JP7005803B1 - Laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate having excellent impact resistance even if it is configured to be thin, and a polarizing plate capable of highly achieving both impact resistance and bending resistance. SOLUTION: The polarizing plate is formed by laminating a protective film and a polarizing element, and the protective film has a piercing elasticity of 200 g / mm or more and 550 g / mm or less and a thickness of 25 μm or less. The polarizing plate contains a polyvinyl alcohol-based resin and boron, has a boron content of 4.5% by mass or less, and is a polarizing plate used in a flexible display device. [Selection diagram] Fig. 1

Description

The present invention relates to a polarizing plate used in a flexible display device, and further relates to a flexible display device including the polarizing plate.

As an input device, a display device provided with a touch sensor function is used in a small electronic device such as a smartphone. Since such a display device is used for a small electronic device, it is necessary to make it smaller and thinner, and further, since data is input by touching the display surface with a fingertip or a pen, a fingertip with respect to the display surface is used. It is necessary to have characteristics that do not deteriorate due to contact such as. Therefore, the impact resistance of the display device to the extent that deterioration due to contact with the display surface can be suppressed is required, and along with this, the members applied to the display device are also required to have impact resistance. Further, in recent years, a flexible display device in which the display device can be folded has attracted attention. Members applied to such flexible display devices are required to have flexibility to the extent that they can be bent, in addition to impact resistance. Patent Document 1 describes a laminated body for a flexible display device including a pressure-sensitive adhesive layer and an optical film, and has a storage elastic modulus G'at 25 ° C. of the outermost pressure-sensitive adhesive layer on the convex side when the laminated body is bent. However, there is disclosed a laminate characterized by having substantially the same or smaller storage elastic modulus G'at 25 ° C. of another pressure-sensitive adhesive layer.

Japanese Unexamined Patent Publication No. 2018-028573

As described above, a member (polarizing plate or the like) applied to a display device having a touch sensor function used in a small electronic device is required to have excellent impact resistance. Further, when the display device is required to be flexible, the polarizing plate used in the display device (flexible display device) is thin and easily bent, and is not significantly deteriorated by bending a practical number of times. Desired. That is, there is a demand for a polarizing plate that is resistant to impact and further resistant to impact and bending. As such a polarizing plate, those having a protective film having excellent mechanical strength such as tensile elastic modulus have been widely used. However, a thin polarizing plate (a polarizing plate having excellent bending resistance) is not particularly satisfactory in terms of impact resistance. An object of the present invention is to provide a polarizing plate having excellent impact resistance even if it is made thin, and in particular, a polarizing plate having excellent impact resistance and bending resistance even if it is made thin.

Surprisingly, the present inventors have determined that, in a polarizing plate applied to a flexible display device, the protective film constituting the polarizing plate has a specific piercing elastic modulus and a specific thickness. It was found that both excellent impact resistance and flexibility resistance can be achieved in combination with. Therefore, the present invention provides the following polarizing plate and flexible display device.

[1] A polarizing plate in which a protective film and a polarizing element are laminated.
The protective film has a piercing elastic modulus of 200 g / mm or more and 550 g / mm or less and a thickness of 25 μm or less.
The polarizing plate contains a polyvinyl alcohol-based resin and boron, has a boron content of 4.5% by mass or less, and is a polarizing plate used in a flexible display device.

[2] The polarizing plate according to [1], wherein the polarizing element has a boron content of 3.0% by mass or more.

[3] The polarizing plate according to [1] or [2], wherein the polarizing element has a thickness of 12 μm or less.

[4] The polarizing plate according to any one of [1] to [3], wherein the protective film has a temperature of 40 ° C. and a relative humidity of 92% RH and a moisture permeability of 300 g / ( ^m 2.24 hours) or less.

[5] The polarizing plate according to any one of [1] to [4], wherein the protective film is made of a (meth) acrylic resin.

[6] The polarizing plate according to any one of [1] to [5], further comprising a retardation body arranged on the side opposite to the protective film side of the polarizing element.

[7] The polarizing plate according to [6], wherein the retarder has a layer formed by curing a polymerizable liquid crystal compound.

[8] The polarizing plate according to any one of [1] to [7], wherein the polarizing plate has a thickness of 40 μm or less.

[9] A display device including the polarizing plate according to any one of [1] to [8].

[10] A flexible display device including the polarizing plate according to any one of [1] to [8].

According to the present invention, a polarizing plate having excellent impact resistance even if it is made thin, and a polarizing plate having excellent impact resistance and bending resistance when it is made thin enough to be applied to a flexible display device. Can be provided.

It is a schematic cross-sectional view schematically showing one form of the polarizing plate of this invention. It is a schematic sectional drawing schematically showing another form of the polarizing plate of this invention. It is a schematic view of the glued mount (hereinafter, sometimes referred to as "glued mount") having a void portion used for measuring the piercing elastic modulus from the upper surface. (A) is a schematic perspective view showing a main part when the measurement film is attached to the glued mount, and (b) is a diagram schematically showing the upper part after the measurement film is attached to the glued mount. Is. It is a figure which shows typically the cross section at the time of piercing a needle into a sample (hereinafter, sometimes referred to as "the mount with a measuring film") after attaching a measuring film to a mount with glue. It is a figure which shows the cross section at the time of piercing elastic modulus measurement schematically, and (a) and (b) show the state which the film is deformed by piercing a needle into a film.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all the drawings below, the scales are appropriately adjusted and shown in order to make each component easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

<Polarizer>
FIG. 1 is a schematic cross-sectional view schematically showing one form of the polarizing plate of the present invention. The polarizing plate 100 shown in FIG. 1 includes a protective film 20 and a polarizing element 10. FIG. 2 is a schematic cross-sectional view schematically showing another embodiment of the polarizing plate of the present invention. The polarizing plate 200 shown in FIG. 2 includes a protective film 20, a polarizing element 10, an interlayer bonding layer 40, and a retardation plate 30. The retardation plate 30 includes the first retardation layer 31 and the second retardation layer 32 in this order from the polarizing element 10 side. The first retardation layer 31 and the second retardation layer 32 may be bonded by the interlayer bonding layer 33. The polarizing plates 100 and 200 may further include an interlayer bonding layer (not shown) for bonding the layers shown in FIGS. 1 and 2, and other layers other than the layers shown in FIGS. 1 and 2. Further layers may be provided.

When the thickness of the protective film 20 of the polarizing plates 100 and 200 is as described later, impact resistance and flexibility can be highly compatible with each other. In this case, the polarizing plates 100 and 200 can be bent (hereinafter, also referred to as “infold”) with the protective film 20 side inside. In the present specification, the fact that the polarizing plate can be bent means that the polarizing plate can be bent without causing a crack in the polarizing element 10 even if the polarizing element 10 is bent in an infold with a bending radius of 3 mm. The bending radius is not limited as the bending form of the polarizing plates 100 and 200. Bending also includes a form of refraction in which the refraction angle of the inner surface is greater than 0 ° and less than 180 °, and a form of folding in which the bending radius of the inner surface is close to zero or the refraction angle of the inner surface is 0 °. .. The polarizing plate of the present invention having a protective film 20 having a thickness as described later is suitable for a flexible display device because it can be bent and is excellent in flexibility.

The polarizing plates 100 and 200 may have, for example, a square shape in a plan view, preferably a square shape having a long side and a short side, and more preferably a rectangle. Each layer constituting the polarizing plate 100 may have a corner portion R-processed, an end portion notched, or a perforated portion.

