JP2023102968A - Manufacturing method of polarizing plate - Google Patents

Abstract

To provide a method for manufacturing a polarizing plate that can appropriately transfer a phase difference layer and has excellent adhesion properties of the phase difference layer.SOLUTION: A polarizing plate has a polarizing element and a composite protection film. The composite protection film has a fist protection film, and a phase difference layer containing a cured product layer of a polymerizable liquid crystal compound in order from the side of the polarizing element. A method for manufacturing a polarizing plate includes: a step (1) of laminating a phase difference layer formed on a base material layer and the first protection film by using an ultraviolet curable adhesive, and obtaining a composite protection film having a base material layer by irradiating the ultraviolet curable adhesive with ultraviolet rays; a step (2) of bonding a side of the first protection film of the composite protection film having a base material layer and the polarizing element by using a first water-based adhesive and obtaining a polarizing plate having a base material layer; and a step (3) of separating the base material layer from the polarizing plate having a base material layer.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing a polarizing plate.

Liquid crystal display devices (LCDs) are widely used not only for liquid crystal televisions, but also for mobile terminals such as personal computers and mobile phones, and in-vehicle applications such as car navigation systems. Generally, a liquid crystal display device has a liquid crystal panel in which linear polarizing plates including polarizing elements are attached to both sides of a liquid crystal cell, and displays an image or the like by controlling light from a backlight with the liquid crystal panel. In recent years, like liquid crystal display devices, organic EL display devices have also been widely used for mobile terminals such as televisions and mobile phones, and in-vehicle applications such as car navigation systems. In an organic EL display device, a circularly polarizing plate (a polarizing element and a λ/4 plate) may be placed on the viewer-side surface of the image display element in order to prevent external light from being reflected by the metal electrode (cathode) and viewed as a mirror surface.

Linear polarizers and circular polarizers applied to display devices are required to achieve good viewing angle characteristics. In order to improve viewing angle characteristics, it is known to use a retardation layer containing a cured product layer of a polymerizable liquid crystal compound in a display device together with a polarizing element (for example, Patent Document 1).

As described in Patent Document 1, a cured product layer of a polymerizable liquid crystal compound is formed by applying a composition containing a polymerizable liquid crystal compound onto a substrate film and curing the composition. The cured product layer formed on the substrate film is laminated to an adherend such as a polarizing element together with the substrate film, and then transferred onto the adherend by peeling off the substrate film.

Japanese Patent Application Laid-Open No. 2020-201510

In a linearly polarizing plate and a circularly polarizing plate, when laminating a polarizing element, a retardation layer, a protective film, and the like, the layers are sometimes bonded using an ultraviolet curing adhesive. When transferring a cured material layer onto an adherend using an ultraviolet curable adhesive, the cured material layer on the base film and the adherend are laminated, and the base film is peeled off after curing the ultraviolet curable adhesive. When peeling the base film, the cured layer is not transferred to the adherend and the cured layer is peeled off together with the base film, or the cured layer is transferred but the adhesion to the adherend is not sufficient.

An object of the present invention is to provide a method for producing a polarizing plate in which, when a retardation layer containing a cured product layer of a polymerizable liquid crystal compound is transferred to an adherend using an ultraviolet curable adhesive, the retardation layer is in close contact with the adherend, and the retardation layer can be satisfactorily transferred.

The present invention provides the following method for producing a polarizing plate.
[1] A method for producing a polarizing plate comprising a polarizing element and a composite protective film, comprising:
The composite protective film has, in order from the polarizing element side, a first protective film and a retardation layer containing a cured product layer of a polymerizable liquid crystal compound,
The manufacturing method is
A step (1) of obtaining a composite protective film with a substrate layer by laminating the retardation layer and the first protective film formed on the substrate layer using an ultraviolet curable adhesive and irradiating the ultraviolet curable adhesive with ultraviolet rays;
a step (2) of obtaining a polarizing plate with a base layer by bonding the first protective film side of the composite protective film with a base layer and the polarizing element using a first water-based adhesive;
A method for producing a polarizing plate, comprising the step (3) of peeling the base layer from the base layer-attached polarizing plate.
[2] The method for producing a polarizing plate according to [1], further comprising the step (4) of forming a pressure-sensitive adhesive layer on the surface exposed by peeling off the substrate layer.
[3] The method for producing a polarizing plate according to [1] or [2], wherein the first protective film has a light transmittance of 80% or more at a wavelength of 365 nm.
[4] The method for producing a polarizing plate according to any one of [1] to [3], wherein the first water-based adhesive contains a polyvinyl alcohol-based resin.
[5] The method for producing a polarizing plate according to any one of [1] to [4], wherein the step (2) further includes a step of bonding a second protective film to the side of the polarizing element opposite to the composite protective film side.
[6] The method for producing a polarizing plate according to [5], wherein the polarizing element and the second protective film are bonded using a second water-based adhesive.
[7] The method for producing a polarizing plate according to [6], wherein the second water-based adhesive contains a polyvinyl alcohol-based resin.
[8] The method for producing a polarizing plate according to any one of [5] to [7], wherein the step (2) includes bonding the polarizing element and the second protective film while bonding the composite protective film with the substrate layer and the polarizing element.

According to the method for producing a polarizing plate of the present invention, the retardation layer can be satisfactorily transferred, and a polarizing plate having excellent adhesion of the retardation layer can be produced.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically the polarizing plate which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method of the polarizing plate which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

(Polarizer)
FIG. 1 is a cross-sectional view schematically showing a polarizing plate according to one embodiment of the present invention. The polarizing plate 1 includes a polarizing element 10 and a composite protective film 30 , and can include the composite protective film 30 on one side of the polarizing element 10 . The polarizing plate 1 can include a polarizing element 10, a first adhesive layer 21 formed using a first water-based adhesive, and a composite protective film 30 in this order. The first adhesive layer 21 is a layer for bonding the polarizing element 10 and the composite protective film 30 together, and is in direct contact with the polarizing element 10 and the composite protective film 30 . The composite protective film 30 includes, in order from the polarizing element 10 side, the first protective film 11, a UV adhesive layer 25 which is a cured product layer of an ultraviolet curable adhesive (hereinafter sometimes referred to as "UV adhesive"), and a retardation layer 15. The UV adhesive layer 25 is a layer for bonding the first protective film 11 and the retardation layer 15 and is in direct contact with the first protective film 11 and the retardation layer 15 . The retardation layer 15 includes at least one layer of a cured product layer of a polymerizable liquid crystal compound, and may include at least one layer of an alignment layer having an alignment control force for aligning the polymerizable liquid crystal compound in a desired direction. When the retardation layer 15 includes an alignment layer, the alignment layer preferably constitutes the surface of the retardation layer 15 opposite to the UV adhesive layer 25 .

By bonding the retardation layer 15 and the first protective film 11 with the UV adhesive layer 25, in the polarizing plate 1, the retardation layer 15 containing the cured product layer of the polymerizable liquid crystal compound is formed with an adhesive. As a result, the deformation of the retardation layer 15 is suppressed, so that the retardation layer 15 (particularly, the hardened layer) can be prevented from being scratched or dented when the polarizing plate 1 is transported.

The polarizing plate 1 may further have an adhesive layer 28 on the composite protective film 30 side, and may have a release film for covering and protecting the adhesive layer 28 on the opposite side of the adhesive layer 28 from the composite protective film 30 side. The adhesive layer 28 is a layer for bonding the polarizing plate 1 to, for example, an image display element of a display device. The pressure-sensitive adhesive layer 28 may be provided in direct contact with the composite protective film 30, or may be provided via another layer arranged on the side of the composite protective film 30 opposite to the polarizing element 10 side.

The polarizing plate 1 may further have a second protective film 12 on the polarizing element 10 side. The polarizing element 10 and the second protective film 12 may be laminated in direct contact with each other, or may be bonded by a second adhesive layer 22 formed using a second water-based adhesive. When the polarizing element 10 and the second protective film 12 are bonded by the second adhesive layer 22 , the second adhesive layer 22 is in direct contact with the polarizing element 10 and the second protective film 12 .

In the polarizing plate 1 , a surface protective film (protective film) that can be peeled off from the second protective film 12 may be laminated on the side of the second protective film 12 opposite to the polarizing element 10 . The surface protection film is for protecting the surface of the second protection film 12 .

