JP2011203641A - Polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate excellent in durability, which does not break in a heat cycle test.SOLUTION: The polarizing plate comprises a polarizing film made of a polyvinyl alcohol resin to which a dichroic dye is adsorbed and aligned, and a transparent protective film laminated on at least one surface of the polarizing film via an adhesive layer, wherein a shrinking force X of the polarizing film in a direction perpendicular to the stretch axis and a shrinking force Y of the transparent protective film laminated on at least one surface of the polarizing film, in the same direction as the direction perpendicular to the stretch axis of the polarizing film, satisfy a relational formula of (1):Y≥40X-116X+83.

Description

  The present invention relates to a polarizing plate excellent in durability.

  A polarizing plate is usually a transparent resin film, for example, a cellulose resin film typified by triacetyl cellulose, with an adhesive layer on one or both sides of a polarizing film made of a polyvinyl alcohol resin to which a dichroic dye is adsorbed and oriented. It has a laminated structure. If necessary, this is bonded to the liquid crystal cell via another optical film with an adhesive to form a component of the liquid crystal display device.

  As a method for producing a polarizing film, for example, in JP-A-10-153709 (Patent Document 1), a polyvinyl alcohol-based resin film is immersed in water to swell, then dyed with iodine, then stretched, and further iodine. A method is described in which boric acid treatment (in other words, water resistance treatment by cross-linking) is performed in order to fix the resin, followed by washing with water and drying. The swelling treatment with water is performed for the purpose of uniformly swelling the film prior to dyeing, shortening the dyeing time, and improving dyeing unevenness. At this time, from the viewpoint of uneven dyeing and the like, in Patent Document 1, boric acid is contained in the swelling treatment bath. Further, in Patent Document 1, after dyeing, the film is immersed in an aqueous solution containing boric acid and stretched, and then further immersed in an aqueous boric acid solution, and water-resistant treatment by crosslinking (referred to as fixing or fixing in this document). Is doing.

  In JP-A-7-198939 (Patent Document 2), a dichroic dye is adsorbed on a polyvinyl alcohol-based resin film for the purpose of producing a polarizing plate having excellent optical characteristics and high heat-and-moisture resistance. After that, two or more steps of containing a boron compound are provided, and each step is immersed in a treatment solution having a different boron-based compound concentration, whereby 4. 4 boron atoms are added to the total weight of the polyvinyl alcohol-based resin film. A method for producing a polarizing film containing 5 wt% to 7.0 wt% is described.

  As a technique related to the contraction force of a polarizing plate, for example, in JP-A-2003-185845 (Patent Document 3), a polarizing plate in which a transparent resin film is laminated on at least one surface of a polarizing film is 1 hour at 60 ° C. It is described that the contraction force generated by leaving it to be adjusted is 8 N / 10 mm width or less.

  Further, for example, JP-A-2004-245925 (Patent Document 4) describes that a cured product of a solventless active energy ray-curable composition containing an epoxy compound is suitable as an adhesive for a polarizing plate. Yes.

JP-A-10-153709 JP-A-7-198939 JP 2003-185845 A JP 2004-245925 A

  As a test for evaluating the durability of the polarizing film, in a state where the polarizing plate was bonded to a glass plate or a liquid crystal panel, high-temperature air was circulated in the test tank, and the test tank was left at 70 ° C. for about 1 hour. Conventionally, a heat cycle test in which low temperature air is circulated in a test tank and the inside of the test tank is left at −35 ° C. for about 1 hour is repeatedly performed in this field. When subjected to a heat cycle test in which a state exposed to such a high temperature and a state exposed to a low temperature were repeated for a total of 200 cycles every hour, breakage might occur along the direction of stretching of the polarizing film.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a polarizing plate excellent in durability that does not break in a heat cycle test.

  The present invention is a polarizing plate in which a transparent resin film is bonded to at least one surface of a polarizing film comprising a polyvinyl alcohol-based resin film adsorbed and oriented with a dichroic dye via an adhesive layer, and the polarizing film is stretched When the contraction force in the direction orthogonal to the axis is X, and the contraction force in the same direction as the direction orthogonal to the stretching axis of the polarizing film of the transparent resin film laminated on at least one side of the polarizing film is Y (the following ( It satisfies the relational expression 1).

Y ≧ 40X ² −116X + 83 (1)
In the polarizing plate of the present invention, the content of boron in the polarizing film made of a polyvinyl alcohol-based resin film is preferably in the range of 2.5 wt% to 4.9 wt%.

  The transparent resin film bonded to at least one surface of the polarizing film in the polarizing plate of the present invention is preferably a film made of a polypropylene resin having a xylene-soluble content at 20 ° C. of 1% by weight or less.

  The transparent resin film bonded to at least one surface of the polarizing film in the polarizing plate of the present invention is a retardation film made of a cycloolefin-based resin, and has an in-plane retardation of 40 nm to 100 nm, in the thickness direction. It is also preferable that the phase difference is 80 nm to 300 nm.

  Moreover, the said transparent resin film bonded on the at least single side | surface of the polarizing film in the polarizing plate of this invention can also be a film consisting of a cellulose resin or a polyester-type resin.

  The adhesive layer in the polarizing plate of the present invention can be a cured product of an active energy ray-curable composition containing an epoxy compound.

  The adhesive layer in the polarizing plate of the present invention may be a cured product of a composition using a polyvinyl alcohol resin or a urethane resin.

  ADVANTAGE OF THE INVENTION According to this invention, the polarizing plate excellent in durability which does not fracture | rupture in a heat cycle test can be provided.

It is a graph which shows the heat cycle test result of Examples 1-6 and Comparative Examples 1-3, a horizontal axis is a contraction force (N) of the direction orthogonal to the extending | stretching axis | shaft of a polarizing film, and a vertical axis | shaft is a polarizing film of a transparent resin film. The contraction force (N) in the same direction as the direction perpendicular to the stretching axis.

<Polarizing plate>
The polarizing plate of the present invention is a polarizing plate in which a transparent resin film is bonded to at least one surface of a polarizing film made of a polyvinyl alcohol-based resin film adsorbed and oriented with a dichroic dye via an adhesive layer. When the contraction force in the direction orthogonal to the stretching axis of the film is X, and the contraction force in the same direction as the direction orthogonal to the stretching axis of the polarizing film of the transparent resin film laminated on at least one side of the polarizing film is Y The following relational expression (1) is satisfied.

Y ≧ 40X ² −116X + 83 (1)
This formula (1) is plotted with respect to Examples 1, 4, 5 and 6, which will be described later, with the contraction force X of the polarizing film defined above as the horizontal axis and the contraction force Y of the transparent resin film as the vertical axis. This is determined by obtaining an approximate quadratic curve so that the contraction force relationship in FIG.

  In the polarizing plate of the present invention, the transparent resin film may be bonded to only one surface of the polarizing film of the present invention described above via an adhesive layer, or may be bonded to both surfaces. Good. In the polarizing plate of the present invention, when the transparent resin film is adhered to both surfaces of the polarizing film, both of them may be configured to satisfy the relational expression described above, or only one transparent resin film is related to the relation described above. Although it may be configured to satisfy the equation, it is preferable that both are configured to satisfy the relational expression described above.

  Such a polarizing plate of the present invention has excellent durability that does not break in the heat cycle test, as will be demonstrated in Examples described later.

(Polarizing film)
Specifically, the polyvinyl alcohol-based resin film used for the polarizing film in the present invention is a saponified polyvinyl acetate-based resin. The degree of saponification of the polyvinyl alcohol-based resin is 85 mol% or more, preferably 90 mol% or more, more preferably 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and unsaturated amines. The average degree of polymerization of the polyvinyl alcohol-based resin is usually 1000 to 10000, preferably 1500 to 5000. These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used.

  In the polarizing film of the present invention, the dichroic dye is adsorbed and oriented on the polyvinyl alcohol resin film as described above. As the dichroic dye, for example, iodine, a dichroic dye or the like is used. Examples of dichroic dyes include C.I. I. Dichroic direct dyes composed of disazo compounds such as DIRECT RED 39 and dichroic direct dyes composed of compounds such as trisazo and tetrakisazo are included. Such a dichroic dye can be adsorbed and oriented by dyeing a polyvinyl alcohol-based resin film in a treatment bath containing a dichroic dye, which is a conventionally known process for producing a polarizing film (for details). Will be described later).

  In the polarizing film of the present invention, the boron content is preferably in the range of 2.5% by weight to 4.9% by weight, and more preferably in the range of 3% by weight to 3.9% by weight. . When the boron content is less than 2.5% by weight, sufficient water resistance cannot be obtained, and when the boron content exceeds 4.9% by weight, a polarizing plate is formed and heat cycle is performed. When the test is performed, breakage tends to occur in the stretching direction of the polarizing film. In order to suppress breakage in the heat cycle test while effectively exhibiting water resistance, the content of boron in the polarizing film is 3 wt% to 3.9 wt%, and further 3.4 wt% to 3.9 wt%. It is preferable to be within the range. The boron content in the polarizing film can be calculated as a weight fraction (%) of boron with respect to the weight of the polarizing film by, for example, high frequency inductively coupled plasma (ICP) emission spectroscopy. Boron is considered to be present in the polarizing film in a state where boric acid or it forms a cross-linked structure with the unit of polyvinyl alcohol, and the content of boron here is a value as a boron atom (B). .

  The polarizing film in the present invention preferably has a low shrinkage force in the direction perpendicular to the stretching axis, and the stretching axis when heated to 80 ° C. in a size of 2 mm × 8 mm with the stretching axis direction of the polarizing film as the short side The contractive force in the orthogonal direction is preferably in the range of 0.1N to 2.8N practically. When the contraction force of the polarizing film exceeds 2.8 N, when the heat cycle test is performed after forming the polarizing plate, breakage tends to occur in the stretching direction of the polarizing film. Although this shrinkage force is ideally zero, it is difficult to make this shrinkage force zero. Therefore, the polarizing film of the present invention is 80 mm in size of 2 mm × 8 mm with the direction of the stretching axis of the polarizing film as the short side. Practically, the shrinkage force in the direction orthogonal to the stretching axis when heated to ° C is preferably in the range of 0.1N to 2.8N. It is also effective for durability that the shrinkage force of the transparent resin film laminated on at least one surface relatively relaxes the shrinkage force of the polarizing film. In addition, the measurement of the shrinkage force in the direction perpendicular to the stretching axis is performed by cutting out a measurement sample of a polarizing film of 2 mm × 8 mm with the stretching axis direction as the short side, and using the measurement sample as a thermo-mechanical analyzer (TMA). ) And is measured as the contraction force in the direction of 8 mm length generated when heated at 80 ° C. for 200 minutes while keeping the dimensions constant. As a commercial item of a thermomechanical analyzer (TMA), for example, EXSTAR-6000 sold by SII Nano Technology Co., Ltd. can be mentioned.

