JP2008299175A - Polarizing plate, manufacturing method therefor, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance adhesion between a polarizer and a protective film, in a polarizing plate in which the transparent protective films are bonded on one face or both faces of the polarizer comprising a polyvinyl alcohol resin via an adhesive. <P>SOLUTION: The polarizing plate is bonded with the transparent protective films 30, 35 on the one or both faces of the polarizer 20 comprising the polyvinyl alcohol resin via the adhesive, and at least one of the protective films 30, 35 has inorganic oxide layers 50, 55 on an adhesive layer onto the polarizer 20. This constitution is advantageous, in particular, when the one protective film 30 comprises an olefin resin such as an amorphous polyolefin resin or polypropylene resin. The olefin resin constituting the protective film may be a retardation film having an in-plane phase difference. The polarizing plate is arranged at least one side of a liquid crystal cell to form a liquid crystal display. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing plate with improved adhesion between a polarizer and a protective film and a method for producing the same. The present invention also relates to a liquid crystal display device using the polarizing plate.

  The polarizing plate generally has a structure in which a transparent protective film is laminated on one or both sides of a polarizer made of a polyvinyl alcohol-based resin having a dichroic dye adsorbed and oriented. The polarizer is manufactured by a method in which a polyvinyl alcohol resin film is uniaxially stretched and dyed with a dichroic dye, then treated with boric acid to cause a crosslinking reaction, and then washed with water and dried. As the dichroic dye, iodine or a dichroic organic dye is used. A protective film is laminated on one or both sides of the polarizer thus obtained to form a polarizing plate, which is used by being incorporated in a liquid crystal display device. As the protective film, a cellulose acetate-based resin film typified by triacetylrose is often used, and the thickness thereof is usually about 30 to 120 μm. In general, a protective film made of triacetylcellulose is subjected to saponification treatment and then bonded to the polarizer in order to increase the adhesive force with the polarizer. Further, an adhesive made of an aqueous solution of a polyvinyl alcohol resin is often used for bonding the polarizer and the protective film.

  In many cases, a surface treatment layer having optical functionality such as a hard coat layer, an antiglare layer, an antireflection layer (AR layer), and a low reflection layer (LR layer) is formed on the surface of the polarizing plate. These surface-treated layers are formed on the surface of a triacetyl cellulose film in advance, and are subjected to saponification treatment with the surface-treated layer attached and bonded to a polarizer to produce a polarizing plate with an optical function. ing. Since the saponification treatment is performed by contacting with an alkaline aqueous solution, when the triacetyl cellulose film with the surface treatment layer is saponified, the surface treatment layer may be altered or uneven. . In order to prevent this, a protective film made of a polyolefin resin or a polyester resin is generally attached to the surface treatment layer, and the surface treatment layer is protected before being subjected to a saponification treatment. These protective films are used only for the saponification process (so-called process paper) and have been a factor in increasing the cost of the polarizing plate.

  On the other hand, the liquid crystal display device is composed of many materials such as a liquid crystal cell, a polarizing plate, a retardation film, a light collecting sheet, a diffusion film, a light guide plate, and a light reflecting sheet. Therefore, improvements aimed at productivity, weight reduction, brightness improvement, and the like have been actively performed by reducing the number of constituent films or reducing the thickness of the film or sheet. Depending on the application, a product that can withstand severe durability conditions is required. For example, a liquid crystal display device for a car navigation system may have a high temperature and humidity in a vehicle in which the liquid crystal display device is placed, and the temperature and humidity conditions are severe compared to a monitor for a normal television or personal computer. For such applications, polarizing plates that are highly durable are also required.

  A polarizing plate in which a protective film made of triacetyl cellulose is laminated on one or both sides of a polarizer on which a dichroic dye as described above is adsorbed and oriented via an adhesive made of an aqueous solution of a polyvinyl alcohol resin is wet heat When used for a long time under the conditions, there are problems that the polarization performance is deteriorated and the protective film and the polarizer are easily peeled off.

  Therefore, there is an attempt to configure at least one protective film with a resin other than cellulose acetate. For example, Japanese Patent Laid-Open No. 7-287123 (Patent Document 1) describes that a protective layer of a polarizer is composed of a norbornene-based resin having a small photoelastic coefficient and a low moisture permeability. (Patent Document 2) describes that, in a polarizing plate in which protective films are laminated on both sides of a polarizer, at least one of the protective films is composed of a thermoplastic norbornene resin having the function of a retardation film. Has been. Japanese Patent Application Laid-Open No. 2002-174729 (Patent Document 3) discloses a protection made of an amorphous polyolefin resin on one surface of a polarizer made of a polyvinyl alcohol resin film adsorbed and oriented by iodine or a dichroic organic dye. A polarizing plate on which a film is laminated and a protective film made of a resin different from an amorphous polyolefin resin, such as a cellulose acetate resin, is laminated on the other surface. Further, JP-A-2004-334168 (Patent Document 4) discloses a protective film made of a cycloolefin resin via a polyvinyl alcohol polarizer and an adhesive containing a urethane adhesive and a polyvinyl alcohol resin. Are described.

  However, olefin-based resins such as norbornene-based resins generally have a low moisture permeability, and often have poor adhesion even when an adhesive is used, and a desired adhesive force cannot be obtained.

  Further, in a liquid crystal display device, optical compensation is widely performed by providing a retardation film between a liquid crystal cell and a polarizing plate. For this purpose, a polarizing plate in which a protective film as described above is laminated on both sides of a polarizer and a retardation film bonded together with a pressure-sensitive adhesive are used. A structure in which the protective layer of the polarizing plate also serves as a retardation film as disclosed in JP-A-8-43812 is also known. By adopting such a configuration, since one triacetyl cellulose film and one pressure-sensitive adhesive layer as a protective layer can be reduced, it is possible to reduce the cost and thickness, and to provide a retardation film having a small photoelastic coefficient. By selecting and using, there is an advantage that display defects called white spots can be suppressed. Furthermore, by selecting and using a retardation film having a low moisture permeability, it is possible to suppress a dimensional change due to moisture absorption / desorption of the polarizing plate itself and to reduce display defects.

  Now, when a birefringent film is used as a protective layer of a polarizing plate, it is said that there is essentially no correlation between photoelasticity and orientation birefringence, but the photoelastic coefficient is small in order to suppress white spots. When a material is selected, in many materials, there is a problem that a phase difference is difficult to develop at the time of stretching, and a thick film must be used in order to express a desired retardation value. On the other hand, when a material with low moisture permeability is selected in order to suppress the dimensional change due to moisture absorption / release of the polarizing plate, there is a problem that adhesiveness is often poor and a desired adhesive force cannot be obtained.

  Many attempts have also been made to improve the adhesion of the protective film for polarizing plates to the polarizer. For example, Japanese Patent Laid-Open No. 2000-356714 (Patent Document 5) describes that a surface of a protective film in contact with a polarizer is subjected to plasma treatment such as flame plasma treatment. JP-A-2002-103410 (Patent Document 6) discloses that a surface of a resin film is subjected to surface activation treatment such as flame treatment, and then a coating layer is provided on the activation treatment surface to provide a polarizing plate. It is described as a protective film. In JP 2002-148436 A (Patent Document 7), when a polyvinyl alcohol polarizing film and a protective film are bonded via a one-pack type silicone moisture-curable adhesive, a frame (flame) is formed on the bonding surface. It describes that processing is performed. Further, JP 2005-309401 A (Patent Document 8) discloses a birefringent minute region in a matrix formed of a light-transmitting water-soluble resin containing an iodine-based absorber as a polarizer. It is described that when a film having a dispersed structure is employed and a protective film is laminated on the surface of the film via a curable adhesive, a frame (flame) treatment or the like is applied to the adhesive surface of the protective film. A general flame treatment is activated by spraying a flame from a burner. However, even if such a treatment is performed, it is not necessarily sufficient to increase the adhesion between the polarizer and the protective film.

  On the other hand, a method for surface modification by spraying a flame containing a modifier compound containing silicon, titanium, or aluminum as a constituent element on a film-like material and an apparatus therefor are disclosed in, for example, JP-A-2006-16685 (Patent Document 9).

JP 7-287123 A JP-A-8-43812 JP 2002-174729 A JP 2004-334168 A JP 2000-356714 A JP 2002-103410 A JP 2002-148436 A JP 2005-309401 A JP 2006-16685 A

  One of the objects of the present invention is to provide a polarizing plate in which a transparent protective film is bonded to one or both sides of a polarizer made of polyvinyl alcohol resin via an adhesive. There is to increase.

  Another object of the present invention is to provide a polarizing plate in which a transparent protective film is bonded to one or both sides of a polarizer made of a polyvinyl alcohol-based resin via an adhesive, and at least one of the protective films has a dimensional change. It is intended to improve the dimensional stability and adhesiveness, especially under wet heat conditions, by using a resin film that is small, has a low water vapor transmission rate, and has a small photoelastic coefficient. .