The polarizing plate 1 can be used by being laminated on an image display element of a display device such as a liquid crystal display device or an organic EL display device.

(Manufacturing method of polarizing plate)
FIG. 2 is a cross-sectional view schematically showing a method for manufacturing a polarizing plate according to one embodiment of the present invention. The method for manufacturing the polarizing plate 1 is the method for manufacturing the polarizing plate 1 described above,
The retardation layer 15 formed on the substrate layer 17 and the first protective film 11 are laminated using a UV adhesive, and the UV adhesive is irradiated with ultraviolet rays (hereinafter sometimes referred to as “UV irradiation”) to obtain a composite protective film 31 with a substrate layer (1) ((a) and (b) in FIG. 2);
Step (2) of bonding the first protective film 11 side of the composite protective film 31 with the base layer and the polarizing element 10 using the first water-based adhesive to obtain the polarizing plate 2 with the base layer (FIG. 2(c));
It includes a step (3) of peeling the base layer 17 from the base layer-attached polarizing plate 2 ((d) in FIG. 2).

The method for manufacturing the polarizing plate 1 may further include a step (4) of forming a pressure-sensitive adhesive layer 28 on the surface of the polarizing plate 2 with a base layer that is exposed by peeling off the base layer 17 in step (3). The adhesive layer 28 may be formed on the surface exposed by peeling the base material layer 17, or may be formed on this other layer by providing another layer on the exposed surface.

In step (2), the method for manufacturing the polarizing plate 1 may further include a step of bonding a second protective film 12 to the side of the polarizing element 10 opposite to the composite protective film 30 (FIG. 2(c)). In this step, it is preferable to bond the polarizing element 10 and the second protective film 12 together using the second water-based adhesive. In the step (2), it is preferable to bond the polarizing element 10 and the second protective film 12 while bonding the composite protective film 31 with the substrate layer and the polarizing element 10 .

The cured product layer contained in the retardation layer 15 is usually formed on the substrate layer 17 or on the alignment layer formed on the substrate layer 17, after applying a composition containing a polymerizable liquid crystal compound, and then polymerizing and curing the polymerizable liquid crystal compound. Therefore, when the retardation layer 15 containing the above-described cured product layer is laminated on another film such as the first protective film 11 or the polarizing element 10, the retardation layer 15 is provided on at least one side of the substrate layer 17. Use a substrate layer-attached retardation film 19 ((a) in FIG. 2). When laminating the retardation layer 15 of the retardation film 19 with the base layer to an adherend such as the polarizing element 10, after bonding the retardation film 19 with the base layer to the adherend, by peeling the base layer 17, A method of transferring the retardation layer 15 to the adherend can be considered. As a method for manufacturing the polarizing plate 1 with such a transfer of the retardation layer 15, [i] first, the polarizing element with a protective film in which the polarizing element 10 and the first protective film 11 are laminated, a UV adhesive is used to laminate the retardation film 19 with the base layer, [ii] the UV adhesive is subjected to UV irradiation, and then the base layer 17 is peeled off. The present inventor found that when the substrate layer 17 is peeled off as in [i] and [ii] above, the retardation layer 15 is not transferred to the polarizing element with the protective film, and the retardation layer 15 is peeled off along with the substrate layer 17.

The reason for the poor transfer or poor adhesion of the retardation layer 15 is presumed as follows. The polarizing element 10 and the retardation layer 15 have absorption in the ultraviolet region (wavelength region of 280 to 390 nm) and are often difficult to transmit ultraviolet rays. Therefore, even if the polarizing element with a protective film and the retardation film with a base layer are laminated via a UV adhesive and the UV adhesive is irradiated with ultraviolet rays through the polarizing element 10 and / or the retardation layer 15, the ultraviolet rays are absorbed by the polarizing element 10 and / or the retardation layer 15, making it difficult for the ultraviolet rays to reach the UV adhesive, so the UV adhesive cannot be sufficiently cured. This is thought to cause poor transfer or poor adhesion of the retardation layer 15 .

On the other hand, according to the method for manufacturing the polarizing plate 1 of the present embodiment, first, in the step (1), the laminated structure in which the substrate layer-attached retardation film 19 and the first protective film 11 are laminated via a UV adhesive is irradiated with UV. Therefore, by irradiating ultraviolet rays from the first protective film 11 side, it is considered that the UV adhesive can be sufficiently cured by the ultraviolet rays transmitted through the first protective film 11 . As a result, in the step (3), the occurrence of poor transfer or poor adhesion of the retardation layer 15 when the base layer 17 is peeled off from the base layer-attached polarizing plate 2 obtained in the step (2) can be suppressed.

The method of manufacturing the polarizing plate 1 may be carried out using a sheet body or a long body. From the viewpoint of continuous production of polarizing plates, it is preferable to use elongated plates. In this case, the layer or film obtained in each process or during the process may be wound into a roll to form a roll, and the layer or film may be unwound from the roll for the next step. As used herein, a long body refers to a layer or film having a length of, for example, 30 to 10,000 m.

Each step of the method for manufacturing the polarizing plate 1 will be specifically described below.
(Step (1))
Step (1) is a step of laminating the retardation layer 15 of the retardation film 19 with the base layer and the first protective film 11 using a UV adhesive, and irradiating the UV adhesive with the base layer to obtain a composite protective film 31 (FIG. 2(b)). The UV irradiation in step (1) can cure the UV adhesive between the substrate layer 17 and the retardation layer 15 to form the UV adhesive layer 25 . The base layer-attached composite protective film 31 has a base layer 17, a retardation layer 15, a UV adhesive layer 25, and a first protective film 11 in this order.

In step (1), the UV adhesive may be applied to the surface of the retardation layer 15 of the substrate layer-attached retardation film 19, may be applied to the surface of the first protective film 11, or may be applied to both of them. In order to improve the applicability of the UV adhesive and improve the adhesion with the UV adhesive, the surfaces of the retardation layer 15 and the first protective film 11 on the side contacting the UV adhesive are preferably subjected to surface treatment such as corona treatment, plasma treatment, Itro treatment, and saponification treatment prior to application of the UV adhesive.

As the coating method of the UV adhesive, known coating methods such as a bar coater method such as a wire bar coating method, a gravure coater method, a doctor blade method, a die coater method and a comma coater method can be employed. Among these methods, one of the bar coater method and the gravure coater method is preferably used from the viewpoint of applying the UV adhesive to a thin film.

The UV adhesive interposed between the retardation layer 15 of the substrate layer-attached retardation film 19 and the first protective film 11 can be cured by UV irradiation to form the UV adhesive layer 25 . The cured product layer of the polymerizable liquid crystal compound contained in the retardation layer 15 tends to have low light transmittance in the vicinity of a wavelength of 365 nm due to its molecular structure. Therefore, from the viewpoint of irradiating sufficient ultraviolet rays to the UV adhesive, it is preferable to perform UV irradiation from the first protective film 11 side. As a result, deterioration of the retardation layer 15 due to UV irradiation can be suppressed, and deterioration of the optical properties of the polarizing plate can also be suppressed. From the viewpoint of efficiently curing the UV adhesive, the light transmittance of the first protective film 11 at a wavelength of 365 nm is preferably 80% or more as described later.

For UV irradiation, light sources such as low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, and metal halide lamps, which have an emission distribution particularly at a wavelength of 400 nm or less, are suitably used. The intensity of ultraviolet irradiation to the UV adhesive is determined according to the target composition, and is not particularly limited. For example, it is preferable that the irradiation intensity in the wavelength range effective for activating the photopolymerization initiator (for example, the ultraviolet region with a wavelength of 280 to 390 nm) is 5 to 1000 mW/cm ² . If the intensity of UV irradiation to the UV adhesive is too low, the reaction time will be too long, and if the intensity of UV irradiation to the UV adhesive is too high, the heat radiated from the light source and heat generated during polymerization of the UV adhesive may cause yellowing of the UV adhesive.

^The irradiation time of ultraviolet rays to ^the UV adhesive is controlled according to the composition to be cured, and is not particularly limited. If the integrated amount of light to the UV adhesive is too small, the generation of active species derived from the photopolymerization initiator may not be sufficient, and the obtained UV adhesive layer 25 may not be cured sufficiently. If the integrated amount of light to the UV adhesive is increased, the irradiation time for curing the UV adhesive becomes very long, which is disadvantageous in improving the productivity of the polarizing plate 1.