  The thickness of the polarizing film in the present invention is not particularly limited, and is usually 1 μm to 50 μm.

  The polarizing film in the present invention is a method in which, for example, a polyvinyl alcohol-based resin film is treated in the order of a swelling treatment step, a dyeing treatment step, and a boric acid treatment step, and uniaxially stretched in at least one of these treatment steps. It can manufacture suitably. A water immersion step may be provided between the swelling treatment step and the dyeing step. The polarizing film in the present invention is the first boric acid treatment step performed at a temperature of 50 ° C. to 70 ° C. in an aqueous solution containing 2 parts by weight to 5 parts by weight of boric acid with respect to 100 parts by weight of water in the boric acid treatment step. By performing an acid treatment and a second boric acid treatment performed at a lower temperature than the first boric acid treatment in an aqueous solution having a lower boric acid concentration than the aqueous solution used for the first boric acid treatment. Can be advantageously produced.

(1) Swelling treatment step In the swelling treatment step, first, the unstretched film of the polyvinyl alcohol-based resin film that is the original fabric of the polarizing film is subjected to a swelling treatment in a swelling tank. The unstretched film of the polyvinyl alcohol-based resin film is usually supplied in a roll shape, and has a thickness in the range of 20 μm to 100 μm, preferably in the range of 30 μm to 80 μm, and has an industrially practical width. It is in the range of 1500 mm to 6000 mm.

  The swelling treatment is performed for the purpose of removing foreign substances on the film surface, removing a plasticizer in the film, imparting easy dyeability in a subsequent process, and plasticizing the film. The conditions for the swelling treatment are determined within a range in which these objects can be achieved and in a range in which problems such as extreme dissolution and devitrification of the film do not occur. Specifically, the swelling treatment is performed by immersing the unstretched film of the polyvinyl alcohol-based resin film described above in a treatment bath at a temperature of 10 ° C. to 50 ° C., preferably 20 ° C. to 50 ° C., for example. The swelling treatment time is usually 5 seconds to 300 seconds, preferably 20 seconds to 240 seconds.

  In the swelling process, the film swells in the width direction and wrinkles into the film, so problems such as expansion rolls, spiral rolls, crown rolls, cross guiders, bend bars, tenter clips, etc. It is preferable to transport the film while removing the wrinkles. In order to stabilize the film transport in the bath, the water flow in the swelling bath is controlled with an underwater shower, or an EPC device (Edge Position Control device: a device that detects the edge of the film and prevents meandering of the film) It is also useful to use these together. In this step, since the film swells and expands in the film transport direction, in order to eliminate the sag of the film in the transport direction, for example, measures such as controlling the speed of the transport roll before and after the swelling tank may be taken. preferable. Specifically, the ratio of the peripheral speed of the outlet side transport roll to the peripheral speed of the inlet side transport roll of the swelling tank (hereinafter sometimes referred to as roll speed ratio) is 1.2 times depending on the temperature of the treatment bath. It is preferable to make it about 2 times. If desired, uniaxial stretching can also be performed in this step.

  The treatment bath used in the swelling tank contains 0.01% by weight of pure water, boric acid as described in Patent Document 1, chlorides and other inorganic salts, water-soluble organic solvents, alcohols and the like. An aqueous solution added in the range of 10% to 10% by weight can also be used. However, in this swelling tank, pure water having substantially no dissolved component is preferably used.

(2) Water immersion treatment step The polyvinyl alcohol-based resin film after the swelling treatment may be subjected to water immersion treatment in a water immersion tank after draining. This water immersion treatment is performed in order to improve the water absorption state in the film width direction, and to increase the mechanical properties of the film and further the uniformity of the optical properties of the finally obtained polarizing film. In this step, it is preferable to treat the film so as to have a draw ratio of 1 to 1.05 times with respect to the machine direction (MD, ie, film transport direction). A draw ratio of 1 means that the film does not stretch or shrink in the machine direction. Since a series of steps is performed by applying a tension that does not sag the film in the running direction, the draw ratio in this step is not usually less than 1 times, but when the draw ratio exceeds 1.05 times The uniformity of optical properties in the obtained polarizing film tends to be poor.

  The temperature of the treatment bath accommodated in the water immersion tank is preferably 10 ° C to 50 ° C. When the temperature of the treatment bath is less than 10 ° C, a large-scale cooling facility is required for temperature control, which is uneconomical. Conversely, when the temperature of the treatment bath exceeds 50 ° C, the film dissolves. There is a risk of it. Moreover, it is preferable that the treatment bath used for this water immersion treatment is pure water substantially free of dissolved components. This is because when the treatment bath contains a chemical such as boric acid, the uniformity of the film may be impaired.

(3) Dyeing process The dyeing process which dye | stains a film with the dyeing | staining tank containing a dichroic dye is performed after passing through the swelling process mentioned above and the subsequent water immersion process. Such a dyeing process is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film, and the conditions are within a range where such an object can be achieved, and the film is extremely dissolved and devitrified. It is determined within a range where no defect occurs.

  When iodine is used as the dichroic dye, for example, the temperature is 10 ° C to 50 ° C, preferably 20 ° C to 40 ° C, and 0.003 parts by weight to 0.2 parts by weight of iodine with respect to 100 parts by weight of water. The dyeing treatment is performed by immersing in an aqueous solution containing 0.1 part by weight to 10 parts by weight of potassium iodide and 10 parts by weight to 10 parts by weight for 10 seconds to 600 seconds, preferably 30 seconds to 200 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used, and other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. Even when boric acid is added, it is distinguished from the subsequent boric acid treatment in that the treatment bath contains iodine. Any bath containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing bath.

  On the other hand, when a water-soluble dichroic dye is used as the dichroic dye, the dichroic dye is used at a temperature of, for example, 20 ° C to 80 ° C, preferably 30 ° C to 60 ° C, and 100 parts by weight of water. The dyeing treatment is performed by immersing in an aqueous solution containing 0.001 part by weight to 0.1 part by weight for 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. Only one type of dichroic dye may be used, or two or more types of dichroic dyes may be used in combination according to the desired hue.

  In the dyeing process, as in the swelling process, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, and the like may be appropriately installed in the treatment bath and / or at the bath entrance / exit. In the dyeing process, the film may be uniaxially stretched in the machine direction at the same time. The draw ratio is preferably in the range of 1.1 times to 3 times, for example.

(4) Boric acid treatment step In the polarizing film of the present invention, as described above, the boron content is preferably in the range of 2.5 wt% to 4.9 wt%, and such a boron content is obtained. Thus, the boric acid treatment is performed on the polyvinyl alcohol-based resin film that has undergone the dyeing process. This boric acid treatment is performed by immersing a polyvinyl alcohol-based resin film dyed with a dichroic dye in a boric acid tank containing a treatment bath containing an aqueous boric acid solution. Preferably, this boric acid treatment step The second boric acid treatment is carried out at a temperature lower than that of the first boric acid treatment in an aqueous solution having a lower boric acid concentration than the aqueous solution used for the first boric acid treatment. The acid treatment is roughly divided into two steps.

  The first boric acid treatment is performed in an aqueous solution containing 2 to 5 parts by weight of boric acid with respect to 100 parts by weight of water. When the content of boric acid in the treatment bath used for the first boric acid treatment is less than 2 parts by weight with respect to 100 parts by weight of water, a sufficient crosslinking effect cannot be obtained, and 5 parts by weight When exceeding, it is because a film becomes weak and mechanical strength is inferior. In order to more effectively express the crosslinking effect by boric acid treatment, the aqueous solution used for the first boric acid treatment may contain 3 parts by weight to 4.5 parts by weight of boric acid with respect to 100 parts by weight of water. ,preferable.

  The first boric acid treatment is usually performed at a temperature of 50 ° C to 70 ° C, preferably 53 ° C to 65 ° C. When the temperature of the first boric acid treatment is lower than 50 ° C., sufficient boric acid crosslinking reaction does not proceed, and when it is higher than 70 ° C., the film is likely to be cut in the boric acid treatment bath and the processing stability is improved. There is a risk of significant reduction. The treatment time in the first boric acid treatment is usually 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds, more preferably 20 seconds to 100 seconds.

  When iodine is used as the dichroic dye in the dyeing process described above, the treatment bath used for the first boric acid treatment contains 5 to 20 iodides with respect to 100 parts by weight of water in addition to boric acid. Part by weight, preferably 8 to 15 parts by weight is contained. This is because when the iodide in the boric acid treatment bath is less than 5 parts by weight with respect to 100 parts by weight of water, the orthogonal hue of the polarizing film may not be neutral, and the boric acid treatment bath When the iodide in the amount exceeds 20 parts by weight with respect to 100 parts by weight of water, the boric acid crosslinking reaction is inhibited, which is not preferable. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfite, potassium sulfate, sodium sulfate, etc. may coexist. If necessary, a crosslinking agent such as glyoxal or glutaraldehyde can be used together with boric acid.

  In the first boric acid treatment, stretching may be performed in the transport direction. In this case, the draw ratio is usually 1.2 to 3 times, and the rolls may be stretched in multiple stages.

  The first boric acid treatment in the boric acid treatment step may be performed in one stage or in multiple stages. When the first boric acid treatment is performed in multiple stages, the boric acid content and temperature in the treatment bath may be set to be different from each other within the above-described range.

  The second boric acid treatment in the boric acid treatment step is performed at a temperature lower than that of the first boric acid treatment in an aqueous solution having a lower boric acid content than the aqueous solution used for the first boric acid treatment. It is. When the second boric acid treatment is performed in a treatment bath containing an aqueous solution having the same or higher boric acid content as the aqueous solution used for the first boric acid treatment, the boron content and shrinkage in the polarizing film It is difficult to bring the stress within a predetermined range, and when the second boric acid treatment is performed at the same or higher temperature as the first boric acid treatment, the boron content and the shrinkage stress in the polarizing film It is difficult to keep the value within a predetermined range.