  Another object of the present invention is that one of the protective films is composed of a retardation film having an in-plane retardation, thereby providing excellent dimensional stability, a small photoelastic coefficient, and a desired retardation value. It is to provide a polarizing plate having good adhesion between the polarizer and the retardation film.

  Still another object of the present invention is to apply this polarizing plate to a liquid crystal display device.

  As a result of intensive studies to increase the adhesive force between the polarizer and the protective film, the present inventors have found that when the protective film is laminated on the polarizer made of polyvinyl alcohol resin via an adhesive, the polarizer of the protective film It was found that by forming an inorganic oxide layer on the adhesive surface, sufficient adhesion between the polarizer and the protective film is exhibited, and a polarizing plate with few defects can be provided at low cost.

  At this time, by using a specific olefin resin as a protective film to be bonded to the polarizer, the photoelastic coefficient is sufficiently small, the moisture permeability is low, and the adhesiveness to the polarizer is also good. I found it. Furthermore, if a retardation film having an in-plane retardation is employed as the olefin resin, a polarizing plate having excellent dimensional stability, avoiding display defects called white spots, and having good adhesion can be obtained. I found. The present invention has been completed based on such findings and further various studies.

  That is, according to the present invention, a transparent protective film is bonded to one or both sides of a polarizer made of polyvinyl alcohol resin via an adhesive, and at least one of the protective films is an adhesive surface with the polarizer. A polarizing plate having an inorganic oxide layer is provided. The presence of the inorganic oxide layer on the surface of the protective film that adheres to the polarizer allows the protective film to be bonded to the polarizer with sufficient adhesive strength without subjecting the protective film to saponification.

  This polarizing plate can be constituted, for example, by laminating a transparent protective film made of a cellulose acetate resin having the inorganic oxide layer on one side or both sides of a polarizer. In this case, it is particularly advantageous to paste a transparent protective film made of cellulose acetate resin having the inorganic oxide layer on both sides of the polarizer.

  In addition, a transparent protective film is bonded to both surfaces of the polarizer, at least one of which is composed of an olefin resin, and the film of the olefin resin has the inorganic oxide layer on the adhesive surface with the polarizer. It is also effective to have it. Thereby, dimensional stability and adhesiveness can be improved particularly under wet heat conditions.

  In the polarizing plate in which the olefin resin film is bonded as a protective film, the olefin resin can be composed of an amorphous polyolefin resin or a polypropylene resin. The non-crystalline polyolefin resin mentioned here specifically has a unit derived from a cyclic olefin such as norbornene or a polycyclic norbornene monomer, and is usually cyclic in the main chain of the polymer structure. It has a structure. Polypropylene resin is a resin mainly composed of units derived from propylene, and is generally crystalline. In addition to a homopolymer of propylene, it is a copolymer with other monomers mainly composed of propylene. There may be. In the case of a copolymer, a copolymer of propylene and ethylene containing a unit derived from ethylene at a ratio of 10% by weight or less is preferable.

  In the polarizing plate in which the olefin resin film is bonded as a protective film, the protective film made of the olefin resin bonded to one surface of the polarizer is substantially optically isotropic, Specifically, the in-plane retardation can be 10 nm or less.

  Moreover, the protective film which consists of an olefin resin bonded by the one surface of a polarizer can also be comprised with the phase difference film which has an in-plane phase difference of 20 nm or more. The retardation film in this case is preferably a biaxially stretched raw film obtained by extrusion molding of an olefin resin. Further, the retardation film in this case preferably has an in-plane retardation in the range of 20 to 500 nm and a thickness direction retardation in the range of 20 to 500 nm.

  In the polarizing plate in which the olefin resin film is bonded as described above, an olefin resin film having the inorganic oxide layer is bonded to one surface of the polarizer, and cellulose is bonded to the other surface. A protective film made of an acetate-based resin can be bonded to form.

  In these polarizing plates, the inorganic oxide layer formed on the adhesive surface of the protective film with the polarizer can be composed of a metal oxide selected from silicon, titanium and aluminum. This inorganic oxide layer can be formed by flame treatment. Specifically, it can be formed by blowing a flame of a gas containing an organometallic compound such as an alkylsilane compound, an alkoxysilane compound, an alkyltitanium compound, an alkoxytitanium compound, an alkylaluminum compound, or an alkoxyaluminum compound.

  In the above polarizing plate, the protective film having an inorganic oxide layer and the polarizer can be bonded with a water-based adhesive. The aqueous adhesive used here preferably contains a crosslinkable epoxy resin.

  According to the present invention, there is also provided a method for producing a polarizing plate by laminating a transparent protective film on a polarizer comprising a polyvinyl alcohol resin via an adhesive, and this method is provided on the surface of the transparent protective film. The step of forming an inorganic oxide layer by blowing a gas flame containing a metal compound, and the protective film is bonded to a polarizer via an adhesive on the surface side on which the inorganic oxide layer is formed. Process.

  Furthermore, according to the present invention, there is also provided a liquid crystal display device in which any one of the polarizing plates described above is laminated on at least one side of a liquid crystal cell.

  The polarizing plate of the present invention can be supplied stably and inexpensively with much less possibility of occurrence of defects while exhibiting the same durability as the conventional polarizing plate.

  In addition, by configuring the protective film disposed on at least one surface of the polarizer with an olefin-based resin, a change in dimensions compared to a polarizing plate in which protective films made of an acetylcellulose-based resin are laminated on both surfaces of the polarizer, Since both moisture permeability and photoelastic coefficient are small, it has excellent dimensional stability, optical properties such as degree of polarization do not deteriorate under various durability conditions, and it is difficult for white spots to occur. Show the effect. And when laminating an olefin resin film on a polarizer, by forming an inorganic oxide layer on the surface of the olefin resin film to be bonded to the polarizer, high adhesion between the two is ensured. Obtainable.

  Furthermore, it can be set as the polarizing plate to which the desired phase difference value was provided by comprising the film which consists of said olefin resin with the phase difference film which has an in-plane phase difference. And, by using an inorganic oxide layer on the adhesive surface of the retardation film made of an olefin resin with the polarizer, for example, using a known adhesive containing an epoxy resin or a urethane resin as a component is good. Adhesiveness can be obtained. In addition, by constituting the retardation film made of this olefin resin with a general-purpose polypropylene resin, the cost can be significantly reduced compared to the retardation film specified for conventional optical applications. Can be mentioned as a big merit.

  Hereinafter, embodiments of the present invention will be described in detail. In this invention, a transparent protective film is bonded via the adhesive to the single side | surface or both surfaces of the polarizer which consists of polyvinyl alcohol-type resin, and it is set as a polarizing plate. At that time, at least one of the protective films is composed of an inorganic oxide layer on the adhesive surface with the polarizer. When bonding a transparent protective film on both surfaces of a polarizer, one protective film may have the layer of the said inorganic oxide, and both protective films each have the layer of the said inorganic oxide. May be.

[Polarizer]
An example of the layer structure of the polarizing plate according to the present invention is shown in FIG. 1 in a schematic cross-sectional view with some layers separated. In the polarizing plate 10 shown in FIG. 1A, a protective film 30 is bonded to one surface of a polarizer 20 via an adhesive 40, and this protective film 30 is inorganic oxidized on an adhesive surface with the polarizer 20. It has a physical layer 50. In this case, for example, a pressure-sensitive adhesive layer for bonding to a liquid crystal cell or another optical film can be provided on the side opposite to the surface on which the protective film 30 of the polarizer 20 is provided. In the polarizing plate 11 illustrated in FIG. 1B, the first protective film 30 and the second protective film 35 are disposed on both surfaces of the polarizer 20 via the first adhesive 40 and the second adhesive 45, respectively. The first protective film 30 and the second protective film 35 have the first inorganic oxide layer 50 and the second inorganic oxide layer 55 on the adhesive surface with the polarizer 20, respectively. is doing. Further, in the polarizing plate 12 shown in FIG. 1C, the first protective film 30 and the second protective film are disposed on both surfaces of the polarizer 20 via the first adhesive 40 and the second adhesive 45, respectively. Although the film 35 is bonded and the 1st protective film 30 has the inorganic oxide layer 50 in the adhesive surface with the polarizer 20, the 2nd protective film 35 has an inorganic oxide layer. It does not have, but is directly bonded to the polarizer 20 through the second adhesive 45.

