JP7642364B2 - Polarizing plate and image display device - Google Patents

Description

The present invention relates to a polarizing plate and an image display device.

Liquid crystal display devices (LCDs) are widely used not only in LCD televisions, but also in personal computers, mobile devices such as mobile phones, and in-vehicle applications such as car navigation systems. Typically, LCDs have a liquid crystal panel with polarizing plates attached to both sides of a liquid crystal cell with an adhesive, and display is achieved by controlling the light from the backlight with the liquid crystal panel. In recent years, organic electroluminescence (EL) display devices have also been widely used in televisions, mobile devices such as mobile phones, and in-vehicle applications such as car navigation systems, in the same way as LCDs. In organic EL display devices, a circular polarizing plate (a laminate including a polarizing element and a λ/4 plate) may be placed on the viewing side surface of the image display panel to prevent external light from being reflected by the metal electrode (cathode) and being viewed as a mirror surface.

As mentioned above, polarizing plates are increasingly being installed in vehicles as components of image display devices such as liquid crystal displays and organic EL displays. Polarizing plates used in in-vehicle image display devices are more often exposed to high-temperature environments than those used in mobile applications such as televisions and mobile phones, so they are required to have small dimensional changes even at higher temperatures, i.e., dimensional stability.

A widely known technique for suppressing dimensional changes in polarizing plates in high-temperature environments is to reduce the shrinkage force by keeping the boron content of polarizing elements made of polyvinyl alcohol resin low (see, for example, Patent Document 1).

JP 2013-148806 A

However, in high-temperature environments of 90°C or higher, lowering the boron content of the polarizing element can result in changes in optical properties, such as a decrease in the degree of polarization. In image display devices mounted on vehicles, the polarizing plate can be exposed to high-temperature environments of 90°C or higher. The present invention aims to provide a polarizing plate in which dimensional changes in high-temperature environments are suppressed even without keeping the boron content of the polarizing element low, and an image display device using said polarizing plate.

The present invention provides a polarizing plate and an image display device as exemplified below.
[1] A polarizing plate having, in this order, a polarizing element in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin layer, an adhesive layer, and a transparent protective film,
the polarizing plate contains a urea-based compound, and the content of the urea-based compound is 0.1 g/ ^m2 or more and 2.00 g/m2 or ^less ;
The adhesive layer contains the urea compound,
The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives.
[2] The polarizing plate according to [1], wherein the polarizing element contains boron, and the boron content is 4.0% by mass or more and 8.0% by mass or less.
[3] The polarizing plate according to [1] or [2], wherein the adhesive layer contains a polyvinyl alcohol-based resin.
[4] The polarizing plate according to any one of [1] to [3], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.
[5] An image display device comprising the polarizing plate according to any one of [1] to [4].

The present invention provides a polarizing plate in which dimensional changes at high temperatures are suppressed, and an image display device including such a polarizing plate.

The following describes an embodiment of the present invention, but the present invention is not limited to the following embodiment.

[Polarizing plate]
A polarizing plate according to an embodiment of the present invention includes a polarizing element in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin layer, an adhesive layer, and a transparent protective film, in this order.

The polarizing plate contains a urea-based compound, and the content of the urea-based compound is 0.1 g/ ^m2 or more and 2.00 g/ ^m2 or less. The adhesive layer contains a urea-based compound. The polarizing plate may be one in which the adhesive layer contains a urea-based compound, and further, a layer other than the adhesive layer contains a urea-based compound. In this specification, an adhesive layer containing a urea-based compound is also referred to as a "urea-based compound-containing adhesive layer". Specific examples of the "urea-based compound" in this specification will be described later.

As a polarizing plate in which dimensional change in a high-temperature environment is suppressed, a technology is known in which the boron content of the polarizing element is suppressed to a low level, for example, 3.5% by mass or less, to suppress the contraction force of the polarizing element. However, when such a polarizing plate is exposed to a high-temperature environment of 90°C or more, the optical properties may be easily deteriorated due to the low degree of crosslinking of the polarizing element. The polarizing plate according to this embodiment contains a urea-based compound in the above content, so that dimensional change in a high-temperature environment can be suppressed even if the boron content of the polarizing element is 4.0% by mass or more. In addition, dimensional change can be suppressed even when the polarizing plate is exposed to a high-temperature environment of 90°C or more, or even 95°C or more, for more than two hours.

