JP2013161021A - Polarizer, method for manufacturing the same, and liquid-crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer a little prone to be deformed even under a severe condition such as a high temperature by improving the rigidity of a polypropylene resin film and using it as a protective film for the polarizer, and a method for manufacturing the polarizer, and to apply the polarizer to a liquid crystal display panel.SOLUTION: A polarizer comprises a polarizing film made of a polyvinyl alcohol resin in which dichroic dye is absorbed and oriented, and a transparent protective film or two laminated on one or both sides of the polarizing film. At least one of the transparent protective films is made of an unstretched polypropylene resin and heat-treated at temperatures lower than the melting point and equal to or higher than the melting point minus 55°C, so that a polarizer with a transparent protective film having a tensile elasticity of 200 MPa or greater at 80°C is provided. Heat-treatment of a polypropylene resin film 50 can be carried out by putting it in contact with heating rollers 51 to 54 or having it pass through a heating oven 56.

Description

  The present invention relates to a polarizing plate, a method for producing the same, and a liquid crystal display panel, and more particularly, to a polarizing plate having a polypropylene resin film as a protective film, a method for producing the polarizing plate, and a liquid crystal display panel including the polarizing plate.

  A liquid crystal display device using a liquid crystal display panel as a display element is rapidly expanding its use as a thin display device such as a liquid crystal television, a liquid crystal monitor, and a personal computer. In particular, the market for liquid crystal televisions is remarkably expanding, and with this, there is a strong demand for cost reduction. A liquid crystal display device such as a liquid crystal television is configured by incorporating various members such as a backlight into a liquid crystal panel including a liquid crystal cell and a polarizing plate as constituent members.

  The polarizing plate is usually a transparent protective film, for example, cellulose acetate represented by triacetyl cellulose, with an adhesive layer on one or both sides of a polarizing film made of a polyvinyl alcohol-based resin in which a dichroic dye is adsorbed and oriented. It is the structure which bonded the protective film which consists of a resin. This is bonded to the liquid crystal cell with an adhesive via another optical film as necessary, to obtain a component part of the liquid crystal display device.

  However, when a protective film made of a hydrophilic resin such as cellulose acetate resin is used on both sides of the polarizing plate, it affects the moisture content of the polarizing film made of polyvinyl alcohol resin under high temperature and high humidity conditions. The performance as a board may change somewhat. Therefore, a polarizing plate having a configuration in which a hydrophobic resin, for example, a protective film made of a polypropylene resin, is used instead of the protective film made of a hydrophilic resin and the influence of the environment can be suppressed as much as possible has been studied. For example, Japanese Patent Application Laid-Open No. 2007-334295 (Patent Document 1) discloses that a polarizing film is formed by pasting a protective film made of polypropylene resin on at least one surface of a polarizing film. Japanese Utility Model Publication No. 2009-258588 (Patent Document 2) discloses that a polypropylene-based resin film serving as a protective film for a polarizing plate is composed of a xylene-soluble component at 20 ° C. of 1% by weight or less. .

  When a polypropylene resin film is used as a protective film for a polarizing plate, low rigidity is pointed out. For example, in Japanese Patent Application Laid-Open No. 2011-197642 (Patent Document 3), on the premise that a resin film having low rigidity such as a polypropylene resin film is used as a protective film on the liquid crystal cell side, an adhesive layer and a separator are formed on the surface. A resin film with a pressure-sensitive adhesive layer formed in this order with a film is prepared in advance, and after surface activation treatment is performed on the surface of the resin film, a polarizing film is bonded through an adhesive layer, and a polarizing plate is attached. A method of manufacturing is disclosed.

  On the other hand, in liquid crystal display devices, the usage environment may be high for in-vehicle applications, and in televisions and monitors, the polarizing plate, which is a component, becomes hot due to the heat from the backlight. There is. In order to exhibit stable performance even in such a harsh state, it is desired that a polarizing plate using a protective film made of a polypropylene resin disclosed in Patent Documents 1 to 3 has higher performance.

  A polarizing plate in which a polypropylene resin film is disposed on at least one surface of a polarizing film has little influence on the polarizing film due to the use environment. However, since the polypropylene resin film has a low glass transition temperature and is a flexible material, when a polarizing film made of a polyvinyl alcohol resin is contracted greatly when used at a high temperature, the performance of suppressing the contraction is slightly There was a problem that it may be insufficient, and the polarizing plate may be deformed.

JP 2007-334295 A JP 2009-258588 A JP 2011-197642 A

  The inventors of the present invention believe that a polarizing plate having a polypropylene resin film disposed on at least one surface of a polarizing film is deformed under a severe environment such as a high temperature condition because the polypropylene resin film as a protective film is flexible. I thought it was too much.

  Therefore, the object of the present invention is to improve the rigidity of the polypropylene resin film and apply it as a protective film for the polarizing plate, so that the polarizing plate is less likely to be deformed even under harsh environments such as high temperature conditions. It is to provide. Another object of the present invention is to produce a polypropylene-based resin film with improved rigidity and apply it to a protective film for a polarizing plate to produce a polarizing plate that is less likely to be deformed even in harsh environments. It is to provide a method. Yet another object of the present invention is to apply the above polarizing plate to a liquid crystal cell to obtain a liquid crystal display panel and a liquid crystal display device.

  As a result of researches under such problems, the present inventors have found that heat treatment at a predetermined temperature on a polypropylene resin film is effective in improving the rigidity, and the present invention has been completed. It came to do.

  That is, according to the present invention, a polarizing film comprising a polyvinyl alcohol-based resin in which a dichroic dye is adsorbed and oriented, and a transparent protective film bonded to one or both sides of the polarizing film, the transparent protective film. At least one of these is made of an unstretched polypropylene resin, which is lower than its melting point but heat-treated at a temperature of (melting point−55 ° C.) or higher and exhibits a tensile elastic modulus of 200 MPa or higher at 80 ° C. A polarizing plate is provided.

  In this polarizing plate, the polypropylene-based resin preferably has an ethylene unit content of 1% by weight or less, and in particular, is a copolymer of propylene and ethylene containing ethylene units at a rate of 1% by weight or less. Is preferred. In these polarizing plates, a transparent protective film made of a polypropylene resin having an increased tensile elastic modulus is bonded to one surface of a polarizing film, and another transparent protective film is bonded to the other surface. Can take form. In this case, it is advantageous that another transparent protective film bonded to the other surface of the polarizing film is composed of a cyclic olefin resin or a cellulose acetate resin.

  According to the present invention, there is also provided a method for producing a polarizing plate by laminating an unstretched polypropylene resin film to a polarizing film comprising a polyvinyl alcohol resin on which a dichroic dye is adsorbed and oriented. A heat treatment step of heat-treating the polypropylene resin film so that the polypropylene resin film exhibits a tensile modulus of elasticity of 200 MPa or more at 80 ° C. at a temperature lower than its melting point but (melting point−55 ° C.); A manufacturing method of a polarizing plate provided with the pasting process of pasting the applied polypropylene resin film on a polarizing film is also provided.

  In this method, the heat treatment of the polypropylene resin film is carried out by bringing the polypropylene resin film into contact with a roll heated to the above temperature or passing it through an oven heated to the above temperature. Is preferred.

