JP7358739B2 - Polarizing plate and polarizing plate manufacturing method - Google Patents

Description

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

Liquid crystal display devices and organic electroluminescence (EL) display devices are used in various display devices, taking advantage of their characteristics such as low power consumption, low voltage operation, light weight, and thinness. A liquid crystal panel constituting a liquid crystal display device has a structure in which a pair of linearly polarizing plates are laminated on both sides of a liquid crystal cell. As a linear polarizing plate, one having a structure in which a polarizer and a protective film are laminated via an adhesive is usually used. The organic EL display device includes a circularly polarizing plate placed on the viewing side of the organic EL display element. As a circularly polarizing plate, one having a structure in which a polarizer and a retardation film are laminated via an adhesive layer is usually used.

With the development of linearly polarizing plates and circularly polarizing plates (hereinafter collectively referred to as polarizing plates) in mobile devices, there is an increasing demand for thinner polarizers, protective films, etc. that constitute polarizing plates. When the thickness of a polarizer, protective film, etc. becomes thin, the adhesive shrinks when it is cured or dried, resulting in wavy-like unevenness on the surface of the protective film. When a polarizing plate is laminated onto an image display element, such as a liquid crystal cell or an organic EL display element, such unevenness leads to poor surface uniformity, especially on the viewing side surface, leading to appearance defects such as a lack of luxury. .

Patent Document 1 discloses a polarizing plate in which a protective film is laminated on the viewing side surface of a polarizer via an adhesive layer. In the polarizing plate described in Patent Document 1, the shrinkage force of the adhesive is reduced by making the adhesive layer relatively thinner than the total thickness of the polarizer and the protective film. By doing so, the unevenness that occurs on the viewing side surface of the protective film can be reduced, but there is still a large room for improvement.

Further, when the polarizing plate includes a retardation film, the irregularities are emphasized and visually recognized more than the physical irregularities on the surface, so that defects in appearance are easily recognized.

Japanese Patent Application Publication No. 2015-114538

An object of the present invention is to improve the appearance of a polarizing plate by making it difficult to visually recognize the unevenness that occurs on the viewing side surface of the polarizing plate even when the polarizing plate includes a retardation film.

[1] A polarizer and a retardation film are laminated via an adhesive layer,
When the one-dimensional power spectrum with respect to the period f (μm) of surface irregularities is H ² (f), the surface of the retardation film opposite to the polarizer satisfies the following formula (1),
The retardation film is a polarizing plate that is a film laminated on the image display element side.
H ² (425)/H ² (212)≦10 (1)

[2] The retardation film includes a liquid crystal layer having a thickness of 0.5 to 5.0 μm and a base film having a thickness of 10 to 50 μm, and has an in-plane retardation value of 100 to 150 nm at a wavelength of 590 nm [ 1].

[3] The polarizing plate according to [1] or [2], wherein the adhesive layer is a cured layer of an active energy ray-curable adhesive.

[4] A step of laminating process paper on the retardation film to obtain a laminated film,
Peeling the processing paper from the laminated film to obtain a retardation film;
A step of laminating a polarizer on the retardation film via an adhesive to obtain a polarizing plate,
Manufacturing a polarizing plate in which the surface of the process paper to which the retardation film is bonded satisfies the following formula (2), where the one-dimensional power spectrum with respect to the period f (μm) of surface irregularities is H ² (f). Method.
H ² (425)/H ² (212)≦10 (2)

According to the present invention, even when the polarizing plate includes a retardation film, it is possible to make the unevenness that occurs on the viewing side surface of the polarizing plate difficult to see, thereby improving the appearance of the polarizing plate.

FIG. 1 is a cross-sectional view showing an example of a polarizing plate of the present invention. FIG. 1 is a cross-sectional view showing an example of a polarizing plate of the present invention.

The polarizing plate and the method for manufacturing the polarizing plate of the present invention will be described with reference to the drawings as appropriate.

In one embodiment, the polarizing plate of the present invention includes the member shown in FIG. In the polarizing plate 100 shown in FIG. 1, a polarizer 2 and a retardation film 20 are laminated with an adhesive layer 10 interposed therebetween. In FIG. 1, a retardation film 20 includes a base film 3 and a liquid crystal layer 5.

The polarizing plate of the present invention may further include a protective film, an adhesive layer, and the like. In one embodiment, the polarizing plate of the present invention includes the member shown in FIG. In the polarizing plate 101 shown in FIG. 2, a retardation film 20 is laminated on one surface of the polarizer 2 with an adhesive layer 10 interposed therebetween, and a protective film 4 is laminated on the other surface of the polarizer 2 with an adhesive layer 11 interposed therebetween. are laminated, and an adhesive layer 6 is laminated on the retardation film 20. The adhesive layer 6 may be, for example, an adhesive layer for bonding to an image display element such as a liquid crystal cell.

In the polarizing plate of the present invention, when the one-dimensional power spectrum with respect to the period f (μm) of surface irregularities is H ² (f), the surface of the retardation film opposite to the polarizer is expressed by the following formula (1 ) is satisfied. The left side of the following formula (1) is preferably 6 or less, more preferably 4 or less. The lower limit value is not particularly limited, but can be 2 or more.
H ² (425)/H ² (212)≦10 (1)
H ² (425) represents a one-dimensional power spectrum at a period of 425 μm, and H ² (212) represents a one-dimensional power spectrum at a period of 212 μm, which can be measured by the method described in the Examples below. .

When the surface unevenness of the retardation film satisfies the above formula (1), it is possible to make it difficult to visually recognize the unevenness occurring on the viewing side surface of the polarizing plate. The viewing side surface of the polarizing plate is, for example, the surface of the polarizer 2 in the polarizing plate 100 shown in FIG. 1, and the surface of the protective film 4 in the polarizing plate 101 shown in FIG. 2, for example. In other words, by making sure that the surface shape of the retardation film placed on the side closer to the image display element with respect to the polarizer satisfies formula (1), the unevenness on the surface of the polarizer on the side far from the image display element can be visually recognized. It is possible to make it difficult to clean and improve the appearance.

It is estimated as follows how the above formula (1) contributes to making it difficult to visually recognize the unevenness on the viewing side surface, but this does not limit the present invention in any way. A one-dimensional power spectrum with a period of 212 μm or a period of 425 μm in the surface unevenness represents the magnitude of waviness at a period of around 200 μm or around 400 μm on the surface of the retardation film, respectively. As will be described later, during the manufacturing process of the retardation film, process paper is sometimes pasted to the retardation film in order to prevent scratches and to prevent blocking between the retardation films. As a result, the surface shape of the processing paper may be transferred to the retardation film. It has become clear that the ease with which a surface shape can be transferred depends on the periodicity of the surface shape. Specifically, the inventor's studies have revealed that a surface shape with a period of about 400 μm is easily transferred, and a surface shape with a period of 300 μm or less is difficult to be transferred. That is, simply reducing the physical irregularities on the surface of the retardation film by reducing the arithmetic mean waviness Wa to a predetermined value or less is insufficient to make the irregularities on the viewing side surface difficult to visually recognize. It is considered that by setting the magnitude of the undulations with a period of around 400 μm to a predetermined range with respect to the undulations with a period of 200 μm, it is possible to make it difficult to visually recognize the irregularities on the viewing side surface.