Although the mechanism by which the urea-based compound in the above content can suppress the dimensional change of the polarizing plate is not clear, it can be assumed that the shrinkage of the polarizing element is suppressed because the dimensional change can be suppressed in a high temperature environment even if the boron content of the polarizing element is 4.0 mass% or more. In the polarizing plate, the content of the urea-based compound is preferably 0.15 g/ ^m2 or more and 1.60 g/ ^m2 or less, and more preferably 0.2 g/ ^m2 or more and 1.55 g/ ^m2 or less. As an example of a method for measuring the content of the urea-based compound in the polarizing plate, the method described in the examples below can be mentioned.

<Polarizing element>
A well-known polarizing element can be used as the polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA")-based resin (hereinafter also referred to as a "PVA-based resin layer"). Examples of the polarizing element include a polarizing element formed by using a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye, and uniaxially stretching the film, and a polarizing element formed by using a laminated film obtained by applying a coating liquid containing a PVA-based resin onto a base film, dyeing the PVA-based resin layer, which is the coating layer of the laminated film, with a dichroic dye, and uniaxially stretching the laminated film.

PVA resins are obtained by saponifying polyvinyl acetate resins. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers that can be copolymerized with it. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

The degree of saponification of the PVA-based resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and even more preferably about 99 mol% to 100 mol%. The degree of polymerization of the PVA-based resin is 1000 to 10000, preferably 1500 to 5000. This PVA-based resin may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

The thickness of the polarizing element in this embodiment is preferably 5 to 50 μm, more preferably 8 to 28 μm, even more preferably 12 to 22 μm, and most preferably 12 to 15 μm. By making the polarizing element 50 μm or less in thickness, it is possible to suppress the effect of polyenation of the PVA-based resin on the deterioration of optical properties in a high-temperature environment, and by making the polarizing element 5 μm or more in thickness, it becomes easy to achieve a configuration that achieves the desired optical properties. Note that the thinner the polarizing element, the lower the contraction force tends to be, so when similar properties are to be obtained, it is preferable to use a thinner polarizing element.

The polarizing element contains boron, and the boron content is preferably 4.0% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, and even more preferably 4.4% by mass or more and 6.0% by mass or less. If the boron content of the polarizing element exceeds 8.0% by mass, the contraction force of the polarizing element increases, and problems such as peeling between the polarizing element and other members such as a front panel to which the polarizing element is bonded when the polarizing element is incorporated into an image display device may occur. If the boron content is less than 4.0% by mass, the desired optical characteristics may not be achieved, particularly when the polarizing element is exposed to a high-temperature environment. The boron content of the polarizing element can be measured by the method described in the examples below. Alternatively, the boron content can be calculated as the mass fraction (mass%) of boron relative to the mass of the polarizing element by high-frequency inductively coupled plasma (ICP) emission spectroscopy. Boron is thought to exist in the polarizing element in the form of boric acid or in the form of a crosslinked structure formed between the components of the PVA-based resin, but the boron content here is the value in terms of boron atoms (B).

The polarizing element preferably contains potassium, and the potassium content is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.34% by mass or more, from the viewpoint of suppressing deterioration of the optical properties of the polarizing element in a high-temperature environment, and is preferably 0.60% by mass or less, more preferably 0.55% by mass or less, and even more preferably 0.50% by mass or less, from the viewpoint of suppressing hue change in a high-temperature environment.

The method for producing the polarizing element is not particularly limited, but typical methods include a method in which a pre-wound PVA-based resin film is sent out and stretched, dyed, crosslinked, etc. (hereinafter referred to as "production method 1"), and a method including a step of applying a coating liquid 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 "production method 2").

Manufacturing method 1 can be achieved by carrying out the steps of uniaxially stretching a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, treating the PVA-based resin film with the adsorbed dichroic dye with an aqueous boric acid solution, and rinsing the film with water after the treatment with the aqueous boric acid solution.

The boron content and potassium content in the polarizing element can be controlled by the concentration of boron component donors such as boric acid, borate salts, borax, and other boron compounds contained in any of the treatment baths in the swelling, dyeing, crosslinking, stretching, and water washing processes, the concentration of potassium component donors such as potassium halides such as potassium iodide, and the treatment temperature and treatment time in each of the above treatment baths. In particular, the crosslinking and stretching processes make it easy to adjust the boron content to a desired range depending on treatment conditions such as the concentration of the boron component donor. In addition, the water washing process makes it easy to adjust the boron content and potassium content to a desired range, taking into account treatment conditions such as the amount of boron component donor and potassium component donor used in the dyeing, crosslinking, or stretching processes, from the viewpoint of being able to dissolve or adsorb boron, potassium, and other components from the PVA-based resin film or adsorb to the PVA-based resin film.