  The second boric acid treatment has a boric acid content that is 0.5 parts by weight or more (more preferably 1 part by weight or more) lower than the boric acid content with respect to 100 parts by weight of water in the aqueous solution used in the first boric acid treatment. It is preferable that the reaction be performed in an amount of an aqueous solution at a temperature that is 5 ° C. or more (more preferably 10 ° C. or more) lower than the temperature in the first boric acid treatment. Specifically, the boric acid content in the aqueous solution used for the second boric acid treatment is usually in the range of 1 to 4 parts by weight, preferably 1 to 3 parts by weight with respect to 100 parts by weight of water. And it is chosen so that it may become lower than the boric acid content in the aqueous solution used for the first boric acid treatment. Further, the temperature in the second boric acid treatment needs to be equal to or higher than the temperature at which the boric acid is completely dissolved, and depends on the boric acid content. Specifically, the second boric acid treatment is performed at a temperature within the range of 20 ° C. to 45 ° C. and lower than the temperature of the first boric acid treatment.

  The time for the second boric acid treatment is usually about 1 second to 300 seconds, preferably 2 seconds to 100 seconds. In the second boric acid treatment, as in the first boric acid treatment, iodide may be added to the treatment bath. In this case, from the viewpoint of making the orthogonal hue of the polarizing film neutral, The content is preferably in the range of 5 to 20 parts by weight with respect to 100 parts by weight of water. Further, the second boric acid treatment may be stretched in the transport direction as in the case of the first boric acid treatment. In this case, the stretch ratio is usually 1.1 to 1.3 times. .

  Further, the second boric acid treatment may be performed in a single stage or may be performed in multiple stages, similarly to the first boric acid treatment described above. Even when the second boric acid treatment is performed in multiple stages, the content and temperature of boric acid in the treatment bath may be set to be different from each other within the above-described range.

(5) Water-washing process The water-washing process is normally given after a boric-acid treatment process. The water washing treatment is performed, for example, by a method in which a boric acid-treated polyvinyl alcohol resin film is immersed in water, a method in which water is sprayed as a shower, or a method in which immersion and spraying are used in combination. The water temperature in the water washing treatment is usually 2 ° C. to 40 ° C., and the treatment time is usually 2 seconds to 120 seconds. The washing process may be one stage, but may be multistage. In the case of multiple stages, the washing may be performed with an aqueous solution of an inorganic salt in any tank. The inorganic salt is selected from, for example, potassium iodide, sodium iodide, zinc iodide, zinc chloride, sodium sulfate, sodium sulfite and the like. These inorganic salts may be used alone or in combination. Moreover, you may extend | stretch in this washing tank, for example, may be extended 1.05-1.2 times. Moreover, tension is given in this washing tank, and the tension is, for example, 300 N / m to 1000 N / m.

  In addition, although the conveyance speed of the film at the time of manufacturing the polarizing film in this invention is selected suitably, it is 5 m / min-50 m / min as a film running speed after a water washing process, for example. If it is faster than 50 m / min, the film slips on the roll, so that problems such as inability to stably stretch tend to occur.

(6) Drying process The film after a water-washing process is normally guide | induced to a drying furnace, and a drying process is given. This drying is usually performed for about 30 seconds to 600 seconds in a drying oven maintained at a temperature of 40 ° C. to 100 ° C., preferably 50 ° C. to 100 ° C. There may be a plurality of drying ovens, and each temperature may be the same or different. When drying using a plurality of drying furnaces, it is preferable to provide a temperature gradient so that the temperature increases from the front stage of the drying furnace to the rear stage of the drying furnace.

(7) Uniaxial stretching In producing the polarizing film of the present invention, uniaxial stretching is performed in at least one of the above-described swelling treatment step, dyeing treatment step, and boric acid treatment step. This uniaxial stretching may be performed in one step, or may be performed in any two steps, or may be performed in all steps, but uniaxial stretching is performed in the dyeing process and the boric acid process. It is preferable to do so. The stretching can be performed by, for example, a method of making a difference in peripheral speed between the transport roll on the tank inlet side and the transport roll on the tank exit side.

  In producing the polarizing film in the present invention, the final integrated draw ratio from the swelling treatment step to the water washing treatment step is preferably 4.5 to 8 times, more preferably 5 to 7 times. . The cumulative stretching ratio here means how long the reference length in the length direction of the original film is in the film after completion of all stretching treatments, and in the swelling treatment process and water immersion treatment process When stretched, the value includes those stretches. For example, if the portion that was 1 m in the original fabric film is 5 m in all the films after the stretching process, the cumulative stretching ratio at that time is 5 times.

(Transparent resin film)
In the polarizing plate of the present invention, examples of the transparent resin film bonded to at least one surface of the polarizing film include a polypropylene resin film, a cycloolefin resin film, a cellulose resin film, a polyester resin film, and a polycarbonate resin. Examples thereof include films that have been widely used in the art, such as films and acrylic resin films.

Especially, as a transparent resin film bonded on the at least single side | surface of a polarizing film in this invention, at least any selected from the following (i)-(iv) is preferable.
(I) a film comprising a polypropylene resin having a xylene-soluble content at 20 ° C. of 1% by weight or less,
(Ii) a retardation film comprising a cycloolefin-based resin having an in-plane retardation of 40 nm to 100 nm and a thickness direction retardation of 80 nm to 300 nm;
(Iii) a film made of a cellulose-based resin,
(Iv) A film made of a polyester resin.

(I) Propylene-based resin film As the polypropylene-based resin constituting the polypropylene-based resin film that can be used for the transparent resin film in the polarizing plate of the present invention, the xylene-soluble content is preferably 1% by weight or less, more preferably 0. Polypropylene resin having a content of 0.8% by weight or less, more preferably 0.5% by weight or less is used. When the xylene-soluble content of the polypropylene resin film exceeds 1% by weight, when the polarizing plate is exposed to a high temperature environment, the surface of the polypropylene resin film is whitened, and the transmittance of the polarizing plate is significantly reduced. . The whitening of the surface of the polypropylene resin film in such a high temperature environment is presumed to be caused by a bleed out due to a low molecular weight component or a component inferior in stereoregularity present in the resin film. A typical example of such a low molecular weight component is not particularly limited, and examples thereof include an atactic low molecular weight oligomer.

  The xylene-soluble content [wt%] of the polypropylene resin film is measured as follows. First, 5 g of a polypropylene resin film is added to 500 ml of boiling xylene and completely dissolved, and then the temperature is lowered to 20 ° C. and held at 20 ° C. for 4 hours. Next, the xylene liquid is filtered to separate into a precipitate and a filtrate, and the solvent is removed from the filtrate, followed by drying at 70 ° C. under reduced pressure to obtain a dried xylene-soluble component. The xylene-soluble content is obtained from the following formula.

Xylene soluble content [% by weight] = (weight of dried xylene soluble component [g]) / (5 [g]) × 100
The polypropylene resin may be a homopolymer of propylene or a copolymer of propylene and another monomer copolymerizable therewith. These may be used in combination. Examples of other monomers copolymerizable with propylene include ethylene and α-olefin. The α-olefin has 4 or more carbon atoms, preferably an α-olefin having 4 to 10 carbon atoms. Specific examples of the α-olefin having 4 to 10 carbon atoms include linear monoolefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and 1-decene; Branched monoolefins such as 3-methyl-1-butene, 3-methyl-1-pentene and 4-methyl-1-pentene; vinylcyclohexane and the like. The copolymer of propylene and other monomers copolymerizable therewith may be a random copolymer or a block copolymer.

  In the case of using the copolymer as the polypropylene resin, since a polypropylene resin having a xylene-soluble content of 1% by weight or less is relatively easily obtained, the copolymerization ratio of other monomers copolymerized with propylene Is preferably 8% by weight or less, and more preferably 4% by weight or less. In addition, the content rate of the structural unit derived from the said other monomer in a copolymer is infrared (IR) according to the method described on page 616 of "Polymer Analysis Handbook" (1995, published by Kinokuniya) ) It can be obtained by performing a spectrum measurement.

  Among the above, as a polypropylene resin constituting a polypropylene resin film, propylene homopolymer, propylene-ethylene random copolymer, propylene-1-butene random copolymer, and propylene-ethylene-1-butene random A copolymer is preferably used. These homopolymers and copolymers are relatively easy to obtain a polymer having a reduced xylene-soluble content by selecting an appropriate polymerization catalyst. In particular, by using a propylene homopolymer, a polymer having a reduced xylene-soluble content tends to be obtained more easily.

  Moreover, it is preferable that the stereoregularity of the polypropylene resin constituting the polypropylene resin film is substantially isotactic or syndiotactic. A polypropylene resin film made of a polypropylene resin having substantially isotactic or syndiotactic stereoregularity has relatively good handling properties and excellent mechanical strength in a high temperature environment. In addition, such a stereoregular polypropylene resin has a relatively low generation of atactic low molecular weight components that cause whitening of the polarizing plate in the polymerization stage, and the transmittance decreases under a high temperature environment. A suppressed polarizing plate is easily obtained.

In the present invention, the polypropylene resin may be a polymer or copolymer polymerized using a known polymerization catalyst, and examples of the polymerization catalyst 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) include catalyst systems described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. In addition, preferable examples of the organoaluminum compound in the catalyst system of (2) include triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, tetraethyldialumoxane, and the like. Preferable examples include cyclohexylethyldimethoxysilane, tert-butylpropyldimethoxysilane, tert-butylethyldimethoxysilane, dicyclopentyldimethoxysilane and the like.

  Examples of the metallocene catalyst (3) include catalyst systems described in Japanese Patent No. 2587251, Japanese Patent No. 2627669, Japanese Patent No. 2668732, and the like.

  Among these, metallocene catalysts are preferably used because a polymer or copolymer having a reduced xylene-soluble content is easily obtained.

  Polypropylene resins are, for example, solution polymerization methods using an inert solvent typified by hydrocarbon compounds such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, and liquid monomers as solvents. 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.