The surface of the retardation film opposite to the polarizer satisfies the above formula (1). The arithmetic mean roughness Ra (JIS B 0601-2001) of this surface is usually 0 nm or more, preferably 10 nm or more, usually 1000 nm or less, preferably 500 nm or less, and the kurtosis Pku (JIS B 0601-2001) is usually 0 or more, It is preferably 1.0 or more, usually 10 or less, preferably 5 or less, and the skewness Psk (JIS B 0601-2001) is usually -5 to +5, preferably -1 to +1.

Each member constituting the polarizing plate of the present invention will be explained below.

(polarizer)
The polarizer used in the present invention is usually produced by a process of uniaxially stretching a polyvinyl alcohol resin film, a process of dyeing the polyvinyl alcohol resin film with a dichroic dye to adsorb the dichroic dye, and a process of adsorbing the dichroic dye. It is manufactured through the steps of treating a polyvinyl alcohol-based resin film on which is adsorbed with a boric acid aqueous solution, and washing with water after the treatment with the boric acid aqueous solution.

As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

The degree of saponification of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. This polyvinyl alcohol resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, etc. modified with aldehydes can also be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

A film made of polyvinyl alcohol resin is used as the original film of the polarizer. The polyvinyl alcohol resin can be formed into a film by a known method. The thickness of the polyvinyl alcohol base film is preferably about 5 to 35 μm, more preferably 5 to 20 μm, considering that the thickness of the obtained polarizer is 15 μm or less. If the thickness of the raw film is 35 μm or more, it is necessary to increase the stretching ratio when producing a polarizer, and the resulting polarizer tends to have large dimensional shrinkage.
On the other hand, if the film thickness of the raw film is 5 μm or less, handling properties during stretching are reduced, and problems such as cutting tend to occur during manufacturing.

The uniaxial stretching of the polyvinyl alcohol resin film can be performed before, simultaneously with, or after dyeing with the dichroic dye. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before or during boric acid treatment. Further, uniaxial stretching may be performed in these plural steps.

In the uniaxial stretching, it may be uniaxially stretched between rolls having different circumferential speeds, or it may be uniaxially stretched using hot rolls. Further, the uniaxial stretching may be dry stretching in which the film is stretched in the atmosphere, or wet stretching in which the polyvinyl alcohol resin film is stretched in a swollen state using a solvent. The stretching ratio is usually about 3 to 8 times.

As a method for dyeing a polyvinyl alcohol resin film with a dichroic dye, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing a dichroic dye is employed. Specifically, iodine and dichroic dyes are used as the dichroic dye. In addition, it is preferable that the polyvinyl alcohol resin film is subjected to a immersion treatment in water before the dyeing treatment.

When using iodine as a dichroic dye, a method is usually employed in which a polyvinyl alcohol resin film is immersed in an aqueous solution containing iodine and potassium iodide for dyeing. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. Further, the content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is usually about 20 to 40°C.
The immersion time (staining time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, when using a dichroic dye as the dichroic dye, a method of dyeing a polyvinyl alcohol resin film by immersing it in an aqueous solution containing a water-soluble dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1×10 ⁻⁴ to 10 parts by weight, preferably about 1×10 ⁻³ to 1 part by weight, per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dichroic dye aqueous solution used for dyeing is usually about 20 to 80°C. The immersion time (staining time) in this aqueous solution is usually about 10 to 1,800 seconds.

The boric acid treatment after dyeing with a dichroic dye can usually be carried out by immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid.

The amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight, per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50°C or higher, preferably 50 to 85°C, more preferably 60 to 80°C.

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

After washing with water, a drying process is performed to obtain a polarizer. The drying process can be performed using a hot air dryer or a far-infrared heater. The temperature of the drying treatment is usually about 30 to 100°C, preferably 50 to 80°C. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

The drying process reduces the moisture content of the polarizer to a practical level. Its moisture content is usually 5 to 20% by weight, preferably 8 to 15% by weight. When the moisture content is less than 5% by weight, the flexibility of the polarizer is lost and the polarizer may be damaged or broken after drying.
Furthermore, if the moisture content exceeds 20% by weight, the polarizer may have poor thermal stability.

Further, the stretching, dyeing, boric acid treatment, water washing step, and drying step of the polyvinyl alcohol resin film in the polarizer manufacturing process may be performed according to the method described in JP-A No. 2012-159778, for example. . In the method described in this document, a polyvinyl alcohol resin layer that becomes a polarizer is formed by coating a base film with a polyvinyl alcohol resin.

The effect of the present invention is remarkable when the thickness of the polarizer is thinner (when there is no stiffness). For example, the thickness of the polarizer may be 15 μm or less, or 10 μm or less. From the viewpoint of improving optical properties, the thickness of the polarizer is, for example, 3 μm or more.

(Protective film)
The protective film is made of a resin film, and can be made of a transparent resin film. In particular, it is preferable to use a material that is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, etc. In this specification, a transparent resin film refers to a resin film having a single transmittance of 80% or more in the visible light region.

The resin that forms the protective film is not particularly limited, but examples include methyl methacrylate resin, polyolefin resin, cyclic olefin resin, polyvinyl chloride resin, cellulose resin, styrene resin, and acrylonitrile.・Butadiene/styrene resin, acrylonitrile/styrene resin, polyvinyl acetate resin, polyvinylidene chloride resin, polyamide resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polybutylene tephthalate resin, Examples include films made of polyethylene terephthalate resins, polysulfone resins, polyethersulfone resins, polyarylate resins, polyamideimide resins, polyimide resins, and the like.
These resin films include films made from raw material resins, uniaxially stretched films obtained by horizontally stretching after film formation, and biaxially stretched films obtained by longitudinally stretching and then laterally stretching after film formation. be able to.

These resins can be used alone or in combination of two or more. These resins can also be used after undergoing any appropriate polymer modification, such as copolymerization, crosslinking, molecular terminal modification, stereoregularity control, and reaction between different polymers. Examples include denaturation such as mixing, including cases involving .

Among these, it is preferable to use methyl methacrylate resin, polyethylene terephthalate resin, polyolefin resin, or cellulose resin as the material for the protective film. The polyolefin resin mentioned here includes a chain polyolefin resin and a cyclic polyolefin resin.