  As described above, in the present invention, a transparent protective film is bonded to at least one surface of the polarizer 20 via an adhesive, and at least one of the protective films has an inorganic oxide on the adhesive surface with the polarizer. There is a layer of. When the transparent protective films 30 and 35 are bonded to both surfaces of the polarizer 20, if the two transparent protective films 30 and 35 are the same type, the inorganic oxide layer 50 and the adhesive oxide 50 are bonded to the polarizer 20. 55 is preferably formed. On the other hand, if the two transparent protective films 30 and 35 are different types, an inorganic oxide layer 50 is formed only on one transparent protective film 30 and an inorganic oxide film is formed on the other transparent protective film 35 by a combination thereof. It may not be necessary to form a physical layer, and it may be preferable to form inorganic oxide layers 50 and 55 on both transparent protective films 30 and 35, respectively.

[Polarizer]
The polarizer 20 is made of a polyvinyl alcohol-based resin, and can be composed of a material generally used in this field. Specifically, the dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin to absorb linearly polarized light having a vibration surface in a certain direction and to transmit linearly polarized light having a vibration surface in a direction perpendicular thereto. A linear polarizer can be used. As the dichroic dye, iodine or a dichroic organic dye is used. A polyene polarizing film obtained by partially dehydrating a polyvinyl alcohol resin film can also be used as the polarizer 20.

  The polyvinyl alcohol resin constituting the polarizer 20 is not only polyvinyl alcohol, which is a saponified product of polyvinyl acetate, but also a copolymer of vinyl acetate and other monomers, such as a vinyl acetate / ethylene copolymer. It can be a compound or the like. The saponification degree of the polyvinyl alcohol-based resin is, for example, about 80 to 100 mol%, preferably about 98 to 100 mol%. The degree of polymerization of the polyvinyl alcohol resin is, for example, about 1,000 to 10,000, preferably about 1,700 to 5,000. This polyvinyl alcohol-based resin may be further modified. For example, polyvinyl butyral modified with butyraldehyde, polyvinyl acetal modified with acetaldehyde, polyvinyl formal modified with formaldehyde, and the like may be used. Among these, a film of polyvinyl alcohol which is a saponified product of polyvinyl acetate is preferably used as a raw material for a polarizer.

  A method for producing a polarizer (polarizing film) by using a polyvinyl alcohol-based resin film as a raw material and adsorbing and orienting a dichroic dye will be described as appropriate. Specifically, a film made of a polyvinyl alcohol resin as described above is used as a raw material, and this is subjected to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment after dyeing. Film) is produced. Although the thickness of the raw film is not particularly limited, for example, a thickness of about 50 to 150 μm is preferable. Further, the thickness of a polarizer (polarizing film) obtained by subjecting the raw film to uniaxial stretching is not particularly limited, but is, for example, about 5 to 50 μm.

  Uniaxial stretching may be performed before dyeing, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, the uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural stages. For the uniaxial stretching, for example, a method of uniaxial stretching between rolls having different peripheral speeds can be employed. Further, it may be a uniaxial stretching method using a heat roll, a dry stretching method such as stretching in the air, or a wet stretching method in which stretching is performed in a state swollen with a solvent. The draw ratio is usually about 3 to 8 times. In the case of dry stretching, it is preferable to stretch in the temperature range of the glass transition temperature of the polyvinyl alcohol-based resin film to 160 ° C.

  In order to dye the polyvinyl alcohol resin film with the dichroic dye, for example, the polyvinyl alcohol resin film may be immersed in an aqueous solution containing the dichroic dye.

  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 and potassium iodide in this aqueous solution is, for example, about 0.01 to 0.5 parts by weight of iodine and about 0.5 to 10 parts by weight of potassium iodide with respect to 100 parts by weight of water.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of dyeing a polyvinyl alcohol resin film by immersing it in an aqueous solution containing a water-soluble dichroic organic dye is usually employed. The content of the dichroic organic dye in this aqueous solution is, for example, about 1 × 10 ⁻⁴ to 10 parts by weight, preferably 1 × 10 ⁻³ to 1 part by weight with respect to 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant.

  After adsorbing the dichroic dye, it is treated with an aqueous solution containing boric acid. The treatment method is not particularly limited, but a method of immersing in a boric acid-containing aqueous solution is preferably employed. The amount of boric acid in the boric acid treatment bath is not particularly limited, and is, for example, about 2 to 15 parts by weight with respect to 100 parts by weight of water, preferably about 5 to 12 parts with respect to 100 parts by weight of water. Parts by weight. When iodine is used as the dichroic dye, it is preferable to contain potassium iodide in this boric acid-containing aqueous solution, and the amount is, for example, about 2 to 20 parts by weight with respect to 100 parts by weight of water. More preferably, it is about 5 to 15 parts by weight with respect to 100 parts by weight of water.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. After washing with water, a drying process is performed to obtain a polarizer (polarizing film). The drying process is usually performed using a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 50 to 80 ° C. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

In order to prevent thermal relaxation after the adsorption orientation of the dichroic dye on the polyvinyl alcohol-based resin film, boric acid treatment, and further washing with water as necessary, the film is subjected to high-temperature humidification treatment under tension. May be applied. The tension in the tension state is about 3 to 30 kg / cm ² , preferably about 8 to 20 kg / cm ² . Typically, the high-temperature humidification treatment is performed under such a tension state, for example, using a thermo-hygrostat or the like in an atmosphere having a temperature of about 40 to 90 ° C. and a relative humidity of about 50 to 95% for about 1 minute to It takes 24 hours. Preferably, it is performed for about 10 minutes to 10 hours in an atmosphere having a temperature of about 60 to 80 ° C. and a relative humidity of about 60 to 90%. When uniaxial stretching is performed before dyeing, the dichroic dye adsorption orientation, boric acid treatment, and water washing as necessary are maintained while maintaining the tension state when the polyvinyl alcohol-based resin film is uniaxially stretched. In general, a high-temperature humidification treatment is performed.

[Protective film]
Next, the protective films 30 and 35 will be described. As the protective films 30 and 35, transparent resin films conventionally used in the field of polarizing plates can be used. For example, cellulose acetate resin film, acrylic resin film, polyester resin film, olefin resin film, polycarbonate resin film, polyarylate resin film, polyethersulfone resin represented by triacetyl cellulose and diacetyl cellulose A film etc. are mentioned. The thickness of the protective films 30 and 35 is, for example, about 5 to 200 μm.

  In a preferred embodiment of the present invention, a first transparent protective film 30 and a second transparent protective film 35 made of cellulose acetate resin are bonded to both sides of the polarizer 20, and both of them are adhesive surfaces with the polarizer 20. Each includes a first inorganic oxide layer 50 and a second inorganic oxide layer 55 (see FIG. 1B). In the case where a cellulose acetate resin is used as a protective film, as described above, saponification treatment has been conventionally performed in order to increase the adhesive strength with a polarizer. And when using as a protective film the cellulose acetate type-resin film in which the surface treatment layer was formed beforehand, it will be pasted to a polarizer on the surface on the opposite side to the surface treatment layer, but a surface treatment layer is attached. If the saponification treatment is performed as it is, the surface treatment layer may be altered or uneven. To prevent this, a protective film made of polyolefin resin or polyester resin is applied to the surface treatment layer, and the surface treatment is performed. It was common to subject the layer to saponification after protection. Such a protective film is a so-called process paper used only for the saponification process, and has been a factor in increasing the cost of the polarizing plate. Therefore, in the present invention, even when a cellulose acetate-based resin is used as a protective film, an ordinary adhesive is formed by forming an inorganic oxide layer on the adhesive surface of the protective film with the polarizer. It is used so that the polarizer and the protective film are firmly bonded. For this reason, a saponification process is not required, and therefore the above-described protective film is not required.

  In another preferred embodiment of the present invention, a transparent protective film is bonded to both surfaces of the polarizer, at least one of which is composed of an olefin resin, and the olefin resin film is bonded to the polarizer on the adhesive surface. It has an oxide layer. The olefin resin used here is a resin mainly composed of a unit derived from a chain or cyclic olefin, and can be an amorphous polyolefin resin or a polypropylene resin. Specifically, the amorphous polyolefin-based resin has a unit derived from a cyclic olefin and does not exhibit crystallinity, and usually has a cyclic structure in the main chain of the polymer structure. Yes. Polypropylene resins are resins mainly composed of units derived from propylene, and are generally crystalline.