The polarizing plates 100 and 200 have a specific protective film thickness and have bending resistance suitable for a flexible display device. The thickness of the entire polarizing plate is preferably 40 μm or less, more preferably 30 μm or less, although a suitable range varies depending on the layer structure. When the thickness of the polarizing plates 100 and 200 is 40 μm or less, the polarizing plate can be further thinned, the flexible display device can be further thinned, and the flexible display device is resistant to bending (excellent in bending resistance). It is possible to realize a flexible display device. The thickness of the entire polarizing plate referred to here is the total thickness of the polarizing elements 10 and the protective film 20 constituting the polarizing plate, and the thickness of the interlayer bonding layer for joining the polarizing plates. Examples of the method for reducing the thickness of the polarizing plates 100 and 200 include a method of reducing the thickness of each layer (including the interlayer bonding layer), a method of reducing the total number of layers, and the like, and specifically, the method of reducing the total number of layers. , The thickness of the protective film 20 is 20 μm or less, the thickness of the polarizing element 10 is 12 μm or less, the configuration is such that no protective film other than the protective film 20 is provided, and the like.

[Bending resistance]
Hereinafter, the polarizing plate of the present invention having a high degree of compatibility with bending resistance suitable for a flexible display device in addition to impact resistance will be described in detail. In order to realize a flexible display device having excellent bending resistance, the polarizing plate applied to the flexible display device must also have excellent bending resistance.

When the polarizing plates 100 and 200 are repeatedly bent in an infold having a bending radius of 3 mm in an environment of a temperature of 25 ° C., the number of bendings at which cracks first occur in the polarizing plates 100 and 200 is preferably. It is 100,000 times or more, more preferably 200,000 times or more, and further preferably 300,000 times or more. The present inventors have found that cracks are likely to occur in the inner protective film of a polarizing plate when it is repeatedly bent in an infold. The present inventors have achieved excellent bending resistance by using a resin film as the protective film 20 which does not cause cracks in the bending resistance test described in detail in Examples or has a crack length of 5 mm or less. Confirmed that the board can be provided. According to the present invention, there is provided a polarizing plate capable of suppressing the occurrence of cracks in the polarizing plate even if the bending is repeated 100,000 times with an infold having a bending radius of 3 mm in an environment of a temperature of 25 ° C. be able to.

[Impact resistance]
The polarizing plates 100 and 200 have excellent impact resistance. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a polarizing plate having excellent impact resistance without causing cracks in the polarizing element in the impact resistance test using the evaluation pen described in detail in Examples.

[Protective film]
The protective film 20 has a function of protecting the surface of the polarizing element 10. The polarizing plates 100 and 200 can be arranged and used on the visual recognition side of the display element in the flexible display device.
In the polarizing plates 100 and 200, the protective film 20 can be arranged and used so as to be on the visible side of the polarizing element 10.

The protective film 20 has a piercing elastic modulus of 200 g / mm or more and 550 g / mm or less. The puncture elastic modulus of the protective film 20 is preferably 230 g / mm or more, more preferably 250 g / mm or more, particularly preferably 300 g / mm or more, and preferably 530 g / mm or less. It is preferably 500 g / mm or less, more preferably 450 g / mm or less, and particularly preferably 400 g / mm or less. By using a protective film having a piercing elastic modulus as described above as the protective film 20, even when a protective film having a thickness of 20 μm or less is used, the polarizing plate has excellent impact resistance and bending resistance. A board can be provided.

Here, although described in Examples, a means for measuring the puncture elastic modulus of the protective film will be described with reference to the drawings. In the present specification, the piercing elastic modulus uses a measurement sample in which a protective film is attached to a glued mount cut out in a square having a central portion of 30 mm × 30 mm, and a needle having a tip diameter of 1 mm φ0.5 R is 0.33 cm. The amount of displacement due to the deflection of the protective film in the piercing direction, which is measured when the protective film is pierced perpendicularly to the surface of the protective film at a speed of / sec and breaks, is defined as the strain amount S (mm). When the stress applied to the protective film is F (g), the proportional constant (stress F / strain S) between the stress F and the strain S is the equation (1) :.
Puncture elastic modulus A (g / mm) = F (g) / S (mm) (1)
It is a physical characteristic value calculated by. The puncture elastic modulus can be measured using a compression tester equipped with a load cell. Examples of the compression tester include the puncture tester "NDG5" manufactured by Kato Tech Co., Ltd. and the handy compression tester "". Examples include "KES-G5" and "EZTest", a small desktop testing machine manufactured by Shimadzu Corporation. From the stress-strain curve obtained by using such a compression tester, it is possible to measure the stress applied to the film when fracture occurs and the amount of strain generated in the film up to that point. The breakage that occurs in the film when the piercing jig is pressed includes the case where a through hole is formed in the film by the tip of the jig. Specifically, as described in the examples, the puncture elastic modulus is measured by using a measurement sample in which a film is attached to a glued mount having a gap portion cut out by a square having a central portion of 30 mm × 30 mm. A needle with a tip diameter of 1 mm φ0.5 R is pierced into the center of the film in the gap at a speed of 0.33 cm / sec approximately perpendicular to the surface of the film, and is measured when a break occurs. The amount of displacement due to the deflection of the film in the piercing direction is calculated by the above equation (1) from the strain amount S (mm) and the stress F (g) applied to the film.

The main part of the measuring means of the puncture elastic modulus when the puncture tester "NDG5" manufactured by Kato Tech Co., Ltd. is used will be described with reference to the drawings.

FIG. 3 is a schematic view of a glued mount (glued mount 7) having a gap portion for determining the puncture elastic modulus of the protective film as viewed from above. The glued mount 7 has a portion (gap portion 6) hollowed out in a 30 mm × 30 mm square, which is a portion to which a protective film to be used for measurement (hereinafter, also referred to as “measurement film 12”) is attached to the central portion. Have.

FIG. 4 is a schematic view showing a main part when the measuring film 12 is attached to the glued mount 7, and FIG. 4A is a perspective view when the measuring film 12 is attached to the glued mount 7. b) is a schematic view of the backing sheet 1 with the measuring film after the measuring film 12 is attached to the backing sheet 7 with the glue as seen from the upper part (direction A in FIG. 4A). The dotted line indicates the outer circumference 8 of the gap portion 6. The position M for piercing the needle N, which is located in the substantially central portion of the gap portion 6, is an intersection of two straight lines connecting points (R and R') facing diagonally in the outer peripheral portion 8 of the gap portion 6. FIG. 5 schematically shows a cross-sectional view (before piercing the needle N) along I-I'on the mount 1 with a measuring film.

The needle N is pierced into the substantially center M of the measurement film 12 (for example, the intersection of two diagonal lines connecting R and R'of the vertices of the outer circumference 8 of the gap portion in FIG. 4B). In such piercing, the stress F (g) applied to the needle N is correlated with the strain amount S (mm) due to the bending in the piercing direction of the film, and the stress F (g) and the strain when the film breaks occur. From the quantity S (mm), the piercing elastic modulus is obtained according to the above formula (1). When determining the puncture elasticity, when the film is broken when it is deformed (when the film is broken in the state shown in FIG. 6A), when the film is further deformed and the fracture occurs. Although there is (a case where fracture occurs in the state of FIG. 6B), the piercing elasticity in the present invention is determined from the applied stress in the piercing tester and the strain amount S, and the strain amount S is defined as the strain amount S. , S may be the case where the break occurs in the state of FIG. 6 (a), or may be S when the break occurs in the state of FIG. 6 (b). It should be noted that when the film breaks, the applied stress changes from an increasing tendency to a decreasing tendency, and it can be understood that the breaking occurred at this change point.