  The polarizing plate of the present invention can be combined with a liquid crystal cell to form a liquid crystal display panel. A transparent protective film made of a polypropylene resin with an increased tensile modulus is bonded to one side of the polarizing film, and another transparent protective film such as a cyclic olefin resin or a cellulose acetate resin is attached to the other surface. If it is a polarizing plate with which the film which becomes is bonded, it is advantageous to stick to a liquid crystal cell by the said another transparent protective film side.

  The polarizing plate of the present invention is composed of an unstretched polypropylene-based resin film, and is heat-treated at a temperature lower than its melting point but higher than (melting point−55 ° C.) and exhibits a tensile elastic modulus of 200 MPa or higher at 80 ° C. Is used as a protective film bonded to at least one surface of the polarizing film. Therefore, even if it uses a polarizing plate for a long period of time, the polypropylene resin film cannot peel easily, Therefore It can be set as the polarizing plate which is excellent in durability. Moreover, according to the method of the present invention, this polarizing plate can be produced industrially advantageously. A liquid crystal display panel and a liquid crystal display device to which this polarizing plate is applied can maintain high durability over a long period of time.

It is sectional drawing which shows the example of the laminated constitution of a polarizing plate typically. It is sectional drawing which shows typically the specific form of the method of heat-processing to a polypropylene resin film. It is sectional drawing which shows typically the example of a layer structure of a liquid crystal display panel provided with a polarizing plate, and a liquid crystal display device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, this invention is not limited by the member, arrangement | positioning, etc. which are shown below, These members, arrangement | positioning, etc. can be suitably changed along the meaning of this invention.

  Referring to FIG. 1, a polarizing plate 10 has a configuration in which protective films 12 and 13 made of a transparent resin are bonded to one side or both sides of a polarizing film 11. Usually, an adhesive layer 22 is provided on one surface thereof, specifically, a surface to be adhered to a liquid crystal cell when a liquid crystal panel is formed, and the surface is temporarily protected by a separate film 24 and distributed in the market. To do. The separate film 24 is peeled and removed immediately before being attached to the liquid crystal cell. Moreover, another optical film may be bonded through the pressure-sensitive adhesive layer 22, another pressure-sensitive adhesive layer may be provided thereon, and the liquid crystal cell may be bonded through the pressure-sensitive adhesive layer.

  In the illustrated example, transparent protective films 12 and 13 are bonded to both surfaces of the polarizing film 11, respectively. In general, such a form is often taken, but the transparent protective film is applied only to one surface of the polarizing film 11. It may be pasted. In that case, it is normal to provide the transparent protective film 12 in the surface which becomes a side far from the liquid crystal cell of the polarizing film 11 when it is set as a liquid crystal panel. Thus, when providing the transparent protective film 12 only on the single side | surface of the polarizing film 11, the adhesive layer 22 is normally provided in the other side of the polarizing film 11 directly. That is, in a form in which the transparent protective film is bonded only to one surface of the polarizing film 11, it is common that one transparent protective film 13 is omitted in FIG.

  In the present invention, when the protective films 12 and 13 are bonded to at least one of the transparent protective films, that is, both surfaces of the polarizing film 11, the protective film is bonded only to at least one of the transparent films 11 and one surface of the polarizing film 11. In that case, the protective film, usually the transparent protective film 12 that is on the side far from the liquid crystal cell when a liquid crystal panel is formed, is composed of an unstretched polypropylene resin film. Even when the transparent protective films 12 and 13 are provided on both surfaces of the polarizing film 11, it is advantageous that the transparent protective film 12 on the side far from the liquid crystal cell is formed of an unstretched polypropylene resin film. This polypropylene-based resin film is heat-treated at a temperature lower than its melting point and (melting point−55 ° C.) or higher, whereby the tensile elastic modulus at 80 ° C. is set to 200 MPa or higher and the rigidity is enhanced.

  First, each film which comprises the polarizing plate 10 is demonstrated.

[Polarized film]
The polarizing film 11 serving as the central element of the polarizing plate 10 is a film having a function of converting natural light into linearly polarized light. The polarizing film 11 is made of a polyvinyl alcohol resin, and is formed by adsorbing and orienting a dichroic dye therein. The polyvinyl alcohol resin can be obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin can be a copolymer of vinyl acetate which is a homopolymer of vinyl acetate, or a copolymer 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 saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of the polarizing film 11. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. The thickness of the polyvinyl alcohol-based raw film can be, for example, about 3 to 150 μm.

  The polarizing film 11 is usually a stretching process for uniaxially stretching such a polyvinyl alcohol resin film, a dyeing process for adsorbing a dichroic dye by dyeing the polyvinyl alcohol resin film with a dichroic dye, a dichroic dye It is manufactured through a boric acid treatment process in which a polyvinyl alcohol resin film adsorbed with boric acid is treated with a boric acid aqueous solution, and a water washing process in which water is washed after the boric acid treatment.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before the dyeing process, simultaneously with the dyeing process, or after the dyeing process. When uniaxial stretching is performed after the dyeing step, the uniaxial stretching may be performed before the boric acid treatment step or may be performed during the boric acid treatment step. Moreover, uniaxial stretching can also be performed in several steps. Uniaxial stretching can be performed by a method of stretching uniaxially between rolls having different peripheral speeds, a method of stretching uniaxially using a heating roll, or the like. Uniaxial stretching may be performed by dry stretching in which stretching is performed in the air, or may be performed by wet stretching in which a polyvinyl alcohol-based resin film is swollen using a solvent such as water. The draw ratio is usually about 3 to 8 times.

  The polyvinyl alcohol resin film can be dyed with a dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye. The polyvinyl alcohol-based resin film is preferably subjected to a treatment of immersing and swelling 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 aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. It is. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

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 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 usually about 1 × 10 ⁻⁴ to 10 parts by weight, preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dichroic organic dye solution used for dyeing is usually about 20 to 80 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with the dichroic dye can be carried out by a method of immersing the dyed polyvinyl alcohol resin film in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid aqueous solution preferably further contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is usually about 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight per 100 parts by weight of water. The immersion time in the boric acid aqueous solution is usually about 60 to 1,200 seconds, preferably 150 to 600 seconds, and more preferably 200 to 400 seconds. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by a method of immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain the polarizing film 11. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of a drying process is about 30-100 degreeC normally, Preferably it is 50-80 degreeC. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

  In this way, the polyvinyl alcohol resin film is subjected to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment, and the polarizing film 11 in which the dichroic dye is adsorbed and oriented is obtained. The thickness of the polarizing film 11 can be about 2-40 micrometers, for example.

  The polarizing film 11 thus obtained is preferably bonded to the transparent protective films 12 and 13 in the subsequent production line. Thereby, it can start from the raw film of polyvinyl alcohol-type resin, and can produce the polarizing plate 10 continuously.

  The transparent protective films 12 and 13 are provided for the purpose of preventing the polarizing film 11 and protecting the surface of the polarizing film 11 because the polarizing film 11 is easily stretched due to being highly stretched. Even if only a transparent protective film is bonded to one side of the polarizing film 11, a corresponding effect is exhibited. In general, it is preferable to bond a transparent protective film to both sides of the polarizing film 11. When the transparent protective films 12 and 13 are bonded to both surfaces of the polarizing film 11, the transparent protective film 13 on the liquid crystal cell side when the liquid crystal display panel is used has a function as a protective film and optical compensation for the liquid crystal cell. May have the function of. It is effective that the unstretched polypropylene-based resin film with increased rigidity defined in the present invention is the transparent protective film 12 on the side far from the liquid crystal cell when it is used as a liquid crystal display panel.