The amorphous polyolefin-based resin will be described. This usually has a unit derived from a cyclic olefin such as norbornene, a polycyclic norbornene-based monomer, or a substituted product thereof (sometimes collectively referred to as a norbornene-based monomer). Examples include hydrogenated cyclic olefin ring-opening polymers, addition polymers of cyclic olefins, addition copolymers of cyclic olefins and chain olefins, and the like. A polar group may be introduced into this resin. Such amorphous polyolefin-based resins are, for example, “Chemical Industry”, February 1991, pages 20 to 26 (Chemical Industry), “Functional Materials”, January 1993 (Vol.13, No.1). 40-52 (CMC) and the like. Among them, a thermoplastic saturated norbornene resin mainly composed of units derived from norbornene monomers is representative. Commercially available thermoplastic saturated norbornene resins such as “ZEONEX” and “ZEONOR” sold by Nippon Zeon Co., Ltd., “ARTON” sold by JSR Corporation, and Mitsui Chemicals, Inc. “APO” and “Apel” (both are trade names). These norbornene-based resin films and stretched films are also available, for example, under the trade name “ZEONOR FILM” from Optes Co., Ltd., under the trade name “ARTON FILM” from JSR Corporation, and from Sekisui Chemical Co., Ltd. It is sold under the name “Essina”.

  Next, a polypropylene resin will be described. This is a resin mainly composed of units of propylene and is generally crystalline. In addition to a homopolymer of propylene, propylene and other olefins such as ethylene Or a copolymer with unsaturated hydrocarbons such as butene. From the viewpoint of improving transparency and workability, it is preferable to use propylene as a main component and a copolymer of other unsaturated hydrocarbons to a small amount, for example, about 20% by weight. Of these, a copolymer with ethylene is preferred. When making it into a copolymer, it is advantageous that unsaturated hydrocarbons other than propylene have a copolymerization ratio of about 1 to 10% by weight, and a more preferable copolymerization ratio is 3 to 7% by weight. By setting the unit of unsaturated hydrocarbons other than propylene to 1% by weight or more, there is a tendency that an effect of improving processability and transparency appears. However, an increase in the proportion is not preferable because the melting point of the resin tends to decrease and the heat resistance tends to deteriorate. A copolymer of propylene and ethylene containing a unit derived from ethylene at a ratio of 10% by weight or less is one of preferred polypropylene resins.

  A protective film made of an olefin resin including an amorphous polyolefin resin and a polypropylene resin can be composed of a film having substantially no in-plane retardation. In this case, the in-plane retardation is usually 20 nm or less, preferably 10 nm or less. A protective film made of such an olefin-based resin can be formed into a protective film by an arbitrary method. For example, the protective film can be produced by extrusion molding from a molten resin. When an olefin-based resin having substantially no in-plane retardation is used as the protective film, the thickness is preferably about 5 to 200 μm, more preferably 10 μm or more and 150 μm or less.

  Moreover, the protective film which consists of olefin resin can also be comprised with the phase difference film which has an in-plane phase difference. In this case, the protective film disposed on one surface of the polarizer 20 is a retardation film, and the protective film disposed on the other surface of the polarizer 20 is a general protective film having substantially no in-plane retardation. It is customary to do this. In the example shown in FIGS. 1B and 1C, the following description will be made on the assumption that the first protective film 30 is composed of such a retardation film.

  In this case, the retardation film usually has an in-plane retardation of 20 nm or more. Such a retardation film is, for example, a film having substantially no in-plane retardation produced by extrusion from a molten resin as described above, and is stretched to express a retardation. It can produce by the method to make. In particular, those in which biaxial birefringence is developed by biaxial stretching are preferred. The draw ratio at this time is about 1.1 to 10 times in the direction in which the main axis is developed (the direction in which the draw ratio is large) among the longitudinal direction and the transverse direction, and 1 in the direction perpendicular to it (the direction in which the draw ratio is small). It may be appropriately selected from the range of about 1 to 7 times according to the required phase difference value. The main axis may be developed in the horizontal direction of the film, or the main axis may be developed in the vertical direction.

  When the first protective film 30 in FIG. 1 (B) or (C) is composed of a retardation film, the retardation value will be described. The in-plane retardation value (Ro) is in the range of 20 to 500 nm. And the thickness direction retardation value (Rth) is preferably in the range of 20 to 500 nm. From this range, an appropriate selection may be made according to the characteristics required for the applied liquid crystal display device. The in-plane retardation value (Ro) is more preferably 40 nm or more and 100 nm or less, and the thickness direction retardation value (Rth) is more preferably 80 nm or more and 300 nm or less.

The refractive index of in-plane slow axis direction n _x of the film, the refractive index n _y in-plane fast axis direction (direction orthogonal with the slow axis and the plane), the refractive index in the thickness direction n _z, thickness Where d is the in-plane retardation value (Ro) and the thickness direction retardation value (Rth) are defined by the following equations (I) and (II), respectively.

_{Ro = (n x -n y)} × d (I)
_{Rth = [(n x + n} y) / 2-n z] × d (II)

Amorphous polyolefin resin, a phase difference is hardly exhibited by stretching, therefore, the difference between n _x and n _y in above formula or the difference n _x or n _y and n _z are less likely to become large. Thus, when such an amorphous polyolefin-based resin is used as a retardation film, a desired retardation value can be expressed by increasing the draw ratio and securing a certain thickness. Therefore, when the retardation film is formed from an amorphous polyolefin-based resin, the thickness is preferably in the range of 10 to 100 μm. However, if it is too thin or too thick, the handleability may be deteriorated, and therefore, it is more preferably 20 μm or more and 80 μm or less.

On the other hand, polypropylene resin, the phase difference is easily expressed by stretching, therefore, the difference between n _x and n _y or difference n _x or n _y and n _z, tends to be large in the above equation. Therefore, a film obtained by stretching such a polypropylene resin film can exhibit a desired retardation value by appropriate stretching even if the thickness d is reduced. Therefore, when the retardation film is formed from polypropylene resin, the thickness may be 60 μm or less. However, if it is too thin, the handleability may be lowered, and therefore it is preferably 5 μm or more. The thickness of the retardation film is more preferably 10 μm or more and 40 μm or less. For these reasons, the polypropylene resin is particularly suitable for thinning the protective film having a retardation.

  When the first protective film 30 is composed of a retardation film, the axial relationship between the first protective film 30 and the polarizer 20 should be selected in consideration of viewing angle characteristics and color change characteristics in the target liquid crystal display device. Good. In large liquid crystal television applications where front contrast is important, the slow axis of the first protective film (retardation film) 30 and the absorption axis of the polarizer 20 are in a substantially parallel or substantially orthogonal relationship. Often placed. Here, “substantially” in the case of substantially parallel or substantially orthogonal is preferably the relationship described therein (parallel or orthogonal), but it is acceptable that a deviation of about ± 10 degrees is allowed around that. means. The angle deviation is preferably within ± 5 degrees, more preferably within ± 2 degrees.

  When an olefin resin including an amorphous polyolefin resin or a polypropylene resin is used as a protective film, a protective film made of an olefin resin on both sides of the polarizer may be bonded. It is also effective to paste a protective film made of an olefin resin and laminate a protective film made of a resin other than the olefin resin on the other surface of the polarizer. In particular, when a retardation film made of an olefin-based resin is used as one protective film, the other protective film is preferably composed of other resins. Examples of resins other than olefin resins include cellulose acetate resins such as triacetyl cellulose and diacetyl cellulose, polyester resins, acrylic resins, and polycarbonate resins. Considering the ease of adhesion with the polarizer and the ease of forming the surface treatment layer, a cellulose acetate resin film, particularly a triacetyl cellulose film is preferably used. When using a cellulose acetate resin film as one protective film, it is desirable to saponify the surface with an alkaline aqueous solution prior to bonding with a polarizer. Apart from this, it is also effective to form an inorganic oxide layer on the adhesive surface of the cellulose acetate resin film with the polarizer according to the present invention. When a resin other than an olefin resin is used as one protective film, the thickness is usually about 30 to 200 μm, preferably 30 to 120 μm, more preferably 30 to 85 μm. You may have various surface treatment layers, such as an antireflection layer and a glare-proof layer, in the surface of the protective film on the side different from the surface bonded to a liquid crystal cell.

Bisphenol A type polycarbonate, which has been widely used for retardation films, has excellent photoelasticity, but has a large photoelastic coefficient of about 27 × 10 ⁻¹³ cm ² / dyne. It is easy to cause uneven pasting and white spots. On the other hand, triacetyl cellulose, which has been widely used for the protective layer of the polarizer, has excellent adhesion to the polarizer, but has a large photoelastic coefficient of about 13 × 10 ⁻¹³ cm ² / dyne, which is caused by stretching. The expression of the phase difference is also small. For this reason, there were not many examples which extend | stretch a triacetylcellulose film and use it as a retardation film. In addition, since the triacetyl cellulose film has high moisture permeability, it has been pointed out that a polarizing plate using the pressure-sensitive adhesive side protective layer as a result of a large dimensional change due to moisture absorption contributes to white spots.

