TWI819119B - Method for manufacturing polarizing plate with retardation layer - Google Patents

Abstract

To provide a polarizing plate with a retardation layer that is thin, has excellent handleability, and has excellent optical properties. The polarizing plate with a retardation layer of the present invention has a polarizing plate and a retardation layer. The polarizing plate includes a polarizing film and a protective layer located on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing dichroic substances. Its thickness is less than 8 μm , the monomer transmittance is more than 48%, and the polarization degree is more than 85%. Re(550) of the retardation layer is 100nm~190nm, and Re(450)/Re(550) is 0.8 or more and less than 1. The angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40°~50°.

Description

Method for manufacturing polarizing plate with retardation layer

The present invention relates to a polarizing plate with a retardation layer and an image display device using the same.

Background of the invention

In recent years, image display devices, represented by liquid crystal display devices and electroluminescence (EL) display devices (such as organic EL display devices and inorganic EL display devices), have rapidly become popular. Typical image display devices use polarizing plates and phase difference plates. In practical applications, polarizing plates with a retardation layer in which a polarizing plate and a retardation plate are integrated are widely used (for example, Patent Document 1). Recently, as the demand for thinner image display devices has increased, the need for retardation layers has increased. The demand for thinner polarizing plates has also increased. In addition, in recent years, the demand for curved image display devices and/or flexible or bendable image display devices has increased, and polarizing plates and polarizing plates with retardation layers are also required to be further thinned and further improved. of softening. In order to make the polarizing plate with the retardation layer thinner, the protective layer of the polarizing film and the retardation film, which have a great influence on the thickness, are being made thinner. However, if the protective layer and the retardation film are made thinner, the impact of shrinkage of the polarizing film will become relatively larger, causing problems such as warping of the image display device and reduced operability of the polarizing plate with the retardation layer.

In order to solve the above problems, even the polarizing film needs to be thinned typing. However, if the thickness of the polarizing film is simply reduced, the optical properties will be reduced. More specifically, one or both of the polarization degree and the monomer transmittance, which have a trade-off relationship, are reduced to a level that is unacceptable for practical applications. As a result, the optical properties of the polarizing plate with the retardation layer become insufficient.

Prior technical literature

patent documents

Patent Document 1: Japanese Patent No. 3325560

Summary of the invention

The present invention was made in order to solve the above-mentioned conventional problems, and its main purpose is to provide a polarizing plate with a retardation layer that is thin, has excellent handleability, and has excellent optical properties.

The polarizing plate with a retardation layer of the present invention has a polarizing plate and a retardation layer. The polarizing plate includes a polarizing film and a protective layer located on at least one side of the polarizing film. The polarizing film is composed of a polyvinyl alcohol resin film containing dichroic substances. Its thickness is less than 8 μm , its monomer transmittance is more than 48%, and its polarization degree is more than 85%. Re(550) of the retardation layer is 100nm~190nm, Re(450)/Re(550) is 0.8 or more and less than 1, and the angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40°. ~50°.

In one embodiment, the protective layer is composed of a base material with an elastic modulus of 3000 MPa or more.

In one embodiment, the total thickness of the polarizing plate with the retardation layer is 90 μm or less, the front reflection hue is 3.5 or less, and the protective layer is composed of a resin film with an elastic coefficient of 3000 MPa or more.

In one embodiment, the protective layer is composed of a cellulose triacetate-based resin film.

In one embodiment, the polarizing plate includes the polarizing film and the protective layer disposed only on one side of the polarizing film, and the retardation layer is bonded to the polarizing film through an adhesive layer.

In one embodiment, the retardation layer is composed of a polycarbonate resin film.

In one embodiment, the retardation layer is composed of a polycarbonate resin film having a thickness of 40 μm or less.

In one embodiment, the difference between the maximum value and the minimum value of the single transmittance of the polarizing film in an area of 50 cm ² is 0.5% or less.

In one embodiment, the width of the polarizing plate with the retardation layer is 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance at a position along the width direction of the polarizing film is 1% or less.