[Polypropylene resin film]
The polypropylene resin film bonded to at least one surface of the polarizing film 11, preferably the surface far from the liquid crystal cell will be described. This polypropylene-based resin film is an unstretched film and is heat-treated to increase the rigidity, and the storage elastic modulus at 80 ° C. is 200 MPa or more.

  From the viewpoint of rigidity, the polypropylene resin film is allowed to have an ethylene unit content of about 1% by weight, but is preferably substantially a propylene homopolymer. That is, the polypropylene resin constituting the film is preferably a propylene homopolymer or a copolymer of propylene and ethylene having an ethylene unit content of 1% by weight or less. From the viewpoint of transparency and workability of the film, it is more preferable to use a copolymer of propylene and ethylene containing ethylene units at a ratio of 1% by weight or less.

  When the content of the ethylene unit in the polypropylene resin exceeds 1% by weight, the glass transition temperature (Tg) of the resin is lowered, and thus the rigidity of the obtained film tends to be lowered. Therefore, the ethylene unit content is more preferably 0.75% by weight or less, and further preferably 0.5% by weight or less. On the other hand, when there is too little content of an ethylene unit, the workability and transparency of the film which are obtained may not necessarily be enough. Therefore, the ethylene unit content is more preferably 0.01% by weight or more, further 0.05% by weight or more, and particularly preferably 0.1% by weight or more. The ethylene unit content can be obtained, for example, by measuring infrared (IR) spectrum by the method described on page 616 of "Polymer Analysis Handbook" (1995, published by Kinokuniya Shoten). When a copolymer of propylene and ethylene is used, it may be a random copolymer or a block copolymer. However, since the ethylene unit content is small as described above, a random copolymer is generally used. Often a polymer.

  The stereoregularity of the polypropylene resin can be any of isotactic, syndiotactic, or atactic, but is preferably isotactic from the viewpoint of heat resistance, rigidity, and transparency. In accordance with JIS K 7210: 1999 “Testing methods for plastics-thermoplastic melt mass flow rate (MFR) and melt volume flow rate (MVR)”, this polypropylene resin is used at a temperature of 230 ° C. and a load of 21.18 N. The measured melt mass flow rate (MFR) is preferably in the range of 0.1 to 200 g / 10 minutes, more preferably in the range of 0.5 to 50 g / 10 minutes. If a polypropylene resin having an MFR within this range is used, a uniform film can be obtained without imposing a large load on the extruder.

This polypropylene resin can be produced by a method of homopolymerizing propylene or a method of copolymerizing propylene and ethylene using a known polymerization catalyst. Examples of known polymerization catalysts include the following.
(1) Ti—Mg-based catalyst comprising a solid catalyst component containing magnesium, titanium and halogen as essential components,
(2) a catalyst system in which a solid catalyst component containing magnesium, titanium and halogen as essential components is combined with an organoaluminum compound and, if necessary, a third component such as an electron donating compound,
(3) Metallocene catalysts.

  Examples of the solid catalyst component (1) and (2) include catalyst systems described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. . Examples of the metallocene catalyst of (3) above include catalyst systems described in Japanese Patent No. 2587251, Japanese Patent No. 2627669, Japanese Patent No. 2667732, and the like.

  Polypropylene resin is, for example, a solution polymerization method using an inert solvent typified by a hydrocarbon compound such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene or xylene, and a liquid monomer as a solvent. It can be produced by a bulk polymerization method to be used or a gas phase polymerization method in which a gaseous monomer is polymerized as it is. Polymerization by these methods may be carried out batchwise or continuously.

  A well-known additive may be mix | blended with the polypropylene resin. Examples of additives that can be blended include antioxidants, light stabilizers, ultraviolet absorbers, antistatic agents, lubricants, nucleating agents, antifogging agents, and antiblocking agents.

  Examples of antioxidants include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, and the like, and for example, phenolic antioxidant mechanisms and phosphorus antioxidant mechanisms in one molecule. It is also possible to use a composite type antioxidant having a unit having both. A typical example of the light stabilizer is a hindered amine light stabilizer. Examples of the UV absorber include 2-hydroxybenzophenone UV absorbers, hydroxyphenylbenzotriazole UV absorbers, and benzoate UV absorbers. The antistatic agent may be polymer type, oligomer type or monomer type. Examples of the lubricant include higher fatty acid amides such as erucic acid amide and oleic acid amide, higher fatty acids such as stearic acid, and salts thereof. Examples of the nucleating agent include sorbitol nucleating agents, organophosphate nucleating agents, and polymer nucleating agents such as polyvinylcycloalkane. As the anti-blocking agent, fine particles having a spherical shape or a shape close thereto can be used regardless of inorganic type or organic type. A plurality of these additives may be used in combination.

  The polypropylene resin can be formed into a film by molding by a known method used industrially. Specific examples of the film forming method include an extrusion molding method, a blow molding method, an injection molding method, a compression molding method, and a calendar molding method. In particular, the polypropylene resin can be suitably manufactured by an extrusion molding method such as a T-die molding method or a tubular molding method. Of these, the melt extrusion method using a T die is particularly preferable.

  In the present invention, an unstretched polypropylene-based resin film obtained as described above is subjected to a heat treatment at a temperature lower than its melting point (melting point−55 ° C.), but at a temperature of 80 ° C. Use a film with a significantly increased rate of 200 MPa or more.

  The tensile elastic modulus can be measured using a general tensile testing machine. An example of a tensile tester is Autograph “AG-1” manufactured by Shimadzu Corporation. A test piece having an appropriate size is cut and held in an oven at 80 ° C. for about 5 minutes to stabilize the temperature, and then a tensile test is performed. The oven temperature is controlled at about 80 ° C. ± 2 ° C. In the examples described later, the film was cut into a size of 20 mm × 100 mm, 20 mm at both ends in the longitudinal direction were held with a chuck, a gauge distance was 60 mm, and a tensile test was performed at a pulling speed of 5 mm / min. The tensile modulus is defined as the slope of the elastic region in the stress strain diagram obtained by a tensile test of the material. At this time, the relationship between the stress σ and the strain ε can be expressed by the formula: σ = Eε, where E is a longitudinal elastic modulus and a tensile elastic modulus.

Polypropylene resin has a small photoelastic coefficient of about 2 × 10 ⁻¹³ cm ² / dyne and low moisture permeability. Therefore, if the polarizing plate 10 having a polypropylene resin film as a protective film is applied to a liquid crystal cell, wet heat It can be set as the liquid crystal panel and liquid crystal display device which are excellent in durability on conditions. Furthermore, the adhesiveness of the polypropylene resin film to the polarizing film 11 is good, if not as high as that of the triacetyl cellulose film. When various known adhesives are used, the polypropylene resin film can be polarized with sufficient strength. The film 11 can be adhered.

  The polypropylene resin film used in the present invention preferably has an internal haze of 5% or less, more preferably 3% or less, and a total haze of 30% or less. When the internal haze exceeds 5% or the total haze exceeds 30%, the light transmitted through the film is scattered, and when the liquid crystal display panel or the liquid crystal display device is attached to the liquid crystal cell, the display characteristics are There is a possibility of lowering.