In contrast, amorphous polyolefin resins such as those described in Patent Document 1 (JP-A-7-287123) and Patent Document 2 (JP-A 8-43812) have a photoelastic coefficient. It is as small as about 4 × 10 ⁻¹³ cm ² / dyne, and is effective for suppressing uneven pasting and white spots. However, the amorphous polyolefin resin has difficulty in bonding with the polarizer. Therefore, in the present invention, the protective film made of an amorphous polyolefin-based resin disposed on one surface of the polarizer forms an inorganic oxide layer on the adhesive surface with the polarizer, and the polarizer is interposed via an adhesive. It is made to adhere.

Amorphous polyolefin-based resin film has a small photoelastic coefficient and is effective in suppressing uneven sticking and white spots, but it is difficult to develop a phase difference even by stretching.To obtain a desired phase difference, Some thickness was required. On the other hand, the polypropylene resin has a small photoelastic coefficient of around 2 × 10 ⁻¹³ cm ² / dyne and low moisture permeability. Moreover, a phase difference is easily developed by stretching. Furthermore, it has been found that even when various known adhesives are used, particularly by applying a corona treatment to the surface, the surface can be adhered to a polarizer made of a polyvinyl alcohol resin with sufficient strength. In order to meet the demand for higher durability, the adhesiveness was not always sufficient. Therefore, in the present invention, the protective film made of a polypropylene resin disposed on one surface of the polarizer forms an inorganic oxide layer on the adhesive surface with the polarizer, and is adhered to the polarizer via an adhesive. ing.

[Inorganic oxide layer and flame treatment]
In the polarizing plate of the present invention, at least one of the protective films 30 and 35 bonded to one surface or both surfaces of the polarizer 20 has an inorganic oxide layer 50 or 55 on the surface bonded to the polarizer 20. Is formed. The presence of the inorganic oxide layers 50 and 55 can increase the adhesive force between the protective film and the polarizer. Specifically, the inorganic oxide layers 50 and 55 are preferably metal oxides selected from the group consisting of silicon, titanium, and aluminum. Note that in this specification, silicon is regarded as a metal. Such a metal oxide layer can be formed relatively easily by a flame treatment in which a flame of a gas containing an organometallic compound is blown onto one surface of the protective films 30 and 35.

  Specifically, a method of spraying a flame generated by mixing an organometallic compound as a surface modifier and a fuel gas and burning the mixed gas onto the surface of the protective films 30 and 35 can be employed. Here, the organometallic compound serves as a precursor of the inorganic oxide constituting the inorganic oxide layer, and the organometallic compound is oxidized by a flame to form the corresponding inorganic oxide layers 50 and 55. Is done. As the organometallic compound, a compound having silicon, titanium, or aluminum as a constituent element and liquid in a normal temperature and normal pressure state and having a boiling point in the range of 10 to 100 ° C. is preferably used. More specifically, an organometallic compound having a boiling point in the range of 10 to 100 ° C. may be selected from alkyl silane compounds, alkoxy silane compounds, alkyl titanium compounds, alkoxy titanium compounds, alkyl aluminum compounds, alkoxy aluminum compounds, and the like. .

  The mixed gas is further selected from the group consisting of alkylsilane compounds, alkoxysilane compounds, alkyltitanium compounds, alkoxytitanium compounds, alkylaluminum compounds and alkoxyaluminum compounds, and an organometallic compound having a boiling point of 100 ° C. or higher is added. The amount of the high-boiling organometallic compound is preferably set to a value in the range of 0.01 to 50 mol%, with the total amount of the organometallic compound being 100 mol%. Such a compound having a slightly high boiling point, which is handled by the low boiling point of the modifier compound by adding a compound having a high compatibility with the low boiling point organometallic compound which is the main component of the modifier compound. The badness of property can be improved, and the surface modification effect on the protective film can be further enhanced.

  In modifying the surface of the protective film by applying a flame treatment, it is preferable to heat the organometallic compound, which is the surface modifier, to be in a gaseous state and then to burn it. At this time, the flame temperature is about 500 to 1,500 ° C., and the treatment time is about 0.1 seconds to 100 seconds.

  Flame treatment includes, for example, a first storage tank with heating means for storing organometallic compounds that are precursors of inorganic oxides, and a second storage for storing flammable gases with compressed air. Burning tank, mixed gas containing organometallic compound gas and flammable gas (sometimes referred to as combustion gas), burner part for blowing the obtained flame, and transferring combustion gas to burner part It is performed using the flame processing apparatus comprised with the transfer part for. As described above, the combustion gas is a mixture containing an organometallic compound gas and a flammable gas, and the flammable gas referred to here is a mixture containing air and a fuel gas such as LP gas (liquefied petroleum gas). It is. It is preferable that the flame treatment apparatus includes a moving unit that moves the protective film to be treated at a substantially constant speed so that the flame treatment is continuously performed. A suitable flame treatment method and apparatus are described in, for example, Patent Document 9 (Japanese Patent Laid-Open No. 2006-16685).

  The type of the burner part is not particularly limited, and may be any of a premix burner, a diffusion burner, a partial premix burner, a spray burner, an evaporation burner, and the like. The form of the burner is not particularly limited, and any form such as a fan shape or a rectangle may be used.

  Moreover, it is preferable that the flame treatment apparatus is provided with a thermal diffusion means in order to quickly absorb and thermally diffuse the thermal energy generated in the film to be treated with the flame treatment. The specific form of the heat diffusion means is not particularly limited, and for example, a heat cooling roll using various refrigerants can be used.

Since the concentration of the organometallic compound as the surface modifier in the combustion gas is extremely important, a pressure gauge is installed in the first storage tank to monitor the vapor pressure of the organometallic compound in order to control the concentration. It is preferable to do. Although the concentration of the organometallic compound in the combustion gas depends on the type of the organometallic compound, the amount of the fuel gas such as LP gas constituting the combustion gas is set to 100 mol%, for example, 1 × 10 ⁻¹⁰ to It is preferable to be within the range of about 10 mol%.

  Specific flame processing using the above-described flame processing apparatus is performed as follows, for example. First, using a heating means (for example, a heater or heating wire) provided in the first storage tank, the organometallic compound that is liquid at normal temperature and normal pressure is vaporized and sent from the second storage tank. It is uniformly mixed with a flammable gas (for example, a mixture of air and LP gas) to form a combustion gas, which is transferred to a burner section through a transfer section. The combustion gas transferred to the burner portion is burned, and the obtained flame is sprayed on the surface of the protective film that is the object to be processed.

  The flame treatment time can be controlled, for example, by adjusting the moving speed of the protective film that is the object to be treated. The thickness of the inorganic oxide layers 50 and 55 is not particularly limited as long as the adhesion between the polarizer 20 and the protective films 30 and 35 is ensured, and is an extremely thin film that is formed by a general flame treatment. It's okay.

[adhesive]
As described above, after forming the inorganic oxide layer 50 (or 50, 55) on the adhesive surface of the protective film 30 (or 30, 35) with the polarizer 20, the adhesive 40 (or 40) is formed on the treated surface. , 45), the polarizer 20 is bonded.

  The adhesive used for bonding the polarizer 20 and the protective film 30 (or 30, 35) may be, for example, an adhesive containing an epoxy resin, a urethane resin, a cyanoacrylate resin, an acrylamide resin, or the like as a component. Even if any of these is used, good adhesive force can be obtained. From the viewpoint of thinning the adhesive layer, it is preferable to use a water-based adhesive, that is, an adhesive component dissolved in water or dispersed in water. Examples of the adhesive component that can be a water-based adhesive include water-soluble crosslinkable epoxy resins and urethane resins.

  Examples of water-soluble crosslinkable epoxy resins are obtained by reacting epichlorohydrin with a polyamide polyamine obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a dicarboxylic acid such as adipic acid. The polyamide epoxy resin which can be mentioned can be mentioned. Examples of such commercially available polyamide epoxy resins include “Smiles Resin 650” and “Smiles Resin 675” sold by Sumika Chemtex Co., Ltd.

  When a water-soluble epoxy resin is used as the adhesive component, it is preferable to mix other water-soluble resins such as a polyvinyl alcohol-based resin in order to further improve coatability and adhesiveness. Polyvinyl alcohol resins are modified such as partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, as well as carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, and amino group-modified polyvinyl alcohol. Polyvinyl alcohol resin may be used. Among these, a saponified product of a copolymer of vinyl acetate and unsaturated carboxylic acid or a salt thereof, that is, carboxyl group-modified polyvinyl alcohol is preferably used. Here, the “carboxyl group” is a concept including —COOH and a salt thereof.

  Examples of suitable commercially available carboxyl group-modified polyvinyl alcohols include, for example, “Kuraraypoval KL-506”, “Kuraraypoval KL-318” and “Kuraraypoval KL-118” sold by Kuraray Co., Ltd. “GOHSENAL T-330” and “GOHSENAL T-350” sold by Nippon Synthetic Chemical Industry Co., Ltd., “DR-0415” sold by Denki Kagaku Kogyo Co., Ltd. Examples include “AF-17”, “AT-17”, and “AP-17” sold by Co., Ltd.