In one embodiment, the single transmittance of the polarizing film is 50% or less, and the polarization degree is 92% or less.

In one embodiment, the polarizing plate with a retardation layer further has another retardation layer outside the retardation layer, and the refractive index characteristics of the other retardation layer show the relationship nz>nx=ny.

In one embodiment, the polarizing plate with a retardation layer further has a conductive layer or an isotropic base material with a conductive layer outside the retardation layer.

In one embodiment, the above-mentioned polarizing plate with a retardation layer is in a long strip shape, the above-mentioned polarizing film has an absorption axis in the long direction, and the above-mentioned retardation layer is 40° to 50° with respect to the long direction. An obliquely stretched film with a slow axis in the direction of the angle. In one embodiment, the polarizing plate with a retardation layer is wound into a roll shape.

According to another aspect of the present invention, an image display device is provided. This image display device includes the above-mentioned polarizing plate with a retardation layer.

In one embodiment, the image display device is an organic electroluminescent display device or an inorganic electroluminescent display device.

According to the present invention, a polarizing film that is thin but has extremely excellent optical properties can be obtained by combining the following methods: adding a halide (typically potassium iodide) to a polyvinyl alcohol (PVA) resin, including air-assisted stretching and water 2-stage stretching, drying and shrinking with heated rollers. By using the polarizing film, a polarizing plate with a retardation layer that is thin, has excellent handleability, and has excellent optical properties can be realized.

10:Polarizing plate

11:Polarizing film

12: 1st protective layer

13: 2nd protective layer

20: Phase difference layer (first phase difference layer)

50: Another phase difference layer (second phase difference layer)

60: Conductive layer or isotropic substrate with conductive layer

100, 101: Polarizing plate with phase difference layer

200:Laminated body

G1~G4: guide roller

R1~R6: conveyor roller

FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention.

2 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention.

3 is a schematic view showing an example of drying and shrinkage treatment using a heating roller in the manufacturing method of the polarizing film used in the polarizing plate with a retardation layer of the present invention.

Form used to implement the invention

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)

The definitions of terms and symbols in this manual are as follows.

(1)Refractive index (nx, ny, nz)

"nx" is the refractive index in the direction where the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and " nz" is the refractive index in the thickness direction.

(2) In-plane phase difference (Re)

"Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is d(nm).

(3) Phase difference in thickness direction (Rth)

"Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d when the layer (film) thickness is d(nm).

(4)Nz coefficient

The Nz coefficient can be obtained by Nz=Rth/Re.

(5)Angle

When an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise relative to the reference direction. So, for example, "45°" means ±45°.

A. Overall composition of polarizing plate with retardation layer

FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention. The polarizing plate with retardation layer 100 of this embodiment has the polarizing plate 10 and the retardation layer 20 . The polarizing plate 10 includes a polarizing film 11 , a first protective layer 12 disposed on one side of the polarizing film 11 , and a second protective layer 13 disposed on the other side of the polarizing film 11 . One of the first protective layer 12 and the second protective layer 13 may be omitted depending on the purpose. For example, when the retardation layer 20 can function as a protective layer for the polarizing film 11, the second protective layer 13 can also be omitted. In the embodiment of the present invention, the polarizing film is typically composed of a polyvinyl alcohol-based resin film containing a dichroic substance. The thickness of the polarizing film is less than 8 μm , the single transmittance is more than 48%, and the degree of polarization is more than 85%.

As shown in FIG. 2 , the polarizing plate 101 with a retardation layer in another embodiment may also be provided with another retardation layer 50 and/or a conductive layer or an isotropic base material 60 with a conductive layer. The other retardation layer 50 and the conductive layer or the isotropic substrate 60 with the conductive layer can typically be provided outside the retardation layer 20 (the side opposite to the polarizing plate 10 ). The refractive index characteristics of another phase difference layer representative show the relationship nz>nx=ny. The other phase difference layer 50 and the conductive layer or the isotropic base material 60 with the conductive layer are arranged sequentially from the phase difference layer 20 side. The other phase difference layer 50 and the conductive layer or the isotropic substrate 60 with the conductive layer represent any of the above layers that can be provided as needed, and any one or both of them can be omitted. In addition, for convenience, the phase difference layer 20 may be called a first phase difference layer, and the other phase difference layer 50 may be called a second phase difference layer. In addition, when a conductive layer or an isotropic substrate with a conductive layer can be provided, the polarizing plate with a retardation layer can be used in an image display unit (such as Such as an organic EL unit) and a polarizing plate, a so-called internal touch panel input display device is formed by integrating a touch sensor.