  Here, the haze is the ratio of the diffuse light transmittance to the total light transmittance when visible light is incident on the film, and the smaller the haze is, the better the film is. The haze obtained by allowing visible light to enter the film as it is is also called the total haze, which is the external haze caused by the light diffusion due to the surface shape of the film and the light diffusion factor (light diffusing agent or It is the sum of internal haze caused by light diffusion due to crystal grain boundaries. For example, if a film is placed in a liquid having a refractive index substantially equal to that of the film and visible light is incident from one side, the haze in the state where there is no light diffusion due to the surface shape, that is, the internal haze can be obtained. Accordingly, the external haze can be expressed as a value obtained by subtracting the internal haze from the total haze.

[Another transparent protective film]
As described above with reference to FIG. 1, in the present invention, the transparent protective film 12 that is on the side far from the liquid crystal cell when the polarizing plate 10 is attached to the liquid crystal cell comprises an unstretched polypropylene resin, It is preferable to use a film with increased rigidity. When providing the transparent protective film 13 also on the other surface of the polarizing film 11, the protective film 13 can be composed of various transparent resin films depending on the use of the polarizing plate 10. The transparent protective film 13 may have a retardation film function as well as a protective film function.

  Examples of resins that can be the transparent protective film 13 include polycarbonate resins, polyvinyl alcohol resins, polystyrene resins, (meth) acrylate resins, polyolefin resins including cyclic olefin resins and polypropylene resins, triacetyl Examples include cellulose acetate-based resins including cellulose, polyarylate-based resins, polyimide-based resins, and polyamide-based resins. The film made of these transparent resins may be unstretched or may be stretched uniaxially or biaxially. The film thickness of the transparent protective film 13 is usually about 10 to 200 μm, preferably 20 to 120 μm.

  When the transparent protective film 13 is a stretched film, an appropriate retardation is imparted by stretching. The film provided with the phase difference may be a wave plate such as a quarter wave plate or a half wave plate, or may be a film for optical compensation. In the case where a retardation film for optical compensation is used as the transparent protective film 13, a film provided with an appropriate retardation may be selected in consideration of the mode employed in the liquid crystal cell.

For example, vertical alignment: If (Vertical Alignment VA) mode liquid crystal cell, a polymer film having a positive intrinsic birefringence is uniaxially stretched, the refractive index ellipsoid has the relationship of n _x> n _y ≒ n _z positive a plate, the transverse stretching or biaxial stretching is performed, using n _x> n _y> biaxial film having a relation of n _z, or n _x ≒ n _y> negative C plate having a relationship of n _z be able to. Here, n _x plane slow axis (x-axis) of the film refractive index in the direction of, n _y in-plane fast axis (y-axis: Axis perpendicular in slow axis in-plane) direction of the refractive index, N _z is the refractive index in the thickness (z-axis) direction.

Among these, a biaxially stretched retardation film is suitably used as the transparent protective film 13. The Nz coefficient that is a measure of the biaxiality of the film is defined by the following formula (1). Further, assuming that the film thickness is d, the in-plane retardation Re and the thickness direction retardation Rth are defined by the following equations (2) and (3), respectively.
_{Nz = (n x -n z)} / (n x -n y) ··· (1)
_{Re = (n x -n y)} × d ··· (2)
Rth = _{[(n x + n y) /} 2-n z ] × d ··· (3)

Further, from the above formulas (1) to (3), the Nz coefficient, the in-plane phase difference Re and the thickness direction phase difference Rth have a relationship represented by the following formula (4).
Nz = Rth / Re + 0.5 (4)

  When a biaxial retardation film is used as the transparent protective film 13, the in-plane retardation Re is preferably in the range of 30 to 300 nm, particularly in the range of 50 to 260 nm. The Nz coefficient is preferably in the range of 1.1-7, particularly in the range of 1.4-5. From these ranges, an appropriate value may be set according to the viewing angle characteristics required for the applied liquid crystal display device.

  When the transparent protective film 13 is a retardation film, the polarizing film 11 and the transparent protective film 13 that is a retardation film have an angle formed by the former absorption axis and the latter slow axis, depending on the application. What is necessary is just to select suitably. For example, when the transparent protective film 13 is a retardation film for optical compensation, the angle formed between the absorption axis of the polarizing film 11 and the slow axis of the retardation film is substantially 0 ° or 90 °. It is said.

  On the other hand, when the transparent protective film 13 is an unstretched film, the in-plane retardation Re hardly develops and functions as a protective film for the polarizing film 11. In particular, a substantially non-oriented film in which the in-plane retardation Re is almost zero and the thickness direction retardation Rth is almost zero, for example, 10 nm or less, is, for example, an in-plane switching (IPS) mode. Since it functions as a kind of optical compensation film, it is preferably used.

  When the above-described retardation film or virtually non-oriented film is used as the transparent protective film 13 on the liquid crystal cell side when the liquid crystal display panel is used, the transparent protective film 13 is a cyclic olefin resin or a cellulose acetate type. The resin is advantageous because it has a small photoelastic coefficient and is easily available. In particular, when a retardation film is used, a cyclic olefin-based resin is preferably used because various desired retardations can be easily imparted depending on stretching conditions.

[Production method of polarizing plate]
The polarizing plate of the present invention heat-treats a polypropylene resin film at a temperature lower than its melting point but higher than (melting point -55 ° C) so that the polypropylene resin film exhibits a tensile modulus of 200 MPa or more at 80 ° C. It can manufacture by the method provided with the heat processing process to perform, and the bonding process which bonds the polypropylene resin film to which the heat processing was performed to a polarizing film.

(Heat treatment process)
First, the heat treatment process will be described. As described above, the polypropylene resin film is formed by an appropriate method such as melt extrusion. In the present invention, the unstretched polypropylene resin film thus obtained is subjected to heat treatment to increase the tensile elastic modulus at 80 ° C. of the film, thereby strengthening so-called “strain”, in other words, rigidity. It is increasing. The heat treatment is performed at a temperature lower than the melting point of the polypropylene resin, but higher than (melting point−55 ° C.).

  FIG. 2 is a cross-sectional view schematically showing a specific form of a method for performing a heat treatment on the polypropylene resin film 50, (A) is a form in which heat treatment is performed with a heating roll, and (B) is a heat treatment in a heating oven. The form is shown. In these forms, the polypropylene-based resin film 50 to be subjected to heat treatment may be transferred as it is from a molten state, or the film formed from the molten state may be temporarily transferred to a roll, for example. It may be wound up, fed out from there, and transferred here. In FIG. 2, a solid straight arrow represents the traveling direction of the film, and a curved arrow represents the rotation (winding) direction of the roll.

  In one embodiment, the heat treatment is performed by heating rolls 51, 52, 53, and 54 as shown in FIG. In this embodiment, the polypropylene resin film 50 fed in the form of a sheet is sequentially wound around heated rolls 51, 52, 53, and 54 and subjected to heat treatment. The heating rolls 51 to 54 may be any roll-shaped member having a smooth surface and capable of being heated to a predetermined temperature.

  The surfaces of the heating rolls 51 to 54 are preferably formed of a metal having high thermal conductivity and high rigidity. As a metal material which comprises the surface of the heating rolls 51-54, chromium, stainless steel, etc. can be mentioned, for example. Although there may be one heating roll, in order to heat uniformly from both surfaces of the polypropylene resin film 50, it is preferable to provide a plurality of, especially four or more even numbers. In the illustrated form, four heating rolls 51, 52, 53, and 54 are arranged along the traveling direction of the polypropylene resin film 50, and the second heating roll 51 arranged on the inlet side is connected to the second heating roll 51. One surface and the other surface of the polypropylene-based resin film 50 are alternately brought into contact with the heating roll 52, the third heating roll 53, and the fourth heating roll 54 in order, and heat treatment is performed. Yes.