  When an adhesive containing a water-soluble epoxy resin is used, the epoxy resin and other water-soluble resins such as a polyvinyl alcohol-based resin added as necessary are dissolved in water to constitute an adhesive solution. In this case, the water-soluble epoxy resin preferably has a concentration in the range of about 0.2 to 2 parts by weight per 100 parts by weight of water. Moreover, when mix | blending polyvinyl alcohol-type resin, the quantity is about 1-10 weight part per 100 weight part of water, Furthermore, it is preferable to set it as about 1-5 weight part.

  The adhesive containing a water-soluble epoxy resin may contain zinc chloride, tin chloride, zinc borofluoride, a tertiary amine, a quaternary ammonium salt, an imidazole compound, etc., for promoting the curing of the epoxy resin.

  On the other hand, when a water-based adhesive containing a urethane resin is used, examples of suitable urethane resins include ionomer-type urethane resins, particularly polyester-type ionomer-type urethane resins. Here, the ionomer type is obtained by introducing a small amount of an ionic component (hydrophilic component) into the urethane resin constituting the skeleton. The polyester ionomer type urethane resin is a urethane resin having a polyester skeleton, into which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer-type urethane resin is suitable as a water-based adhesive because it is emulsified directly in water without using an emulsifier to form an emulsion. Examples of commercially available polyester ionomer urethane resins include “Hydran AP-20” and “Hydran APX-101H” sold by Dainippon Ink and Chemicals, Inc., both of which are available in the form of emulsions. it can.

  When an ionomer type urethane resin is used as an adhesive component, it is preferable to further add a crosslinking agent such as an isocyanate. The isocyanate-based crosslinking agent is a compound having at least two isocyanato groups (—NCO) in the molecule. Examples thereof include 2,4-tolylene diisocyanate, phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1, Examples thereof include monomers or oligomers such as 6-hexamethylene diisocyanate and isophorone diisocyanate, and adducts obtained by reacting these compounds with polyols. Examples of commercially available isocyanate-based crosslinking agents that can be suitably used include “Hydran Assist C-1” sold by Dainippon Ink and Chemicals, Inc.

  When an aqueous adhesive containing an ionomer type urethane resin is used, the concentration of the urethane resin is about 10 to 70% by weight, further 20% by weight or more, and 50% by weight or less from the viewpoint of viscosity and adhesiveness. Thus, those dispersed in water are preferred. When the isocyanate crosslinking agent is blended, the blending amount may be appropriately selected so that the isocyanate crosslinking agent is about 5 to 100 parts by weight with respect to 100 parts by weight of the urethane resin.

  The polarizing plate of the present invention can be obtained by applying the adhesive as described above to the adhesive surface of the inorganic oxide layer 50 and / or the polarizer 20 formed on the protective film 30 and bonding them together. As shown in FIG. 1 (B), when the inorganic oxide layer 55 is also formed on the adhesive surface of the second protective film 35 with the polarizer 20, the second adhesive 45 is interposed on that side as well. Then, the polarizer 20 and the protective film 35 are bonded together. Moreover, after lamination | stacking, a drying process is performed at the temperature of about 60-100 degreeC, for example. Furthermore, after that, it is preferable that the curing is performed at a temperature slightly higher than room temperature, for example, at a temperature of about 30 to 50 ° C. for about 1 to 10 days, in order to further increase the adhesive force.

  As shown in FIG. 1 (C), the second protective film 35 bonded to one surface of the polarizer 20 is directly connected to the polarizer 20 via the second adhesive 45 without using the inorganic oxide layer. When bonding to, as the second adhesive 45, the same adhesive as above may be used, or an adhesive different from that may be used, but the polarizer 20 and the first protective film 30. It is preferable to use the same adhesive between the inorganic oxide layer 50 formed above and between the polarizer 20 and the second protective film 35 because the number of steps and materials can be reduced.

[Production method of polarizing plate]
The method for producing a polarizing plate according to the present invention comprises a step of forming an inorganic oxide layer by blowing a gas flame containing an organometallic compound on the surface of a transparent protective film, and the protective film comprises an inorganic oxide layer. It includes a step of bonding to the polarizer via an adhesive on the formed surface side. Each process can be performed according to the above description.

[Liquid Crystal Display]
The polarizing plates 10 to 12 configured as described above can be bonded to a liquid crystal cell by disposing a pressure-sensitive adhesive (pressure-sensitive adhesive) on one surface thereof. That is, the liquid crystal display device according to the present invention is such that the polarizing plate described above is laminated on at least one side of the liquid crystal cell. As shown in FIG. 1A, if the polarizing plate 10 is provided with the protective film 30 only on one side of the polarizer 20, the pressure-sensitive adhesive is usually applied to the surface of the polarizer 20 opposite to the protective film 30. Is attached to the liquid crystal cell on that side. As shown in FIG. 1B, the polarizing plate 11 has protective films 30 and 35 disposed on both sides of the polarizer 20, and the protective films 30 and 35 are made of the same kind of resin, for example, cellulose acetate resin. In that case, a pressure sensitive adhesive is provided on one side, and is bonded to the liquid crystal cell on that side. As shown in FIGS. 1B and 1C, the polarizing plate 12 has protective films 30 and 35 disposed on both surfaces of the polarizer 20, and the first protective film 30 is made of an olefin resin. When this is done (including the case of using this as a retardation film), a pressure-sensitive adhesive is usually provided on the first protective film 30 and bonded to the liquid crystal cell on that side.

  As the pressure-sensitive adhesive, those using a base polymer such as an acrylic ester, methacrylic ester, butyl rubber, or silicone can be used. Although not particularly limited, based on (meth) acrylate esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate And polymers based on copolymers using two or more of these (meth) acrylic esters are preferably used. A pressure-sensitive adhesive usually has a polar monomer copolymerized in these base polymers. Examples of the polar monomer include (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, and (meth) acrylic. Examples include monomers having a carboxyl group, a hydroxyl group, an amino group, an epoxy group, such as 2-hydroxypropyl acid, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, and glycidyl (meth) acrylate. it can. A pressure-sensitive adhesive usually contains a crosslinking agent. Examples of the crosslinking agent include a divalent or polyvalent metal compound that forms a divalent or polyvalent metal salt with a carboxyl group, a polyisocyanate compound that forms an amide bond with a carboxyl group, and the like. These compounds are used as a crosslinking agent in a mixture of one or two or more base polymers. A typical pressure-sensitive adhesive layer has a thickness of about 2 to 50 μm. When the pressure-sensitive adhesive layer is applied to the polarizing plate, surface treatment such as corona treatment may be applied to the protective film surface of the polarizing plate depending on the situation.

  The polarizing plate of the present invention can have optical characteristics by combining with a light collecting sheet, a diffusion film, a light guide plate, a light reflecting sheet, an antiglare sheet, and the like, if necessary. Thereby, an excellent liquid crystal display device can be obtained. In forming a liquid crystal display device, a pressure-sensitive adhesive layer is formed on the outside of one of the protective films as described above to form a polarizing plate with a pressure-sensitive adhesive (adhesive), and the pressure-sensitive adhesive layer side faces the liquid crystal cell. It is pasted to do. The liquid crystal cell constituting the liquid crystal display device has various modes known in this field such as TN (Twisted Nematic), STN (Super Twisted Nematic), VA (Vertical Alignment), IPS (In-Plane Switching), etc. Can be.

  The polarizing plate of the present invention can be disposed on both sides of the liquid crystal cell, the polarizing plate of the present invention can be disposed on one side of the liquid crystal cell, and another polarizing plate can be disposed on the other side.

  FIG. 2 is a schematic perspective view showing an example in which the polarizing plate of the present invention in which the first protective film 30 is formed of a retardation film is arranged on both surfaces of the liquid crystal cell. In this example, the layers are shown separated from each other, but actually, adjacent layers are in close contact with each other. The example shown here is the polarizing plate shown in FIG. 1 (C), in which the first protective film 30 made of a retardation film is arranged on both surfaces of the liquid crystal cell 60, but the inorganic oxidation is performed. The physical layer, the adhesive, and the pressure-sensitive adhesive layer are not shown. In the example shown in FIG. 2, a polarizing plate including a first protective film 30 / a polarizer 20 / a second protective film 35 that is a retardation film is provided below the liquid crystal cell 60. A polarizing plate comprising the first protective film 30 / polarizer 20 / second protective film 35, which is a retardation film, is laminated on the upper side of the liquid crystal cell 60 so that the side faces the liquid crystal cell 60. The protective film 30 side is laminated so as to face the liquid crystal cell 60. It will be understood from the above description that in each polarizing plate, an inorganic oxide layer is present between the first protective film 30 and the polarizer 20 according to the present invention. In this example, the slow axis 32 of the first protective film 30 that is a retardation film and the absorption axis 22 of the polarizer 20 are orthogonal to each other, and the lower polarizer 20 has an absorption axis 22 of The absorption axis 22 of the upper polarizer 20 is orthogonal to the long side direction 62 of the liquid crystal cell 60 and is parallel to the long side direction 62 of the liquid crystal cell 60. A backlight is disposed outside one of the protective films 35 to form a liquid crystal display device. This configuration is particularly effective when the liquid crystal cell is in the vertical alignment (VA) mode.