In the embodiment of the present invention, Re(550) of the first retardation layer 20 is 100 nm to 190 nm, and Re(450)/Re(550) is 0.8 or more and less than 1. Furthermore, the angle formed by the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is 40° to 50°.

The above-mentioned embodiments may be combined appropriately, and changes evident in the industry may be added to the constituent elements of the above-mentioned embodiments. For example, the structure in which the isotropic base material 60 with a conductive layer is provided outside the second retardation layer 50 may be replaced with an optically equivalent structure (for example, a laminate of a second retardation layer and a conductive layer).

The polarizing plate with a retardation layer according to the embodiment of the present invention may further include other retardation layers. The optical properties (such as refractive index properties, in-plane phase difference, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of other retardation layers can be appropriately set according to the purpose.

The polarizing plate with a retardation layer of the present invention can be in the form of a sheet or a strip. The term "elongated shape" in this specification means an elongated shape that is sufficiently long relative to the width. For example, it includes an elongated shape that is 10 times or more in length relative to the width, and preferably is an elongated shape that is 20 times or more in length relative to the width. . The long polarizing plate with retardation layer can be rolled into a roll. When the polarizing plate with the retardation layer is in a strip shape, both the polarizing plate and the retardation layer are in a strip shape. In this case, it is preferable that the polarizing film has an absorption axis in the longitudinal direction. The first retardation layer is preferably an obliquely extending film having a slow axis in a direction at an angle of 40° to 50° with respect to the longitudinal direction. As long as the polarizing film and the first retardation layer have the above-mentioned structures, Once completed, a polarizing plate with a retardation layer can be produced from roll-to-roll.

In actual use, an adhesive layer (not shown) can be provided on the side of the retardation layer opposite to the polarizing plate, and the polarizing plate with the retardation layer can be attached to the image display unit. Furthermore, the surface of the adhesive layer should be temporarily adhered to the release film before the polarizing plate with the retardation layer is used. By temporarily adhering the release film, a roll can be formed while protecting the adhesive layer.

The front reflection hue (√(a ^*2 +b ^*2 )) of the polarizing plate with the retardation layer is preferably 3.5 or less, and 3.0 or less. As long as the front reflection hue is within the above range, undesirable coloring, etc. can be suppressed, and as a result, a polarizing plate with a retardation layer having excellent reflection characteristics can be obtained.

The total thickness of the polarizing plate with the retardation layer is preferably less than 140 μm , and preferably less than 120 μm , more preferably less than 100 μm , more preferably less than 90 μm , and more preferably less than 85 μm . . The lower limit of the total thickness may be, for example, 30 μm . According to the embodiment of the present invention, it is possible to realize the extremely thin polarizing plate with a retardation layer as described above. The polarizing plate with a retardation layer can have excellent flexibility and bending durability. The polarizing plate with a retardation layer is particularly suitable for use in curved image display devices and/or flexible or bendable image display devices. In addition, the total thickness of the polarizing plate with a retardation layer refers to the polarized light with the retardation layer after deducting the adhesive layer used to adhere the polarizing plate with a retardation layer to an external adherend such as a panel or glass. The total thickness of all layers of the plate (that is, the total thickness of the polarizing plate with a retardation layer does not include the adhesive layer used to attach the polarizing plate with the retardation layer to adjacent components such as the image display unit and the adhesive layer that can be temporarily adhered to The thickness of the peeling film on its surface).

The components of the polarizing plate with a retardation layer will be described in more detail below.