Films used as protective films are easily available commercially, and methyl methacrylate resin films are available under the trade names of Sumipex (manufactured by Sumitomo Chemical Co., Ltd.), Acrylite (registered trademark), Acryprene (registered trademark) (manufactured by Mitsubishi Rayon Co., Ltd.), Delaglas (registered trademark) (manufactured by Asahi Kasei Corporation), Paraglass (registered trademark), Comoglass (registered trademark) (manufactured by Kuraray Co., Ltd.), and Acriview (registered trademark) (manufactured by Kuraray Co., Ltd.). (registered trademark) (manufactured by Nippon Shokubai Co., Ltd.). Examples of polyolefin resin films include Zeonor (registered trademark) (Nippon Zeon Co., Ltd.), Arton (registered trademark) (JSR Co., Ltd.) and the like, each with its trade name. Examples of polyethylene terephthalate-based resin films include Novaclear (registered trademark) (manufactured by Mitsubishi Chemical Corporation) and Teijin A-PET sheet (manufactured by Teijin Kasei Corporation) under their respective trade names. For polypropylene resin films, the product names are FILMAX CPP film (manufactured by FILMAX), Suntox (registered trademark) (manufactured by Suntox Co., Ltd.), Torcello (registered trademark) (manufactured by Tocello Co., Ltd.), and Toyobo Pyrene film. (registered trademark) (manufactured by Toyobo Co., Ltd.), Torefane (registered trademark) (manufactured by Toray Film Kako Co., Ltd.), Nihon Polyace (manufactured by Nihon Polyace Co., Ltd.), and Taiko (registered trademark) FC (Futamura Chemical Co., Ltd.) (manufactured by), etc. Further, as for cellulose-based resin films, the respective trade names include Fujitac (registered trademark) TD (manufactured by Fuji Film Corporation), KC2UA, and Konica Minolta TAC film KC (manufactured by Konica Minolta Corporation).

Moreover, the protective film can also contain additives as necessary. Examples of additives include lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light resistance agents, and impact resistance modifiers.

The effect of the present invention is remarkable when the thickness of the protective film is thinner (when there is no stiffness). For example, the thickness of the protective film may be 1 to 50 μm or 10 to 40 μm. However, it may be 10 to 35 μm.

The protective film may be subjected to saponification treatment, corona treatment, plasma treatment, etc. prior to lamination with the polarizer. The protective film can further be provided with functional layers such as a conductive layer, a hard coat layer, an antiglare layer, and a low reflection layer.

(Retardation film)
The retardation film can be formed, for example, from the resins exemplified as the materials for the protective film, and among them, cyclic olefin resins and styrene resins are preferred. The retardation film may be formed from a single layer or from a plurality of layers. Examples of retardation films having multiple layers include a resin film (base film) exemplified as the material for the protective film, a liquid crystal layer formed by polymerizing a liquid crystal compound, and a liquid crystal layer having multiple (for example, two layers) liquid crystal layers. It may also include. The layer having a retardation can be a resin film and/or a liquid crystal layer.

When the in-plane retardation value at the wavelength λ (nm) is Re (λ), and the retardation value in the thickness direction is Rth (λ), in one embodiment, the in-plane retardation value Re (590 ) can be set to, for example, 100 to 150 nm, and the retardation value Rth (590) in the thickness direction can be set, for example, to -200 to +200 nm.

The in-plane retardation value Re and the thickness direction retardation value Rth are defined as nx, the refractive index in the in-plane slow axis direction, and ny, the refractive index in the in-plane fast axis direction (direction orthogonal to the in-plane slow axis direction). , where nz is the refractive index in the thickness direction and d is the thickness of the retardation film, defined by the following formulas (3) and (4).

Re=(nx-ny)×d (3)
Rth=[{(nx+ny)/2}-nz]×d (4)

The liquid crystal layer included in the retardation layer can be a λ/4 plate, a λ/2 plate, or a positive C layer.
When the retardation layer includes a plurality of liquid crystal layers, a combination of a quarter-wave plate and a half-wave plate, and a combination of a quarter-wave plate and a positive C plate are preferred. The λ/4 plate is a layer whose in-plane retardation value Re (550) at a wavelength of 550 nm satisfies the relationship 100 nm≦Re (550)≦200 nm. The λ/4 plate may exhibit reverse wavelength dispersion satisfying Re(450)<Re(550)<Re(650). The λ/2 plate is a layer that satisfies Re(550) of 210 nm≦Re(550)≦300 nm. The positive C layer satisfies the relationship nz>nx≧ny (the difference between the size of nx and the size of ny is, for example, within ±1%), and has a retardation in the thickness direction at the wavelength λ [nm]. It is preferable that the value Rth(λ) satisfies the relationship -300nm≦Rth(550)≦-20nm.

When the retardation layer includes a liquid crystal layer, poor appearance is more easily recognized than when the retardation layer is composed of only a resin film. This is because the liquid crystal layer is thinner than the resin film, so the change in retardation per unit thickness becomes large.

The liquid crystal layer included in the retardation layer is a layer including a layer obtained by polymerizing and hardening a liquid crystal compound. Although the type of liquid crystal compound is not particularly limited, it can be classified into a rod-like type (rod-like liquid crystal compound) and a disc-like type (disc-like liquid crystal compound, discotic liquid crystal compound) based on its shape. Furthermore, there are low-molecular type and high-molecular type, respectively. Note that polymers generally refer to those having a degree of polymerization of 100 or more (Polymer Physics/Phase Transition Dynamics, Masao Doi, p. 2, Iwanami Shoten, 1992). In this embodiment, any liquid crystal compound can be used.
Furthermore, two or more kinds of rod-like liquid crystal compounds, two or more kinds of discotic liquid crystal compounds, or a mixture of a rod-like liquid crystal compound and a discotic liquid crystal compound may be used.

As the rod-shaped liquid crystal compound, for example, those described in claim 1 of Japanese Patent Publication No. 11-513019 or paragraphs [0026] to [0098] of JP-A-2005-289980 are preferably used. I can do it. As the discotic liquid crystal compound, for example, those described in paragraphs [0020] to [0067] of JP-A No. 2007-108732 or paragraphs [0013] to [0108] of JP-A No. 2010-244038 are preferable. It can be used for.

The liquid crystal layer is more preferably formed using a liquid crystal compound (a rod-like liquid crystal compound or a discotic liquid crystal compound) having a polymerizable group. Thereby, temperature changes and humidity changes in optical characteristics can be reduced.