  The method for reducing the xylene-soluble content of the polypropylene resin to 1% by weight or less is not particularly limited. For example, in the polymerization stage, the degree of polymerization of the polypropylene resin is increased and the ratio of relatively low molecular weight components is increased. Methods known to those skilled in the art, such as a method of lowering, a method of washing a polypropylene-based resin obtained by polymerization with a solvent and extracting and removing solvent-soluble components such as low molecular weight components, and a combination of these methods. be able to. Note that, for example, a polypropylene catalyst obtained by appropriately selecting a polymerization catalyst and controlling the stereoregularity of the polypropylene resin to isotactic or syndiotactic and / or polymerizing with propylene alone. When the xylene-soluble content of the resin is 1% by weight or less, the treatment for reducing the xylene-soluble content of the polypropylene resin obtained by polymerization is not necessarily required.

  The polypropylene resin used in the present invention has a melt flow rate (MFR) measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K 7210 in a range of 0.1 g / 10 min to 200 g / 10 min. It is preferably within the range, more preferably within the range of 0.5 g / 10 min to 50 g / 10 min, and even more preferably within the range of 0.5 g / 10 min to 15 g / 10 min. By using a polypropylene resin having an MFR within this range, a uniform polypropylene resin film can be obtained without imposing a large load on the extruder.

  The polypropylene resin may contain a known additive as long as the effects of the present invention are not impaired. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent. Examples of antioxidants include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, hindered amine light stabilizers, and the like, and for example, phenolic antioxidant mechanisms in one molecule. It is also possible to use a composite antioxidant having a unit having both a phosphorus-based antioxidant mechanism and a phosphorus-based antioxidant mechanism. Examples of the UV absorber include UV absorbers such as 2-hydroxybenzophenone and hydroxyphenylbenzotriazole, 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. 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.

  The nucleating agent may be either an inorganic nucleating agent or an organic nucleating agent. Examples of the inorganic nucleating agent include talc, clay, calcium carbonate and the like. Examples of the organic nucleating agent include metal salts such as aromatic carboxylic acid metal salts and aromatic phosphoric acid metal salts, high-density polyethylene, poly-3-methylbutene-1, polycyclopentene, and polyvinylcyclohexane. It is done. Among these, organic nucleating agents are preferable, and the above metal salts and high density polyethylene are more preferable. The amount of the nucleating agent added to the polypropylene resin is preferably 0.01% by weight to 3% by weight, and more preferably 0.05% by weight to 1.5% by weight. A plurality of these additives may be used in combination.

  A transparent resin film composed of a polypropylene resin film suitably used for the polarizing plate of the present invention can be obtained by forming the polypropylene resin. Specifically, the transparent resin film comprising such a polypropylene resin film is preferably excellent in transparency so that the total haze value measured according to JIS K 7105 is 10% or less, preferably 7% or less. .

  The thickness of the transparent resin film made of a polypropylene resin film is preferably about 5 μm to 200 μm. More preferably, it is 10 μm or more, and more preferably 150 μm or less.

  The film forming method of the polypropylene resin is not particularly limited, but is an extrusion method from a molten resin, a solvent cast method in which a resin dissolved in an organic solvent is cast on a flat plate, and the solvent is removed to form a film. According to these film forming methods, a polypropylene resin film having substantially no in-plane retardation can be obtained.

  A method for producing a polypropylene resin film by extrusion molding will be described in detail. In this method, a polypropylene resin is melt-kneaded by rotation of a screw in an extruder and extruded from a T die into a sheet. The temperature of the extruded molten sheet is about 180 ° C to 300 ° C. If the temperature of the molten sheet at this time is lower than 180 ° C., the spreadability is not sufficient, the thickness of the resulting film becomes non-uniform, and there is a possibility that the film has phase difference unevenness. Further, when the temperature exceeds 300 ° C., the resin is easily deteriorated or decomposed, and bubbles may be generated in the sheet or carbides may be contained.

The extruder may be a single screw extruder or a twin screw extruder. For example, when a single screw extruder is used, L / D, which is the ratio of the screw length L to the diameter D, is about 24 to 36, the screw groove space volume V ₁ in the resin supply section, and the screw groove in the resin metering section. The compression ratio, which is the ratio (V ₁ / V ₂ ) to the space volume V ₂ , is about 1.5 to 4 and is kneaded such as full flight type, barrier type, further dull image type, unimelt type, or Maddock type. A screw having a part or the like can be used. From the viewpoint of suppressing deterioration and decomposition of the polypropylene resin and uniformly melting and kneading, it is preferable to use a screw having an L / D of 28 to 36 and a compression ratio V ₁ / V _{2 of 2} to 3. Moreover, in order to suppress deterioration and decomposition | disassembly of polypropylene resin, it is preferable to purge oxygen in an extruder, for example by purging nitrogen from a hopper. Furthermore, it is also preferable to provide an orifice of about 1 mmφ to 5 mmφ at the tip of the extruder to increase the resin pressure at the tip of the extruder. Increasing the resin pressure at the leading end of the extruder by installing an orifice means increasing the back pressure at the leading end, thereby improving the stability of extrusion. The diameter of the orifice to be used is more preferably 2 mmφ to 4 mmφ.

  The T die used for extrusion has a channel hanger shape and is designed so that the flow rate and pressure of the molten polypropylene resin are uniform in the width direction of the T die slit portion. preferable. Also, it is preferable that the surface of the resin flow path does not have minute steps or scratches, and the lip portion is plated or coated with a material having a low friction coefficient with the molten polypropylene resin, and the lip tip is 0.3 mmφ or less. A sharp edge shape that has been polished is preferred. Examples of the material having a small friction coefficient include tungsten carbide ceramic materials and fluorine special plating. By using such a T-die, it is possible to suppress the generation of eyes and simultaneously suppress the die line, so that a resin film excellent in appearance uniformity can be easily obtained.

  In addition, it is preferable to attach a gear pump via an adapter between an extruder and a T die from a viewpoint of suppressing the extrusion fluctuation | variation of polypropylene resin. In addition, it is preferable to attach a leaf disk filter to remove foreign substances in the polypropylene resin.

  The desired polypropylene resin film can be obtained by moving the molten sheet extruded from the T-die while in close contact with a metal cooling roll (also referred to as a chill roll or a casting roll) and cooling and solidifying it.

In producing a polypropylene resin film by such a melt extrusion method, depending on the processing speed and the diameter of the cooling roll, in the cooling process by the cooling roll, the temperature of the cooling roll was set to 30 ° C. or less and extruded. It is preferable to rapidly cool the molten sheet-like polypropylene resin. At this time, the method of adhering the extruded molten sheet-like polypropylene resin to the cooling roll may affect the haze value of the obtained polypropylene resin film. When the preferable form of the method of sticking the molten sheet-like polypropylene resin to the cooling roll is given, for example,
a) A method in which static electricity is imparted to a molten sheet-like polypropylene resin, and the surface state is closely adhered to a mirror-like cooling roll to cool it,
b) A method in which a molten sheet-like polypropylene-based resin is sandwiched between an elastically deformable roll or a metal belt and is cooled in close contact with a cooling roll,
c) There is a method in which a molten sheet-like polypropylene resin is cooled by adhering it to a cooling roll having a semi-matt surface state by an air chamber method.

  The method of a) cooling the molten sheet-like polypropylene resin by adhering to the cooling roll by static electricity is called an electrostatic pinning method, and the ears of the molten sheet-like polypropylene resin extruded from the T-die. There are an edge pinning method in which only the portion is charged with static electricity and is brought into close contact with the cooling roll, and an entire surface pinning method in which static electricity is applied to the entire surface in the width direction of the molten sheet from an electrode arranged in parallel with the T die. Since the polypropylene resin has poor adhesion to the cooling roll due to static electricity, the whole surface pinning method is preferably applied from the viewpoint of easily stabilizing the cooling.

  In the method of b), the molten sheet extruded from the T-die is moved between a metal cooling roll and a touch roll or belt including an elastic body that rotates by pressing in the circumferential direction of the metal cooling roll. The film is obtained by pinching and cooling and solidifying. When the touch roll is used, an elastic body such as rubber may be used as it is, or the surface of the elastic roll may be covered with an outer cylinder made of a metal sleeve. When using a touch roll in which the surface of the elastic roll is covered with an outer cylinder made of a metal sleeve, cooling is usually performed by directly sandwiching a molten sheet of polypropylene resin between the metal cooling roll and the touch roll. . On the other hand, in the case of using a touch roll whose surface is an elastic body, a biaxially stretched film of a thermoplastic resin can be interposed between the molten sheet of polypropylene resin and the touch roll for sandwiching. When using a belt (endless belt), a metal endless belt is bridged between two rolls, the two rolls are rotated in the same direction, the metal belt is also rotated, and the molten sheet is made of metal. What is necessary is just to make it cool and solidify, pressing against a cooling roll made.

  When the molten sheet of polypropylene resin is sandwiched between the cooling roll and the touch roll or belt as described above and solidified by cooling, the surface temperature of the cooling roll and the touch roll or belt is lowered, and the molten sheet is It is preferable to cool rapidly. For example, each surface temperature is preferably adjusted to a range of 0 ° C to 30 ° C. When these surface temperatures exceed 30 ° C., it takes time to cool and solidify the molten sheet, so that the crystal component in the polypropylene resin grows, and the resulting film may be inferior in transparency. . On the other hand, when the surface temperature is lower than 0 ° C., the surface of the metal cooling roll is dewed and water droplets are attached, which tends to deteriorate the appearance of the resulting film.

  Since the surface state of the metal cooling roll used is transferred to the surface of the polypropylene resin film, there is a possibility that the thickness accuracy of the resulting polypropylene resin film may be lowered if the surface is uneven. . Therefore, it is preferable that the surface of the metal cooling roll is in a mirror surface state as much as possible. Specifically, the roughness of the surface of the metal cooling roll is preferably 0.3 S or less, more preferably 0.1 S to 0.2 S, expressed as a standard sequence of the maximum height. .

  When an elastically deformable touch roll is used, the surface hardness of the elastic roll of the touch roll forming the nip portion with the metal cooling roll is measured by a spring type hardness test (A type) defined in JIS K 6301. Is preferably in the range of 65 to 80 degrees, and more preferably in the range of 70 to 80 degrees. By using a rubber roll having such a surface hardness, it becomes easy to maintain a uniform linear pressure applied to the molten sheet, and a bank (resin) of the molten sheet is provided between the metal cooling roll and the touch roll. It becomes easy to form into a film without making a reservoir.