  When three or more heating rolls are arranged, the case of the illustrated four cases will be described as an example. The surface of the first heating roll 51 on the inlet side and the fourth heating roll 54 on the outlet side is mirror-finished. On the other hand, it is preferable that the surface of the second heating roll 52 and the third heating roll 53 disposed between them is semi-matted. The reason why the second heating roll 52 and the third heating roll 53 arranged in the middle are semi-mats is to improve the peelability, from the second heating roll 52 to the third heating roll 53, and to the third heating roll 53. This is because the film can be easily fed from the heating roll 53 to the fourth heating roll 54. On the other hand, the reason why the first heating roll 51 on the inlet side and the fourth heating roll 54 on the outlet side are mirror-finished products is to reduce surface irregularities, and at least the inlet side and outlet side rolls The surface state of the film is also made good by making the mirror-finished. If moderate peelability is ensured, it is also effective to use the second heating roll 52 and the third heating roll 53 located in the middle as mirror-finished products.

  The temperature of each heating roll may be the same, but the first heating roll 51 on the inlet side and the fourth heating roll 54 on the outlet side are set slightly lower than the predetermined heat treatment temperature and arranged between them. The second heating roll 52 and the third heating roll 53 are preferably set to a predetermined heat treatment temperature. Thereby, the film temperature can be raised stepwise to reach a predetermined heat treatment temperature, and after the heat treatment is performed at that temperature, the film temperature can be lowered stepwise. In this case, the temperature of the 1st heating roll 51 and the 4th heating roll 54 should just be suitably set between predetermined heat processing temperature and room temperature, for example, between about 30-70 degreeC. In this case, the heat treatment time to be described later is the time for contacting the heating roll maintained at a predetermined heat treatment temperature, in the example shown in FIG. It will be time to leave.

  As described above, in this embodiment, the polypropylene-based resin film 50 is heated from the roll side in contact therewith, that is, from one surface side. Therefore, an even number (at least two) of heating rolls maintained at a predetermined heat treatment temperature are arranged so that the heating is performed uniformly from both sides of the film, and the inlet side and outlet side rolls have a relaxed temperature. Therefore, it is preferable to provide an even number of four or more heating rolls 51 to 54.

  The heating rolls 51 to 54 themselves may be known ones, and examples thereof include a roll in which a heating element is provided. The heating element can be, for example, an electrical resistance heating element or a dielectric heating coil. The heat generated in the heating element is transmitted to the surfaces of the heating rolls 51 to 54, and the polypropylene resin film 50 is heated on the surfaces.

  In another embodiment, the heat treatment is performed by a heating oven 56 as shown in FIG. In this form, the polypropylene resin film 50 fed in the form of a sheet is introduced into a heating oven 56 maintained at a predetermined temperature, where heat treatment is performed. The heating oven 56 may have a structure in which, for example, a pair of nozzle rows each having a plurality of nozzles are arranged to face each other so as to sandwich the polypropylene resin film 50 from above and below. A hot air blowing port may be provided at the tip of each nozzle so that the hot air is blown onto the upper and lower surfaces of the polypropylene resin film 50. In FIG. 2B, the direction of the hot air to be blown is indicated by a broken line arrow. In this embodiment, the heat treatment time described later may be the residence time of the film in the heating oven 56.

  In any of the form shown in FIG. 2A and the form shown in FIG. 2B, the heat-treated polypropylene resin film 50 is wound around a take-up roll 58 and stored in a roll shape. The wound polypropylene resin film 50 is unwound from the winding roll 58 and sent to the next bonding step. Of course, if circumstances permit, the heat-treated polypropylene resin film can be supplied as it is to the next bonding step without being wound.

  In the heat treatment step performed as described above, the temperature is lower than the melting point of the polypropylene resin film 50 but is set to (melting point−55 ° C.) or higher. When this temperature is too low, the imparting of rigidity by heat treatment becomes insufficient, and the tensile elastic modulus at 80 ° C. of the film cannot be sufficiently increased. The heat treatment temperature is preferably (melting point−25 ° C.) or more, more preferably (melting point−5 ° C.) or more. As the heat treatment temperature approaches the melting point of the polypropylene-based resin, the tensile elastic modulus of the polypropylene-based resin film 50 increases and the durability of the polarizing plate is easily improved. If the melting point of the polypropylene resin is, for example, 162 ° C., the melting point is −55 ° C. = 107 ° C. On the other hand, if the heat treatment temperature is higher than the melting point, the film tends to shrink or melt, so the heat treatment is performed at a temperature lower than the melting point.

  The heat treatment time may be set according to the melting point and heating temperature of the polypropylene-based resin film 50 and further according to the heating means, but is generally appropriately selected from the range of 1 second to 5 minutes. If the heat treatment time is too short, sufficient heat cannot be transmitted to the polypropylene-based resin film 50, and the purpose of increasing the tensile modulus at 80 ° C. is difficult to be achieved. On the other hand, if the heat treatment time is too long, the polypropylene-based resin film 50 receives an excessive heat history and tends to cause inconveniences such as heat shrinkage. The closer the heat treatment temperature is to the melting point of the polypropylene resin film 50, the shorter the time for which the temperature is maintained. On the contrary, it is preferable to set a longer time for maintaining the temperature as the heat treatment temperature is further away from the melting point of the polypropylene resin film 50.

  In addition, when heat-processing using the heating rolls 51-54 like FIG. 2 (A), since heat processing is performed in the state which the metal roll with smooth surface and the polypropylene resin film 50 contacted, the polypropylene system after heat processing There is an advantage that the surface of the resin film 50 is easy to be smooth with few irregularities. On the other hand, in the heating rolls 51 to 54, both surfaces of the polypropylene resin film 50 cannot be heated at the same time, and one surface and the other surface are alternately heated. The thermal histories are different, and the possibility of causing a difference in optical characteristics on each surface is slightly increased.

  On the other hand, when heat treatment is performed using the heating oven 56 as shown in FIG. 2 (B), the heat history on both sides of the film becomes almost the same because the heat can be simultaneously applied from both sides of the polypropylene resin film 50. There is an advantage that the characteristics are likely to be uniform. On the other hand, in the heating oven 56, hot air is blown onto the polypropylene-based resin film 50, so that the possibility of deformation such as irregularities on the surface due to the pressure of the hot air is slightly increased.

  In the heat treatment, whether to use the heating rolls 51 to 54 as shown in FIG. 2 (A) or the heating oven 56 as shown in FIG. 2 (B) is determined appropriately in consideration of the above merits and demerits. Should be selected. For example, while using the heating oven 56 as shown to FIG. 2 (B), it is also possible to employ | adopt the form which conveys a film along a some roll in it.

(Bonding process)
The polypropylene resin film after the heat treatment step is bonded to the polarizing film in the next bonding step. With reference to FIG. 1, when a polypropylene-based resin film defined in the present invention as a transparent protective film 12 is bonded to one surface of a polarizing film 11 and the same or different transparent protective film 13 is bonded to the other surface, It is advantageous that the transparent protective film 13 is also bonded at the same time in this bonding step. An adhesive is usually used for bonding the transparent protective film 12 and the transparent protective film 13 to the polarizing film 11. The adhesive for laminating the polarizing film 11 and the transparent protective film 12 and the adhesive for laminating the polarizing film 11 and the transparent protective film 13 may be the same or different. From the viewpoint of productivity, it is more advantageous to use the same type as long as appropriate adhesive strength can be obtained.