  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 examples, parts and% representing the amount used or content are based on weight unless otherwise specified. Further, the adhesive used in the following examples is prepared by mixing the following components.

[Example 1]
In this example, a polarizing plate was produced in which protective films made of triacetyl cellulose were bonded to both surfaces of a polyvinyl alcohol polarizer.

(A) Production of Polarizer A 75 μm thick polyvinyl alcohol film (trade name “Kuraray Vinylon # 7500”) sold by Kuraray Co., Ltd. was uniaxially stretched at a stretching temperature of 110 ° C. and a stretching ratio of 5 times. A polarizing substrate was used. The polarizing substrate was immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.075 / 5/100 for 60 seconds while maintaining the tensioned state. Next, it was immersed in a boric acid-containing aqueous solution at 65 ° C. in which the weight ratio of potassium iodide / boric acid / water was 6 / 7.5 / 100 for 300 seconds. This was washed with pure water and dried to obtain a polarizer having iodine adsorbed and oriented on a polyvinyl alcohol film.

(B) Flame treatment of protective film The 80 μm thick triacetyl cellulose film sold by FUJIFILM Corporation is used as a protective film, and this is entrusted to Ishimat Japan Co., Ltd. A triacetyl cellulose film having an inorganic oxide layer formed on the surface was obtained. The composition of the combustion gas in the flame treatment is as described in Patent Document 9 (Japanese Patent Laid-Open No. 2006-16685), with LP gas being 100 mol%, tetramethylsilane being 0.01 mol% and tetramethoxysilane being It contains 0.001 mol%, and these are further mixed with air.

(C) Preparation of polarizing plate It arrange | positions so that the inorganic oxide layer of the protective film obtained by (b) may touch a polarizer on both surfaces of the polarizer obtained by (a), and it sticks through the said adhesive agent Combined, dried and bonded in an oven at 80 ° C. for 5 minutes to obtain a polarizing plate.

[Comparative Example 1-1]
As the protective film, the same triacetyl cellulose film as used in (b) of Example 1 (but without flame treatment) was used, and the protective film was adhered to both sides of the polarizer in the same manner as in Example 1. A polarizing plate was obtained.

[Comparative Example 1-2]
As the protective film, the same triacetyl cellulose film (no flame treatment) as used in (b) of Example 1 was subjected to saponification treatment. A protective film was adhered to a polarizing plate.

  The polarizing plates of Example 1 and Comparative Examples 1-1 and 1-2 obtained as described above were evaluated by the following methods, and the results are summarized in Table 1.

Adhesion test: Only the protective film of the polarizing plate was cut using a cutter knife, and whether or not the protective film could be peeled off from the cut portion was evaluated according to the following criteria.
○: Cannot be peeled off.
(Triangle | delta): Although there exists some resistance, it can peel.
X: It can peel easily.

Hot water resistance test: The polarizing plate was cut into 2 cm × 5 cm and immersed in hot water at 60 ° C. for 4 hours, and then the deterioration state of the polarizing plate was evaluated according to the following criteria.
○: Almost no deterioration of the polarizing plate is observed.
Δ: Degradation of polarizing plate such as shrinkage of polyvinyl alcohol is observed.
X: Degradation of the polarizing plate is severe, for example, the polyvinyl alcohol shrinks significantly.

  The polarizing plate of Example 1 according to the present invention showed sufficient adhesion and good durability. Also, the optical characteristics were equivalent to the conventional product.

  Comparative Example 1-1 in which the inorganic oxide layer was not formed and the saponification treatment was not performed was poor in both adhesion and hot water resistance, and did not function sufficiently as a protective film. Comparative Example 1-2 produced by a conventional method was good in both adhesiveness and hot water resistance, but, as described above, when the saponification treatment of the triacetyl cellulose film having the surface treatment layer was performed as it was, Alteration and unevenness may occur in the surface treatment layer. So, conventionally, a protective film was applied to the surface treatment layer, and the surface treatment layer was protected before being saponified, but this protective film is a so-called process paper used only for the saponification process, This was a factor in increasing the cost of polarizing plates.

  On the other hand, since the operation for forming the inorganic oxide layer as in Example 1 is performed in a cyclic manner called flame treatment, there is almost no possibility of causing defects in the surface treatment layer. Therefore, the polarizer of Example 1 does not require a saponification treatment and does not require a protective film as a process paper, and the polarizer and the protective film are bonded with sufficient strength, and the polarizing plate has few defects. Become.

[Example 2]
In this example, a polarizing plate was produced in which a protective film made of triacetyl cellulose was bonded to one side of a polyvinyl alcohol polarizer and a retardation film made of a norbornene resin was bonded to the other side.

(A) Retardation film and flame treatment thereof A norbornene resin biaxially stretched retardation film (trade name “Zeonor film”) sold by Optes Co., Ltd. has Ro = 55 nm, Rth = 124 nm, and 70 μm. It had a thickness of Entrust this phase difference film to Ishimat Japan Co., Ltd. to have a flame treatment with silicic acid flame on one side and obtain a phase difference film made of norbornene resin with an inorganic oxide layer formed on one side did. The composition of the combustion gas in the flame treatment is as described in Patent Document 9 (Japanese Patent Laid-Open No. 2006-16685), with LP gas being 100 mol%, tetramethylsilane being 0.01 mol% and tetramethoxysilane being It contains 0.001 mol%, and these are further mixed with air.

(B) Preparation of polarizing plate and evaluation of adhesiveness Separately, a polarizing plate was prepared in which a protective film made of triacetyl cellulose was bonded to one surface of a polyvinyl alcohol / iodine polarizer through a polyvinyl alcohol adhesive. The surface on the inorganic oxide layer side of the retardation film obtained in (a) was adhered to the polarizer surface using the adhesive. After pasting, it is dried in an oven at 80 ° C. for 5 minutes, and is further allowed to stand at 40 ° C. for about 120 hours to obtain a triacetyl cellulose film / adhesive / polarizer / adhesive / inorganic oxide layer / norbornene phase difference. A polarizing plate composed of a film was prepared. This polarizing plate was subjected to a 90-degree peel test between the polarizer and the retardation film in accordance with JIS K 6854-1: 1999 using a universal tensile tester. The width of the peeled sample was 25 mm, and the test was performed at a peeling speed of 200 m / min. As a result, a good peel strength of 4 N / 25 mm was obtained.

[Comparative Example 2]
A polarizing plate comprising a triacetyl cellulose film / adhesive / polarizer / adhesive / norbornene-based retardation film was prepared in the same manner as in Example 2 except that the retardation film was not subjected to flame treatment. About this polarizing plate, when the 90 degree | times peeling test between a polarizer and retardation film was done by the method similar to Example 2, since the adhesive force was too low, it was not able even to obtain the value of adhesive force. .

[Example 3]
In this example, a polarizing plate was produced in which a protective film made of triacetyl cellulose was bonded to one side of a polyvinyl alcohol polarizer and a retardation film made of a polypropylene resin was bonded to the other side.

(A) Production of retardation film and flame treatment thereof Propylene / ethylene random copolymer (trade name “Sumitomo Nobrene W151”) containing about 5% by weight of ethylene units sold by Sumitomo Chemical Co., Ltd. was formed. Thereafter, biaxial stretching was performed successively to obtain a biaxial retardation film. This retardation film had Ro = 65 nm and Rth = 215 nm. This phase difference film is entrusted to Ishimat Japan Co., Ltd., and one side of the film is subjected to a flame treatment with silicic acid flame to obtain a phase difference film made of polypropylene resin with an inorganic oxide layer formed on one side. did. As described in Patent Document 9 (Japanese Patent Laid-Open No. 2006-16685), the composition of the combustion gas is such that LP gas is 100 mol%, tetramethylsilane is 0.01 mol% and tetramethoxysilane is 0.001. These are those that are further mixed with air.