Step (1) may include a step of preparing the substrate layer-attached retardation film 19 . The preparing step can include a step of forming the retardation layer 15 on the substrate layer 17 . The step of forming the retardation layer 15 on the substrate layer 17 includes, for example, forming an alignment layer on the substrate layer 17 having an alignment control force for aligning the polymerizable liquid crystal compound in a desired direction, and forming a cured product layer of the polymerizable liquid crystal compound on the alignment layer.

Examples of the method of forming an alignment layer on the substrate layer 17 include a method of forming an alignment polymer layer formed of an alignment polymer on the substrate layer 17, a method of forming a photo-alignment polymer layer formed of a photo-alignment polymer, and a method of forming a groove alignment layer having an uneven pattern or a plurality of grooves (grooves) on the surface of the substrate layer 17. Examples of the method of forming a cured product layer of a polymerizable liquid crystal compound on the alignment layer include a method of coating a composition containing a polymerizable liquid crystal compound on the alignment layer and polymerizing and curing the polymerizable liquid crystal compound.

(Step (2))
Step (2) is a step of obtaining a substrate layer-attached polarizing plate 2 (FIG. 2(c)) by bonding the first protective film 11 side of the substrate layer-attached composite protective film 31 obtained in step (1) to the polarizing element 10 using a first water-based adhesive. In step (2), the first adhesive layer 21 can be formed by drying the first water-based adhesive between the composite protective film 31 with the substrate layer and the polarizing element 10 . The substrate layer-attached polarizing plate 2 has a substrate layer 17, a retardation layer 15, a UV adhesive layer 25, a first protective film 11, a first adhesive layer 21, and a polarizing element 10 in this order.

The step (2) may further include a step of bonding a second protective film 12 on the side of the polarizing element 10 opposite to the base layer-attached composite protective film 31 side, and may include a step of bonding the polarizing element 10 and the second protective film 12 using a second water-based adhesive. The second adhesive layer 22 can be formed by drying the second aqueous adhesive between the polarizing element 10 and the second protective film 12 . The substrate layer-attached polarizing plate 2 having the second protective film 12 includes the substrate layer 17, the retardation layer 15, the UV adhesive layer 25, the first protective film 11, the first adhesive layer 21, the polarizing element 10, the second adhesive layer 22, and the second protective film 12 in this order. A surface protective film may be laminated on the second protective film 12 on the side opposite to the polarizing element 10 .

In the step (2), it is preferable to bond the polarizing element 10 and the second protective film 12 while bonding the composite protective film 31 with the substrate layer and the polarizing element 10 . This lamination can be realized, for example, by a method in which the composite protective film 31 with a base material layer, the polarizing element 10, and the second protective film 12 are superimposed and passed between a pair of lamination rolls to apply a pressing force. Between the pair of bonding rolls, the composite protective film 31 with the base layer, the polarizing element 10, and the second protective film 12 are arranged such that the first protective film 11 side of the composite protective film 31 with the base layer faces one side of the polarizing element 10 via the first water-based adhesive, and the second protective film 12 faces the other side of the polarizing element 10 via the second water-based adhesive. When the polarizing plate 1 does not have the second protective film 12, the composite protective film 31 with the base layer and the polarizing element 10 are arranged between a pair of bonding rolls so as to face each other via the first water-based adhesive.

The first water-based adhesive is preferably injected between the substrate layer-attached composite protective film 31 and the polarizing element 10 before being passed between the pair of bonding rolls by an adhesive injection device. The second water-based adhesive is preferably injected between the polarizing element 10 and the second protective film 12 before being passed between the pair of bonding rolls by an adhesive injection device.

Instead of using an adhesive injection device, the first water-based adhesive may be applied to the first protective film 11 side of the base layer-attached composite protective film 31, may be applied to the polarizing element 10, or may be applied to both of them. Similarly, the second water-based adhesive may be applied to the polarizing element 10, may be applied to the second protective film 12, or may be applied to both of them. When the first water-based adhesive is applied to the composite protective film 31 with a base material layer and/or the polarizing element 10, the coating method may be selected according to the viscosity of the first water-based adhesive or the second water-based adhesive.

Prior to applying the first water-based adhesive, it is preferable to perform a surface treatment such as corona treatment, plasma treatment, Itro treatment, saponification treatment, etc. on the surfaces of the composite protective film 31 with a base material layer and the polarizing element 10 on the side in contact with the first water-based adhesive in order to improve the applicability of the first water-based adhesive and improve the adhesion with the first water-based adhesive. For the same reason, the surfaces of the polarizing element 10 and the second protective film 12, which are to be in contact with the second water-based adhesive, are preferably subjected to the above surface treatment.

The first water-based adhesive interposed between the composite protective film 30 and the polarizing element 10 and the second water-based adhesive interposed between the polarizing element 10 and the second protective film 12 become the first adhesive layer 21 and the second adhesive layer 22, respectively, by heat drying or the like. Heat drying may be carried out by a known method, and examples thereof include heat drying using hot air and heat drying using a far-infrared heater.

The heat drying temperature is preferably 30°C or higher and 90°C or lower. If the temperature is less than 30°C, the drying time will be long and the productivity will be lowered, which is disadvantageous for improving the productivity. If the heat-drying temperature exceeds 90° C., the heat may deteriorate the polarization performance of the polarizing element 10 . The heat drying time can be about 10 seconds to 1000 seconds, preferably 60 seconds to 750 seconds, more preferably 150 seconds to 600 seconds, from the viewpoint of productivity.

After drying the first water-based adhesive or the first water-based adhesive and the second water-based adhesive by heating, curing (storage) may be performed at room temperature or higher for half a day or longer, preferably for several days or longer, in order to improve the adhesive strength between the composite protective film 30 and the polarizing element 10 or between the composite protective film 30 and the polarizing element 10 and the second protective film 12. The curing temperature is more preferably 30° C. or higher and 50° C. or lower, and still more preferably 35° C. or higher and 45° C. or lower. The humidity during curing is not particularly limited, but the relative humidity is preferably in the range of 0% RH or more and 70% RH or less. The curing time is usually about 1 to 10 days, preferably about 2 to 7 days.

(Step (3))
Step (3) is a step of peeling off the substrate layer 17 from the polarizing plate 2 with the substrate layer. The substrate layer 17 may be peeled off by peeling the substrate layer 17 or by peeling off the orientation layer together with the substrate layer 17 .

(Step (4))
Step (4) is a step of forming an adhesive layer 28 on the surface exposed by peeling the substrate layer 17 of the polarizing plate 2 with the substrate layer (hereinafter sometimes referred to as "exposed surface"). The adhesive layer 28 may be formed directly on the exposed surface, or may be formed on another layer if another layer is formed on the exposed surface. Examples of the method of forming the adhesive layer 28 include a method of laminating the exposed surface or other layer and the adhesive layer 28 formed on the release film, a method of applying an adhesive to the exposed surface or another layer, and the like. Prior to bonding the exposed surface or other layer and the adhesive layer 28, the exposed surface or other layer and the surface of the adhesive layer 28 on the side in contact with the exposed surface or other layer are preferably subjected to surface treatment such as corona treatment, plasma treatment, or Itro treatment.

Details of the layers and films constituting the polarizing plate 1 will be described below.
(Polarizing element)
A polarizing element is an absorption-type polarizing film having properties of absorbing linearly polarized light having a plane of vibration parallel to its absorption axis and transmitting linearly polarized light having a plane of vibration perpendicular to the absorption axis (parallel to the transmission axis).

The polarizing element has a polyvinyl alcohol-based resin layer (hereinafter sometimes referred to as a "PVA-based resin layer") in which a dichroic dye is adsorbed and oriented. A known polarizing element can be used. Examples of the polarizing element include a stretched film obtained by dyeing a polyvinyl alcohol-based resin film (hereinafter sometimes referred to as "PVA-based resin film") with a dichroic dye and uniaxially stretching it, and a stretched layer obtained by dyeing the coated layer with a dichroic dye and uniaxially stretching the laminated film using a laminated film having a coating layer formed by applying a coating solution containing a polyvinyl alcohol-based resin (hereinafter sometimes referred to as "PVA-based resin") on a substrate film. Stretching may be performed after dyeing with a dichroic dye, stretching may be performed while dyeing, or dyeing may be performed after stretching.