The swelling step is a treatment step in which the PVA-based resin film is immersed in a swelling bath, which can remove dirt and blocking agents from the surface of the PVA-based resin film, and can suppress uneven dyeing by swelling the PVA-based resin film. The swelling bath usually uses a medium whose main component is water, distilled water, pure water, or the like. The swelling bath may contain an appropriate amount of surfactant, alcohol, or the like, according to a conventional method. In addition, potassium iodide may be used in the swelling bath from the viewpoint of controlling the potassium content of the polarizing element. 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 even more preferably 0.5% by mass or less.

The temperature of the swelling bath is preferably about 10 to 60°C, more preferably about 15 to 45°C, and even more preferably about 18 to 30°C. The immersion time in the swelling bath cannot be determined in general because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath, but is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds, and even more preferably about 20 to 100 seconds. The swelling process may be carried out only once, or may be carried out multiple times as necessary.

The dyeing process is a process in which the PVA-based resin film is immersed in a dye bath (iodine solution), and iodine or a dichroic substance such as a dichroic dye can be adsorbed and oriented in the PVA-based resin film. The iodine solution is usually preferably an aqueous iodine solution, and contains iodine and an 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 preferred from the viewpoint of controlling the potassium content in the polarizing element.

In the dye bath, the concentration of iodine is preferably about 0.01 to 1% by mass, and more preferably about 0.02 to 0.5% by mass. In the dye bath, the concentration of iodide is preferably about 0.01 to 10% by mass, and more preferably about 0.05 to 5% by mass, and even more preferably about 0.1 to 3% by mass.

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

The crosslinking process is a process in which the PVA-based resin film dyed in the dyeing process is immersed in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the PVA-based resin film, allowing iodine molecules or dye molecules to be adsorbed to the crosslinked structure. Examples of boron compounds include boric acid, borate salts, and borax. The crosslinking bath is generally an aqueous solution, but may also be, for example, a mixed solution of water and an organic solvent that is miscible with water. In addition, the crosslinking bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element.

In the crosslinking bath, the concentration of the boron compound is preferably about 1 to 15 mass%, more preferably about 1.5 to 10 mass%, and even more preferably about 2 to 5 mass%. In addition, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15 mass%, more preferably about 1.5 to 10 mass%, and even more preferably about 2 to 5 mass%.

The temperature of the crosslinking bath is preferably about 20 to 70°C, and more preferably about 30 to 60°C. The immersion time in the crosslinking bath cannot be determined in general because the degree of crosslinking of the PVA-based resin film is affected by the temperature of the crosslinking bath, but is preferably about 5 to 300 seconds, and more preferably about 10 to 200 seconds. The crosslinking process may be carried out only once, or may be carried out multiple times as necessary.

The stretching process is a process in which the PVA-based resin film is stretched to a predetermined ratio in at least one direction. In general, the PVA-based resin film is uniaxially stretched in the conveying direction (longitudinal direction). There are no particular limitations on the stretching method, and either a wet stretching method or a dry stretching method can be used. The stretching process may be carried out only once, or may be carried out multiple times as necessary. The stretching process may be carried out at any stage in the production of the polarizing element.

In the wet stretching method, the treatment bath (stretching bath) can usually use water or a solvent such as a mixed solution of water and an organic solvent miscible with 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 stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15 mass%, more preferably about 2 to 10 mass%, and more preferably about 3 to 6 mass%. In addition, the treatment bath (stretching bath) can contain a boron compound from the viewpoint of suppressing film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15 mass%, more preferably about 1.5 to 10 mass%, and more preferably about 2 to 5 mass%.

The temperature of the stretching bath is preferably about 25 to 80°C, more preferably about 40 to 75°C, and even more preferably about 50 to 70°C. The immersion time in the stretching bath cannot be determined in general because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but is preferably about 10 to 800 seconds, and more preferably about 30 to 500 seconds. The stretching process in the wet stretching method may be performed together with one or more of the following processing steps: swelling, dyeing, crosslinking, and washing.

