprising a liquid crystal cell and a polarizing plate according to any one of claims 1 to 7 disposed on at least one surface, the liquid crystal panel. The liquid crystal panel according to claim 8 , wherein a thickness of a substrate constituting the liquid crystal cell is 0.5 mm or less.