The liquid crystal compound may be a mixture of two or more types. In that case, it is preferable that at least one has two or more polymerizable groups. That is, the liquid crystal layer is preferably a layer in which a rod-like liquid crystal compound having a polymerizable group or a discotic liquid crystal compound having a polymerizable group is fixed by polymerization. In this case, it is no longer necessary to exhibit liquid crystallinity after forming a layer.

The type of polymerizable group contained in the rod-like liquid crystal compound or the disk-like liquid crystal compound is not particularly limited, and for example, a functional group capable of an addition polymerization reaction such as a polymerizable ethylenically unsaturated group or a ring polymerizable group. is preferred. More specifically, examples include (meth)acryloyl group, vinyl group, styryl group, and allyl group. Among these, a (meth)acryloyl group is preferred. Note that the (meth)acryloyl group is a concept that includes both a methacryloyl group and an acryloyl group.

The method for forming the liquid crystal layer is not particularly limited, and known methods may be used. For example, a coating film is formed by applying an optically anisotropic layer-forming composition (hereinafter simply referred to as "composition") containing a liquid crystal compound having a polymerizable group to a resin film (base film), A retardation layer can be manufactured by subjecting the obtained coating film to a curing treatment (irradiation with ultraviolet rays (light irradiation treatment) or heat treatment). The produced retardation layer can be transferred, for example, onto a polarizer, onto a protective film, or onto another resin film (base film).

The composition can be applied by known methods such as wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, and die coating.

The composition may contain components other than the above-mentioned liquid crystal compound. For example, the composition may include a polymerization initiator. The polymerization initiator used is selected from, for example, a thermal polymerization initiator or a photopolymerization initiator depending on the type of polymerization reaction. Examples of the photopolymerization initiator include α-carbonyl compounds, acyloin ethers, α-hydrocarbon-substituted aromatic acyloin compounds, polynuclear quinone compounds, and combinations of triarylimidazole dimer and p-aminophenyl ketone. The amount of the polymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the total solid content of the composition.

Further, the composition may contain a polymerizable monomer from the viewpoint of uniformity of the coating film and strength of the film. Examples of the polymerizable monomer include radically polymerizable or cationically polymerizable compounds. Among these, polyfunctional radically polymerizable monomers are preferred.

The polymerizable monomer is preferably one that is copolymerizable with the above-mentioned liquid crystal compound containing a polymerizable group. Specific examples of polymerizable monomers include those described in paragraphs [0018] to [0020] of JP-A No. 2002-296423. The amount of the polymerizable monomer used is preferably 1 to 50% by weight, more preferably 2 to 30% by weight, based on the total weight of the liquid crystal compound.

Further, the composition may contain a surfactant from the viewpoint of uniformity of the coating film and strength of the film. Examples of the surfactant include conventionally known compounds. Among these, fluorine compounds are particularly preferred.

Further, the composition may contain a solvent, and organic solvents are preferably used. Examples of organic solvents include amides (e.g., N,N-dimethylformamide), sulfoxides (e.g., dimethyl sulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene, hexane), alkyl halides (e.g. , chloroform, dichloromethane), esters (eg, methyl acetate, ethyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), and ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane).
Among them, alkyl halides and ketones are preferred. Furthermore, two or more types of organic solvents may be used in combination.

The composition also includes a vertical alignment promoter such as a vertical alignment agent on the polarizer interface side and a vertical alignment agent on the air interface side, and a horizontal alignment promoter such as a horizontal alignment agent on the polarizer interface side and a horizontal alignment agent on the air interface side. Various alignment agents such as these may be included. Furthermore, the composition may contain adhesion improvers, plasticizers, polymers, etc. in addition to the above components.

The liquid crystal layer may include an alignment film having a function of defining the alignment direction of the liquid crystal compound. The alignment film generally has a polymer as its main component. Polymer materials for alignment films are described in many documents, and many commercially available products are available.

Note that the alignment film is usually subjected to a known alignment treatment. Examples include rubbing treatment, photo-alignment treatment using polarized light, etc., but photo-alignment treatment is preferable from the viewpoint of arithmetic mean waviness of the alignment film.

The effect of the present invention is remarkable when the thickness of the retardation film is thinner (when there is no stiffness), and the thickness of the retardation film may be, for example, 60 μm or less, or 40 μm or less. . The thickness of the retardation film is usually 5 μm or more. Further, when the retardation film includes a base film and a liquid crystal layer, the thickness of the base film is preferably 10 to 50 μm, more preferably 10 to 30 μm, and the thickness of the liquid crystal layer is 0.5 μm. The thickness is preferably 5 to 5.0 μm.

Further, the elastic modulus of the retardation film at 23°C may be 5000 MPa or less, 3000 MPa or less, and usually 2000 MPa or more. The elastic modulus can be measured in accordance with JIS K 7161. When there is anisotropy in the elastic modulus in the MD direction and the TD direction, the elastic modulus can be the average of both in this specification.

Even if the retardation film has a thickness and an elastic modulus within such a range, according to the present invention, by satisfying formula (1), unevenness on the viewing side surface can be made difficult to see.

In addition, from the viewpoint of improving the appearance of the polarizing plate, the surface of the retardation film opposite to the polarizer side preferably has an arithmetic mean waviness Wa of 50 nm or less, and preferably 40 nm or less. The thickness is more preferably 30 nm or less. The arithmetic mean waviness Wa of the surface of the retardation film opposite to the polarizer side is usually 10 nm or more.

(Adhesive layer)
As the adhesive forming the adhesive layer, an active energy ray-curable adhesive or a water-based adhesive can be used. That is, the adhesive layer is a cured layer of adhesive.

As mentioned above, one of the causes of unevenness on the surface of a polarizing plate is curing shrinkage when the adhesive is cured or dried. When using an active energy ray-curable adhesive that cures the adhesive in a short period of time by light irradiation, the shrinkage force (per unit time) is generally determined by the shrinkage force (per unit time) after drying the solvent (e.g., water) by heating. It is larger than water-based adhesives, which take a relatively long time to bond with curing as necessary. Therefore, in the present invention, when the adhesive layer for laminating the retardation film is formed from an active energy ray-curable adhesive, it can be particularly suitably applied, and the resulting unevenness suppressing effect is high.

When a protective film and a retardation film are arranged on both sides of a polarizer as in the polarizing plate 101 shown in FIG. 2, the adhesive for laminating the protective film and the adhesive for laminating the retardation film are as follows: They may be the same or different. For the same reason as above, both the adhesive for laminating the protective film and the adhesive for forming the adhesive layer are preferably active energy ray-curable adhesives.