A PVA-based resin is obtained by saponifying a polyvinyl acetate-based resin. Polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. Other copolymerizable monomers include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, unsaturated sulfonic acids and the like.

The degree of saponification of the PVA-based resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, still more preferably about 99 mol% or more and 100 mol% or less. The degree of polymerization of the PVA-based resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA-based resin may be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like.

Examples of the dichroic dye adsorbed and oriented on the PVA-based resin layer include iodine and dichroic dyes. Preferably, the dichroic dye is iodine. Dichroic dyes include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Splat Blue G, and Splat Blue. GL, Supra Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black, and the like.

The thickness of the polarizing element is preferably 3 μm or more and 35 μm or less, more preferably 4 μm or more and 30 μm or less, still more preferably 5 μm or more and 25 μm or less. When the thickness of the polarizing element is 35 μm or less, for example, it is possible to suppress the influence of the polyene conversion of the PVA-based resin on the deterioration of the optical properties in a high-temperature environment. When the thickness of the polarizing element is 3 μm or more, it becomes easy to achieve the desired optical characteristics.

(Manufacturing method of polarizing element)
The manufacturing method of the polarizing element is not particularly limited, but a typical example is a method in which a pre-rolled PVA-based resin film is sent out and stretched, dyed, cross-linked, etc. (hereinafter referred to as "manufacturing method 1"); and a method including a step of applying a coating solution containing a PVA-based resin onto a substrate film to form a PVA-based resin layer as a coating layer, and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

Production method 1 includes a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, a step of treating the PVA-based resin film to which the dichroic dye has been adsorbed with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution.

The swelling step is a treatment step of immersing the PVA-based resin film in a swelling bath. The swelling step can remove stains, blocking agents, and the like on the surface of the PVA-based resin film, and swelling the PVA-based resin film can suppress uneven dyeing. A medium containing water as a main component, such as water, distilled water, or pure water, is usually used for the swelling bath. Surfactants, alcohols and the like may be appropriately added to the swelling bath according to conventional methods. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and further preferably 0.5% by mass or less.

The temperature of the swelling bath is preferably about 10° C. or higher and 60° C. or lower, more preferably about 15° C. or higher and 45° C. or lower, even more preferably about 18° C. or higher and 30° C. or lower. The immersion time in the swelling bath cannot be unconditionally determined because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath. The swelling step may be performed only once, or may be performed multiple times as necessary.

The dyeing step is a treatment step in which the PVA-based resin film is immersed in a treatment bath (dyeing bath) containing a dichroic dye, and the dichroic dye such as iodine can be adsorbed and oriented on the PVA-based resin film. The dyeing bath is a dyeing solution containing a dichroic dye, preferably an iodine solution. The iodine solution is preferably an aqueous iodine solution, and preferably contains iodine and iodide as a dissolution aid. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferable from the viewpoint of controlling the content of potassium in the polarizing element.

The concentration of iodine in the iodine solution is preferably about 0.01% by mass or more and 1% by mass or less, more preferably about 0.02% by mass or more and 0.5% by mass or less. The concentration of iodide in the iodine solution is preferably about 0.01% by mass or more and 10% by mass or less, more preferably about 0.05% by mass or more and 5% by mass or less, and more preferably about 0.1% by mass or more and 3% by mass or less.

The temperature of the dyeing bath is preferably about 10°C to 50°C, more preferably about 15°C to 45°C, and even more preferably about 18°C to 30°C. The immersion time in the dyeing bath cannot be generally determined because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath, but it is preferably about 10 seconds to 300 seconds, and more preferably about 20 seconds to 240 seconds. The dyeing step may be performed only once, or may be performed multiple times as necessary.

The cross-linking step is a treatment step in which the PVA-based resin film dyed in the dyeing step is immersed in a treatment bath (cross-linking bath) containing a boron compound, the PVA-based resin film is cross-linked by the boron compound, and iodine molecules or dye molecules can be adsorbed on the cross-linked structure. Boron compounds include, for example, boric acid, borates, and borax. The cross-linking bath is generally an aqueous solution, but may be a mixed solution of an organic solvent miscible with water and water. The cross-linking bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element.

The concentration of the boron compound in the cross-linking bath is preferably about 1% by mass to 15% by mass, more preferably about 1.5% by mass to 10% by mass, and more preferably about 2% by mass to 5% by mass. When potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and more preferably about 2% by mass or more and 5% by mass or less.

The temperature of the cross-linking bath is preferably about 20° C. or higher and 70° C. or lower, more preferably about 30° C. or higher and 60° C. or lower. The immersion time in the cross-linking bath cannot be unconditionally determined because the degree of cross-linking of the PVA-based resin film is affected by the temperature of the cross-linking bath. The cross-linking step may be performed only once, or may be performed multiple times as necessary.

The stretching step is a processing step of stretching the PVA-based resin film in at least one direction to a predetermined magnification. In general, a PVA-based resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and both wet stretching and dry stretching can be employed. The stretching step may be performed only once, or may be performed multiple times as necessary. The stretching step may be performed at any stage in the production of the polarizing element.

A treatment bath (stretching bath) in the wet stretching method can usually use a solvent such as water or a mixed solution of an organic solvent miscible with water and water. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element. When potassium iodide is used in the drawing bath, the concentration of potassium iodide in the drawing bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 2% by mass or more and 10% by mass or less, and more preferably about 3% by mass or more and 6% by mass or less. The treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. When a boron compound is included, the concentration of the boron compound in the drawing bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and more preferably about 2% by mass or more and 5% by mass or less.

The temperature of the drawing bath is preferably 25° C. or higher and 80° C. or lower, more preferably 40° C. or higher and 80° C. or lower, further preferably 50° C. or higher and 75° C. or lower, and particularly preferably 65° C. or higher and 75° C. or lower. The immersion time in the stretching bath cannot be generally determined because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath. The stretching treatment in the wet stretching method may be performed together with one or more of the swelling process, dyeing process, cross-linking process and washing process.

Examples of the dry drawing method include a roll-to-roll drawing method, a hot roll drawing method, a compression drawing method, and the like. The dry stretching method may be applied together with the drying process.

The total draw ratio (cumulative draw ratio) applied to the PVA-based resin film can be appropriately set according to the purpose, but it is preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and even more preferably about 3.5 to 6.5 times.

The washing step is a treatment step in which the PVA-based resin film is immersed in a washing bath, and foreign matter remaining on the surface of the PVA-based resin film can be removed. As the cleaning bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Further, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1% by mass or more and 10% by mass or less, more preferably about 1.5% by mass or more and 4% by mass or less, and further preferably about 1.8% by mass or more and 3.8% by mass or less.

The temperature of the washing bath is preferably about 5° C. or higher and 50° C. or lower, more preferably about 10° C. or higher and 40° C. or lower, even more preferably about 15° C. or higher and 30° C. or lower. The immersion time in the cleaning bath cannot be unconditionally determined because the degree of cleaning of the PVA-based resin film is affected by the temperature of the cleaning bath, but it is preferably about 1 second to 100 seconds, more preferably about 2 seconds to 50 seconds, and even more preferably about 3 seconds to 20 seconds. The washing step may be performed only once, or may be performed multiple times as necessary.

Furthermore, it is preferable to include a metal ion treatment step in the above steps or as a separate step from the above steps. The metal ion treatment step can be performed by immersing the PVA-based resin film in a metal salt solution containing a metal salt of metal ions. The metal salt solution is preferably an aqueous solution containing a metal salt. Metal ions can be incorporated into the PVA-based resin film by the metal ion treatment step.

The metal ions are not limited as long as they are metal ions other than potassium ions, and are preferably ions of metals other than alkali metals. In particular, from the viewpoint of adjusting color tone and imparting durability, it is preferable to include at least one metal ion of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron. Among these metal ions, zinc ions are preferable from the viewpoint of adjusting color tone and imparting heat resistance. Zinc salts include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and the like.