Examples of dry stretching methods include roll-to-roll stretching, heated roll stretching, and compression stretching. The dry stretching method may be carried out together with a drying process.

The total stretch ratio (cumulative stretch ratio) applied to the PVA-based resin film can be set appropriately depending on the purpose, but 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 cleaning process is a process in which the PVA-based resin film is immersed in a cleaning bath, and foreign matter remaining on the surface of the PVA-based resin film can be removed. The cleaning bath usually uses a medium whose main component is water, such as distilled water or pure water. In addition, 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 to 10% by mass, more preferably about 1.5 to 4% by mass, and even more preferably about 1.8 to 3.8% by mass.

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

The drying process is a process in which the PVA-based resin film cleaned in the cleaning process is dried to obtain a polarizing element. The drying can be performed by any suitable method, such as natural drying, air drying, or heat drying.

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

The polarizing element may contain a urea-based compound. Methods for incorporating a urea-based compound into a polarizing element include immersing a PVA-based resin film or a PVA-based resin layer in a treatment solution containing a urea-based compound, or spraying, flowing, or dripping a treatment solution containing a urea-based compound onto a PVA-based resin film or a PVA-based resin layer. Among these, the method of immersing a PVA-based resin film or a PVA-based resin layer in a treatment solution containing a urea-based compound is preferably used. Specific examples of urea-based compounds include those exemplified as those to be incorporated into the adhesive layer described below.

The process of immersing the PVA-based resin film or PVA-based resin layer in a treatment solution containing a urea-based compound may be carried out simultaneously with the swelling, stretching, dyeing, crosslinking, washing, and other processes in the manufacturing method of a polarizing element described below, or may be provided separately from these processes. The process of incorporating a urea-based compound into the PVA-based resin film or PVA-based resin layer is preferably carried out after dyeing with iodine, and more preferably carried out simultaneously with the crosslinking process after dyeing. This method results in small changes in hue and can reduce the effect on the optical properties of the polarizing element.

<Transparent protective film>
The transparent protective film (hereinafter also simply referred to as "protective film") used in this embodiment is bonded to at least one surface of the polarizing element via an adhesive layer. This transparent protective film is bonded to one or both surfaces of the polarizing element, but it is more preferable that it is bonded to both surfaces. Furthermore, in a configuration in which a protective film is bonded to both surfaces of the polarizing element via an adhesive layer, only the adhesive layer on one surface of the adhesive layers on both surfaces of the polarizing element may be a urea-based compound-containing adhesive layer, but it is more preferable that both adhesive layers on both surfaces are urea-based compound-containing adhesive layers.

The protective film may also have other optical functions, and may be formed into a laminated structure in which multiple layers are laminated. From the viewpoint of optical properties, it is preferable that the thickness of the protective film is thin, but if it is too thin, the strength decreases and the processability becomes poor. The appropriate thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

The protective film may be a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. In a configuration in which protective films are provided on both sides of a polarizing element, when bonding is performed using a water-based adhesive such as a PVA adhesive, it is preferable that the protective film on at least one side is either a cellulose acylate film or a (meth)acrylic polymer film in terms of moisture permeability, and of these, a cellulose acylate film is preferred.

At least one of the protective films may have a retardation function for the purpose of compensating for viewing angle, etc. In that case, the film itself may have a retardation function, may have a separate retardation layer, or may be a combination of both.
Although the configuration in which the film having retardation function is directly bonded to the polarizing element via an adhesive layer has been described, the film may also be bonded via a pressure-sensitive adhesive layer or an adhesive layer via another protective film that is bonded to the polarizing element.

<Adhesive Layer>
The adhesive constituting the adhesive layer for laminating the protective film to the polarizing element can be any suitable adhesive. The adhesive can be a water-based adhesive, a solvent-based adhesive, an active energy ray curing adhesive, or the like, but is preferably a water-based adhesive. From the viewpoint of improving heat resistance, the adhesive layer is preferably a urea-based compound-containing adhesive layer that contains a urea-based compound. In a polarizing plate having a configuration having a plurality of adhesive layers for laminating the protective film to the polarizing element, at least one adhesive layer is a urea-based compound-containing adhesive layer.

The thickness of the adhesive when applied can be set to any appropriate value. For example, it is set so that an adhesive layer having the desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, even 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.