Active energy ray-curable adhesives refer to adhesives that cure by irradiation with active energy rays such as electron beams and ultraviolet rays, such as those containing polymerizable compounds and photopolymerization initiators, and photoreactive resins. Examples include those containing a binder resin and a photoreactive crosslinking agent. Examples of the polymerizable compound include photocurable epoxy compounds; photocurable vinyl compounds such as photocurable acrylic compounds; and photocurable urethane compounds. Examples of the photopolymerization initiator include cationic photopolymerization initiators (for example, when using a photocurable epoxy compound) and radical photopolymerization initiators (for example, when using a photocurable acrylic compound). .

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

Polyvinyl alcohol-based resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as vinyl alcohol homopolymers obtained by saponifying vinyl acetate and other monomers that can be copolymerized with vinyl acetate. A polyvinyl alcohol copolymer obtained by saponifying a polymer, or a modified polyvinyl alcohol copolymer obtained by partially modifying the hydroxyl groups thereof can be used. The water-based adhesive can contain additives such as polyhydric aldehydes, water-soluble epoxy compounds, melamine compounds, zirconia compounds, zinc compounds, and the like.

The thickness of the adhesive layer is, for example, 5 μm or less, preferably 2 μm or less, and 1 μm or less, from the viewpoint of reducing shrinkage when curing or drying the adhesive and further reducing unevenness of the polarizing plate. It may be. Further, from the viewpoint of developing sufficient adhesive strength, the thickness of the adhesive layer is usually 0.01 μm or more.

The adhesive may contain additives. Examples of additives include ion trapping agents, antioxidants, chain transfer agents, sensitizers, tackifiers, thermoplastic resins, fillers, fluidity regulators, plasticizers, antifoaming agents, and the like.

(Adhesive layer)
An adhesive layer can be laminated on the surface of the polarizing plate. A polarizing plate can be bonded to an image display element such as a liquid crystal cell via the adhesive layer. In FIG. 2, the adhesive layer 6 corresponds to this. The thickness of the adhesive layer formed from the adhesive is preferably 5 to 25 μm. More preferably, it is 10 to 25 μm.

Examples of the adhesive forming the adhesive layer include acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy type, fluorine type, natural rubber, Those having a base polymer made of a rubber-based polymer such as synthetic rubber can be appropriately selected and used. The adhesive is particularly preferably one that has excellent optical transparency, exhibits appropriate adhesive properties such as wettability, cohesiveness, and adhesiveness, and is excellent in weather resistance, heat resistance, and the like.

The adhesive may also contain various other additives. Examples of additives include silane coupling agents and antistatic agents.

Hereinafter, a method for manufacturing a polarizing plate of the present invention will be explained. The polarizing plate of the present invention can be manufactured, for example, by a method including the following steps.

Step (1): After forming an alignment film on a base film, a liquid crystal compound is applied onto the alignment film and polymerized to form a liquid crystal layer to obtain a retardation film.
Step (2): A step of laminating a process paper on the retardation film to obtain a laminated film.
Step (3): Step of peeling off the processing paper from the laminated film to obtain a retardation film.
Step (4): A step of laminating a polarizer (or a polarizer with a protective film) onto a retardation film via an adhesive to obtain a polarizing plate.

(Step (1))
Step (1) is a step of manufacturing a retardation film. When the retardation film includes a base film and a liquid crystal layer, as described above, an alignment film for aligning a liquid crystal compound is first formed on the base film. Examples of the alignment film include an alignment film containing an alignment polymer, a photo-alignment film, and a groove alignment film in which a concavo-convex pattern or a plurality of grooves are formed on the surface for alignment, and can be formed by a conventionally known method.

Next, a composition containing a liquid crystal compound is applied onto the alignment film, and after drying the solvent if necessary, the liquid crystal compound is polymerized. The liquid crystal compound can be polymerized by a known method of polymerizing a compound having a polymerizable functional group. Specific examples include thermal polymerization and photopolymerization, with photopolymerization being preferred from the viewpoint of ease of polymerization. Photopolymerization can be performed by irradiating the liquid crystal compound with active energy rays such as ultraviolet rays. The active energy rays may be irradiated from the base film side, from the liquid crystal compound side, or from both the base film side and the liquid crystal compound side.

(Step (2))
Step (2) is a step of laminating a process paper on the retardation film to obtain a laminated film. Laminating process paper on top of the retardation film makes it easier to handle when storing and transporting the retardation film, prevents the retardation films from blocking each other, and prevents dust from adhering to the retardation film. It is possible to prevent defects from occurring. From this point of view, it is preferable that the process paper be laminated on the liquid crystal layer in the retardation film.

The process paper in step (2) may be formed from a single layer or from a plurality of layers. Although the paper may or may not include an adhesive layer, a process paper having a self-adhesive layer is preferable because defects such as adhesive residue can be reduced. Examples of the material for forming the process paper include resins similar to those for forming the protective film, and among them, polyolefin resins and polyethylene terephthalate resins are preferred.

As the process paper, any commercially available paper can be used. An example of a commercially available product having a base film of polyethylene terephthalate resin is "Cosmoshine (registered trademark) A4100" manufactured by Toyobo Co., Ltd. Examples of commercial products having a base film of polyethylene resin include "Force Field (registered trademark) 1035" manufactured by Tredegar Film Products Corporation and "Tretec (registered trademark)" manufactured by Toray Film Kako Co., Ltd.

In order to achieve a surface shape that satisfies the above formula (1), the surface shape of the processing paper used in step (2) is particularly important, and the surface of the processing paper on which the retardation film is laminated has an uneven surface. It is preferable that the following formula (2) is satisfied when the one-dimensional power spectrum with respect to the period f (μm) is H ² (f). The power spectrum can be measured by the method described in Examples below. The lower limit value of H ² (425)/H ² (212) is not particularly limited, but can be 2 or more.
H ² (425)/H ² (212)≦10 (2)

The arithmetic mean roughness Ra (JIS B 0601-2001) of the surface of the process paper is usually 0 nm or more, preferably 10 nm or more, usually 500 nm or less, preferably 200 nm or less, and the kurtosis Pku (JIS B 0601-2001) is usually 0. The above is preferably 1.0 or more, usually 10 or less, preferably 5 or less, and the skewness Psk (JIS B 0601-2001) is usually -5 to +5, preferably -1 to +1.

By laminating a process paper with such a surface shape on a retardation film, a desired surface shape that satisfies formula (1) can be transferred to the retardation film, and the appearance of the viewing side surface of the polarizing plate can be improved. can be taken as a thing.

When using the above-mentioned commercially available film as the process paper, the surface shape may vary depending on the grade or lot, so a film that satisfies formula (2) is appropriately selected and used. Moreover, if the surface shapes of one surface and the other surface of the processing paper are different, the surface satisfying the formula (2) may be the surface on which the retardation film is laminated.