As the metal ion treatment step, a step of immersing the PVA-based resin film in a zinc salt aqueous solution, which is a zinc-containing solution, will be described. The concentration of zinc ions in the zinc salt aqueous solution is in the range of approximately 0.1% by mass to 10% by mass, preferably 0.3% by mass to 7% by mass. From the viewpoint of facilitating the impregnation of zinc ions into the PVA-based resin film, the zinc salt aqueous solution is preferably an aqueous solution containing potassium ions and iodine ions with potassium iodide or the like. The concentration of potassium iodide in the zinc salt aqueous solution is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 5% by mass or less.

In the immersion treatment in the zinc salt aqueous solution, the temperature of the zinc salt aqueous solution is usually about 15°C or higher and 85°C or lower, preferably 25°C or higher and 70°C or lower. The immersion time is usually about 1 second or more and 120 seconds or less, preferably 3 seconds or more and 90 seconds or less. In the immersion treatment in the zinc salt aqueous solution, the concentration of the zinc salt aqueous solution, the immersion temperature of the PVA resin film in the zinc salt aqueous solution, the immersion time, and other conditions are adjusted so that the zinc content in the PVA resin film falls within the above range. The timing of the immersion treatment in the zinc salt aqueous solution is not particularly limited. The immersion treatment in the zinc salt aqueous solution may be performed alone, or may be performed simultaneously with at least one step of the dyeing step, the cross-linking step, and the stretching step in the presence of a zinc salt in the dyeing bath, the cross-linking bath, and the stretching bath.

The drying step is a step of drying the PVA-based resin film washed in the washing step to obtain a polarizing element. Drying is performed by any appropriate method, such as natural drying, air drying, and heat drying.

Production method 2 can be produced through a step of applying a coating liquid containing a PVA-based resin onto a base film, a step of uniaxially stretching the obtained laminated film, a step of dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb it to form a polarizing element, a step of treating the film having the dichroic dye adsorbed with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution. The base film used to form the polarizing element may be used as the second protective film for the polarizing element. If necessary, the base film may be peeled off from the polarizing element.

(retardation layer)
The retardation layer can include at least one cured layer of a polymerizable liquid crystal compound. The retardation layer includes a cured product layer of a polymerizable liquid crystal compound, and may include at least one alignment layer for orienting the polymerizable liquid crystal compound. The retardation value of the retardation layer preferably has reverse wavelength dispersion. Since the cured product layer forming the retardation layer with reverse wavelength dispersion tends to have low light transmittance in the ultraviolet region, when producing a polarizing plate having excellent transferability and adhesion of the retardation layer, it is preferable to adopt the above-described method for producing a polarizing plate.

Materials constituting the retardation layer include, for example, JP 5463666, JP 2010-031223, JP 2010-030979, JP 2009-173893, JP 2009-227667, JP 2010-241919, JP 2010-024438, JP 2011-162678, JP 2011-20 7765, JP 2010-270108, JP 2011-246381, JP 2012-021068, JP 2016-121339, JP 2018-087152, JP 2017-179367, JP 2017-210601, JP 2019-151763, JP 6700468, JP 2020 -074021, etc., and materials for forming an alignment layer (orientation film).

The retardation layer is preferably formed by coating a composition containing a polymerizable liquid crystal compound on the substrate layer or an alignment layer provided on the substrate layer, and polymerizing and curing the polymerizable liquid crystal compound. Thereby, the cured product layer of the polymerizable liquid crystal compound can be formed to have a thickness of 0.1 μm or more and 10 μm or less. Since the substrate layer used for forming the retardation layer can be peeled off and removed in the manufacturing process of the polarizing plate, a thin retardation layer can be formed, and furthermore, the thickness of the polarizing plate can be reduced.

The retardation layer can be used, for example, as a viewing angle compensation film for optical compensation of a liquid crystal cell (IPS mode liquid crystal cell) comprising a liquid crystal layer containing liquid crystal molecules aligned in a homogeneous alignment in the absence of an electric field. The retardation layer used as the viewing angle compensation film can have a first optical compensation layer and a second optical compensation layer in order from the polarizing element 10 side, and the second optical compensation layer is arranged on the liquid crystal cell side. At least one of the first optical compensation layer and the second optical compensation layer is preferably a cured layer of a polymerizable liquid crystal compound, and more preferably both are cured layers from the viewpoint of thinning the polarizing plate.

The viewing angle compensation film and the polarizing element are usually laminated so that the slow axis of the second optical compensation layer and the absorption axis of the polarizing element are substantially parallel. As used herein, the term "substantially parallel" includes not only completely parallel but also substantially parallel, and the angle is generally within ±2°, preferably within ±1°, more preferably within ±0.5°. As used herein, the term “substantially orthogonal” includes not only completely orthogonal but also substantially orthogonal, and the angle is generally in the range of 90±2°, preferably 90±1°, more preferably 90±0.5°.

The first optical compensation layer and the second optical compensation layer may be directly laminated, or may be laminated via an adhesive layer. As the adhesive, a water-based adhesive or a UV adhesive, which will be described later, can be used.

Although the thicknesses of the first optical compensation layer and the second optical compensation layer are not particularly limited, they can each independently be usually 0.1 μm or more and 10 μm or less.

The first optical compensation layer and the second optical compensation layer can satisfy the following formulas (1) and (2).
nz1>nx1=ny1 (1)
nx2>ny2≧nz2 (2)
[In formulas (1) and (2),
nx1 represents the refractive index in the in-plane slow axis direction of the first optical compensation layer,
nx2 represents the refractive index in the in-plane slow axis direction of the second optical compensation layer,
ny1 represents the refractive index in the in-plane fast axis direction of the first optical compensation layer,
ny2 represents the refractive index in the in-plane fast axis direction of the second optical compensation layer,
nz1 represents the refractive index in the thickness direction of the first optical compensation layer,
nz2 represents the refractive index in the thickness direction of the second optical compensation layer.
Each refractive index in the above formula (1) is a value measured at the same wavelength, and each refractive index in the above formula (2) is a value measured at the same wavelength. ]

The first optical compensation layer and the second optical compensation layer may be made of the same material, or may be made of different materials. A known compound can be used for the polymerizable liquid crystal compound used in the first optical compensation layer and the second optical compensation layer. The wavelength dispersion characteristics of the retardation values of the first optical compensation layer and the second optical compensation layer are not particularly limited, and from positive wavelength dispersion to reverse wavelength dispersion can be suitably used.

Both the first optical compensation layer and the second optical compensation layer preferably have reverse wavelength dispersion characteristics satisfying the following formulas (3) to (6).
Rth1(450)/Rth1(550)≤1.00 (3)
1.00≦Rth1(650)/Rth1(550) (4)
Re2(450)/Re2(550)≤1.00 (5)
1.00≦Re2(650)/Re2(550) (6)

In formulas (3) to (6),
Rth1(λ)={(nx1+ny1)/2−nz1}×d1
Re2(λ)=(nx2−ny2)×d2
[In the above formula, d1 represents the thickness of the first optical compensation layer, d2 represents the thickness of the second optical compensation layer, and λ represents the measurement wavelength. ] represents.

The optical properties of the first optical compensation layer and the second optical compensation layer preferably satisfy the following formulas (7) to (10).
0 nm≦Re1(550)≦5 nm (7)
−200 nm≦Rth1(550)≦−20 nm (8)
110nm≦Re2(550)≦150nm (9)
35 nm≦Rth2(550)≦105 nm (10)

More preferably, the optical properties of the first optical compensation layer and the second optical compensation layer satisfy the following formulas (7a) to (10a).
0 nm≦Re1(550)≦5 nm (7a)
−120 nm≦Rth1(550)≦−50 nm (8a)
120 nm≦Re2(550)≦140 nm (9a)
50 nm≦Rth2(550)≦80 nm (10a)

In the above formulas (7) to (10) and formulas (7a) to (10a),
Rth1(λ)={(nx1+ny1)/2−nz1}×d1
Rth2(λ)={(nx2+ny2)/2−nz2}×d2
Re1(λ)=(nx1−ny1)×d1
Re2(λ)=(nx2−ny2)×d2
[In the above formula, d1 represents the thickness of the first optical compensation layer, d2 represents the thickness of the second optical compensation layer, and λ represents the measurement wavelength. ] represents.

(Base material layer)
The substrate layer can be used for forming the retardation layer as described above. A resin film can be used as the base material layer, and an optically transparent resin film may be used. The resin film may be a single-layer film or a film having a multi-layer structure of two or more layers. Examples of the resin material forming the resin film include a resin material forming the first protective film described later.