  As the adhesive, an adhesive having epoxy resin, urethane resin, cyanoacrylate resin, acrylamide resin, or the like as an adhesive component can be used. One of the adhesives preferably used is a solventless adhesive. Solventless adhesives do not contain a significant amount of solvent, and are curable components (monomers or oligomers) that are reactively cured by heating or irradiation with active energy rays (for example, ultraviolet rays, visible light, electron beams, X-rays, etc.). The adhesive layer is formed by curing of the curable component, and typically includes a curable component that is reactively cured by heating or irradiation with active energy rays, and a polymerization initiator.

  In particular, in the present invention, at least one of the transparent protective films 12 and 13 is made of a polypropylene resin, but the polypropylene resin film has a low water vapor transmission rate, so water drainage is poor when an aqueous adhesive is used. The moisture of the adhesive may cause damage to the polarizing film 11 or deterioration of the polarizing performance. Accordingly, when the presence of moisture is disliked, a solventless adhesive is preferably used.

  From the viewpoint of quick curing and productivity improvement of the polarizing plate 10 associated therewith, an example of a preferable adhesive is an active energy ray-curable adhesive that is cured by irradiation with active energy rays. As an example of such an active energy ray-curable adhesive, a photocurable adhesive that cures with light energy, typically ultraviolet light, can be cited. From the viewpoint of reactivity, the photocurable adhesive is preferably one that is cured by cationic polymerization. In particular, a solvent-free epoxy adhesive having an epoxy compound as a curable component is a kind of the transparent protective films 12 and 13. Regardless, since it shows high adhesiveness to the polarizing film 11, it is preferably used.

  In a solvent-free epoxy adhesive, an epoxy compound serving as a curable component is generally cured by cationic polymerization. In particular, from the viewpoint of weather resistance and refractive index, an epoxy compound having no aromatic ring in the molecule is preferably used. Examples of the epoxy compound having no aromatic ring in the molecule include a nuclear hydride of an aromatic epoxy compound, an alicyclic epoxy compound, and an aliphatic epoxy compound. The epoxy compound serving as the curable component usually has at least two epoxy groups in one molecule.

  After the transparent protective films 12 and 13 are bonded to the polarizing film 11 via an uncured epoxy adhesive, the adhesive is cured by irradiation with active energy rays or heating, and the transparent protective film is formed on the polarizing film 11. 12 and 13 are fixed. In the case of curing by irradiation with active energy rays, ultraviolet rays are preferably used. Specific examples of the ultraviolet light source include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a black light lamp, and a metal halide lamp.

  The irradiation intensity and irradiation amount of active energy rays such as ultraviolet rays are appropriately selected so as to sufficiently activate the cationic polymerization initiator and not adversely affect the cured adhesive layer, the polarizing film 11 and the like. . In addition, when cured by heating, it may be heated by a generally known method, and the temperature and time at that time sufficiently activate the cationic polymerization initiator, and the cured adhesive layer or polarized light. It is appropriately selected so as not to adversely affect the film such as the film 11.

  When an epoxy adhesive is used, the thickness of the adhesive layer after curing by irradiation with active energy rays or heating is generally 20 μm or less, preferably 10 μm or less, more preferably 3 μm or less. be able to.

  In the case where the presence of water is not disliked, a water-based adhesive can also be used from the viewpoint of thinning the adhesive layer. The water-based adhesive is an adhesive in which an adhesive component is dissolved in water or an adhesive component is dispersed in water. Examples of such water-based adhesives include those mainly composed of a polyvinyl alcohol resin or a urethane resin.

  When the transparent protective films 12 and 13 are bonded to the surface of the polarizing film 11 using an aqueous adhesive, a conventionally known method can be used. For example, the polarizing film 11 and / or a transparent protective film bonded to the polarizing film 11 by the casting method, the Mayer bar coating method, the gravure coating method, the comma coater method, the doctor blade method, the die coating method, the dip coating method, the spraying method, etc. The method of apply | coating an adhesive agent to the adhesive surface of 12 and 13 and superimposing both is mentioned. The casting method is a method of spreading and spreading an adhesive on the surface of a film to be coated while moving the film in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two.

  When the transparent protective films 12 and 13 are bonded to the polarizing film 11 using a water-based adhesive, a drying process is usually performed thereafter to remove moisture and cure the adhesive. The drying process can be performed by, for example, a method of blowing hot air. A drying temperature is normally selected from the range of about 40-100 degreeC, Preferably it is 60-100 degreeC. The drying time is, for example, about 20 to 1,200 seconds. The thickness of the adhesive layer after drying can be about 0.001 to 5 μm, preferably 0.01 μm or more, preferably 2 μm or less, more preferably 1 μm or less. If the adhesive layer is too thick, the appearance of the polarizing plate 10 tends to be poor.

  Regardless of which adhesive is used, plasma treatment, corona treatment, ultraviolet irradiation treatment, frame is applied to the adhesion surface of the polarizing film 11 and / or the transparent protective films 12 and 13 bonded to the polarizing film 11 in order to improve adhesion. Surface treatments such as (flame) treatment and saponification treatment may be applied as appropriate. The saponification treatment can be performed by a method of immersing the film in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

[Adhesive layer and separate film]
As described above with reference to FIG. 1, the polarizing plate 10 thus obtained usually has an adhesive layer 22 on one surface thereof, specifically, a surface bonded to a liquid crystal cell when a liquid crystal panel is formed. And a separate film 24 is provided on the surface thereof. The pressure-sensitive adhesive layer 22 is generally formed from a so-called acrylic pressure-sensitive adhesive in which an acrylic resin is used as a pressure-sensitive adhesive component, a crosslinking agent is blended therein, and a silane coupling agent is further blended. Further, the separate film 24 is generally composed of a transparent resin film such as polyethylene terephthalate which has been subjected to a release treatment, and is peeled off immediately before being attached to the liquid crystal cell.

[Liquid crystal panel and liquid crystal display device]
The polarizing plate 10 of the present invention having the layer configuration shown in FIG. 1 as a representative example can be used as a constituent member of a liquid crystal panel. FIG. 3 is a schematic cross-sectional view showing an example of a basic layer configuration of the liquid crystal panel 20 and the liquid crystal display device 30 to which the liquid crystal panel 20 is applied. As shown in this figure, the polarizing plate 10 is bonded to the liquid crystal cell 27 through the pressure-sensitive adhesive layer 22 to form the liquid crystal panel 20. The liquid crystal panel 20 includes a liquid crystal cell 27, a back side polarizing plate 10 attached to the back side thereof, and a front side polarizing plate 15 attached to the viewing side of the liquid crystal cell 17. In the illustrated example, the back side polarizing plate is constituted by the polarizing plate 10 of the present invention shown in FIG.

  The front-side polarizing plate 15 also includes a polarizing film 16 and transparent protective films 17 and 18 bonded to at least one surface thereof, preferably both surfaces, and on one transparent protective film 18 side, an adhesive is provided. It is attached to the liquid crystal cell 27 via the layer 23. For the polarizing film 16, the same description as that for the polarizing film 11 with reference to FIG. For the transparent protective films 17 and 18, the same description as that described for the transparent protective films 12 and 13 with reference to FIG. 1 is applied except that the resin is changed as necessary. In many cases, a surface treatment layer such as a hard coat layer, an antiglare layer, or an antireflection layer is provided on the surface of the transparent protective film 17 on the side far from the liquid crystal cell 27 of the front side polarizing plate 15. The pressure-sensitive adhesive layer 23 is also usually formed from an acrylic pressure-sensitive adhesive.