In the glued mount 7, the glue for fixing the measurement film is particularly limited as long as it can prevent the measurement film from peeling off even partially from the mount with the measurement film during the piercing elastic modulus measurement. Not done. An appropriate preliminary experiment may be performed to find the glue of the glued mount 7 used for the piercing elastic modulus measurement.

The thickness of the protective film 20 is 25 μm or less, preferably 20 μm or less. When the thickness of the protective film 20 is 25 μm or less and the puncture elastic modulus is in the above range, the impact resistance of the obtained polarizing plate is surprisingly excellent. Further, when the thickness is 20 μm or less, a polarizing plate having good flexibility as well as impact resistance can be obtained. The lower limit of the thickness of the protective film 20 is, for example, 8 μm or more, preferably 10 μm or more, and particularly preferably 15 μm or more. When the thickness of the protective film 20 is 25 μm or less, the thin polarizing plates 100 and 200 can be easily constructed.

As described above, the protective film 20 has a thin thickness and a moisture permeability of a temperature of 40 ° C. and a relative humidity of 92% RH of preferably 300 g / (m 2.24 hours) or less, more preferably ^{250 g / (m 2 )} .・ 24 hours) or less. Since the moisture permeability of the protective film 20 is within the above range, the displacement of the end position between the polarizing element 10 and the protective film 20 is less likely to occur even in a moist heat environment, and a polarizing plate having excellent moist heat resistance is provided. be able to.

As the protective film 20, for example, a resin film having excellent transparency, mechanical strength, thermal stability, moisture barrier property, isotropic property, stretchability and the like can be used. The resin film may be a thermoplastic resin film. Specific examples of such resins include cellulose-based resins such as triacetyl cellulose; polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate; polyether sulfone-based resins; polysulfone-based resins; polycarbonate-based resins; nylon and aromatic polyamides. Polyamide-based resin such as; Polyimide-based resin; Polyethylene-based resin such as polyethylene, polypropylene, ethylene / propylene copolymer; Cyclic polyolefin-based resin having cyclo-based and norbornene structure (also referred to as norbornene-based resin); (meth) acrylic-based Examples thereof include resins; polyarylate-based resins; polystyrene-based resins; polyvinyl alcohol-based resins, and mixtures thereof. The protective film 20 made of such a material is easily available on the market, and is applied to the present invention by selecting a commercially available product having a thickness of 20 μm or less and determining the puncture elastic modulus by the above method. Select the protective film 20 to be used. In the commercially available protective film 20, the specific value of the thickness is a value that allows a thickness accuracy of about ± 10%, preferably about ± 5%.

As the protective film 20, a protective film made of a (meth) acrylic resin is preferably used from the viewpoint that it is easy to obtain a film having a moisture permeability in the above range while having a thin thickness. A protective film made of a (meth) acrylic resin is particularly preferable because it has a thin thickness but has an appropriate piercing elastic modulus. This effect is remarkable in the protective film made of (meth) acrylic resin when the thickness is 15 to 25 μm.

The protective film 20 can have a protective layer that is an organic layer or an inorganic layer. The organic layer can be formed by using a composition for forming a protective layer, for example, a (meth) acrylic resin composition, an epoxy resin composition, a polyimide resin composition, or the like. The composition for forming a protective layer may be an active energy ray-curable type or a thermosetting type. The inorganic layer can be formed from, for example, silicon oxide. When the protective layer is an organic layer, the protective layer may be what is called a hardcourt layer. By providing a protective layer on the protective film having high moisture permeability, the moisture permeability of the protective film can be reduced.
In this way, the protective film provided with the protective layer has an effect that it is easy to obtain a protective film having a moisture permeability in the above-mentioned preferable range, although the thickness is thin.

When the protective film 20 has a protective layer of an organic material layer, for example, an active energy ray-curable protective layer forming composition is applied onto a base film and irradiated with active energy to cure the protective layer. Can be produced. The base film may be left as a component of the protective film 20, or may be peeled off and removed. As the base film, the above-mentioned resin film can be used. Examples of the method for applying the protective layer forming composition include a spin coating method and the like. When the protective film 20 has a protective layer of an inorganic layer, the protective layer can be formed by, for example, a sputtering method, a thin-film deposition method, or the like.

[Polarizer]
The splitter 10 has a function of selectively transmitting linearly polarized light from unpolarized light rays such as natural light. The polarizing element 10 contained in the polarizing plate 100 or the polarizing plate 200 of the present invention contains a polyvinyl alcohol-based resin and boron. The splitter 10 is preferably a stretched film on which a dichroic dye is adsorbed. When the dichroic dye is dispersed in a polymer chain (polyvinyl alcohol-based resin chain) in which anisotropy is generated by stretching, it appears to be colored from a certain direction and almost colorless from a direction perpendicular to it. Sometimes. Iodine is preferably used as the dichroic dye. Further, as a stretched film on which a bicolor dye is adsorbed, in addition to a polarizing element obtained by adsorbing and stretching a bicolor dye on a single resin film, for example, it is described in Japanese Patent Application Laid-Open No. 2012-73563. A polyvinyl alcohol-based resin layer is provided on a base film (thermoplastic resin film) such as an ester-based thermoplastic resin base material, and this resin layer is stretched for each base material, and then a bicolor dye is used. It is also possible to manufacture a polarizing element by adsorbing and orienting the film. The polarizing element obtained by such a method may be hereinafter referred to as a “stretched layer”. A general method for producing this stretched layer will be described later.

When the polarizing element 10 is a stretched layer, it is manufactured by using an appropriate base film (thermoplastic resin film) as shown above. The configuration is supported by film). The polarizing plates 100 and 200 may be configured such that the base film supporting the polarizing element 10 is the protective film 20 of the polarizing element 10.

The splitter 10 has a contractile force of preferably 2.4 N / 2 mm or less, and more preferably 2.1 N / 2 mm or less. When the contractile force of the polarizing element 10 is within the above-mentioned numerical range, the polarizing element 10 is less likely to be cracked even when subjected to an impact, and a polarizing plate having excellent impact resistance can be provided. In addition, the shrinkage of the polarizing element 10 in a moist heat environment can be suppressed. The contractile force of the splitter 10 is usually 1.0 N / 2 mm or more. The contractile force of the polarizing element 10 is measured by the method described in Examples described later. When the polarizing element 10 is a stretched film or a stretched layer manufactured by using a polyvinyl alcohol-based resin film (layer), the contractile force of the polarizing element 10 can be adjusted by the boron content described later. It can also be controlled by the type and amount of the dichroic dye used. When the polarizing element 10 is a liquid crystal layer, it can be controlled by the degree of cross-linking of the polymerizable liquid crystal compound constituting the liquid crystal layer. Among these, the polarizing element 10 preferably contains a polyvinyl alcohol-based resin from the viewpoint of easy control of the contractile force.