The thickness of the base material layer is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength is lowered and workability is poor. An appropriate thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

(First protective film)
The first protective film is preferably an optically transparent resin film. The light transmittance of the first protective film at a wavelength of 365 nm is preferably 80% or higher, may be 85% or higher, may be 90% or higher, or may be 92% or higher. The light transmittance can be measured by the method described in Examples below. The first protective film may be a single-layer film or a film having a multi-layer structure of two or more layers.

The thickness of the first protective film is preferably thin from the viewpoint of optical properties. An appropriate thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

The first protective film is preferably one that is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, etc., and is less likely to cause optical unevenness due to distortion. A resin film is preferably used as the first protective film.

Examples of resin materials constituting the first protective film include polycarbonate resins, polyvinyl alcohol resins, cellulose resins, polyester resins, polyarylate resins, polyimide resins, cyclic polyolefin resins, polysulfone resins, polyethersulfone resins, polyolefin resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Thermosetting resins such as urethane-based, acrylic urethane-based, epoxy-based, and silicone-based resins or UV-curable resins can also be used as the resin material constituting the first protective film. The first protective film may contain one or more of any suitable additives.

The cellulose-based resin constituting the first protective film is preferably a cellulose-ester-based resin that is a fatty acid ester of cellulose. Specific examples of cellulose ester resins include triacetyl cellulose, diacetyl cellulose, cellulose acylate, tripropionyl cellulose, dipropionyl cellulose and the like. Among these, triacetyl cellulose is particularly preferred. Many products of triacetyl cellulose are commercially available, and it is also advantageous in terms of availability and cost. Triacetyl cellulose often has a retardation (Rth) of more than 10 nm in the thickness direction, but by using an additive that cancels these retardations or by adjusting the film-forming method, it is possible to obtain a cellulose-based resin film with small retardation in the thickness direction as well as in-plane retardation. Examples of the film-forming method include a method in which a substrate film such as polyethylene terephthalate, polypropylene, or stainless steel coated with a solvent such as cyclopentanone or methyl ethyl ketone is laminated to a general cellulose film, dried by heating (for example, at 80 to 150° C. for about 3 to 10 minutes), and then the substrate film is peeled off; for about 3 to 10 minutes at 80 to 150° C.), and then the coated film is peeled off. "(Meth)acryl" is at least one of acryl and methacryl.

As a cellulose resin film having a small retardation (Rth) in the thickness direction, a fatty acid cellulose resin film having a controlled degree of fat substitution can be used. Generally used triacetyl cellulose has a degree of acetic acid substitution of about 2.8, and Rth can be reduced by preferably controlling the degree of acetic acid substitution to 1.8 to 2.7. By adding a plasticizer such as dibutyl phthalate, p-toluenesulfonanilide, or acetyltriethyl citrate to the fatty acid-substituted cellulose resin, Rth can be controlled to be small. The amount of the plasticizer to be added is preferably 40 parts by weight or less, more preferably 1 to 20 parts by weight, still more preferably 1 to 15 parts by weight, based on 100 parts by weight of the fatty acid cellulose resin.

As the first protective film,
A polymer film containing a resin composition containing a thermoplastic resin having a substituted and/or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted and/or unsubstituted phenyl and nitrile group in a side chain, as described in JP-A-2001-343529 (WO01/37007);
Polymer films containing acrylic resins having a lactone ring structure described in JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, JP-A-2005-146084, JP-A-2006-171464, etc., JP-A-2004-70290 , JP 2004-70296, JP 2004-163924, JP 2004-292812, JP 2005-314534, JP 2006-131898, JP 2006-206881, JP 2006-265532, JP 2006-283013, JP 20 06-299005, JP 2006-335902 A polymer film containing a (meth)acrylic resin having a structural unit of unsaturated carboxylic acid alkyl ester and a structural unit of glutaric anhydride;
JP 2006-309033, JP 2006-317560, JP 2006-328329, JP 2006-328334, JP 2006-337491, JP 2006-337492, JP 2006-337493, JP 2006-337569, etc. A film or the like containing a thermoplastic resin having the described glutarimide structure can also be used.
Since these films have small front retardation and thickness direction retardation and also have a small photoelastic coefficient, defects such as unevenness are less likely to occur even when the polarizing plate is distorted due to heating or the like.

It is also preferable to use a cyclic polyolefin resin as the resin material constituting the first protective film. A specific example of the cyclic polyolefin-based resin is preferably a norbornene-based resin. Cyclic polyolefin resin is a general term for resins polymerized with cyclic olefins as polymerized units, and examples thereof include resins described in JP-A-1-240517, JP-A-3-14882 and JP-A-3-122137. Specific examples include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, cyclic olefins and α-olefins such as ethylene and propylene and copolymers thereof (typically random copolymers), graft polymers modified with unsaturated carboxylic acids and derivatives thereof, and hydrides thereof. Specific examples of cyclic olefins include norbornene-based monomers.

Various products are commercially available as cyclic polyolefin resins. Specific examples include the trade name “Zeonor” manufactured by Nippon Zeon Co., Ltd., the trade name “Arton” manufactured by JSR Corporation, the trade name “Topas” manufactured by TICONA, and the trade name “Appel” manufactured by Mitsui Chemicals, Inc.

The first protective film is preferably an optically isotropic film having optical isotropy. An optically isotropic film is one that satisfies the following formulas (11) and (12).
0 nm≦|Re3(590)|≦20 nm (11)
0 nm≦|Rth3(590)|≦20 nm (12)

In formulas (11) and (12),
Rth3(λ)={(nx3+ny3)/2−nz3}×d3
Re3(λ)=(nx3−ny3)×d3
[In the above formula,
nx3 represents the refractive index in the in-plane slow axis direction of the optically isotropic film,
ny3 represents the refractive index in the in-plane fast axis direction of the optically isotropic film,
d3 represents the thickness of the optically isotropic film,
λ represents the measurement wavelength. ] represents.

Materials and manufacturing methods for the optically isotropic film are not particularly limited as long as they satisfy the above optical properties, and the above resin materials can be used. The optically isotropic film may be an optical film having a single-layer structure or an optical film having a multilayer structure of two or more layers. Preferably, the optically isotropic film is a monolayer film. This is because the contraction stress of the polarizing element and the occurrence of birefringence and unevenness due to the heat of the light source can be reduced, and the thickness of the liquid crystal panel can be reduced.

The absolute value of the photoelastic coefficient of the optically isotropic film is preferably 1.0×10 ⁻¹⁰ m ² /N or less, more preferably 5.0×10 ⁻¹¹ m ² /N or less, further preferably 1.0×10 ⁻¹¹ m ² /N or less, and particularly preferably 5.0×10 ⁻¹² m ² /N or less. By setting the value of the photoelastic coefficient within the above range, when the polarizing plate is applied to a display device, it is possible to obtain a display device that has excellent optical uniformity, small changes in optical properties even in environments such as high temperature and high humidity, and excellent durability. Although the lower limit of the photoelastic coefficient is not particularly limited, it is generally 5.0×10 ⁻¹³ m ² /N or more.

(Ultraviolet curable adhesive (UV adhesive))
A known UV adhesive can be used as the UV adhesive, and preferably contains at least one of a cationic polymerizable curable compound and a radically polymerizable curable compound. The UV adhesive can be, for example, a mixture of a radically polymerizable (meth)acrylic compound and a photoradical polymerization initiator, or a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator. For the UV adhesive, a mixture of a cationic polymerizable epoxy compound and a photoradical polymerizable (meth)acrylic compound, and a photocationic polymerization initiator and a photoradical polymerization initiator as an initiator can also be used.

(UV adhesive layer)
The UV adhesive layer 25 is a cured UV adhesive layer, and bonds the retardation layer 15 and the first protective film 11 together. As described above, since the retardation layer 15 is supported by the UV adhesive layer 25, the cured layer of the polymerizable liquid crystal compound contained in the retardation layer 15 can be prevented from being scratched or dented when the polarizing plate 1 is transported.

The thickness of the UV adhesive layer 25 in the polarizing plate 1 can be arbitrarily set.