(Water-based adhesive)
Any suitable aqueous adhesive may be used as the aqueous adhesive. Among them, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average polymerization degree of the PVA-based resin contained in the aqueous adhesive is preferably about 100 to 5500, more preferably 1000 to 4500, from the viewpoint of adhesiveness. The average saponification degree 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 aqueous adhesive is preferably one containing an acetoacetyl group, because it has excellent adhesion between the PVA-based resin layer and the protective film and excellent durability. The acetoacetyl-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of acetoacetyl modification of the acetoacetyl-containing PVA-based resin is typically 0.1 mol% or more, and preferably about 0.1 mol% to 20 mol%.
The resin concentration of the water-based adhesive is preferably 5% by mass to 60% by mass, and more preferably 5% by mass to 50% by mass.

Water-based adhesives can also contain crosslinking agents. Any known crosslinking agent can be used. Examples include water-soluble epoxy compounds, dialdehydes, and isocyanates.

When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the crosslinking agent is preferably any one of glyoxal, glyoxylate, and methylolmelamine, more preferably any one of glyoxal and glyoxylate, and particularly preferably glyoxal.

The water-based adhesive may also contain an organic solvent. The organic solvent is preferably an alcohol because it is miscible with water, and among alcohols, methanol or ethanol is more preferable. Some urea compounds have low solubility in water, but some have sufficient solubility in alcohol. In this case, one preferred embodiment is to dissolve the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add the alcohol solution of the urea compound to the aqueous PVA solution to prepare the adhesive. By including an alcohol with a boiling point of less than 100°C in the adhesive, the drying efficiency of the adhesive can be increased, and the dimensional suppression effect can be easily achieved even in a short drying time.

The methanol concentration of the water-based adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. By having a methanol concentration of 10% by mass or more, it becomes easier to suppress polyenation in a high-temperature environment. In addition, by having a methanol content of 70% by mass or less, deterioration of the hue can be suppressed.

(Active energy ray curing adhesive)
The active energy ray curable adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, and examples thereof include an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, and an adhesive containing a binder resin and a photoreactive crosslinking agent. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of the photopolymerization initiator include a compound containing a substance that generates active species such as neutral radicals, anion radicals, and cation radicals when irradiated with active energy rays such as ultraviolet rays.

(Urea compounds)
The urea-based compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method for incorporating a urea-based compound into the adhesive layer, it is preferable to incorporate a urea-based compound into the above-mentioned adhesive. In the process of forming the adhesive layer from the adhesive through a drying process or the like, a part of the urea-based compound may move from the adhesive layer to the polarizing element or the like. That is, the polarizing element may contain a urea-based compound. There are water-soluble and poorly water-soluble urea-based compounds, and both types of urea-based compounds can be used in the adhesive of this embodiment. When a poorly water-soluble urea-based compound is used in the water-based adhesive, it is preferable to devise a dispersion method so that haze increase does not occur after the adhesive layer is formed.

When the adhesive is a water-based adhesive containing a PVA-based resin, the total amount of urea-based compounds added is preferably 0.1 to 2000 parts by mass, more preferably 1 to 1500 parts by mass, even more preferably 5 to 1000 parts by mass, particularly preferably 50 to 1000 parts by mass, and may be 150 to 1000 parts by mass, relative to 100 parts by mass of the PVA resin.

(Urea Derivatives)
A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom.

Specific examples of urea derivatives include monosubstituted ureas such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea.

Examples of disubstituted ureas include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), and tetrahydro-2-pyrimidinone (propyleneurea).

Examples of 4-substituted ureas include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

(Thiourea derivatives)
A thiourea derivative is a compound in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom.

Specific examples of thiourea derivatives include monosubstituted thioureas such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea.

Examples of disubstituted thioureas include 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, and ethylenethiourea.

An example of a trisubstituted urea is trimethylthiourea, and an example of a tetrasubstituted urea is tetramethylthiourea or 1,1,3,3-tetraethylthiourea.

Among urea-based compounds, urea is preferred because it can better suppress dimensional changes in high-temperature environments. Urea derivatives or thiourea derivatives can also be preferably used, with urea derivatives being more preferred among these. Among urea derivatives, mono- or di-substituted ureas are preferred, with mono-substituted ureas being more preferred. Di-substituted ureas include 1,1-substituted ureas and 1,3-substituted ureas, with 1,3-substituted ureas being more preferred.