Hereinafter, the polarizing element 10 containing a polyvinyl alcohol-based resin is also referred to as a “polyvinyl alcohol-based resin-containing polarizing element”. A polyvinyl alcohol-based resin-containing polarizing element having a boron content (hereinafter referred to as “boron content”) of 4.5% by mass or less is preferable, and a polyvinyl alcohol-based resin-containing polarizing element having a boron content of 4.3% by mass or less is more preferable. When the boron content is within the above-mentioned numerical range, it is possible to provide a polarizing plate having excellent impact resistance because the polarizing element 10 is less likely to be cracked even when subjected to an impact. In addition, the shrinkage of the polarizing element 10 in a moist heat environment can be suppressed. The boron content of the stator 10 can be, for example, 2.5% by mass or more, preferably 3.0% by mass or more. The boron content of the polarizing element 10 containing the polyvinyl alcohol-based resin is the ratio of the mass of the contained boron to the total mass of the polarizing element, and the measuring means thereof will be described later.

(A polarizing film that is a stretched film or a stretched layer on which a dichroic dye is adsorbed)
Here, a method for producing a polyvinyl alcohol-based resin-containing polarizing element will be briefly described.
The polarizing element, which is a stretched film on which a dichroic dye is adsorbed, has a dichroic property by dyeing the polyvinyl alcohol-based resin film with a dichroic dye such as iodine in the step of uniaxially stretching the polyvinyl alcohol-based resin film. It can be produced through a step of adsorbing a dye, a step of treating a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution. Such a polyvinyl alcohol-based resin film (before uniaxial stretching) can be easily obtained from the market, and as described later, a polyvinyl acetate-based resin is produced by a known means and saponified to produce a polyvinyl alcohol-based resin. , The polyvinyl alcohol-based resin may be made into a film. Further, the polyvinyl acetate-based resin may be formed into a film at the stage of the polyvinyl acetate-based resin, and the polyvinyl acetate-based resin contained in the film may be saponified.

The boron content of the polyvinyl alcohol-based resin-containing polarizing element is determined by boric acid in the polyvinyl alcohol-based resin film on which the dichroic dye is adsorbed, especially when the polyvinyl alcohol-based resin-containing polarizing element is produced by the above-mentioned production method. It can be controlled by adjusting the conditions of the process of treating with an aqueous solution. For example, the boron content of the polyvinyl alcohol-based resin-containing polarizing element can be controlled by changing the concentration and amount of boric acid used in the boric acid aqueous solution or changing the temperature of the boric acid aqueous solution. Appropriate preliminary experiments can be performed to derive the conditions under which the polyvinyl alcohol-based resin-containing polarizing element has a desired boron content.

The thickness of the splitter is usually 30 μm or less, preferably 18 μm or less, and more preferably 12 μm or less. Reducing the thickness of the polarizing element is advantageous for thinning the polarizing plates 100 and 200. The thickness of the splitter is usually 1 μm or more, and may be, for example, 5 μm or more.
When the polarizing element is a stretched film on which a dichroic dye is adsorbed, the thickness of the preferred polarizing element can be controlled from the thickness of the raw material film (before stretching) before forming the stretched film and the stretching ratio. As will be described later, when the polarizing element is a stretched layer on which a dichroic dye is adsorbed, it can be controlled from the thickness of the coating film formed on the substrate and the stretching ratio.

The thickness of the splitter can be measured, for example, with a contact film thickness meter as shown in Examples described later.

The polyvinyl alcohol-based resin is obtained by saponifying the polyvinyl acetate-based resin. As the polyvinyl acetate-based resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and another monomer copolymerizable therewith is used. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acid compounds, olefin compounds, vinyl ether compounds, unsaturated sulfone compounds, and (meth) acrylamide compounds having an ammonium group. Be done.

The saponification degree of the polyvinyl alcohol-based resin is usually about 85 mol% or more and 100 mol% or less, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and polyvinyl formal, polyvinyl acetal and the like modified with aldehydes can also be used. The degree of polymerization of the polyvinyl alcohol-based resin is usually 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less.

The polyvinyl alcohol-based resin-containing polarizing element, which is a stretched layer on which a dichroic dye is adsorbed, is usually obtained by applying a coating liquid containing the polyvinyl alcohol-based resin on a base film to form a laminated film. A step of uniaxially stretching the laminated film, a step of dyeing the polyvinyl alcohol-based resin layer of the uniaxially stretched laminated film with a dichroic dye, and adsorbing the dichroic dye on the resin layer to form a dichroic dye. It can be produced through a step of treating the resin layer on which the sex dye is adsorbed with an aqueous boric acid solution and a step of washing with water after the treatment with the aqueous boric acid solution. The base film used for forming the substituent may be used as a protective film on the substituent. If necessary, the base film may be peeled off from the polarizing element. The material and thickness of the base film may be the same as the material and thickness of the protective film 20 described later. Further, also in the production of a polyvinyl alcohol-based resin-containing polarizing element which is a stretched layer on which such a dichroic dye is adsorbed, the amount of boric acid used in the step of treating with a boric acid aqueous solution described later can be controlled. The boron content of the polarizing element 10 can be set in a desired range.

Iodine and organic dyes can be used as the dichroic dye, but iodine is particularly preferable as the dichroic dye used for the substituent of the present invention.

When iodine is used as the bicolor dye, a polyvinyl alcohol-based resin film or a laminated film containing a base film and a polyvinyl alcohol-based resin film is usually immersed in a dyeing bath containing iodine and potassium iodide. The polyvinyl alcohol-based resin is dyed with iodine. The iodine content in this dyeing bath can be about 0.003 to 1 part by mass per 100 parts by mass of water. The content of potassium iodide can be about 0.15 to 20 parts by mass per 100 parts by mass of water. The temperature of the dyeing bath can be about 10 to 45 ° C.

In the step of treating a polyvinyl alcohol-based resin film on which a bicolor dye, particularly iodine is adsorbed, or a laminated film containing a polyvinyl alcohol-based resin film and a base film with a boric acid aqueous solution, the bicolor dye is usually adsorbed. Immerse the polyvinyl alcohol-based resin film in a boric acid aqueous solution (cross-linking bath). As the boric acid source contained in the boric acid aqueous solution, a boron compound such as boric acid or borax is used. Further, a cross-linking agent such as glyoxal or glutaraldehyde may be used together with the boron compound. Water can be used as the solvent of the boric acid aqueous solution, but an organic solvent compatible with water may be further contained. In order to adjust the boron content of the stator, it is preferable to set the concentration of boric acid in the boric acid aqueous solution to 3 to 8% by mass, appropriately adjust the immersion time in the cross-linking bath, and adjust the concentration of boric acid to 4. It is more preferable to set the concentration to about 7% by mass and appropriately adjust the immersion time in the cross-linking bath.

The boric acid aqueous solution can further contain iodide. By adding iodide, the in-plane polarization performance of the obtained polarizing element can be made more uniform. Specific examples of iodide are the same as above. The concentration of iodide in the boric acid aqueous solution is preferably 0.1 to 20 parts by mass.

The cross-linking treatment with an aqueous boric acid solution is usually carried out at a temperature of 40 to 80 ° C, preferably 50 to 70 ° C. If the temperature is too low, the progress of the crosslinking reaction tends to be insufficient, while if the temperature is too high, the film tends to be cut in the crosslinking bath, and the processing stability tends to be significantly lowered. The time for the crosslinking treatment is usually 10 to 600 seconds, preferably 60 to 420 seconds, and more preferably 90 to 300 seconds. The conditions for such cross-linking treatment are adjusted according to the desired boron content, as described below.