In addition, from the viewpoint of improving the appearance of the polarizing plate, the surface of the process paper on which the retardation film is laminated preferably has an arithmetic mean waviness Wa of 200 nm or less, more preferably 150 nm or less. , 100 nm or less. The arithmetic mean waviness Wa of the surface of the process paper on which the retardation film is laminated is usually 50 nm or more.

(Step (3))
Step (3) is a step of peeling the process paper from the laminated film to obtain a retardation film. The peeling method is not particularly limited, but for example, the process paper or retardation film may be peeled while being held in a roll. Further, the peeled process paper may be rolled up.

(Step (4))
Step (4) is a step of laminating a polarizer (or a polarizer with a protective film) onto the retardation film via an adhesive to obtain a polarizing plate. The adhesive may be applied to the retardation film, the polarizer, or both the retardation film and the polarizer.
Further, when the retardation film includes a liquid crystal layer and a resin film, the surface to be bonded to the polarizer may be the surface of the resin film or the surface of the liquid crystal layer. When a water-based adhesive is used as the adhesive, the retardation film and the polarizer can be bonded together by drying. When an active energy ray-curable adhesive is used as the adhesive, the retardation film and the polarizer can be bonded together by irradiation with active energy rays such as ultraviolet rays.

When using a water-based adhesive, drying can be performed, for example, by introducing the bonded film into a drying oven. The drying temperature (temperature of the drying oven) is preferably 30 to 90°C. When the temperature is lower than 30°C, the retardation film and the protective film tend to be easily peeled off from the polarizer. Furthermore, if the drying temperature exceeds 90° C., the polarization performance of the polarizer may deteriorate due to heat. The drying time can be about 10 to 1000 seconds.

After the drying step, a curing step may be performed in which the material is cured for about 12 to 600 hours at room temperature or a slightly higher temperature, for example, about 20 to 45°C. The curing temperature is generally set lower than the drying temperature.

The active energy rays may be irradiated from the retardation film side, the polarizer side, or both the retardation film side and the polarizer side.

The irradiation intensity of active energy rays to the active energy ray curable adhesive is appropriately determined depending on the composition of the active energy ray curable adhesive, but the irradiation intensity in the wavelength region effective for activating the polymerization initiator is 0. It is preferable to set it to 1 to 6000 mW/cm ² . When the irradiation intensity is 0.1 mW/cm2 or ^more , the reaction time is not too long, and when it is 6000 mW/ ^cm2 or less, the heat radiated from the radiation source and the active energy rays cure the adhesive. There is little risk of yellowing of the active energy ray-curable adhesive or deterioration of the polarizer due to heat generation.

The light irradiation time for the active energy ray curable adhesive is also determined appropriately depending on the composition of the active energy ray curable adhesive, but the cumulative light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 10,000 mJ. It is preferable to set it so that it becomes / ^cm2 . When the cumulative light amount is 10 mJ/cm2 or ^more , a sufficient amount of active species derived from the polymerization initiator can be generated and the curing reaction can proceed more reliably, and when the cumulative light amount is 10,000 mJ/ ^cm2 or less, the irradiation time is long. Good productivity can be maintained without becoming too much.

When laminating a polarizer onto a retardation film, the surface of the retardation film is subjected to plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification to improve adhesion to the polarizer. Surface treatment such as treatment (adhesive treatment) can be performed. For example, when the retardation film contains a cyclic polyolefin resin, it is preferable to perform plasma treatment or corona treatment. Further, when the retardation film is made of cellulose ester resin, it is preferable to perform saponification treatment. Examples of the saponification treatment include a method of immersion in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

In step (4), a polarizing plate can also be obtained by bonding a polarizer with a protective film to a retardation film. A protective film-attached polarizer may be produced by laminating a protective film on the polarizer in advance via an adhesive, and then the polarizer in the protective film-attached polarizer may be laminated with the retardation film. . Examples of the method for bonding the protective film and the polarizer include the same method as the method for bonding the retardation film and the polarizer. Moreover, a polarizing plate can be obtained by laminating three sheets of a protective film, a polarizer, and a retardation film at the same time.

In the above example, the process paper is peeled off and then the retardation film and the polarizer are laminated. However, of course, the process paper is peeled off after the retardation film and polarizer are laminated. Good too. That is, the order of step (3) and step (4) is arbitrary.

Although a polarizing plate can be manufactured as described above, an adhesive layer may be further formed on the retardation film. This adhesive layer may be, for example, an adhesive layer for laminating on an image display element such as a liquid crystal cell. The adhesive layer may be formed by directly coating the adhesive on the retardation film, or the adhesive layer may be formed by coating the adhesive on the base film in advance, and then It may also be formed by transferring onto a retardation film.

Further, when a long polarizing plate is manufactured continuously, it may be cut into a predetermined shape (for example, a rectangle) to form a sheet of the polarizing plate.

An image display device can be obtained by laminating the polarizing plate of the present invention on an image display element. Examples of the image display element include a liquid crystal cell and an organic EL display element.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not defined by these Examples. In the examples, % and parts expressing the content or amount used are based on weight unless otherwise specified. Note that the evaluation method used in the examples is as follows.

(1) Thickness:
Measurement was performed using a digital micrometer MH-15M manufactured by Nikon Corporation.

(2) In-plane retardation Re and thickness direction retardation Rth:
The measurement was performed with light at a wavelength of 590 nm at 23° C. using a phase difference meter based on the parallel Nicol rotation method, KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd.

(3) One-dimensional power spectrum for the period f (μm) of the retardation film surface and the process paper surface: H ² (f)
The surface irregularities were scanned using a confocal interference microscope, PLμ NEOX (manufactured by Sensofer Japan). The obtained unevenness data was analyzed to calculate H ² (212) and H ² (425) at a period of 212 μm and a period of 425 μm.

(4) Arithmetic mean waviness: Wa
The arithmetic mean waviness Wa was measured using a scanning white interference microscope VS1000 (manufactured by Hitachi High-Tech Science Co., Ltd.). The measurement range was set to X = 4000 μm or more, Y = 2000 μm or more, and the cutoff value was 100 μm.

(5) Appearance evaluation of polarizing plate A pressure-sensitive adhesive layer was laminated on the retardation film of the polarizing plate, and the polarizing plate was bonded to a glass plate via the pressure-sensitive adhesive layer. The appearance was evaluated by reflecting a fluorescent light onto a polarizing plate and observing the reflected image. A case in which the outline of the fluorescent lamp could be clearly observed without distortion was determined to be good, and a case in which the outline of the fluorescent lamp was distorted and could not be clearly observed was determined to be poor.

(6) Surface roughness Ra, kurtosis Pku, and skewness Psk were determined according to JIS B 0601-2001 from unevenness data obtained by measuring a one-dimensional power spectrum.