<Polarizing plate with adhesive>
The polarizing plate of the present embodiment can be made into a polarizing plate with a pressure-sensitive adhesive by providing a pressure-sensitive adhesive layer on at least one surface. A polarizing plate with a pressure-sensitive adhesive having a pressure-sensitive adhesive layer containing a urea-based compound is also one aspect of the polarizing plate according to the present invention. When the polarizing plate has a pressure-sensitive adhesive layer, the pressure-sensitive adhesive used is not particularly limited, and a known pressure-sensitive adhesive can be used.

The adhesive layer may be made of any material that has excellent optical transparency and adhesive properties such as appropriate wettability, cohesiveness, and adhesion, but it is preferable to use one that has excellent durability. Specific examples of adhesives that form the adhesive layer include pressure-sensitive adhesives made of acrylic resins or rubber resins (also called acrylic adhesives or rubber adhesives).

The adhesive layer formed from the acrylic adhesive is not particularly limited, but (meth)acrylic acid ester resins such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and copolymer resins using two or more of these (meth)acrylic acid esters are preferably used. In addition, polar monomers are copolymerized in these resins. Examples of polar monomers include monomers having polar functional groups such as carboxyl groups, hydroxyl groups, amide groups, amino groups, and epoxy groups, such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, (meth)acrylamide, 2-N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate. In addition, a crosslinking agent is usually blended with the adhesive together with the acrylic resin.

The adhesive may also contain various other additives. Suitable additives include silane coupling agents and antistatic agents. Silane coupling agents are effective in increasing adhesion to glass. Antistatic agents are effective in reducing or preventing the generation of static electricity.

The thickness of the adhesive layer is preferably 3 to 50 μm, and more preferably 3 to 30 μm. When the adhesive layer is to be made conductive, its resistance may be appropriately selected, and is preferably in the range of, for example, 1×10 ⁹ to 1×10 ¹¹ Ω/□. The adhesive layer to be formed on the polarizing plate can be formed by a known method.

[Method of manufacturing polarizing plate]
The method for producing the polarizing plate of the present invention is not particularly limited, but for example, a first transparent protective film, a polarizing element, and a second transparent protective film are laminated with an adhesive layer provided between each layer to produce a polarizing plate. At least one adhesive layer is an adhesive layer containing a urea compound. Then, a pressure-sensitive adhesive is applied to the polarizing plate to form a pressure-sensitive adhesive layer. At this time, a separator film is laminated to the surface of the pressure-sensitive adhesive layer to produce a polarizing plate.

[Image display device]
The image display device of the present invention is characterized by having the polarizing plate of the present invention.

Any known type of image display device can be used. For example, the polarizing plate of the present invention can be suitably used in liquid crystal display devices and organic EL display devices.

The present invention will be specifically described below based on examples. The materials, reagents, amounts of substances and their ratios, operations, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following examples.

(1) Measurement of the thickness of the polarizing element:
The thickness of the polarizing element was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(2) Measurement of shrinkage of polarizing plate:
A measurement sample with a width of 3 mm and a length of 25 mm is cut out from the polarizing plate, with the absorption axis direction (MD) or the transmission axis direction (TD) as the long side. The sample is set in a thermomechanical analyzer (TMA) "TMA4000SE" (manufactured by Netzsch Japan Co., Ltd.) so that the chuck distance from the long side of the sample is 20 mm, and while maintaining the force (10 gf) holding the sample constant, the temperature is raised at 10°C/min up to 95°C, and the sample is held as it is for 2 hours, and the dimensional changes in the MD and TD directions are measured.

(3) Measurement of boron content:
0.2 g of the polarizing element was dissolved in 200 g of a 1.9% by mass aqueous mannitol solution. The resulting aqueous solution was then titrated with a 1 mol/L aqueous sodium hydroxide solution, and the amount of the aqueous sodium hydroxide solution required for neutralization was compared with a calibration curve to calculate the boron content of the polarizing element.

(4) Measurement of the content of urea-based compounds in polarizing plates:
The polarizing element and protective film used in the polarizing plate are cut to a size of 10 cm x 10 cm, and their total mass W1 is measured. The mass W2 of the polarizing plate is measured immediately after the polarizing element and protective film are attached with an adhesive (before the adhesive is dried). The urea content per unit area is calculated based on the concentration of the urea compound in the adhesive used and the value of the applied amount of adhesive (W2 - W1).