The fact that the boron content in the polarizing element 10 is in the above range is advantageous in terms of improving the impact resistance of the polarizing plates 100 and 200 and improving the crack resistance of the polarizing plates 100 and 200. Further, it may be advantageous in terms of the optical characteristics of the ligand. Boron in the polarizing element is considered to exist in a free state as boric acid (H ₃ BO ₃ ), or boric acid exists in a state in which a crosslinked structure is formed with a unit of a polyvinyl alcohol-based resin. The boron content in the above is the amount of the boron atom (B) itself, including those existing in the state of the compound.

For the boron content in the stator, for example, the amount of boron is quantified by dissolving the substituent in pure water, adding mannitol, and titrating the obtained solution with an aqueous solution of sodium hydroxide. Then, it can be calculated as a mass percentage of the amount of boron with respect to the mass of the substituent. Inductively coupled plasma (ICP) emission spectroscopy can also be used to quantify the amount of boron in the stator and calculate it as the mass percentage of boron with respect to the mass of the substituent.

When the flexible display device is an organic EL (organic electroluminescence) display device, the polarizing plate of the present invention is used as a circular polarizing plate which is an antireflection plate of the organic EL display device by further assembling a retardation plate. You can also do it. Hereinafter, this retardation plate will be described.

[Phase difference plate]
The polarizing plate 200 can have a function as a circular polarizing plate by including the polarizing element 10 and the retardation plate 30. Hereinafter, the configuration including the polarizing element 10 and the retardation plate 30 is also referred to as a circular polarizing plate.

The retardation plate 30 includes a first retardation layer 31 and a second retardation layer 32. The first retardation layer 31 and the second retardation layer 32 are preferably bonded by the interlayer bonding layer 33. The first retardation layer 31 and the second retardation layer 32 have an overcoat layer that protects the surface thereof, a base film that supports the first retardation layer 31 and the second retardation layer 32, and the like. May be good. The first phase difference layer 31 and the second phase difference layer 32 include, for example, a phase difference layer (λ / 4 layer) that gives a phase difference of λ / 4 and a phase difference layer (λ / 2) that gives a phase difference of λ / 2. Layer) and positive C layer and the like. The retardation plate 30 preferably includes a λ / 4 layer, more preferably a λ / 4 layer and at least one of a λ / 2 layer or a positive C layer.

In the retardation plate 30, the first retardation layer 31 and the second retardation layer 32 are laminated in order from the polarizing element 10 side. When the retardation plate includes the λ / 2 layer, the first retardation layer 31 is the λ / 2 layer and the second retardation layer 32 is the λ / 4 layer. When the retardation plate 30 includes a positive C layer, the first retardation layer 31 is a positive C layer and the second retardation layer 32 is a λ / 4 layer, or the first retardation layer 31 is λ. It is a / 4 layer, and the second retardation layer 32 is a positive C layer. The thickness of the retardation plate 30 is, for example, 0.1 μm or more and 50 μm or less, preferably 0.5 μm or more and 30 μm or less, and more preferably 1 μm or more and 10 μm or less.

The first retardation layer 31 and the second retardation layer 32 may be formed from the resin film exemplified as the material of the resin film of the protective film described above, or may be formed from a layer formed by curing the polymerizable liquid crystal compound. You may. The first retardation layer 31 and the second retardation layer 32 may include an alignment film and a base film in addition to the layer formed by curing the polymerizable liquid crystal compound.

When the first retardation layer 31 and the second retardation layer 32 are formed from a layer formed by curing a polymerizable liquid crystal compound, a composition containing the polymerizable liquid crystal compound is applied to a base film and cured. Can be formed. An alignment film may be formed between the base film and the coating layer. The material and thickness of the base film may be the same as the material and thickness of the resin film. When the first retardation layer 31 and the second retardation layer 32 are formed from a layer formed by curing a polymerizable liquid crystal compound, the first retardation layer 31 and the second retardation layer 32 may be incorporated into the laminate in the form of having an alignment film and a base film.

The polarizing plate in which the polarizing element 10 and the retardation plate 30 are arranged so that the absorption axis of the splitter 10 and the slow axis of the retardation plate 30 are at a predetermined angle has an antireflection function, that is, a circle. Can function as a polarizing plate. When the retardation plate 30 includes the λ / 4 layer, the angle formed by the absorption axis of the polarizing element 10 and the slow axis of the λ / 4 layer can be 45 ° ± 10 °. The first retardation layer 31 and the second retardation layer 32 may have a positive wavelength dispersibility or may have a reverse wavelength dispersibility. The λ / 4 layer preferably has a reverse wavelength dispersibility. The splitter 10 and the retardation plate 30 may be bonded by the interlayer bonding layer 40.

[Interlayer bonding layer]
In the polarizing plates 100 and 200, an interlayer bonding layer can be used between the layers in order to bond the two layers. In FIG. 2, the interlayer bonding layer 40 is used for bonding the polarizing element 10 and the retardation plate 30. Further, in the retardation plate 30, the interlayer bonding layer 33 is used for bonding the first retardation layer 31 and the second retardation layer 32. The interlayer bonding layer can be an adhesive layer or an adhesive layer. The interlayer bonding layer 40 is preferably an adhesive layer, and the interlayer bonding layer 33 is preferably an adhesive layer.

The thickness of the interlayer bonding layer is not particularly limited, but when the pressure-sensitive adhesive layer is used as the interlayer bonding layer, it is preferably 1 μm or more, 5 μm or more, usually 50 μm or less, and 25 μm or less. There may be. When the adhesive layer is used as the interlayer bonding layer, the thickness of the interlayer bonding layer is preferably 0.1 μm or more, may be 0.5 μm or more, is preferably 10 μm or less, and is 5 μm. It may be as follows.

In the present specification, the "adhesive" is a liquid state after the curing reaction and can be adhered by applying a slight pressure at room temperature for a short time, for example, a pressure-sensitive adhesive.
On the other hand, in the present specification, the "adhesive" refers to an adhesive other than an adhesive (pressure sensitive adhesive), which is in a solid state after a curing reaction and has a elastic modulus range of 100 MPa or more after curing. Say something. The pressure-sensitive adhesive layer used for the interlayer bonding layer may be one layer or may be composed of two or more layers, but is preferably one layer.

The pressure-sensitive adhesive layer can be composed of a pressure-sensitive adhesive composition containing a resin as a main component, such as (meth) acrylic, rubber, urethane, ester, silicone, and polyvinyl ether. Among them, a pressure-sensitive adhesive composition using a (meth) acrylic resin having excellent transparency, weather resistance, heat resistance and the like as a base polymer is preferable. The pressure-sensitive adhesive composition may be an active energy ray-curable type or a thermosetting type.

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

The pressure-sensitive adhesive composition may contain only the above-mentioned base polymer, but usually further contains a cross-linking agent. The cross-linking agent is a divalent or higher metal ion that forms a carboxylic acid metal salt with a carboxyl group; a polyamine compound that forms an amide bond with a carboxyl group; poly. Examples thereof include epoxy compounds and polyols that form an ester bond with a carboxyl group; polyisocyanate compounds that form an amide bond with a carboxyl group. Of these, polyisocyanate compounds are preferable.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured by being irradiated with active energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with active energy rays. It is a pressure-sensitive adhesive composition having a property that it can be brought into close contact with an adherend such as, etc., and can be cured by irradiation with active energy rays to adjust the adhesive force. The active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable type. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. Further, if necessary, a photopolymerization initiator, a photosensitizer, or the like may be contained.