The following members were prepared.
(polarizer)
(1) Primer layer forming step Polyvinyl alcohol powder (“Z-200” manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., average degree of polymerization 1100, degree of saponification 99.5 mol%) was dissolved in hot water at 95°C, and the concentration A 3% by weight polyvinyl alcohol aqueous solution was prepared. A crosslinking agent ("Sumirezu Resin 650" manufactured by Taoka Chemical Industry Co., Ltd.) was mixed in the resulting aqueous solution at a ratio of 5 parts by weight to 6 parts by weight of polyvinyl alcohol powder to form a coating liquid for forming a primer layer. Obtained.

An unstretched polypropylene (PP) film (melting point: 163°C) with a thickness of 90 μm was prepared as a base film, one side of which was subjected to corona treatment, and then the above primer layer was formed on the corona treated side using a small diameter gravure coater. A primer layer having a thickness of 0.2 μm was formed by applying a coating solution for the coating and drying it at 80° C. for 10 minutes.

(2) Preparation of laminated film (resin layer formation process)
Polyvinyl alcohol powder (PVA124 manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 98.0-99.0 mol%) was dissolved in hot water at 95°C, and a polyvinyl alcohol aqueous solution with a concentration of 8% by weight was added. This was used as a coating solution for forming a polyvinyl alcohol resin layer.

By applying the above coating liquid for forming a polyvinyl alcohol resin layer on the surface of the primer layer of the base film having the primer layer prepared in (1) above using a lip coater, and then drying it at 80°C for 20 minutes. A polyvinyl alcohol resin layer was formed on the primer layer to obtain a laminated film consisting of base film/primer layer/polyvinyl alcohol resin layer.

(3) Preparation of stretched film (stretching process)
The laminated film produced in (2) above was subjected to free end uniaxial stretching of 5.8 times at 160° C. using a floating longitudinal uniaxial stretching device to obtain a stretched film. The thickness of the polyvinyl alcohol resin layer after stretching was 6.1 μm.

(4) Preparation of polarizing laminated film (dying process)
The stretched film produced in (3) above is placed in a 30°C dyeing aqueous solution containing iodine and potassium iodide (contains 0.6 parts by weight of iodine and 10 parts by weight of potassium iodide per 100 parts by weight of water). After dyeing the polyvinyl alcohol resin layer by immersing it for 180 seconds, excess dyeing aqueous solution was washed away with pure water at 10°C.

Immersion in a first crosslinking aqueous solution at 78°C containing boric acid (contains 9.5 parts by weight of boric acid per 100 parts by weight of water) for 120 seconds, followed by second crosslinking at 70°C containing boric acid and potassium iodide. Aqueous solution (contains 9.5 parts by weight of boric acid and 4 parts by weight of potassium iodide per 100 parts by weight of water).
) for 60 seconds for crosslinking treatment. Thereafter, it was washed with pure water at 10°C for 10 seconds, and finally dried at 40°C for 300 seconds to obtain a polarizing laminate film consisting of base film/primer layer/polarizer.

(Protective film)
A film was prepared in which a hard coat layer was formed on one surface of a cyclic olefin resin film (Nippon Zeon Co., Ltd., Zeonor Film (registered trademark)). The thickness was 50 μm.

(process paper)
The following process paper was prepared. Both are process papers that contain polyethylene resin and have a self-adhesive layer on the surface.
Process paper A: “Force Field 1035” manufactured by Tredegar
Processing paper B: “Toretec (registered trademark) 7332K” manufactured by Toray Film Processing Co., Ltd.
Processing paper C: “Toretec (registered trademark) N711” manufactured by Toray Film Processing Co., Ltd.
Process paper D: “Pearl” manufactured by Tredegar

The arithmetic mean waviness Wa on one surface of the process paper A was 130 nm, H ² (425) was 160, and H ² (212) was 54. The H ² (425)/H ² (212) of this surface was 3.0. Note that the surface of this process paper A was smooth to the naked eye.
The arithmetic mean waviness Wa on one surface of the process paper B was 140 nm, H ² (425) was 2700, and H ² (212) was 41. The H ² (425)/H ² (212) of this surface was 66. Note that the surface of this process paper B was smooth to the naked eye.
H ² (425) on one surface of process paper C is 2.71×10 ⁻⁵ , H ² (212) is 2.69×10 ⁻⁵ , surface roughness Ra is 190 nm, and kurtosis Pku was 2.51, and the skewness Psk was -0.002. The H ² (425)/H ² (212) of this surface is 1.01. Note that the surface of this process paper C was smooth to the naked eye.
H ² (425) on one surface of process paper D is 2.87×10 ⁻⁶ , H ² (212) is 1.24×10 ⁻⁶ , surface roughness Ra is 98 nm, and kurtosis Pku was 2.47 and skewness Psk was -0.114. The H ² (425)/H ² (212) of this surface is 2.31. Note that the surface of this process paper C was smooth to the naked eye.

[Table 1]
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Process paper surface shape
────────────── H ² (425)/H ² (212)
^H2 (425) ^H2 (212)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Process paper A 160 54 3.0
Process paper B 2700 41 66
Process paper C 2.71×10 ^-5 2.69×10 ^-5 1.01
Process paper D 2.87×10 ^-6 1.24×10 ^-6 2.31
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

(Retardation film)
A cyclic olefin resin film manufactured by Zeon Corporation was prepared. The thickness was 20 μm. One side of this film was corona treated. A composition for a vertical alignment film was applied to the corona-treated surface to a film thickness of 1 μm. The coated film was heat treated at a temperature of 100° C. for 120 seconds to form an alignment film. As the composition for the vertical alignment film, Sunever SE610 manufactured by Nissan Chemical Industries, Ltd. was used.

A composition containing the prepared photopolymerizable nematic liquid crystal compound (manufactured by Merck & Co., Ltd., RMM28B) was applied onto the alignment film formed above. The composition includes propylene glycol monomethyl ether acetate (PGMEA) as a solvent and Irgacure (Irg-907) as a photoinitiator. The composition of this composition is as follows.
Photopolymerizable nematic liquid crystal compound [RMM28B]: 20 parts by weight Photopolymerization initiator [Irgacure (Irg-907)]: 5 parts by weight Solvent [propylene glycol monomethyl ether acetate]: 80 parts by weight

After coating, the coated layer was dried at a temperature of 90° C. for 120 seconds. Thereafter, the liquid crystal compound was polymerized by ultraviolet (UV) irradiation to form a 1 μm thick liquid crystal retardation layer in which the liquid crystal compound was cured (the total thickness of the liquid crystal retardation layer was 2 μm). In this way, a retardation film consisting of a base film and a liquid crystal retardation layer was obtained. The elastic modulus of the retardation film at 23° C. was 1900 MPa and 2300 MPa in the MD direction and TD direction, respectively.