<Preparation of Polarizing Element A>
A 40 μm thick polyvinyl alcohol film made of polyvinyl alcohol with an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% or more was uniaxially stretched by about 5 times in a dry state, and then immersed in pure water at 60 ° C for 1 minute while maintaining a tension state, and then immersed in an aqueous solution with a mass ratio of iodine/potassium iodide/water of 0.05/5/100 at 28 ° C for 60 seconds. Then, immersed in an aqueous solution with a mass ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72 ° C for 300 seconds. Then, washed with pure water at 26 ° C for 20 seconds, and dried at 65 ° C to obtain a polarizing element A with a thickness of 15 μm in which iodine was adsorbed and aligned in the polyvinyl alcohol. The boron content of the polarizing element thus obtained was 4.48 mass%.

(Preparation of PVA solution for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group (GOSENEX Z-410, manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90° C. for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesive.

(Preparation of Polarizing Plate Adhesive 1)
A PVA solution for adhesive, urea (manufactured by Tokyo Chemical Industry Co., Ltd.), and pure water were mixed so that the PVA concentration was 3.0%, the urea concentration was 5% (167 parts by mass per 100 parts by mass of the PVA-based resin), and the methanol concentration was 18.0%, to obtain a polarizing plate adhesive 1.

(Preparation of Polarizing Plate Adhesive 2)
A PVA solution for adhesive, urea (manufactured by Tokyo Chemical Industry Co., Ltd.), and pure water were mixed so that the PVA concentration was 3.0%, the urea concentration was 20% (667 parts by mass per 100 parts by mass of the PVA-based resin), and the methanol concentration was 18.0%, to obtain a polarizing plate adhesive 2.

(Preparation of Polarizing Plate Adhesive 3)
A PVA solution for adhesive, urea (manufactured by Tokyo Chemical Industry Co., Ltd.), and pure water were mixed so as to give a PVA concentration of 3.0%, a urea concentration of 45% (1,500 parts by mass per 100 parts by mass of the PVA-based resin), and a methanol concentration of 18.0%, to obtain a polarizing plate adhesive 3.

(Preparation of Polarizing Plate Adhesive 4)
The adhesive PVA solution and pure water were mixed so that the PVA concentration was 3.0% and the methanol concentration was 18.0%, to obtain an adhesive 4 for polarizing plates.

<Preparation of Transparent Protective Film A>
A commercially available cellulose acylate film TD40 (manufactured by Fujifilm Corporation: film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) maintained at 55° C. for 2 minutes. The film was washed with water, and then immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds. The film was passed through a water washing bath under running water for another 30 seconds to neutralize the film. Then, the film was drained three times with an air knife to remove water from the film. The film was allowed to stay in a drying zone at 70° C. for 15 seconds and dried to prepare a saponified film.

<Preparation of Polarizing Plates 1 to 4>
Transparent protective film A was laminated on both sides of polarizing element A via adhesive 1 using a roll laminator, and then dried at 80° C. for 5 minutes to obtain polarizing plate 1. The wet coating thickness of the adhesive was adjusted by lamination nip pressure and lamination roll speed so that the urea content per unit area of the polarizing plate would be the amount shown in Table 1 below.

In the production of polarizing plate 1, adhesive 1 was changed to adhesive 2 to obtain polarizing plate 2.

In the preparation of polarizing plate 1, adhesive 1 was changed to adhesive 3 to obtain polarizing plate 3.

In the preparation of polarizing plate 1, adhesive 1 was changed to adhesive 4 to obtain polarizing plate 4.

The dimensional changes were measured for the polarizing plates 1 to 4 thus obtained. The results are shown in Table 2.

Claims (5)

A polarizing plate having, in this order, a polarizing element in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin layer, an adhesive layer, and a transparent protective film,
the polarizing plate contains a urea-based compound, and the content of the urea-based compound is 0.2 g/m2 ^or more and 2.00 g/m2 or ^less ;
The adhesive layer contains the urea compound,
The adhesive layer is made of a water-based adhesive, and the water-based adhesive contains methanol or ethanol,
the urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
The polarizing element has a thickness of 15 μm or less . The polarizing plate according to claim 1, wherein the polarizing element contains boron and the boron content is 4.0% by mass or more and 8.0% by mass or less. The polarizing plate according to claim 1 or 2, wherein the adhesive layer contains a polyvinyl alcohol-based resin. The polarizing plate according to any one of claims 1 to 3, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. An image display device comprising the polarizing plate according to any one of claims 1 to 4.