The pressure-sensitive adhesive composition includes fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, pressure-sensitive adhesives, and fillers (metal powders and other inorganic powders). Etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoaming agents, corrosion inhibitors, photopolymerization initiators and other additives can be included.

The pressure-sensitive adhesive layer can be formed by applying an organic solvent diluted solution of the pressure-sensitive adhesive composition on a substrate and drying it. When the active energy ray-curable pressure-sensitive adhesive composition is used, the formed pressure-sensitive adhesive layer can be irradiated with active energy rays to obtain a cured product having a desired degree of curing.

As the adhesive, for example, one or a combination of two or more of water-based adhesives, active energy ray-curable adhesives, and the like can be formed. Examples of the water-based adhesive include a polyvinyl alcohol-based resin aqueous solution, a water-based two-component urethane-based emulsion adhesive, and the like. The active energy ray-curable adhesive is an adhesive that cures by irradiating with active energy rays such as ultraviolet rays, and is, for example, an adhesive containing a polymerizable compound and a photopolymerizable initiator, and an adhesive containing a photoreactive resin. , Adhesives containing a binder resin and a photoreactive cross-linking agent, and the like. Examples of the polymerizable compound include a photopolymerizable monomer such as a photocurable epoxy-based monomer, a photocurable acrylic-based monomer, and a photocurable urethane-based monomer, and an oligomer derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anionic radicals, and cationic radicals by irradiating them with active energy rays such as ultraviolet rays.

[Manufacturing method of polarizing plate]
The polarizing plates 100 and 200 can be manufactured by a method including a step of bonding the polarizing element and the protective film to each other via an interlayer bonding layer formed of an appropriate adhesive. When the layers are bonded to each other via the interlayer bonding layer, it is preferable to perform a surface activation treatment such as a corona treatment on one or both of the bonded surfaces for the purpose of adjusting the adhesion. The conditions for corona treatment can be set as appropriate, and the conditions may differ between one surface of the bonded surface and the other surface. It is also possible to perform a treatment such as corona treatment on the protective film without using the interlayer bonding layer, and then bond the corona-treated protective film and the polarizing element. As described above, the optimum bonding between the polarizing element and the protective film can be appropriately selected according to the type of the protective film.

[Display device]
The polarizing plate according to the present invention can be used in a display device and can also be used in a flexible display device. The display device may be configured to include a display element and a polarizing plate laminated on the visual side of the display element. The display device is not particularly limited, and examples thereof include an image display device such as an organic EL display device, an inorganic EL display device, a liquid crystal display device, and an electroluminescence display device. The display device may have a touch panel function. The polarizing plate is suitable for a flexible display device having flexibility that can be bent or bent. In the display device, the polarizing plate is arranged on the visual recognition side of the display element so that the protective film 20 is located on the visual recognition side with respect to the polarizing element 10.

The display device according to the present invention can be used as a mobile device such as a smartphone or tablet, a television, a digital photo frame, an electronic signboard, a measuring instrument or an instrument, an office device, a medical device, a computer device, or the like. It is particularly suitable as a display device mounted on mobile devices that are required to be further miniaturized in the future.

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

[Measurement of thickness]
The thickness of the splitter was measured with a contact film thickness meter [trade name "DIGIMICRO (registered trademark) MH-15M" manufactured by Nikon Corporation].

[Polarizer]
(Manufacturing of a polarizing element a)
A polyvinyl alcohol film having a thickness of 20 μm, a degree of polymerization of 2400, and a degree of polymerization of 99% or more was uniaxially stretched on a thermal roll at a stretching ratio of 4.1 times, and iodine was 0.05 per 100 parts by mass of water while maintaining a tense state. It was immersed in a dyeing bath containing 5 parts by mass of potassium iodide and 5 parts by mass at 28 ° C. for 60 seconds.

Then, it was immersed in boric acid aqueous solution 1 containing 5.5 parts by mass of boric acid and 15 parts by mass of potassium iodide per 100 parts by mass of water at 64 ° C. for 110 seconds. Then, it was immersed in boric acid aqueous solution 2 containing 3.9 parts by mass of boric acid and 15 parts by mass of potassium iodide per 100 parts by mass of water at 67 ° C. for 30 seconds. Then, it was washed with pure water of 10 degreeC and dried, and a polarizing element a was obtained. The thickness of the obtained polarizing element a was 8 μm, the shrinkage force was 1.8 N / 2 mm, and the boron content was 3.6% by mass.

(Preparation of splitter b)
The Boric Acid B was produced by the same method as the Polarizer a, except that the boric acid content of the boric acid aqueous solution 2 was changed to 2.3 parts by mass per 100 parts by mass of water. The thickness of the obtained polarizing element b was 8 μm, the shrinkage force was 1.5 N / 2 mm, and the boron content was 3.0% by mass.

(Preparation of splitter c)
The Boric Acid C was produced by the same method as the Derivator a, except that the boric acid content of the boric acid aqueous solution 2 was changed to 5.5 parts by mass per 100 parts by mass of water. The thickness of the obtained polarizing element c was 8 μm, the shrinkage force was 2.1 N / 2 mm, and the boron content was 4.3% by mass.

(Manufacturing of a polarizing element d)
The Boric Acid C was produced by the same method as the Derivator a, except that the boric acid content of the boric acid aqueous solution 2 was changed to 6.8 parts by mass per 100 parts by mass of water. The thickness of the obtained polarizing element c was 8 μm, the shrinkage force was 2.5 N / 2 mm, and the boron content was 5.0% by mass.

(Manufacturing of a polarizing element e)
The Boric Acid E was produced by the same method as the Hydroxide a, except that the boric acid content of the boric acid aqueous solution 2 was changed to 1.5 parts by mass per 100 parts by mass of water. The thickness of the obtained polarizing element e was 8 μm, the shrinkage force was 1.2 N / 2 mm, and the boron content was 2.5% by mass.

(Measurement of Boron Content of Polarizer)
0.2 g of the stator was dissolved in 200 g of a 1.9 mass% mannitol aqueous solution. The obtained aqueous solution was titrated with a 1 mol / L NaOH aqueous solution, and the boron content of the substituent was calculated by comparing the amount of the NaOH solution required for neutralization with the calibration curve.

(Measurement of contractile force of modulator)
The polarizing element was cut into a rectangle having a short side of 2 mm and a long side of 50 mm by a super cutter (manufactured by Ogino Seiki Seisakusho Co., Ltd.) so that the slow axis of the polarizing element coincided with the long side, and used as a test piece. The shrinkage force of the test piece was measured using a thermomechanical analyzer (manufactured by SII Nanotechnology Co., Ltd., model TMA / 6100). This measurement was carried out in a constant dimensional mode (with a chuck distance of 10 mm), the test piece was left in a room at 20 ° C for a sufficient time, and then the temperature in the sample room was set from 20 ° C to 80 ° C in 10 minutes. The temperature was raised, and after the temperature was raised, the temperature inside the sample chamber was set to be maintained at 80 ° C. After the temperature was raised and left for another 4 hours, the shrinkage force in the long side direction of the test piece was measured in an environment of 80 ° C. In this measurement, the static load was 0 mN, and a SUS probe was used as the jig.