  The liquid crystal display device 30 includes a liquid crystal panel 20 and a backlight 35. As can be seen from this figure, in the liquid crystal panel or liquid crystal display device, the back side means the backlight 35 side when the liquid crystal panel 20 is mounted on the liquid crystal display device 30, and the viewing side means the liquid crystal panel 20. This means the side opposite to the backlight 35 when mounted on the liquid crystal display device 30, and the display is viewed on this side.

  The liquid crystal cell 27 is an element configured to display an image by electrically controlling a cell in which a liquid crystal substance is sealed between two glass substrates. The liquid crystal cell 17 can be of various known modes such as a liquid crystal driving mode using a blue phase liquid crystal in addition to the VA mode and IPS mode described above.

  The backlight 35 is a device for supplying light for display to the liquid crystal cell 27, and can also be composed of a device known in this field including an edge light type and a direct type. The edge-light type backlight is composed of a light guide plate and a light source including a cold cathode tube and an LED disposed on the side surface thereof, and light emitted from the light source is supplied to the liquid crystal cell 27 through the light guide plate. ing. The light guide plate is made of a transparent resin such as acrylic resin or polystyrene. On the other hand, the direct type backlight is disposed directly below the liquid crystal cell 27 with a plurality of cold-cathode tubes and the like (on the liquid crystal cell side), and diffuses the light from the light source to make it uniform. And a uniformly dispersed light is supplied to the liquid crystal cell 27. The light diffusing plate is, for example, a material obtained by dispersing particles as a light diffusing agent in a thermoplastic resin to impart light diffusibility, a surface having irregularities formed on the surface of a thermoplastic resin sheet, and a light diffusing property. It can be composed of a resin resin coating layer in which particles are dispersed on the surface of a plastic resin sheet to impart light diffusibility. The thickness is usually about 0.1 to 5 mm.

  Although not shown, between the backlight 35 and the liquid crystal panel 20, there is a light diffusion sheet, a prism sheet, a brightness enhancement sheet (also referred to as a reflective polarizing film, “DBEF” In many cases, sheets or films exhibiting other optical functionalities are arranged. A plurality of sheets or films exhibiting other optical functionalities may be arranged as necessary.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples,% representing the content or amount used is based on weight unless otherwise specified. In the following examples, particularly in the tables, the melting point of polypropylene resin may be expressed as “Tm”. Moreover, the melt mass flow rate (MFR) and melting | fusing point of a polypropylene resin are the values measured with the following method.

・ Melt mass flow rate (MFR)
Measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K 7210: 1999 “Plastics—Test Methods for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastic Plastics”.

-Melting point 10 mg of a press film of polypropylene resin was used as a sample, and this was placed in a differential scanning calorimeter (DSC), heat-treated at 230 ° C for 5 minutes in a nitrogen atmosphere, and then cooled at 30 ° C at a rate of 10 ° C / min. And then kept at the same temperature for 5 minutes, and further heated from 30 ° C. to 230 ° C. at a heating rate of 10 ° C./min, and the melting peak temperature at that time was taken as the melting point.

[Example 1]
(A) Production of polypropylene-based resin film A propylene / ethylene random copolymer having an ethylene unit content of 0.4%, an MFR of 9 g / 10 min, and a melting point of 162 ° C. was used as the polypropylene-based resin at 260 ° C. Then, the mixture was melt-kneaded with a 50 mmφ extruder heated to 650 mm, then extruded in a molten state from a 600 mm wide T-die, and cooled with a cooling roll adjusted to a temperature of 25 ° C. to obtain a 75 μm thick film. The film after exiting the cooling roll was subsequently led to a heat treatment zone composed of four heating rolls. The heat treatment zone is arranged as shown in FIG. 2A, and the film is sequentially brought into contact with the first heating roll 51, the second heating roll 52, the third heating roll 53, and the fourth heating roll 54. went. Each of the rolls 51 to 54 has a diameter of 300 mmφ, the temperature of the first heating roll 51 is 50 ° C., the temperature of the second heating roll 52 is 120 ° C., the temperature of the third heating roll 53 is 120 ° C., And the temperature of the 4th heating roll 54 was 50 degreeC. The film after passing through the fourth heating roll 54 was wound up on a winding roll 58.

(B) Measurement of tensile modulus A 20 mm × 100 mm test piece was cut from the heat-treated polypropylene resin film, and a tensile test was performed using an autograph “AG-1” manufactured by Shimadzu Corporation. It was. The test was carried out by holding 20 mm at both ends in the length direction of the above sample with a chuck (marking distance 60 mm), placing it in a drying oven controlled at 80 ° C. ± 2 ° C. and holding it for 5 minutes, and then speeding 5 mm / Pulled in minutes to determine the tensile modulus. The results are shown in Table 1.

(C) Measurement of haze Haze was measured using the haze meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd. for the polypropylene resin film subjected to the heat treatment in (a) above. The results are shown in Table 1.

(D) Production of Polarizing Film A long polyvinyl alcohol film having a degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, a thickness of 60 μm, and a width of 3,300 mm [“Kuraray Vinylon VF-PE manufactured by Kuraray Co., Ltd.” # 6000 "] was used as a raw film, and a polarizing film was produced by the following operation. Stretching was performed with a difference in peripheral speed between the driving nip rolls before and after the treatment tank.

  First, the film was sufficiently swollen by immersing it in a swelling tank containing pure water at 37 ° C. for 80 seconds while keeping the tension in the machine direction so that the raw film did not loosen. The roll speed ratio between the inlet and outlet of the swelling tank accompanying the swelling was 1.2. After draining with a nip roll provided at the outlet of the swelling tank, it was immersed in a water immersion tank containing 30 ° C. pure water for 160 seconds. The draw ratio in the machine direction in the water immersion tank was 1.04 times. Next, uniaxial stretching was performed at a stretching ratio of about 1.6 while being immersed in a dyeing tank containing an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.04 / 1.5 / 100. Then, the first boric acid treatment is performed by immersing in a first boric acid bath containing an aqueous solution of potassium iodide / boric acid / water 12 / 3.6 / 100 by weight at 56.5 ° C. for 130 seconds. While being applied, uniaxial stretching was performed until the cumulative draw ratio from the original fabric reached 5.3 times. Further, a second boric acid treatment was performed by immersing in a second boric acid bath containing an aqueous solution of 12 / 1.5 / 100 by weight of potassium iodide / boric acid / water at 30 ° C. for 60 seconds. . Subsequently, after immersing in a washing tank containing 10 ° C. pure water for about 16 seconds and washing, it is sequentially passed through a drying oven at about 60 ° C. and then a drying oven at about 85 ° C., and the residence time in these drying ovens For a total of 160 seconds. Thus, a polarizing film having a thickness of 23 μm with iodine adsorbed and oriented was obtained.