(B) Preparation of polarizing plate and evaluation of adhesiveness Separately, a polarizing plate was prepared in which a protective film made of triacetyl cellulose was bonded to one surface of a polyvinyl alcohol / iodine polarizer through a polyvinyl alcohol adhesive. The surface on the inorganic oxide layer side of the retardation film obtained in (a) was adhered to the polarizer surface using the adhesive. After pasting, it is dried in an oven at 80 ° C. for 5 minutes, and is further allowed to stand at 40 ° C. for about 120 hours to obtain a triacetyl cellulose film / adhesive / polarizer / adhesive / inorganic oxide layer / polypropylene phase difference. A polarizing plate composed of a film was prepared. About this polarizing plate, the 90 degree peeling test between a polarizer and retardation film was done by the method similar to Example 2. FIG. As a result, a good peel strength of 9 N / 25 mm was obtained.

[Comparative Example 3]
A polarizing plate comprising a triacetyl cellulose film / adhesive / polarizer / adhesive / polypropylene retardation film was produced in the same manner as in Example 3 except that the retardation film was not subjected to flame treatment. About this polarizing plate, when the 90 degree | times peeling test between a polarizer and retardation film was done by the method similar to Example 2, since the adhesive force was too low, it was not able even to obtain the value of adhesive force. .

  The results of Examples 2 and 3 and Comparative Examples 2 and 3 are summarized in Table 2.

  Next, an example using an olefin-based protective film having no phase difference in the upper surface will be shown.

[Example 4]
An unstretched film (trade name “ZEONOR FILM”) of norbornene-based resin sold by Optes Co., Ltd. has Ro = 5 nm, Rth = 7 nm, and a thickness of 100 μm. The film is subjected to a flame treatment in the same manner as in Example 2 to form an inorganic oxide layer on one side. The inorganic oxide layer side of this flame-treated norbornene-based resin film is a polarizing plate in which a protective film made of triacetyl cellulose is bonded to one side of a polyvinyl alcohol / iodine-based polarizer via a polyvinyl alcohol-based adhesive. It adhere | attaches on a polarizer surface using the said adhesive agent. After bonding, the film is dried at 80 ° C. for 5 minutes, and further allowed to stand at 40 ° C. for about 120 hours, and is composed of a triacetyl cellulose film / adhesive / polarizer / adhesive / inorganic oxide layer / norbornene protective film. A polarizing plate is obtained. When this polarizing plate is subjected to a 90-degree peel test between the polarizer and the norbornene-based protective film in the same manner as in Example 2, good peel strength can be obtained.

[Comparative Example 4]
A polarizing plate comprising a triacetyl cellulose film / adhesive / polarizer / adhesive / norbornene protective film is obtained in the same manner as in Example 4 except that the norbornene protective film is not subjected to flame treatment. In this polarizing plate, a practically sufficient adhesive force cannot be obtained between the polarizer and the norbornene-based protective film.

[Example 5]
From the same propylene / ethylene random copolymer (“Sumitomo Noblene W151”) used in Example 3, a film having an in-plane retardation of approximately 0 and a thickness of 80 μm can be formed. The film is subjected to a flame treatment in the same manner as in Example 2 to form an inorganic oxide layer on one side. The inorganic oxide layer side of this flame-treated polypropylene resin film is a polarizing plate in which a protective film made of triacetyl cellulose is bonded to one surface of a polyvinyl alcohol / iodine polarizer via a polyvinyl alcohol adhesive. It adhere | attaches on a polarizer surface using the said adhesive agent. After pasting, it is dried at 80 ° C. for 5 minutes, and further allowed to stand at 40 ° C. for about 120 hours, and consists of a triacetyl cellulose film / adhesive / polarizer / adhesive / inorganic oxide layer / polypropylene protective film A polarizing plate is obtained. When this polarizing plate is subjected to a 90-degree peel test between the polarizer and the propylene-based protective film in the same manner as in Example 2, good peel strength can be obtained.

[Comparative Example 5]
A polarizing plate comprising a triacetyl cellulose film / adhesive / polarizer / adhesive / polypropylene protective film is obtained in the same manner as in Example 5 except that the polypropylene protective film is not subjected to flame treatment. In this polarizing plate, a practically sufficient adhesive force cannot be obtained between the polarizer and the propylene-based protective film.

  The polarizing plate of the present invention can be applied to various liquid crystal display devices. In particular, a polarizing plate using a retardation film made of an olefin resin as one protective film is less likely to cause retardation unevenness or white spots when bonded to a liquid crystal cell. It is difficult to cause peeling between the retardation film. A polarizing plate using such a retardation film as one protective film is useful for expanding a viewing angle, particularly for a liquid crystal display device in a vertical alignment mode, and contributes to thinning of the whole. . Among olefin resins, a polarizing plate with a retardation film made of a polypropylene resin as one protective film employs a general-purpose polypropylene resin, so that it can be manufactured at low cost and has a desired retardation value with a small thickness. It can be expressed and contributes further to thinning.

It is sectional drawing which shows typically the structural example of the polarizing plate which concerns on this invention. It is a perspective view which shows typically the example which applied the polarizing plate to the liquid crystal display device.

Explanation of symbols

10, 11, 12 ... Polarizing plate,
20 ... Polarizer,
22 …… Absorption axis of polarizer,
30 ... (first) protective film,
32... Slow axis when the first protective film is a retardation film,
35 …… Second protective film,
40 ... (first) adhesive,
45 …… Second adhesive,
50 ... (first) inorganic oxide layer,
55 …… Second inorganic oxide layer 60 …… Liquid crystal cell,
62... Long side direction of the liquid crystal cell.

Claims (18)

  A polarizing plate in which a transparent protective film is bonded to one or both sides of a polarizer made of polyvinyl alcohol resin via an adhesive, and at least one of the protective films is inorganic on the adhesive surface with the polarizer A polarizing plate having an oxide layer.   The polarizing plate according to claim 1, wherein a transparent protective film made of a cellulose acetate-based resin is bonded to both surfaces of the polarizer, and both of them have the inorganic oxide layer on an adhesive surface with the polarizer.   A transparent protective film is bonded to both surfaces of the polarizer, at least one of which is composed of an olefin resin selected from the group consisting of an amorphous polyolefin resin and a polypropylene resin, and the film of the olefin resin is The polarizing plate according to claim 1, further comprising the inorganic oxide layer on an adhesive surface with the polarizer.   The polarizing plate according to claim 3, wherein the olefin resin is an amorphous polyolefin resin having a unit derived from a cyclic olefin.   The polarizing plate according to claim 3, wherein the olefin-based resin comprises a polypropylene-based resin that is a copolymer of propylene and ethylene containing a unit derived from ethylene at a ratio of 10 wt% or less.   The polarizing plate according to any one of claims 3 to 5, wherein the protective film made of an olefin resin bonded to one surface of the polarizer has an in-plane retardation of 10 nm or less.   The polarizing plate according to any one of claims 3 to 5, wherein the protective film made of an olefin resin bonded to one surface of the polarizer is a retardation film having an in-plane retardation of 20 nm or more.   The polarizing plate according to claim 7, wherein the retardation film is a biaxially stretched raw film obtained by extrusion molding of an olefin resin.   The polarizing plate according to claim 7 or 8, wherein the retardation film has an in-plane retardation in the range of 20 to 500 nm and a thickness direction retardation in the range of 20 to 500 nm.   The film of the olefin resin which has the layer of the said inorganic oxide is bonded to one side of a polarizer, and the protective film which consists of a cellulose acetate type resin is bonded to the other surface. The polarizing plate in any one of.   The polarizing plate according to claim 1, wherein the inorganic oxide layer is made of a metal oxide selected from the group consisting of silicon, titanium, and aluminum.   The polarizing plate according to claim 11, wherein the inorganic oxide layer is formed by flame treatment.   The inorganic oxide layer is formed by blowing a flame of a gas containing an organometallic compound selected from the group consisting of alkylsilane compounds, alkoxysilane compounds, alkyltitanium compounds, alkoxytitanium compounds, alkylaluminum compounds and alkoxyaluminum compounds. The polarizing plate according to claim 12.   The polarizing plate according to claim 1, wherein a protective film having an inorganic oxide layer and a polarizer are bonded with a water-based adhesive.   The polarizing plate according to claim 14, wherein the aqueous adhesive contains a crosslinkable epoxy resin. A method for producing a polarizing plate by bonding a transparent protective film to a polarizer comprising a polyvinyl alcohol resin through an adhesive,
An inorganic oxide layer is formed by spraying a gas flame containing an organometallic compound on the surface of the transparent protective film, and then the protective film is formed on the surface side on which the inorganic oxide layer is formed via an adhesive. A method for producing a polarizing plate, which is bonded to a polarizer.   The method according to claim 16, wherein the organometallic compound is selected from the group consisting of an alkylsilane compound, an alkoxysilane compound, an alkyltitanium compound, an alkoxytitanium compound, an alkylaluminum compound, and an alkoxyaluminum compound.   A liquid crystal display device comprising the polarizing plate according to claim 1 laminated on at least one side of a liquid crystal cell.

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