[Adhesive 1 adjustment]
3 parts by mass of carboxyl group-modified polyvinyl alcohol (Kurare Co., Ltd., trade name "KL-318") is dissolved in 100 parts by mass of water, and a polyamide epoxy-based additive (Taoka Chemical Industry Co., Ltd.), which is a water-soluble epoxy resin, is dissolved in the aqueous solution. A water-based adhesive was prepared by adding 1.5 parts by mass of a trade name "Smiley's Resin (registered trademark) 650 (30), an aqueous solution having a solid content concentration of 30% by mass), and the water-based adhesive was adhered. Let it be agent 1.

[Adhesive 2 adjustment]
Polyester urethane (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Superflex 210, solid content: 33%) 16.8 g, cross-linking agent (oxazoline-containing polymer, manufactured by Nippon Catalyst, trade name: Epocross WS-700, solid content: 25%) ) 4.2g, 1% by mass of ammonia water 2.0g, colloidal silica (manufactured by Fuso Chemical Industry, Quartron PL-3, solid content: 20% by mass) 0.42g and pure water 76.6g are mixed and adhesive. The composition was obtained. This adhesive composition is referred to as adhesive 2.

[Protective film]
(Preparation of protective film a)
As the protective film a, a film made of triacetyl cellulose (TAC) having a thickness of 20 μm (manufactured by Konica Minolta Co., Ltd., trade name “KC2CT”) was used.

(Preparation of protective film b)
Pellets of the thermoplastic resin containing the norbornene polymer (glass transition point 137 ° C.) were dried at 100 ° C. for 5 hours. The pellets were supplied to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, and extruded into a film from a T-die onto a casting drum. The extruded resin was cooled by a casting drum to obtain a long unstretched film having a thickness of 55 μm and a width of 1500 mm. The unstretched film thus obtained was stretched in the longitudinal direction at a stretching temperature of 145 ° C. and a stretching ratio of 1.5 times to obtain a long longitudinally stretched film having a thickness of 45 μm and a width of 1000 mm.

A manufacturing device including a tenter stretching device provided with an inner clip chain and an outer clip chain and an oven covering the tenter stretching device was prepared. The vertically stretched film was continuously supplied as a resin film to the tenter stretching device to perform diagonal stretching. The stretching conditions were a stretching ratio of 2.0 times, a stretching temperature of 142 ° C., and a tension ratio of the inner clip chain and the outer clip chain Tin / Tout × 100 was 105%. As a result, a long diagonally stretched film having a thickness of 22 μm and a width of 1330 mm was obtained. An acrylic hard coat having a thickness of 3 μm was applied to the surface of the obtained stretched film to obtain a protective film b having a thickness of 25 μm.

(Preparation of protective film c)
Pellets of the thermoplastic resin containing the norbornene polymer (glass transition point 137 ° C.) were dried at 100 ° C. for 5 hours. The pellets were supplied to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, and extruded into a film from a T-die onto a casting drum. The extruded resin was cooled by a casting drum to obtain a long unstretched film having a thickness of 50 μm and a width of 1500 mm. The unstretched film thus obtained was stretched in the longitudinal direction at a stretching temperature of 145 ° C. and a stretching ratio of 1.5 times to obtain a long longitudinally stretched film having a thickness of 40 μm and a width of 1000 mm.

A manufacturing device including a tenter stretching device provided with an inner clip chain and an outer clip chain and an oven covering the tenter stretching device was prepared. The vertically stretched film was continuously supplied as a resin film to the tenter stretching device to perform diagonal stretching. The stretching conditions were a stretching ratio of 2.1 times, a stretching temperature of 142 ° C., and a tension ratio of the inner clip chain and the outer clip chain Tin / Tout × 100 was 105%. As a result, a protective film c having a thickness of 18 μm and a width of 1330 mm was obtained.

(Preparation of protective film d)
Pellets of acrylic resin [glass transition temperature: 135 ° C., melt viscosity: 700 Pa · s (temperature 270 ° C., shear rate 100 (1 / sec))] are put into a single-screw extruder (φ = 20.0 mm, L / D). = 25) and a coated hanger type T die (width 150 mm) melt-extruded at 280 ° C., and the melted resin composition was discharged onto a cooling roll held at 110 ° C. to form an acrylic resin film having a thickness of 80 μm. Formed. Next, the easy-adhesive composition obtained above was applied to one surface of the acrylic resin film using a bar coater, and then put into a hot air dryer and dried at 100 ° C. for 90 seconds. Then, the film was uniaxially stretched (stretching ratio: 4 times) using a table stretching machine to obtain a protective film d having a thickness of 20 μm.

(Preparation of protective film e)
An acrylic hard coat having a thickness of 3 μm was applied to the surface of the protective film d to obtain a protective film e having a thickness of 23 μm.

(Measurement of moisture permeability of protective film)
The moisture permeability of the protective film was measured by the cup method specified in JIS Z 0208 at a temperature of 40 ° C. and a relative humidity of 92% RH. The results are shown in Table 1.

(Measurement of piercing elastic modulus of protective film)
A measurement sample is prepared by laminating the protective film to be measured on a glued mount cut out in a square having a central portion of 30 mm × 30 mm. A needle with a tip diameter of 1 mm φ0.5 R is pierced into the central part of the protective film attached to the cut-out part of the glued mount at a speed of 0.33 cm / sec approximately perpendicular to the surface of the protective film. .. Then, the amount of displacement due to the deflection of the protective film in the abutment direction measured at the time of breakage is defined as the strain amount S (mm), the stress applied to the protective film is defined as F (g), and the stress F is defined as F (g). The puncture elastic modulus A (g / mm) was obtained by dividing by the strain amount S. That is, the piercing elastic modulus was obtained by the following equation (1). The results are shown in Table 1.

Puncture elastic modulus A (g / mm) = F (g) / S (mm) (1)
(Bending resistance test of protective film)
The protective film to be measured was subjected to an evaluation test for confirming the durability against bending at a temperature of 25 ° C. using a bending evaluation facility (STS-VRT-500 manufactured by Science Town). The bending axis is determined, bent until the bending radius is 1.5 mm along the bending axis and the regions on both sides of the bending axis face each other so as to be parallel, and then the movement of releasing the bending is repeated 135,000 times. went. Then, the length of the crack formed along the bending axis was measured. The results are shown in Table 1.

[Preparation of phase difference body]
(1) Preparation of "Alignment Layer / First Liquid Crystal Curing Layer" A λ / 4 retardation layer (first liquid crystal curing layer) formed on the base film, which is a layer obtained by curing the alignment layer and the nematic liquid crystal compound, is formed. Got ready. The total thickness of the "aligned layer / first liquid crystal cured layer" was 2 μm.

(2) Preparation of "Alignment Layer / Second Liquid Crystal Curing Layer" As a composition for forming the alignment layer, with 10.0 parts by mass of polyethylene glycol di (meth) acrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., A-600). , Trimethylol Propanetriacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) 10.0 parts by mass and 1,6-hexanediol di (meth) acrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., A-HD-) N) 10.0 parts by mass and 1.50 parts by mass of Irgacure 907 (Irg-907, manufactured by BASF) as a photopolymerization initiator are dissolved in 70.0 parts by mass of the solvent methyl ethyl ketone to form an alignment layer. The working solution was adjusted.

A long cyclic olefin resin (COP) film (manufactured by Nippon Zeon Corporation) with a thickness of 20 μm is prepared as a base film, and a coating liquid for forming an alignment layer is applied to one side of the base film with a bar coater. did.

The coated layer after coating is heat-treated at a temperature of 80 ° C. for 60 seconds, and then irradiated with ultraviolet rays (UVB) at 220 mJ / cm ² to polymerize and cure the composition for forming an alignment layer to form a base film. An oriented layer having a thickness of 2.3 μm was formed on the top.