  The pressure (linear pressure) when sandwiching the molten sheet is determined by the pressure pressing the touch roll or the belt against the metal cooling roll. The linear pressure is preferably 50 N / cm to 300 N / cm, and more preferably 100 N / cm to 250 N / cm. By setting the linear pressure within the above range, it becomes easy to produce a polypropylene resin film while maintaining a constant linear pressure without forming a bank.

  When sandwiching a biaxially stretched film of a thermoplastic resin together with a molten sheet of polypropylene resin between a metal cooling roll and a touch roll, the thermoplastic resin constituting the biaxially stretched film is a polypropylene resin and Any resin that does not strongly heat-seal can be used. Specific examples include polyester, polyamide, polyvinyl chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and polyacrylonitrile. Among these, polyesters that have little dimensional change due to humidity, heat, and the like are most preferable. The thickness of the biaxially stretched film used in this embodiment is usually about 5 μm to 50 μm, preferably 10 μm to 30 μm.

  The air chamber method c) is a method in which air is sent into an air chamber provided along the film contact point of the cooling roll, and the film is brought into close contact with the cooling roll using the static air pressure. In the air chamber method, in order to prevent neck-in of the ear portion of the film or to ensure the stability of the ear portion, it is preferable that the ear portion of the film is brought into close contact with the cooling roll before other portions using an air nozzle. Instead of the air nozzle, an electrostatic pinning type nozzle that is brought into close contact with the cooling roll by static electricity instead of air may be used.

  The pressure in the air chamber is preferably 300 Pa or less, and more preferably 200 Pa or less. When the pressure exceeds 300 Pa, air flows out of the air chamber, and the extruded molten sheet-like polypropylene resin may be shaken, thereby reducing the thickness accuracy of the film.

The cooling roll used in the air chamber method is preferably a semi-matt cooling roll rather than a mirror roll. Specifically, the surface roughness (maximum height R _max ) of the cooling roll in accordance with JIS B 0601 is preferably in the range of 0.5 to 2 μm, and in the range of 0.8 to 1.5 μm. It is more preferable. When the surface roughness (R _max ) is less than 0.5 μm, when air enters between the molten sheet-like polypropylene resin and the cooling roll, the air does not escape, and this causes the surface of the polypropylene resin film to be removed. Concavities and convexities occur, which may cause poor appearance. Further, when the surface roughness (R _max ) exceeds 2 μm, the unevenness on the surface of the cooling roll is transferred to the surface of the polypropylene resin film due to the close contact with the cooling roll, which may similarly cause poor appearance. Also from the viewpoint of surface roughness and transparency of the obtained polypropylene resin film, the surface state of the cooling roll is preferably satin.

  In the melt extrusion method, the distance (air gap) from the lip of the T die to the contact of the molten sheet with the metal cooling roll is preferably 200 mm or less, and more preferably 160 mm or less. The molten sheet extruded from the T-die is stretched from the lip to the roll, and orientation tends to occur. By shortening the air gap as described above, a film having a smaller orientation can be obtained. The lower limit of the air gap is naturally determined by the diameter of the metal cooling roll to be used, the tip shape of the lip to be used, and the diameter when the touch roll is used, and is usually 50 mm or more.

  Moreover, the processing speed when producing a polypropylene resin film by the melt extrusion method is determined by the time required for cooling and solidifying the molten sheet. When the diameter of the metal cooling roll to be used is increased, the distance at which the molten sheet is in contact with the cooling roll becomes longer, so that production at a higher speed is possible. Specifically, when a 600 mmφ metal cooling roll is used, the processing speed can be about 50 m / min at the maximum.

  The film obtained by the melt extrusion method as described above can be wound on a winder after slitting the end as necessary. At this time, in order to protect the surface until the roll-shaped polypropylene resin film is used, even if the surface protective film made of another thermoplastic resin is bonded to one or both surfaces of the roll-shaped polypropylene resin film, Good. When a molten sheet of polypropylene resin is sandwiched between a metal cooling roll and a touch roll together with a biaxially stretched film made of a thermoplastic resin, the biaxially stretched film is used as one surface protective film. You can also. In this way, a transparent resin film made of a polypropylene resin film can be produced.

(Ii) Cycloolefin-based resin film The cycloolefin-based resin that can be used for the transparent resin film in the polarizing plate of the present invention is, for example, a monomer composed of a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene-based monomer. It is a thermoplastic resin (also called a thermoplastic cycloolefin resin) having a unit. In the present invention, the cycloolefin-based resin may be a hydrogenated product of the ring-opening polymer of the cycloolefin or a ring-opening copolymer using two or more kinds of cycloolefin, and the cycloolefin and the chain olefin, It may be an addition copolymer with an aromatic compound having a vinyl group. Those having a polar group introduced are also effective.

The cycloolefin resin film in the present invention is desirably stretched in at least one direction. Thereby, an appropriate optical compensation function is provided, which can contribute to the expansion of the viewing angle of the liquid crystal display device. Cycloolefin resin film that can be used in the present invention, refracts the refractive index in the in-plane slow axis direction nx, the refractive index n _y in the direction perpendicular thereto in the plane (fast axis direction), and the thickness direction When the rate is n _z and the film thickness is d, the in-plane retardation value R ₀ and the thickness direction retardation value R _th of the film represented by the following formulas are preferably in-plane retardation value R _0. it is 40 to 100 nm (more preferably 40 nm to 100 nm) in the range of, and is preferably a thickness direction retardation R _th in the range of 80Nm～300nm (more preferably 100nm~250nm).

_{R 0 = (n x -n y} ) × d
R _th = [(n _x + _ny ) / 2−n _z ] × d
When the in-plane retardation value R ₀ is less than 40 nm or exceeds 100 nm, the viewing angle compensation ability for the panel tends to be lowered. When the thickness direction retardation value _Rth is less than 80 nm or more than 300 nm, the viewing angle compensation ability for the panel tends to be reduced as described above. The in-plane retardation value R ₀ and the thickness direction retardation value R _th described above can be measured using, for example, KOBRA 21ADH (manufactured by Oji Scientific Instruments).

  If the thickness of the cycloolefin-based resin film is too thick, the processability is inferior, and problems such as a decrease in transparency and an increase in the weight of the polarizing plate tend to occur. Therefore, the thickness of the cycloolefin-based resin film is preferably about 40 μm to 80 μm.

  Cycloolefin-based resins are commercially available as appropriate, such as Topas (manufactured by Topas Advanced Polymers GmbH), Arton (manufactured by JSR Corporation), ZEONOR (manufactured by Nippon Zeon Co., Ltd.), ZEONEX (manufactured by Nippon Zeon). (Made by Mitsui Chemical Co., Ltd.) etc. can be used conveniently. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. Further, for example, escina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), arton film (manufactured by JSR Co., Ltd.), ZEONOR film (manufactured by Nippon Zeon Co., Ltd.) and the like are formed in advance. In addition, a commercial product of a cycloolefin-based resin film to which a phase difference is imparted may be used.

(Iii) Cellulose-based resin film The cellulose-based resin that can be used for the transparent resin film in the polarizing plate of the present invention is a cellulose partial or completely esterified film, for example, cellulose acetate, propionate, butyric acid. The film which consists of ester, those mixed esters, etc. can be mentioned. More specifically, a triacetyl cellulose film, a diacetyl cellulose film, a cellulose acetate propionate film, a cellulose acetate butyrate film, and the like can be given.

The cellulose resin film used in the present invention is defined as described above, and the in-plane retardation value R ₀ that can be measured in the same manner is preferably in the range of ₀ to 20 nm (more preferably ₀ nm to 5 nm). and is preferably a thickness direction retardation R _th in the range of 20Nm～70nm (more preferably 30 nm to 50 nm).

  The thickness of the cellulose resin film used in the present invention is not particularly limited, but is preferably in the range of 20 μm to 90 μm, and more preferably in the range of 30 μm to 90 μm. When the thickness of the cellulose resin film is less than 20 μm, the handleability tends to be inferior. On the other hand, when it exceeds 90 μm, the workability is inferior, and the weight of the obtained polarizing plate is increased. This is because there is a possibility of doing so.

  As such a cellulose ester-based resin film, appropriate commercial products such as Fujitac TD80 (Fuji Film Co., Ltd.), Fujitac TD80UF (Fuji Film Co., Ltd.), Fujitac TD80UZ (Fuji Film Co., Ltd.), KC8UX2M (manufactured by Konica Minolta Opto Co., Ltd.), KC8UY (manufactured by Konica Minolta Opto Co., Ltd.) and the like can be suitably used. In addition, when forming a cellulose resin into a film and using it as a film, well-known methods, such as a solvent cast method and a melt extrusion method, can be used suitably.

(Iv) Polyester resin film Examples of the polyester resin film that can be used for the transparent resin film in the polarizing plate of the present invention include a polyethylene terephthalate film and a polyethylene naphthalate film. Among them, a polyethylene terephthalate film is particularly preferable. Can be used.

  Polyethylene terephthalate is a resin in which 80 mol% or more of repeating units are composed of ethylene terephthalate. Other copolymer components include isophthalic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthale Acid, dicarboxylic acid components such as 1,4-dicarboxycyclohexane, and also propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene Examples include diol components such as glycol. These dicarboxylic acid components and glycol components can be used in combination of two or more if necessary. It is also possible to use hydroxycarboxylic acids such as p-hydroxybenzoic acid and p-β-hydroxyethoxybenzoic acid as a copolymerization component. Such other copolymerization component may contain a compound containing a small amount of amide bond, urethane bond, ether bond, carbonate bond and the like.

  As a method for producing polyethylene terephthalate, any production method such as a so-called direct polymerization method in which terephthalic acid and ethylene glycol are directly reacted and a so-called transesterification method in which dimethyl ester of terephthalic acid and ethylene glycol are transesterified is applied. can do. Moreover, a well-known additive can be contained as needed. For example, a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light resistance agent, an impact resistance improver, and the like may be contained. However, since transparency is required in optical applications, it is preferable to keep the additive amount to a minimum.