Subsequently, the process papers A to D prepared above were laminated onto the liquid crystal layer so that the surface (the one surface) having the surface shape shown in Table 1 was the surface to be laminated with the liquid crystal layer. Then, a retardation film with process paper A, a retardation film with process paper B, a retardation film with process paper C, and a retardation film with process paper D were obtained.
This retardation film could function as a λ/4 wavelength plate in the wavelength region of visible light, and also showed a retardation in the thickness direction.

(UV curable adhesive)
An ultraviolet curable adhesive having the following composition was prepared.
3',4'-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (trade name "CEL2021P", manufactured by Daicel Corporation): 70 parts by weight,
Neopentyl glycol diglycidyl ether [trade name "EX-211", manufactured by Nagase ChemteX Corporation]: 20 parts by weight,
2-ethylhexyl glycidyl ether [trade name "EX-121", manufactured by Nagase ChemteX Corporation]: 10 parts by weight,
Photocationic polymerization initiator [trade name "CPI-100P", manufactured by San-Apro Co., Ltd.]: 2.25 parts by weight

[Reference example 1]
When process paper A was peeled off from the retardation film with process paper A obtained above and the surface shape of the retardation film on the peeled surface (liquid crystal layer surface) that appeared was measured, H ² (425) was 7.70. ×10 ⁻⁵ and H ² (212) was 7.51×10 ⁻⁵ . The H ² (425)/H ² (212) of this surface is 1.03. Note that this peeled surface (liquid crystal layer surface) was smooth to the naked eye.

[Example 1]
A polarizing plate was manufactured as follows.
The above protective film was subjected to corona treatment. The above ultraviolet curable adhesive was applied to the corona-treated surface using a small-diameter gravure coater. A protective film was laminated onto the polarizer of the polarizing laminate film using a laminating roll via an ultraviolet curable adhesive. The ultraviolet curable adhesive was cured by ultraviolet irradiation to form an adhesive layer, thereby obtaining a laminated film having a layer structure of protective film/adhesive layer/polarizer/primer layer/base film. The thickness of the adhesive layer was 0.8 μm.

The base film was peeled and removed from the obtained bonded film. The base film was easily peeled off to obtain a polarizing plate with a single-sided protective film having a layer structure of first protective film/adhesive layer/polarizer/primer layer.

Corona treatment was performed on the cyclic olefin resin film in the retardation film with process paper A attached. The above ultraviolet curable adhesive was applied to the corona-treated surface using a small-diameter gravure coater. Using a lamination roll, the retardation film with process paper was laminated onto the primer layer of the polarizing plate with a single-sided protective film via an ultraviolet curable adhesive. The ultraviolet curable adhesive was cured by ultraviolet irradiation to form an adhesive layer. The thickness of the adhesive layer was 0.8 μm.

Process paper A was peeled off to obtain a polarizing plate consisting of first protective film/first adhesive layer/polarizer/primer layer/adhesive layer/retardation film. The appearance of the polarizing plate was evaluated by measuring the power spectrum ratio H ² (425)/H ² (212) on the surface of the liquid crystal layer that appeared when the process paper A was peeled off.
The arithmetic mean waviness Wa of the surface of the retardation film opposite to the polarizer was 50 nm or less. Note that this peeled surface (liquid crystal layer surface) was smooth to the naked eye.

[Comparative example 1]
A polarizing plate was produced in the same manner as in Example 1, except that the retardation film with process paper A was changed to the retardation film with process paper B. The power spectrum ratio H ² (425)/H ² (212) of the surface of the liquid crystal layer that appeared after peeling off the process paper B was measured to evaluate the appearance of the polarizing plate. The arithmetic mean waviness Wa of the surface of the retardation film opposite to the polarizer was 50 nm or less. Note that this peeled surface (liquid crystal layer surface) was smooth to the naked eye.

The above results are shown in Table 2.

[Table 2]
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Surface shape of retardation film
────────────────────── Appearance of polarizing plate
H ² (425) H ² (212) H ² (425)/H ² (212)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Example 1 43 4.6 9.3 Good
Comparative example 1 130 6.4 20 Defective
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

[Reference example 2]
When the processing paper C was peeled off from the retardation film with the processing paper C obtained above and the surface shape of the retardation film on the peeled surface was measured, H ² (425) was 6.09 × 10 ^-4 , H ² (212) was 1.08×10 ⁻³ , surface roughness Ra was 344 nm, kurtosis Pku was 1.84, and skewness Psk was +0.209. The H ² (425)/H ² (212) of this surface is 0.56. Note that this peeled surface (liquid crystal layer surface) was smooth to the naked eye.

[Example 2]
A polarizing plate produced in the same manner as in Example 1 except that the retardation film with process paper A was changed to a retardation film with process paper C has a liquid crystal layer surface that appears when process paper C is peeled off. The power spectrum ratio H ² (425)/H ² (212) is 10 or less, and the appearance is good.

[Reference example 3]
When the process paper D was peeled off from the retardation film with the process paper D obtained above and the surface shape of the retardation film on the peeled surface (liquid crystal layer surface) that appeared was measured, H ² (425) was 3.60. ×10 ⁻⁶ , H ² (212) is 9.48×10 ⁻⁶ , surface roughness Ra is 212 nm, kurtosis Pku is 3.051, and skewness Psk is −0.010. Ta. The H ² (425)/H ² (212) of this surface is 0.38. Note that this peeled surface (liquid crystal layer surface) was smooth to the naked eye.

[Example 3]
A polarizing plate prepared in the same manner as in Example 1 except that the retardation film with process paper A was changed to a retardation film with process paper D has a liquid crystal layer surface that appears when process paper D is peeled off. The power spectrum ratio H ² (425)/H ² (212) is 10 or less, and the appearance is good.

According to the present invention, even when the polarizing plate includes a retardation film, it is possible to make the unevenness that occurs on the viewing side surface of the polarizing plate difficult to see and to improve the appearance of the polarizing plate.

2 Polarizer 3 Base film 4 Protective film 5 Liquid crystal layer 6 Adhesive layer 10, 11 Adhesive layer 20 Retardation film 100, 101 Polarizing plate

Claims (1)

A step of laminating a process paper on the retardation film to obtain a laminated film;
Peeling the processing paper from the laminated film to obtain a retardation film;
A step of laminating a polarizer on the retardation film via an adhesive to obtain a polarizing plate,
When the one-dimensional power spectrum with respect to the period f (μm) of surface irregularities is H2 (f),
A method for manufacturing a polarizing plate, in which a surface of the process paper that is bonded to the retardation film satisfies the following formula (2).
H2(425)/H2(212)≦10 (2)

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