(First water-based adhesive, second water-based adhesive)
Known water-based adhesives can be used for the first water-based adhesive and the second water-based adhesive (hereinafter, both may be collectively referred to as "water-based adhesives"), and the first water-based adhesive and the second water-based adhesive may have the same composition or different compositions. As the water-based adhesive, a water-based adhesive containing a PVA-based resin (hereinafter sometimes referred to as "PVA-based adhesive") is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100-5500, more preferably 1000-4500, from the viewpoint of adhesion. The average degree of saponification of the PVA-based resin is preferably about 85 mol % to 100 mol %, more preferably 90 mol % to 100 mol %, from the viewpoint of adhesiveness.

The PVA-based resin contained in the PVA-based adhesive preferably contains an acetoacetyl group. This is because the adhesiveness between the PVA-based resin layer constituting the polarizing element and the first protective film or the second protective film is excellent, and the durability is excellent. A PVA-based resin containing an acetoacetyl group can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of modification of the acetoacetyl group of the PVA-based resin containing the acetoacetyl group is typically 0.1 mol % or more, preferably about 0.1 mol % to 20 mol %.

The concentration of the PVA-based resin in the PVA-based adhesive is preferably 0.1% by weight to 15% by weight, more preferably 0.5% by weight to 10% by weight.

When the PVA-based resin contains an acetoacetyl group, the PVA-based adhesive preferably contains one or more of glyoxal, glyoxylate, and methylolmelamine as a cross-linking agent, preferably contains at least one of glyoxal and glyoxylate, and particularly preferably contains glyoxal.

The PVA-based adhesive may contain an organic solvent. In this case, since it is miscible with water, the organic solvent is preferably an alcohol, and among the alcohols, methanol or ethanol is preferable.

From the viewpoint of improving heat resistance, the PVA adhesive further includes urea compounds such as urea, urea derivatives, thiourea, and thiourea derivatives; reducing agents such as ascorbic acid, erythorbic acid, thiosulfuric acid, and sulfurous acid; dicarboxylic acids such as maleic acid and phthalic acid; ammonium compounds such as ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride; Phosphorus; blocked isocyanate compounds in which the isocyanate compounds are blocked with a blocking agent; nitroxy radicals such as N-oxyl compounds; compounds having nitroxide groups;

(First adhesive layer, second adhesive layer)
The first adhesive layer 21 can be formed by heating and drying the first water-based adhesive, etc., and bonds the polarizing element 10 and the composite protective film 30 together. The second adhesive layer 22 can be formed by heating and drying a second water-based adhesive, etc., and bonds the polarizing element 10 and the second protective film 12 together.

The thicknesses of the first adhesive layer 21 and the second adhesive layer 22 can be arbitrarily set, but are each independently preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, still more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

(Second protective film)
The second protective film is preferably an optically transparent resin film. For the second protective film, a film having the thickness and material described for the first protective film can be used. When the composite protective film containing the first protective film, the polarizing element, and the second protective film are laminated using a water-based adhesive, at least one of the first protective film and the second protective film is preferably a cellulose resin film or a polymer film containing a (meth)acrylic resin. The second protective film is preferably a cellulose acylate film.

The second protective film may have a surface functional layer such as a hard coat layer, an antireflection layer, an antisticking layer, an antiglare layer, and a diffusion layer on one side of the resin film. The surface functional layer is preferably provided on the side of the resin film opposite to the polarizing element side.

(Adhesive layer)
The pressure-sensitive adhesive layer is used for bonding a polarizing plate to an image display element or the like of a display device. The pressure-sensitive adhesive layer may consist of one layer or two or more layers, but preferably consists of one layer. The thickness of the adhesive layer is preferably 1-100 μm, more preferably 2-80 μm, even more preferably 2-50 μm, and particularly preferably 3-30 μm.

The adhesive layer is a layer formed using an adhesive composition. A pressure-sensitive adhesive composition exhibits adhesiveness when it is attached to an adherend, and is called a pressure-sensitive adhesive. The pressure-sensitive adhesive composition can contain (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, and polyvinyl ether resin as a main component (base polymer). Among them, a pressure-sensitive adhesive composition using a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is suitable. The adhesive composition may be active energy ray-curable or heat-curable.

As the (meth)acrylic resin as the base polymer used in the pressure-sensitive adhesive composition, for example, a polymer or copolymer containing one or more of (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate as a monomer is preferably used. Preferably, the base polymer is copolymerized with a polar monomer. Examples of polar monomers include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

The pressure-sensitive adhesive composition may contain only the above base polymer, but usually further contains a cross-linking agent. Examples of cross-linking agents include those that are divalent or higher metal ions and form carboxylic acid metal salts with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; polyepoxy compounds and polyols that form ester bonds with carboxyl groups; and polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

(Release film)
The release film is releasably provided on the adhesive layer 28 and covers and protects the surface of the adhesive layer 28 . The release film has a base film and a release treatment layer. The base film may be a resin film. The resin film can be formed, for example, from the resin material used for forming the above-described first protective film. The release treatment layer may be any known release treatment layer, and examples thereof include a layer formed by coating a base film with a release agent such as a fluorine compound or a silicone compound.

(Surface protection film)
A surface protective film (protective film) is provided so as to be peelable from the second protective film 12 . The surface protective film may contain a substrate film and an adhesive layer, or may be a self-adhesive film. The base film may be a resin film, and the base film can be formed from, for example, the resin material used to form the first protective film described above. As the surface protective film, a film having an adhesive layer provided on one side of a base film made of a polyester resin such as polyethylene terephthalate and polyethylene naphthalate is preferably used. Examples of the thermoplastic resin that constitutes the self-adhesive film include polypropylene-based resins and polyethylene-based resins.

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

<Fabrication of polarizing element>
A polyvinyl alcohol (PVA) resin film with a thickness of 30 μm was immersed in pure water at a temperature of 21.5° C. for 80 seconds (swelling treatment), and then the mass ratio of potassium iodide/boric acid/water was 2/2/100. Then, it was immersed in an aqueous solution of potassium iodide/boric acid/water in a mass ratio of 2.5/4/100 at a temperature of 63° C. for 76 seconds (first cross-linking step). Subsequently, it was immersed for 10 seconds in an aqueous solution having a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 at a temperature of 45° C. (second cross-linking step, metal ion treatment step). After that, it was washed by immersion in a washing bath (washing step) and dried at a temperature of 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on the PVA-based resin film. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times.

<Production of water-based adhesive>
50 g of a modified polyvinyl alcohol resin containing an acetoacetyl group (Mitsubishi Chemical Corporation: Gohsenex Z-410) was dissolved in 950 g of pure water, heated at a temperature of 90° C. for 2 hours, and then cooled to room temperature to obtain a PVA solution. This PVA solution, pure water, and methanol were blended so that the concentration of the polyvinyl alcohol resin was 3.0% by weight, the concentration of methanol was 35% by weight, and the concentration of urea was 0.5% by weight, to obtain a water-based adhesive that is a PVA-based adhesive.

[Example 1]
(Preparation of composite protective film with substrate layer)
A retardation film with a substrate layer was prepared in which a retardation layer containing a cured product layer of a polymerizable liquid crystal compound was formed on the substrate layer. The retardation layer had reverse wavelength dispersion.

A first protective film (“KC2CT1W” (a triacetyl cellulose (TAC) film with a thickness of 20 μm, manufactured by Konica Minolta, Inc.) was coated with an ultraviolet curing adhesive (UV adhesive) (“Adeka Arcles KR-75T”, manufactured by ADEKA Corporation) using a bar coater so that the thickness was 1.5 μm. The first protective film and the substrate layer-attached retardation film prepared above were laminated so that the retardation layer side was the bonding surface via the applied UV adhesive. Subsequently, from the first protective film side of this laminated structure, ultraviolet rays were irradiated so that the integrated amount of light (UVA) transmitted through the first protective film was 400 mJ/cm ² , and the UV adhesive was cured to form a UV adhesive layer, thereby obtaining a composite protective film with a base layer. The layer structure of the composite protective film with a base layer was first protective film/UV adhesive layer/retardation layer/base layer.

The light transmittance of the first protective film used above at a wavelength of 365 nm was measured using a UV-visible spectrophotometer "U-4100" manufactured by Hitachi High-Tech Science Co., Ltd. After measuring the transmittance of light with a wavelength of 365 nm at an arbitrary sample angle, the sample was further rotated 90° to measure the transmittance of light with a wavelength of 365 nm, and the average value thereof was calculated as the light transmittance at a wavelength of 365 nm. As a result, the light transmittance of the first protective film at a wavelength of 365 nm was 80% or more.