  A stretched polyethylene terephthalate film can be produced by forming the raw material resin into a film and subjecting it to a stretching treatment. Stretching is uniaxial stretching in the MD direction (flow direction) or TD direction (direction orthogonal to the flow direction), biaxial stretching in both the MD direction and the TD direction, and stretching in a direction that is neither the MD direction nor the TD direction. Any method such as oblique stretching may be used. By performing such stretching operation, a polyethylene terephthalate film having high mechanical strength can be obtained. A polyethylene terephthalate film stretched in this way, particularly a biaxially stretched polyethylene terephthalate film, is preferable because interference unevenness tends to be difficult to see in the liquid crystal display device using the polarizing plate of the present invention.

  When using a polyethylene terephthalate film as a transparent protective film, it is preferable that the thickness exists in the range of 20 micrometers-50 micrometers. When a polyethylene terephthalate film having a thickness of less than 20 μm is used, the film tends to be difficult to handle. On the other hand, when a polyethylene terephthalate film having a thickness of more than 50 μm is used, the merit of thinning is reduced.

  The polyethylene terephthalate film can be used with haze in the range of 0.1% to 40%, and the preferred haze value is in the range of 0.1% to 10%, and further in the range of 0.1% to 5%. It is. The haze value is defined as the ratio of the diffuse transmittance to the total light transmittance as defined in JIS K 7136, and can be measured with a commercially available haze meter.

The polyethylene terephthalate film preferably has an in-plane retardation value R ₀ of 1,000 nm or more, and more preferably 3,000 nm or more. When a polyethylene terephthalate film having an in-plane retardation value R ₀ of less than 1,000 nm is used, coloring tends to be conspicuous from the front. The upper limit of the in-plane retardation value R ₀ of the polyethylene terephthalate film is sufficient up to about 10,000 nm.

  An easy adhesion layer may be provided to the polyethylene terephthalate film. An easily bonding layer is a layer provided in order to improve the adhesiveness of a polarizing film and a polyethylene terephthalate film. In order to form an easy-adhesion layer on a polyethylene terephthalate film, for example, a method of forming an easy-adhesion layer on a film that has been subjected to all stretching processes, during the process of stretching polyethylene terephthalate (that is, the longitudinal stretching process and the lateral stretching process) And a method of forming an easy-adhesion layer immediately before or after being adhered to the polarizing film, and the like. In the case of a biaxially stretched film, from the viewpoint of productivity, a method in which an easy-adhesion layer is formed after longitudinal stretching of the polyethylene terephthalate film and then laterally stretched is preferably employed. The easy adhesion layer can be applied to both surfaces of the polyethylene terephthalate film or to one surface bonded to a polarizing film made of a polyvinyl alcohol resin via an adhesive. The component constituting the easy-adhesion layer can be, for example, a polyester resin, a urethane resin, an acrylic resin, or the like having a polar group in the skeleton, a relatively low molecular weight, and a relatively low glass transition temperature. . Moreover, a crosslinking agent, an organic or inorganic filler, a surfactant, a lubricant and the like can be contained as necessary.

  Such a polyethylene terephthalate film can be easily obtained as a commercial product. For example, under the trade name, Diafoil (Mitsubishi Resin Co., Ltd.), Hostafan (Mitsubishi Resin Co., Ltd.), Fusion (Mitsubishi Resin Co., Ltd.), Teijin Tetron Film (Teijin DuPont Film Co., Ltd.), Melinex (Teijin DuPont Film Co., Ltd.), Mylar (Teijin DuPont Film Co., Ltd.), Teflex (Teijin DuPont) Film Co., Ltd.), Toyobo Ester Film (Toyobo Co., Ltd.), Toyobo Espet Film (Toyobo Co., Ltd.), Cosmo Shine (Toyobo Co., Ltd.), Crisper (Toyobo Co., Ltd.) ), Lumirror (manufactured by Toray Film Processing Co., Ltd.), Embron (manufactured by Unitika Ltd.), Emblet (Unitika Ltd.) ), Skyroll (manufactured by SCC Corporation), Kofir (manufactured by Kogo Co., Ltd.), Zuitsu Polyester Film (manufactured by Zuitsu Co., Ltd.), Dazai Polyester Film (manufactured by Phutamura Chemical Co., Ltd.) Can be mentioned.

  The transparent resin film used for the polarizing plate of this invention can contain an additive as needed. Examples of the additive include a lubricant, an antiblocking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light resistance agent, and an impact resistance improver. The addition amount is preferably kept in a range that does not adversely affect the optical properties.

  In order to improve the adhesion between the adhesive and the polarizing film and / or transparent resin film, the polarizing film and / or transparent resin film are subjected to corona treatment, flame treatment, plasma treatment, ultraviolet treatment, primer coating treatment, saponification treatment. A surface treatment such as

  The transparent resin film may be subjected to surface treatments such as antiglare treatment, antireflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment, either singly or in combination of two or more. The transparent resin film may contain an ultraviolet absorber such as a benzophenone compound or a benzotriazole compound, or a plasticizer such as a phenyl phosphate compound or a phthalate compound.

(Adhesive layer)
In the polarizing plate of the present invention, a transparent resin film is bonded to at least one surface of the polarizing film described above via an adhesive layer. For example, a polypropylene resin film may be bonded to one surface of the polarizing film described above via an adhesive layer, and a norbornene resin film may be bonded to the other surface of the polarizing film via an adhesive. it can. In the polarizing plate of the present invention, the same type of adhesive may be used on both sides of the polarizing film, or different types of adhesive may be used. Examples of the adhesive include water-based adhesives, that is, an adhesive component dissolved in water or dispersed in water from the viewpoint of thinning the adhesive layer. For example, a composition using a polyvinyl alcohol resin or a urethane resin as a main component can be mentioned as a preferred adhesive.

  When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin may be partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, or methylol group. Modified polyvinyl alcohol resins such as modified polyvinyl alcohol and amino group-modified polyvinyl alcohol may also be used. In this case, an aqueous solution of a polyvinyl alcohol resin is used as the adhesive. The density | concentration of the polyvinyl alcohol-type resin in an adhesive agent is 1 weight part-10 weight part normally with respect to 100 weight part of water, Preferably it is 1 weight part-5 weight part.

  It is preferable to add a curable component such as glyoxal or a water-soluble epoxy resin or a cross-linking agent to the adhesive composed of an aqueous solution of a polyvinyl alcohol resin in order to increase the adhesiveness. As the water-soluble epoxy resin, for example, a polyamide polyamine epoxy resin obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a polycarboxylic acid such as adipic acid and epichlorohydrin. Can be suitably used. Commercially available products of such polyamide polyamine epoxy resins include Sumire's Resin 650 (manufactured by Sumika Chemtex Co., Ltd.), Sumire's Resin 675 (manufactured by Sumika Chemtex Co., Ltd.), WS-525 (manufactured by Nippon PMC Corporation). Etc. The addition amount of these curable components or crosslinking agents (the total amount when added together) is usually 1 to 100 parts by weight, preferably 1 to 50 parts by weight, per 100 parts by weight of the polyvinyl alcohol resin. Parts by weight. When the addition amount of the curable component or the crosslinking agent is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving adhesiveness tends to be small, and the curable component or This is because the adhesive layer tends to be brittle when the addition amount of the crosslinking agent exceeds 100 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin.

  When a urethane resin is used as the main component of the adhesive, examples of suitable adhesive compositions include a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group. The polyester-based ionomer type urethane resin here 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. Polyester-based ionomer urethane resins are known per se. For example, JP-A-7-97504 describes an example of a polymer dispersant for dispersing a phenol-based resin in an aqueous medium. In JP-A-2005-70140 and JP-A-2005-208456, a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group is used as an adhesive, and a polarizing film made of a polyvinyl alcohol resin is used as a cycloolefin film. The form which joins a resin film is shown.

  The method of laminating the transparent resin film described above to the polarizing film may be generally known, for example, casting method, Meyer bar coating method, gravure coating method, comma coater method, doctor blade method, die coating method. And a method in which an adhesive is applied to the adhesive surface of the polarizing film and / or the film bonded thereto by a dip coating method, a spraying method, etc., and the both are overlapped. The casting method is a method of spreading and spreading an adhesive on the surface of a film to be coated while moving it in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two. After applying the adhesive, the polarizing film and the film bonded thereto are sandwiched by nip rolls and bonded together. In addition, in the method in which the photocurable adhesive is dropped between the polarizing film and the transparent resin film and then uniformly spread by pressing with a roll or the like, it is possible to use metal or rubber as the material of the roll Each roll used when passing between two rolls may be made of the same material or different materials.

  When bonding a transparent resin film to a polarizing film via an adhesive layer, one or both bonding surfaces of both films to be bonded are subjected to plasma treatment, corona treatment, and ultraviolet irradiation in order to increase adhesion. Surface treatment such as treatment, flame (flame) treatment, and saponification treatment may be appropriately performed. Examples of the saponification treatment include a method of immersing in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

  After laminating a transparent resin film via an adhesive layer on one or both sides of the polarizing film, the polarizing film is dried to cure the adhesive layer. This drying process is performed, for example, by blowing hot air, and the temperature is usually in the range of 40 ° C to 100 ° C, preferably in the range of 60 ° C to 100 ° C. The drying time is usually 20 seconds to 1200 seconds.

  The thickness of the adhesive layer after drying is usually about 0.01 μm to 5 μm, preferably 2 μm or less, more preferably 1 μm or less. When the thickness of the adhesive layer is less than 0.01 μm, the adhesion may be insufficient, and when the thickness of the adhesive layer exceeds 5 μm, the appearance of the polarizing plate may be poor.

  After pasting, curing may be performed at room temperature or slightly higher than that for at least half a day, usually several days, so that sufficient adhesive strength can be obtained. The preferable curing temperature is in the range of 30 ° C to 50 ° C, more preferably 35 ° C to 45 ° C. When the curing temperature exceeds 50 ° C., so-called “roll tightening” is likely to occur in the roll winding state. In addition, the humidity at the time of curing may be moderate, and the relative humidity may be in the range of 0% to 70%. The curing time is usually 1 day to 10 days, preferably 2 days to 7 days.