(E) Bonding of polypropylene-based resin film and polarizing film After applying corona treatment to one side of the polypropylene-based resin film prepared in (a) above, a photocurable epoxy resin and a photocationic polymerization initiator are applied to the corona-treated surface. A photo-curable adhesive containing was applied at a thickness of 4 μm. On the other hand, a corona treatment was applied to one side of a biaxially stretched norbornene resin film having a thickness of 50 μm (in-plane retardation Re = 55 nm, thickness direction retardation Rth = 124 nm). The same photo-curing adhesive was applied at a thickness of 4 μm. Next, the adhesive coating surface of the polypropylene resin film coated with the adhesive was superimposed on one surface of the polarizing film prepared in (d), and the adhesive was coated on the other surface. The adhesive-coated surfaces of the norbornene-based resin film were stacked and pressed with a pair of nip rolls of 100 mmφ. Thereafter, ultraviolet rays were irradiated from the norbornene-based resin film side to cure both adhesives to obtain a polarizing plate.

(F) Durability test of polarizing plate The polarizing plate produced in (e) above was cut into a wide 42 type size (width 943 mm × length 532 mm), and a copolymer of butyl acrylate and acrylic acid was cross-linked with a silane coupling agent. An endurance test was performed in which a glass made by Corning Co., Ltd. was bonded to a plate via a pressure-sensitive adhesive in which an agent was blended and held at 80 ° C for 500 hours. The state of peeling of the pressure-sensitive adhesive from the glass plate in the sample after the test was observed, and the durability was evaluated by the peeling length from the end of the pressure-sensitive adhesive layer. The results are shown in Table 1.

[Example 2]
The experiment was performed under the same conditions as in Example 1 except that the temperature of the second heating roll 52 and the third heating roll 53 was 140 ° C., respectively. Table 1 summarizes the haze and tensile modulus of the resulting polypropylene resin film, and the results of the durability test of the polarizing plate.

[Example 3]
The experiment was performed under the same conditions as in Example 1 except that the temperature of the second heating roll 52 and the third heating roll 53 was 160 ° C., respectively. Table 1 summarizes the haze and tensile modulus of the resulting polypropylene resin film, and the results of the durability test of the polarizing plate.

[Comparative Example 1]
A polypropylene resin film was produced without performing heat treatment on the film obtained from the extruded cooling roll, and then the experiment was performed under the same conditions as in Example 1. Table 1 summarizes the haze and tensile modulus of the resulting polypropylene resin film, and the results of the durability test of the polarizing plate.

[Comparative Example 2]
The experiment was performed under the same conditions as in Example 1 except that the temperature of the second heating roll 52 and the third heating roll 53 was 100 ° C., respectively. Table 1 summarizes the haze and tensile modulus of the resulting polypropylene resin film, and the results of the durability test of the polarizing plate.

  As shown in Table 1, in Examples 1 to 3 in which the heat treatment temperature was 120 ° C. or higher, that is, (melting point −42 ° C.) or higher, the tensile modulus of the polypropylene resin film was 200 MPa or more, and the durability of the polarizing plate Even in the test, the pressure-sensitive adhesive layer provided on the surface of the polypropylene resin film was not peeled off from the glass. On the other hand, in Comparative Example 1 where no heat treatment was performed, the tensile modulus of the polypropylene resin film was less than half that of the example, and the polarizing plate was provided on the surface of the polypropylene resin film in the durability test of the polarizing plate. The adhesive layer peeled off. In Comparative Example 2 in which the heat treatment temperature was lower than that in Example, the tensile elastic modulus of the polypropylene resin film was higher than that in Comparative Example 1, but it was not as high as that in Example, and the polarizing plate durability test. Also, the pressure-sensitive adhesive layer provided on the surface of the polypropylene resin film peeled off.

  From these results, when the heat treatment was performed on the polypropylene resin film at a temperature of 120 ° C. or higher, that is, (melting point −42 ° C.) or higher, the tensile elastic modulus was lower than that without heat treatment or when the heat treatment temperature was lower. It was found that the durability of the polarizing plate was improved. In particular, from the comparison between Example 1 and Comparative Example 2, if the heat treatment temperature is approximately (melting point −55 ° C.) or higher, the tensile elastic modulus at 80 ° C. of the polypropylene resin film can be approximately 200 MPa or higher. It is thought that the polarizing plate obtained by sticking to a polarizing film will be excellent in durability.

  Moreover, when each of Examples 1-3 is contrasted, it turns out that the value of a tensile elasticity modulus becomes large, so that heat processing temperature approaches melting | fusing point of a polypropylene resin film. In particular, when Example 1 and Example 2 are compared, Example 2 with a heat treatment temperature of 140 ° C., that is, (melting point−22 ° C.) shows a higher tensile elastic modulus of 350 MPa, compared with Example 1. The tensile modulus is improved. For this reason, in order to increase the tensile modulus of the polypropylene resin film, the heat treatment temperature should be 140 ° C. or higher, and if it is generalized in relation to the melting point, it should be (melting point−25 ° C.) or higher. It can be said that it is preferable.

10 …… Polarizing plate,
11: Polarizing film,
12 ... Transparent protective film (polypropylene resin film),
13 …… Transparent protective film,
15 …… Front side polarizing plate,
16: Polarizing film,
17, 18 ... Transparent protective film,
20 ... Liquid crystal display panel,
22, 23 …… Adhesive layer,
24 …… Separate film,
27 …… Liquid crystal cell,
30 ... Liquid crystal display,
35 …… Backlight,
50 …… Polypropylene resin film,
51-54 ... heating roll,
56 …… Heating oven,
58 …… Take-up roll.

Claims (8)

A polarizing film made of a polyvinyl alcohol-based resin in which a dichroic dye is adsorbed and oriented, and a transparent protective film bonded to one or both sides of the polarizing film,
At least one of the transparent protective films is made of an unstretched polypropylene-based resin and is heat-treated at a temperature lower than its melting point (melting point−55 ° C.) or higher, and exhibits a tensile elastic modulus of 200 MPa or higher at 80 ° C. A polarizing plate characterized by that.   The polarizing plate according to claim 1, wherein the polypropylene resin is a copolymer of propylene and ethylene containing ethylene units at a ratio of 1% by weight or less.   The polarizing plate according to claim 1 or 2, wherein a transparent protective film made of the polypropylene-based resin is bonded to one surface of the polarizing film, and another transparent protective film is bonded to the other surface.   The polarizing plate according to claim 3, wherein another transparent protective film bonded to the other surface of the polarizing film is made of a cyclic olefin-based resin or a cellulose acetate-based resin. A polarizing film comprising a polyvinyl alcohol resin on which a dichroic dye is adsorbed and oriented, and an unstretched polypropylene resin film is bonded to the polarizing film,
A heat treatment step of heat-treating the polypropylene-based resin film at a temperature lower than its melting point but not lower than (melting point -55 ° C) so that the polypropylene-based resin film exhibits a tensile elastic modulus of not less than 200 MPa at 80 ° C;
And a bonding step of bonding the polypropylene-based resin film that has been heat-treated to the polarizing film.   The said heat processing process is a manufacturing method of Claim 5 performed by making the said polypropylene resin film contact the roll heated at the said temperature, or letting it pass in the oven heated at the said temperature.   A liquid crystal display panel comprising the polarizing plate according to claim 1 and a liquid crystal cell.   A polarizing plate according to claim 3 or 4 and a liquid crystal cell, wherein the polarizing plate is bonded to the liquid crystal cell on the side of another transparent protective film bonded to the other surface of the polarizing film. Item 8. A liquid crystal display panel according to item 7.

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