When the first protective film used above was irradiated with ultraviolet rays, it was found that ultraviolet rays with a wavelength range of 280 to 390 nm were sufficiently transmitted through the first protective film. From this, it is considered that the UV adhesive in the UV adhesive layer of the composite protective film with a substrate layer is sufficiently cured.

(Saponification treatment)
The composite protective film with the substrate layer prepared above and the second protective film (“TJ40UL” (cellulose acylate film with a thickness of 40 μm, manufactured by Fujifilm Corporation) were immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) maintained at a temperature of 55° C. for 2 minutes and washed with water. Each film was brought to a neutral state.Then, the water was removed by an air knife three times.After the water was removed, each film was held in a drying zone at a temperature of 70°C for 15 seconds and dried to obtain a saponified composite protective film with a base layer and a saponified second protective film.

(Preparation of polarizing plate (1) with substrate layer)
A saponified composite protective film with a base layer and a saponified second protective film were laminated on both sides of the polarizing element prepared above via the water-based adhesive prepared above. The composite protective film with a substrate layer was laminated on the polarizing element so that the first protective film side was the bonding surface. This laminated structure was dried by heating to form a first adhesive layer and a second adhesive layer between the composite film with the substrate layer and the polarizing element and between the polarizing element and the second protective film, respectively, to obtain a polarizing plate with the substrate layer (1). The layer structure of the base layer-attached polarizing plate (1) was second protective film/second adhesive layer/polarizing element/first adhesive layer/first protective film/UV adhesive layer/retardation layer/base layer.

(Preparation of polarizing plate)
A polarizing plate (1) was obtained by peeling the base material layer from the polarizing plate (1) with the base material layer. In the substrate layer-attached polarizing plate (1), the retardation layer was in close contact with the first protective film side, and the substrate layer was well peeled off to transfer the retardation layer to the first protective film side.

[Comparative Example 1]
(Saponification treatment)
The same procedure as in Example 1 was used to saponify the first protective film and the second protective film. The same film as the film used in Example 1 was used for the first protective film and the second protective film.

(Preparation of polarizing plate (2) with substrate layer)
A saponified first protective film and a saponified second protective film were laminated on both sides of the polarizing element prepared above via the water-based adhesive prepared above, respectively, and dried by heating to obtain a polarizing element with a protective film having a layer structure of second protective film/second adhesive layer/polarizing element/first adhesive layer/first protective film.

A UV adhesive was applied to the first protective film side of the protective film-attached polarizing element using a bar coater so as to have a thickness of 1.5 μm. The polarizing element with the protective film and the retardation film with the base layer were laminated such that the retardation layer side of the retardation film with the base layer was the bonding surface via the applied UV adhesive. Subsequently, from the second protective film side (polarizing element side with a protective film) of this laminated structure, ultraviolet rays were irradiated under the same conditions as in Example 1 (conditions where the UV intensity and irradiation time of the light source were the same) to obtain a polarizing plate with a base layer (2). The same adhesive and film as used in Example 1 were used as the UV adhesive and the retardation film with the substrate layer.

The layer structure of the substrate layer-attached polarizing plate (2) was the same as that of the substrate layer-attached polarizing plate (1), but the curing of the UV adhesive in the UV adhesive layer was considered to be insufficient for the following reasons. When the laminate of the second protective film and the polarizing element used above was irradiated with ultraviolet rays, almost no ultraviolet rays in the wavelength range of 280 to 390 nm were transmitted through this laminate. From this, it is considered that the UV adhesive layer of the substrate layer-attached polarizing plate (2) is insufficiently cured as compared to the UV adhesive layer of the substrate layer-attached polarizing plate (1).

When the substrate layer was peeled off from the polarizing plate with the substrate layer (2), the retardation layer was not adhered to the first protective film side, and the retardation layer was peeled off together with the substrate layer. Therefore, the retardation layer could not be transferred to the first protective film side, and a polarizing plate could not be obtained.

[Comparative Example 2]
A polarizing plate with a base layer (3) was obtained in the same manner as in Comparative Example 1, except that the ultraviolet rays were irradiated from the base layer side (the side of the retardation film with the base layer) instead of irradiating the ultraviolet rays from the second protective film side.

Although the layer structure of polarizing plate with base layer (3) was the same as that of polarizing plate with base layer (1), the curing of the UV adhesive in the UV adhesive layer is considered to be insufficient for the following reasons. When the retardation film with the base layer used above was irradiated with ultraviolet rays, almost no ultraviolet rays in the wavelength range of 280 to 390 nm were transmitted through the retardation film with the base layer. From this, it is considered that the UV adhesive layer of the substrate layer-attached polarizing plate (3) is insufficiently cured as compared to the UV adhesive layer of the substrate layer-attached polarizing plate (1).

A polarizing plate (3) was obtained by peeling the base layer from the base layer-attached polarizing plate (3). The substrate layer was peeled off from the polarizing plate with the substrate layer (3), and the retardation layer could be transferred to the first protective film side, but the retardation layer was not sufficiently adhered to the first protective film side.

[Scratch resistance test]
The second protective film side of each of the substrate layer-attached polarizing plate (1) obtained in Example 1 and the substrate layer-attached polarizing plate (3) obtained in Comparative Example 2 was attached to a glass plate via an acrylic pressure-sensitive adhesive layer, and then the substrate layer was peeled off. The retardation layer exposed by peeling off the substrate layer was subjected to a scratch resistance test using a friction wear tester "Tribogear" (manufactured by Shinto Kagaku Co., Ltd.). The scratch resistance test was performed by setting steel wool #0000 to a contact terminal having a diameter of 25 mm, setting a load of 100 g and a moving speed of 6000 mm/min, and reciprocating a distance of 60 mm 10 times. The state of the surface of the retardation layer after the scratch resistance test was visually confirmed to confirm the presence or absence of deep scratches. Table 1 shows the results. In the polarizing plate (2) with the substrate layer obtained in Comparative Example 1, the retardation layer was peeled off together with the substrate layer, so the scratch resistance test could not be performed.

1 polarizing plate, 2 polarizing plate with base layer, 10 polarizing element, 11 first protective film, 12 second protective film, 15 retardation layer, 17 base layer, 19 retardation film with base layer, 21 first adhesive layer, 22 second adhesive layer, 25 UV adhesive layer, 28 adhesive layer, 30 composite protective film, 31 composite protective film with base layer.

Claims (8)

A method for manufacturing a polarizing plate comprising a polarizing element and a composite protective film,
The composite protective film has, in order from the polarizing element side, a first protective film and a retardation layer containing a cured product layer of a polymerizable liquid crystal compound,
The manufacturing method is
A step (1) of obtaining a composite protective film with a substrate layer by laminating the retardation layer and the first protective film formed on the substrate layer using an ultraviolet curable adhesive and irradiating the ultraviolet curable adhesive with ultraviolet rays;
a step (2) of obtaining a polarizing plate with a base layer by bonding the first protective film side of the composite protective film with a base layer and the polarizing element using a first water-based adhesive;
A method for producing a polarizing plate, comprising the step (3) of peeling the base layer from the base layer-attached polarizing plate. 2. The method for producing a polarizing plate according to claim 1, further comprising a step (4) of forming a pressure-sensitive adhesive layer on the exposed surface side by peeling off the base material layer. 3. The method for producing a polarizing plate according to claim 1, wherein the first protective film has a light transmittance of 80% or more at a wavelength of 365 nm. 4. The method for manufacturing a polarizing plate according to claim 1, wherein the first water-based adhesive contains a polyvinyl alcohol-based resin. The method for producing a polarizing plate according to any one of claims 1 to 4, wherein the step (2) further comprises a step of bonding a second protective film to the side of the polarizing element opposite to the composite protective film side. 6. The method of manufacturing a polarizing plate according to claim 5, wherein the polarizing element and the second protective film are bonded using a second water-based adhesive. 7. The method of manufacturing a polarizing plate according to claim 6, wherein said second water-based adhesive contains a polyvinyl alcohol-based resin. The method for producing a polarizing plate according to any one of claims 5 to 7, wherein the step (2) includes bonding the polarizing element and the second protective film while bonding the composite protective film with the base layer and the polarizing element.

Images