  Moreover, a photocurable adhesive agent can also be used for the adhesive agent in the polarizing plate of this invention. As a photocurable adhesive agent, the mixture containing a photocurable epoxy resin and a photocationic polymerization initiator is mentioned, for example. In this case, the photocurable adhesive is cured by irradiating with active energy rays. The light source of the active energy ray is not particularly limited, but an active energy ray having a light emission distribution at a wavelength of 400 nm or less is preferable. Specifically, the low-pressure mercury lamp, the medium-pressure mercury lamp, the high-pressure mercury lamp, the ultrahigh-pressure mercury lamp, the chemical lamp, and the black light lamp A microwave excitation mercury lamp, a metal halide lamp and the like are preferable. The light irradiation intensity and irradiation time for the photocurable adhesive are appropriately determined depending on the composition of the photocurable adhesive. The thickness of the adhesive layer after irradiation with active energy rays is usually about 0.01 μm to 10 μm, preferably 0.1 μm or more, and preferably 5 μm or less.

  When curing a photo-curable adhesive by irradiation with active energy rays, curing should be performed under conditions that do not deteriorate the functions of the polarizing plate such as the degree of polarization of the polarizing film, the transmittance and hue, and the transparency of the transparent resin film. preferable.

  A combination of an adhesive made of a mixture containing the above-described photocurable epoxy resin and a cationic photopolymerization initiator and a propylene-based resin film is preferable in terms of adhesive strength. This photocurable adhesive is cured by irradiating active energy rays.

  As the photocurable epoxy resin, for example, an alicyclic epoxy compound can be preferably used, and 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 1,2-epoxy-4-vinylcyclohexane, 1, 2-epoxy-1-methyl-4- (1-methylepoxyethyl) cyclohexane, 3,4-epoxycyclohexylmethyl methacrylate, 2,2-bis (hydroxymethyl) -1-butanol 4- (1,2- Epoxyethyl) -1,2-epoxycyclohexane adduct, ethylene bis (3,4-epoxycyclohexanecarboxylate), oxydiethylene bis (3,4-epoxycyclohexanecarboxylate), 1,4-cyclohexanedimethyl bis (3 4-epoxycyclo Hexanecarboxylate), and 3- (3,4-epoxycyclohexylmethoxycarbonyl) propyl 3,4-epoxycyclohexanecarboxylate. An alicyclic epoxy compound and other active energy ray-curable compounds can be used in combination. If the example of the active energy ray hardening compound used together is mentioned, there exists epoxy compounds other than an alicyclic epoxy compound. Examples of the epoxy compound other than the alicyclic epoxy compound include, for example, an aromatic compound having a hydroxyl group or a glycidyl etherified product of a chain compound, a glycidyl aminated product of a compound having an amino group, and a chain compound having a C—C double bond. And epoxidized products. Moreover, an oxetane compound can also be used as an active energy ray-curable compound other than the alicyclic epoxy compound. By using the oxetane compound in combination, the curing rate of the active energy ray-curable resin composition can be improved.

  The cationic photopolymerization initiator generates a cationic species or a Lewis acid by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and initiates an epoxy group polymerization reaction.

  The compound that generates a cationic species or a Lewis acid upon irradiation with active energy rays is not particularly limited. For example, an aromatic diazonium salt; an onium salt such as an aromatic iodonium salt or an aromatic sulfonium salt; Examples include allene complexes.

  Examples of the aromatic diazonium salt include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, and benzenediazonium hexafluoroborate.

  Examples of the aromatic iodonium salt include diphenyliodonium tetrakis (pentafluorophenyl) borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di (4-nonylphenyl) iodonium hexafluorophosphate, and the like.

  Examples of the aromatic sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, diphenyl [4- (phenylthio) phenyl] sulfonium hexafluoroantimonate, 4,4′-bis [diphenylsulfonio] diphenyl sulfide bishexafluorophosphate, 4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluoroantimonate, 4,4′-bis [Di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluorophosphate, 7- [di (p-toluyl) sulfoni ] -2-Isopropylthioxanthone hexafluoroantimonate, 7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate, 4-phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide hexa Fluorophosphate, 4- (p-tert-butylphenylcarbonyl) -4′-diphenylsulfonio-diphenyl sulfide hexafluoroantimonate, 4- (p-tert-butylphenylcarbonyl) -4′-di (p-toluyl) Sulfonio-diphenyl sulfide tetrakis (pentafluorophenyl) borate and the like.

  Examples of iron-allene complexes include xylene-cyclopentadienyl iron (II) hexafluoroantimonate, cumene-cyclopentadienyl iron (II) hexafluorophosphate, xylene-cyclopentadienyl iron (II) -tris. And (trifluoromethylsulfonyl) methanide.

  These cationic polymerization initiators may be used alone or in combination of two or more. Among them, aromatic sulfonium salts are particularly preferably used because they have ultraviolet absorption characteristics even in a wavelength region of 300 nm or more, and therefore can provide a cured layer having excellent curability and good mechanical strength and adhesive strength. .

  The compounding quantity of a cationic polymerization initiator is 0.5 to 20 weight part normally with respect to a total of 100 weight part of an active energy ray hardening compound, and 1 to 15 weight part is preferable. If the amount is less than 0.5 parts by weight, curing may be insufficient, and the mechanical strength and adhesive strength of the cured product layer may be reduced. On the other hand, when the amount exceeds 20 parts by weight, the ionic substance in the cured product layer is increased, so that the hygroscopic property of the cured product layer is increased, and the durability performance of the obtained polarizing plate may be lowered.

  The active energy ray-curable resin composition containing the epoxy compound used in the present invention can contain a photosensitizer as necessary. By using a photosensitizer, the reactivity is improved, and the mechanical strength and adhesive strength of the cured product layer can be further improved.

  Examples of the photosensitizer include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, and photoreductive dyes.

  Specific examples of photosensitizers include benzoin methyl ether, benzoin isopropyl ether, and benzoin derivatives such as α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, o-benzoylbenzoate Benzophenone derivatives such as methyl acid, 4,4′-bis (dimethylamino) benzophenone, and 4,4′-bis (diethylamino) benzophenone; anthraquinone derivatives such as 2-chloroanthraquinone and 2-methylanthraquinone; N-methylacridone And acridone derivatives such as N-butylacridone; acetophenone derivatives such as α, α-diethoxyacetophenone; xanthone derivatives; fluorenone derivatives; anthraces such as 9,10-dibutoxyanthracene Thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; benzyl compounds; uranyl compounds.

  The photosensitizers may be used alone or in combination of two or more. The blending amount of the photosensitizer is preferably 0.1 to 20 parts by weight with respect to 100 parts by weight of the total active energy ray-curable compound.

<Application to liquid crystal display devices>
In the polarizing plate of the present invention, a pressure-sensitive adhesive layer is usually provided on the surface on the liquid crystal cell side when applied to a liquid crystal display device. For example, when the cycloolefin resin film having the predetermined in-plane retardation value and thickness direction retardation value described above is bonded to one surface of the polarizing film, the outer surface of the cycloolefin resin film ( It is preferable to provide an adhesive layer on the surface opposite to the side bonded to the polarizing film. As the pressure-sensitive adhesive used for such a pressure-sensitive adhesive layer, a conventionally known appropriate pressure-sensitive adhesive can be used without particular limitation, and examples thereof include an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, and a silicone pressure-sensitive adhesive. Among these, an acrylic pressure-sensitive adhesive is preferably used from the viewpoints of transparency, adhesive strength, reliability, reworkability, and the like. The pressure-sensitive adhesive layer can be provided by a method in which such a pressure-sensitive adhesive is used, for example, in the form of an organic solvent solution, which is applied to a base film with a die coater or a gravure coater, and dried. Can be provided also by a method of transferring a sheet-like pressure-sensitive adhesive formed on a plastic film (referred to as a separate film) to the base film. Although there is no restriction | limiting in particular also about the thickness of an adhesive layer, Generally it is preferable to exist in the range of 2 micrometers-40 micrometers.

  When the above-mentioned pressure-sensitive adhesive layer is formed on the outer surface of the cycloolefin-based resin film, an optical functional film may be attached via the pressure-sensitive adhesive layer. Examples of the optical functional film used in such a form include an optical compensation film in which a liquid crystal compound is applied to the substrate surface and oriented, a retardation film made of polycarbonate resin or other transparent resin, and the like. Can be mentioned. Commercially available products corresponding to an optical compensation film coated with a liquid crystal compound on the substrate surface and oriented are WV film (Fuji Film Co., Ltd.), NH film (Shin Nippon Oil Co., Ltd.), LC Examples include films (manufactured by Nippon Oil Corporation).

  Moreover, when using the polarizing plate of this invention for the back side polarizing plate of a liquid crystal cell, another optical functional film is stuck on the transparent resin film (protective film) side opposite to the side which faces the liquid crystal cell. You can also Examples of such an optical functional film include: a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties; a reflective film having a reflective function on the surface; There is a transflective film having a transmission function. For example, DBEF (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) is a commercially available product corresponding to a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties. Etc.

  On the other hand, when the polarizing plate of the present invention is used as a polarizing plate on the front side of a liquid crystal cell, another optical functional film is also attached to the surface of the transparent resin film (protective film) opposite to the side facing the liquid crystal cell. can do. Examples of such an optical functional film include a film with an antiglare function having a concavo-convex shape on the surface and a film with a surface antireflection function.

  The polarizing plate of the present invention can be suitably applied to a liquid crystal display device as described above. When applied to a liquid crystal display device, it is bonded to a liquid crystal cell via an adhesive layer provided on one surface of a polarizing plate. In particular, when a cycloolefin resin film having a predetermined in-plane retardation value and thickness direction retardation value is bonded to one surface of the polarizing film, an adhesive provided on the outer surface of the cycloolefin resin film A layer is bonded to the back of the liquid crystal cell to form a liquid crystal panel, and a liquid crystal display device is formed by combining with a backlight or the like. The liquid crystal display device to which the polarizing plate of the present invention is applied includes a liquid crystal panel in which the polarizing plate of the present invention is bonded to the back surface of the liquid crystal cell, so that sufficient mechanical strength can be achieved while corresponding to thinning. It will have. In addition, when a polyester resin film is bonded to one surface of the polarizing film, the liquid crystal panel and the backlight system are in contact with each other by placing the polyester resin film side on the backlight side of the liquid crystal cell back side. The possibility of doing so can be reduced. In such a liquid crystal display device, a conventionally known appropriate configuration can be adopted, and various constituent members (light diffusing plate, backlight, etc.) that the liquid crystal display device normally has in addition to the liquid crystal panel can be adopted. it can. Moreover, although a liquid crystal panel usually provides a polarizing plate also on the front side of the liquid crystal cell, the polarizing plate provided on the front side of the liquid crystal cell is not particularly limited, and any conventionally known appropriate polarizing plate can be used. The “rear side” of the liquid crystal cell and the liquid crystal panel mentioned above means the backlight side when the liquid crystal panel is mounted on the liquid crystal display device, and the “front side” of the liquid crystal cell and the liquid crystal panel means the liquid crystal panel. Means the viewing side when mounted on a liquid crystal display device.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

<Example 1>
As a polyvinyl alcohol raw film, a long polyvinyl alcohol film (obtained from Kuraray Co., Ltd.) having a polymerization degree of 2400, a saponification degree of 99.9 mol%, a thickness of 60 μm and a width of 3000 mm was used. A polarizing film was produced from the original film through the following operations. The stretching was performed with a difference in peripheral speed between the driving nip rolls before and after the treatment tank in each step shown below.