As a composition for forming a retardation layer, 20.0 parts by mass of a photopolymerizable nematic liquid crystal compound (RMM28B, manufactured by Merck) and 1.0 mass of Irgacure 907 (Irg-907, manufactured by BASF) as a photopolymerization initiator. The parts were dissolved in 80.0 parts by mass of the solvent propylene glycol monomethyl ether acetate to prepare a coating liquid for forming a retardation layer.

A coating liquid for forming a retardation layer was applied onto the previously obtained alignment layer, and the coating layer was heat-treated at a temperature of 80 ° C. for 60 seconds. Then, it is irradiated with ultraviolet rays (UVB) at 220 mJ / cm ² to polymerize and cure the composition for forming the retardation layer, and a retardation layer (second liquid crystal curing layer) having a thickness of 0.7 μm is formed on the alignment layer. Formed. In this way, an "alignment layer / second liquid crystal cured layer" having a total thickness of 3 μm was obtained on the base film.

(3) Preparation of Phase Difference Body The "aligned layer / first liquid crystal cured layer" laminated on the base film and the "aligned layer / second liquid crystal cured layer" laminated on the base film are subjected to ultraviolet rays. Each liquid crystal cured layer surface (the surface opposite to the base film) was bonded with a curable adhesive (thickness 1 μm) so as to be a bonding surface. Next, the ultraviolet curable adhesive was cured by irradiating with ultraviolet rays to prepare a retardation body including two liquid crystal curable layers, a first liquid crystal curable layer and a second liquid crystal curable layer.

[Examples 1 to 7, Comparative Examples 1 to 2]
Using the protective film shown in Table 2, the polarizing element shown in Table 2, and the above-mentioned retardation body, a polarizing plate having the configuration shown in FIG. 2 was produced.

[Impact resistance test]
From the polarizing plates of each example and comparative example, a small piece having a rectangular size of 150 mm on the long side and 70 mm on the short side is cut out using a super cutter, and the surface of the small piece on the retarder side is attached to an acrylic plate via an adhesive layer. It fits. Then, in an environment of a temperature of 23 ° C. and a relative humidity of 55% RH, the pen tip is positioned at a height of 5 cm from the outermost surface of the protective film of the small piece with respect to the small piece, and the pen tip is directed downward. The evaluation pen was dropped from that position. As the evaluation pen, a pen having a mass of 11 g and a pen tip diameter of 0.7 mm was used. The small pieces after dropping the evaluation pen were visually observed and evaluated according to the following criteria. Table 2 shows the evaluation results.
A: No cracks or scratches on the stator and protective film.
B: There is no crack in the polarizing element and there is a scratch on the protective film.
C: There is a scratch on the polarizing element.

[Flexibility evaluation]
The bending resistance of the polarizing plates of each example and comparative example was evaluated according to the following criteria based on the results of the bending resistance test of the protective film used. Table 2 shows the evaluation results.
A: The protective film does not crack in the bending resistance test (crack length is 0 mm).
B: For the protective film, the crack length in the bending resistance test is more than 0 mm and 5 mm or less.
C: For the protective film, the crack length in the bending resistance test is more than 5 mm.

[Moisture resistance test]
A rectangular piece having a long side of 140 mm and a short side of 65 mm is cut out from the polarizing plates of each Example and Comparative Example using a super cutter, and the retardation body side surface of the small piece is a non-alkali glass plate via an adhesive layer. It was bonded to the glass using a hand roller. This test piece was placed in a constant temperature and humidity chamber having a temperature of 65 ° C. and a relative humidity of 90% RH, allowed to stand for 500 hours, and then taken out. Place the polarizing plate of the test piece and the standard polarizing plate on the cross Nicol, observe the vicinity of the corner of the polarizing plate of the test piece with an optical microscope, measure the length of iodine withdrawal from the end of the polarizing element, and use the following criteria. It was evaluated at. Table 2 shows the evaluation results.

A: Iodine removal length at the end is less than 0.3 mm B: Iodine removal length at the end is 0.3 mm to less than 0.6 mm C: Iodine removal length at the end is 0.6 mm or more

In Examples 1 to 3, Example 5, Example 7, and Comparative Example 2, the polarizing element and the protective film (PMMA) were bonded via a bonding layer formed of the adhesive 2.
In Example 4, the polarizing element and the protective film (TAC) were bonded via a bonding layer formed from the adhesive 1.
In Example 6, when the polarizing element and the protective film (COP) were bonded, the surface of the protective film was subjected to corona treatment and bonded without passing through the bonding layer.

In Comparative Example 1, when the polarizing element and the protective film (COP) were bonded, the surface of the protective film was subjected to corona treatment and bonded without passing through the bonding layer.

1 Mount with measurement film, 6 Voids, 7 Mount with glue, 8 Outer circumference, 10 Polarizer, 12 Measurement film, 20 Protective film, 30 Phase difference plate, 31 First phase difference layer, 32 Second phase difference layer, 33 , 40 Interlayer bonding layer, 100, 200 polarizing plate, N needle, position where M needle N is pierced, S strain amount.

Claims (10)

A polarizing plate in which a protective film and a polarizing element are laminated, and the protective film is laminated only on one side of the polarizing element.
The protective film has a puncture elastic modulus of 300 g / mm or more and 550 g / mm or less calculated by the following procedure, a thickness of 25 μm or less, and a moisture permeability of 300 g at a temperature of 40 ° C. and a relative humidity of 92% RH. / (M ^2.24 hours) or less,
The polarizing plate contains a polyvinyl alcohol-based resin and boron, has a boron content of 3.0% by mass or more and 4.5% by mass or less, and is a polarizing plate used in a flexible display device.
[Procedure for calculating piercing elastic modulus]
For the puncture elastic modulus, a measurement sample in which a protective film was attached to a glued mount cut out in a square with a central part of 30 mm × 30 mm was used, and a needle with a tip diameter of 1 mm φ0.5 R was used at a speed of 0.33 cm / sec. The amount of displacement due to bending of the protective film in the piercing direction, which is measured when the protective film is pierced perpendicularly to the surface of the protective film and breaks, is defined as a strain amount S (mm) and added to the protective film. Assuming that the stress is F (g), the proportional constant (stress F / strain S) between the stress F and the strain S is the equation (1) :.
Puncture elastic modulus A (g / mm) = F (g) / S (mm) (1)
It is a physical characteristic value calculated by. The polarizing plate according to claim 1, wherein the protective film has a piercing elastic modulus of 500 g / mm or less. The polarizing plate according to claim 1 or 2, wherein the polarizing element has a thickness of 12 μm or less. The protective film has a resin film and a protective layer, and has.
The polarizing plate according to any one of claims 1 to 3, wherein the protective layer is an organic layer. The polarizing plate according to any one of claims 1 to 4, wherein the protective film is made of a (meth) acrylic resin. The polarizing plate according to any one of claims 1 to 5, further comprising a retardation body arranged on the side opposite to the protective film side of the polarizing element. The polarizing plate according to claim 6, wherein the retarder has a layer formed by curing a polymerizable liquid crystal compound. The polarizing plate according to any one of claims 1 to 7, wherein the polarizing plate has a thickness of 40 μm or less. A display device comprising the polarizing plate according to any one of claims 1 to 8. A flexible display device comprising the polarizing plate according to any one of claims 1 to 8.

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