  First, the film was sufficiently swollen by immersing it in a swelling tank containing pure water at 32 ° C. for 80 seconds while keeping the tension state of the film so that the raw film did not loosen. The inlet / outlet roll speed ratio accompanying the swelling in the swelling tank was 1.2. After draining with a nip roll, it was immersed in a water immersion tank containing 30 ° C. pure water for 160 seconds. The draw ratio in the machine direction in this tank was 1.04 times. Next, uniaxial stretching was performed at a draw ratio of about 1.6 times while being immersed in a dyeing tank containing an aqueous solution of 0.02 / 1.5 / 100 in weight ratio of iodine / potassium iodide / water. Then, while being immersed in a boric acid bath containing an aqueous solution of potassium iodide / boric acid / water 12 / 4.0 / 100 by weight at 56.5 ° C. for 130 seconds (first boric acid treatment), Uniaxial stretching was performed until the cumulative stretching ratio from the opposite side reached 5.3 times. Then, it was immersed in a boric acid bath containing an aqueous solution of potassium iodide / boric acid / water 12 / 1.5 / 100 by weight at 30 ° C. for 60 seconds (second boric acid treatment). Furthermore, it wash | cleans for about 16 second with 10 degreeC pure water in a water-washing tank, Then, it passes sequentially about 60 degreeC drying furnace and then about 85 degreeC drying furnace, and the residence time in these drying furnaces is 160 in total. Drying was performed for a second. Thus, a polarizing film having a thickness of 28 μm on which iodine was adsorbed and oriented was obtained.

  The obtained polarizing film was analyzed by high-frequency inductively coupled plasma (ICP) emission spectroscopic analysis and the weight fraction (%) of boron with respect to the weight of the polarizing film was calculated. It was 5%.

  Moreover, about the obtained polarizing film, the heat contraction force of the direction orthogonal to the extending | stretching direction (absorption axis) of a polarizing film was measured. In the measurement, a film having a width of 2 mm and a length of 8 mm was cut out with the stretching axis direction as the short side, and used as a measurement sample. When the sample is set in a thermo-mechanical analyzer (TMA) (EXSTAR-6000 (manufactured by SII Nano Technology Co., Ltd.) and heated at 80 ° C. for 200 minutes while keeping the dimensions constant. The shrinkage force (X) generated in the direction of 8 mm in length was measured and found to be 1.5N.

  A transparent resin film made of polypropylene having a thickness of 50 μm is formed on one surface of the polarizing film, and a biaxially stretched retardation film made of a norbornene-based resin on the other surface (front retardation value: 63 nm, thickness direction retardation value: 225 nm). ) Are laminated via an epoxy UV curable adhesive, respectively, and then a metal halide lamp is irradiated from the biaxially stretched phase difference film made of norbornene resin to cure the adhesive on both sides to obtain a polarizing plate. It was. The epoxy ultraviolet curable adhesive contains the trade name “Celoxide 2021P” manufactured by Daicel Chemical Industries, Ltd. as an adhesive component, and the product name “Adeka Opton CP77” manufactured by ADEKA Corp. as a photocationic polymerization initiator. A solvent-free epoxy adhesive containing was used. In addition, about the transparent resin film which consists of a polypropylene used here, when the shrinkage force (Y) of the length 8mm direction generate | occur | produced when heated at 80 degreeC for 200 minutes like the above was measured, it was 0.1N. .

  The obtained polarizing plate is bonded to a glass plate through an adhesive on the phase difference film side, and a heat cycle test in which a process of keeping at -35 ° C. for 1 hour and a process of keeping at 70 ° C. for 1 hour is one cycle. I did it. As a result, the polarizing film was not broken even after 200 cycles.

<Example 2>
Example 1 except that a transparent resin film made of polypropylene having a thickness of 75 μm (a contraction force (Y) generated in a length of 8 mm when heated at 80 ° C. for 200 minutes is 6.1 N)) is used. Thus, a polarizing plate was produced. About the obtained polarizing plate, it carried out similarly to Example 1, and performed the heat cycle test.

<Example 3>
Example 1 except that a transparent resin film made of polypropylene having a thickness of 100 μm (shrinkage force (Y) in a length of 8 mm direction generated when heated at 80 ° C. for 200 minutes is 7.2 N)) is used. Thus, a polarizing plate was produced. About the obtained polarizing plate, it carried out similarly to Example 1, and performed the heat cycle test.

<Example 4>
A polarizing film was prepared in the same manner as in Example 1 except that a 60-μm-thick polyvinyl alcohol film obtained from Nippon Synthetic Chemical Industry Co., Ltd. was used as the polyvinyl alcohol raw film. The contraction force (X) in the length 8 mm direction generated when the polarizing film was heated at 80 ° C. for 200 minutes was 1.83 N. A polarizing plate was produced in the same manner as in Example 2 except that this polarizing film was used. About the obtained polarizing plate, it carried out similarly to Example 1, and performed the heat cycle test.

<Example 5>
As a polyvinyl alcohol raw film, a long polyvinyl alcohol film (obtained from Kuraray Co., Ltd.) having a polymerization degree of 2400, a saponification degree of 99.9 mol%, a thickness of 75 μm, and a width of 3000 mm was used. Similarly, a polarizing film was produced. The contraction force (X) in the length 8 mm direction generated when the polarizing film was heated at 80 ° C. for 200 minutes was 2.10 N. A polarizing plate was produced in the same manner as in Example 1 except that this polarizing film was used, and a polyethylene terephthalate film having a thickness of 38 μm was used as the transparent resin film instead of the transparent resin film made of polypropylene. The shrinkage force (Y) in the 8 mm length direction generated when the polyethylene terephthalate film (transparent resin film) was heated at 80 ° C. for 200 minutes was 17.5 N. About the obtained polarizing plate, it carried out similarly to Example 1, and performed the heat cycle test.

<Example 6>
A polarizing plate was produced in the same manner as in Example 5 except that a triacetyl cellulose film having a thickness of 80 μm was used as the transparent resin film instead of the polyethylene terephthalate film. The triacetyl cellulose film (transparent resin film) used here had a shrinkage force (Y) in the direction of 8 mm in length when heated at 80 ° C. for 200 minutes, which was 22.4 N. About the obtained polarizing plate, it carried out similarly to Example 1, and performed the heat cycle test.

<Comparative Example 1>
A polarizing plate was produced in the same manner as in Example 1 except that the polarizing film produced in Example 5 (shrinkage force X = 2.10 N) was used. When the obtained polarizing plate was subjected to a heat cycle test in the same manner as in Example 1, the polarizing film was broken in 200 cycles.

<Comparative example 2>
A polarizing plate was produced in the same manner as in Comparative Example 1 except that a transparent resin film made of polypropylene having the same thickness of 75 μm as that used in Example 2 (shrinkage force Y = 6.1 N) was used. When the obtained polarizing plate was subjected to a heat cycle test in the same manner as in Example 1, the polarizing film was broken in 200 cycles.

<Comparative Example 3>
A polarizing plate was produced in the same manner as in Comparative Example 1 except that a transparent resin film made of polypropylene having the same thickness of 100 μm as that used in Example 3 (shrinkage force Y = 7.2 N) was used. When the obtained polarizing plate was subjected to a heat cycle test in the same manner as in Example 1, the polarizing film was broken in 200 cycles.

  The results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1. Moreover, the heat cycle test results of Examples 1 to 6 and Comparative Examples 1 to 3, the horizontal axis is the shrinkage force (N) in the direction orthogonal to the stretching axis of the polarizing film, and the vertical axis is the stretching of the polarizing film of the transparent resin film. A graph expressed as contraction force (N) in the same direction as the direction orthogonal to the axis is shown in FIG.

  In Table 1, PP represents polypropylene, TAC represents triacetyl cellulose, and PET represents polyethylene terephthalate.

  According to the present invention, a polarizing plate that does not break in the heat cycle test can be obtained. This polarizing plate can be effectively applied to various display devices including liquid crystal display devices.

Claims (7)

A polarizing plate in which a transparent resin film is bonded to at least one surface of a polarizing film made of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented via an adhesive layer, and is orthogonal to the stretching axis of the polarizing film When the shrinkage force in the direction is X and the shrinkage force in the same direction as the direction perpendicular to the stretching axis of the polarizing film of the transparent resin film laminated on at least one surface of the polarizing film is Y, the relationship of (1) below A polarizing plate characterized by satisfying the formula.
Y ≧ 40X ² −116X + 83 (1)   The polarizing plate according to claim 1, wherein the content of boron in the polarizing film made of the polyvinyl alcohol-based resin film is in the range of 2.5 wt% to 4.9 wt%.   The polarizing plate according to claim 1 or 2, wherein the transparent resin film bonded to at least one surface of the polarizing film is a film made of a polypropylene resin having a xylene-soluble content at 20 ° C of 1% by weight or less.   The transparent resin film bonded to at least one surface of the polarizing film is a retardation film made of a cycloolefin resin, an in-plane retardation is 40 nm to 100 nm, and a thickness direction retardation is 80 nm to 300 nm. The polarizing plate according to any one of claims 1 to 3.   The polarizing plate according to claim 1 or 2, wherein the transparent resin film bonded to at least one surface of the polarizing film is a film made of a cellulose resin or a polyester resin.   The polarizing plate according to claim 1, wherein the adhesive layer is a cured product of an active energy ray-curable composition containing an epoxy compound.   The polarizing plate according to claim 1, wherein the adhesive layer is a cured product of a composition using a polyvinyl alcohol resin or a urethane resin.

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