B.Polarizing plate

B-1.Polarizing film

The polarizing film 11 is as described above, has a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more. Generally speaking, there is a trade-off relationship between monomer transmittance and polarization degree. Therefore, if the monomer transmittance is increased, the polarization degree will decrease, and if the polarization degree is increased, the monomer transmittance will decrease. Therefore, in the past, thin polarizing films that met the optical characteristics of a single transmittance of 48% or more and a polarization degree of 85% or more were difficult to put into practical use. One of the features of the present invention is the use of a thin polarizing film that has excellent optical properties of a single transmittance of 48% or more and a polarization degree of 85% or more, and the variation in optical properties has been suppressed.

The thickness of the polarizing film should be 1 μm ~8 μm , preferably 1 μm ~7 μm , and 2 μm ~5 μm better.

The polarizing film should show absorption dichroism at any wavelength between 380nm and 780nm. The monomer transmittance of the polarizing film should be less than 50%. The polarization degree of the polarizing film is preferably above 86%, more preferably above 87%, and more preferably above 88%. On the other hand, the degree of polarization is preferably 92% or less. The above-mentioned monomer transmittance represents the Y value obtained by measuring it using an ultraviolet-visible light spectrophotometer and correcting the optical efficiency. The above-mentioned degree of polarization is represented by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and corrected for optical efficiency.

Polarization degree (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is measured using a laminate of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50) using ultraviolet visible light. Measured with a spectrophotometer. Depending on the refractive index of the polarizing film surface and/or the refractive index of the surface of the protective film in contact with the air interface, the reflectance at the interface of each layer will change, and as a result, the measured value of the transmittance will change. Therefore, for example, when using a protective film with a refractive index other than 1.50, the measured value of the transmittance can also be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the correction value C of the transmittance is expressed by the following formula using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective film and the air layer.

C=R ₁ -R ₀

R ₀ =((1.50-1) ² /(1.50+1) ² )×(T ₁ /100)

R ₁ =((n ₁ -1) ² /(n ₁ +1) ² )×(T ₁ /100)

Here, R ₀ is the transmission axis reflectance when using a protective film with a refractive index of 1.50, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. For example, when a base material (cycloolefin-based film, hard-coated film, etc.) with a surface refractive index of 1.53 is used as a protective film, the correction amount C is approximately 0.2%. At this time, adding 0.2% to the measured transmittance can be converted into the transmittance when using a protective film with a surface refractive index of 1.50. In addition, after calculation based on the above formula, the change in correction value C after changing the transmittance T ₁ of the polarizing film by 2% is less than 0.03%. Therefore, the impact of the transmittance of the polarizing film on the correction value C is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be performed based on the amount of absorption.

In one embodiment, the width of the polarizing plate with the retardation layer is 1000 mm or more, so the width of the polarizing film is also 1000 mm or more. At this time, the difference (D1) between the maximum value and the minimum value of the single transmittance at the position along the width direction of the polarizing film is preferably 1% or less, preferably 0.8% or less, more preferably 0.6% or less. The smaller D1 is, the better, and the lower limit of D1 can be, for example, 0.01%. As long as D1 is within the above range, polarizing plates with retardation layers having excellent optical properties can be produced industrially. In another embodiment, the difference (D2) between the maximum value and the minimum value (D2) of the monomer transmittance of the polarizing film in an area of 50 cm ² is preferably 0.5% or less, preferably 0.25% or less, and more preferably 0.15% or less. The smaller D2 is, the better, and the lower limit of D2 can be, for example, 0.01%. As long as D2 is within the above range, the brightness variation of the display screen can be suppressed when the polarizing plate with the retardation layer is used in an image display device.

Any appropriate polarizing film can be used as the polarizing film. Polarizing films can typically be produced using a laminate of two or more layers.

Specific examples of polarizing films obtained using a laminated body include polarizing films obtained using a laminated body of a resin base material and a PVA-based resin layer formed by coating on the resin base material. A polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer coated on the resin base material can be produced, for example, by applying a PVA-based resin solution to the resin base material, and It is dried to form a PVA-based resin layer on the resin base material to obtain a laminated body of the resin base material and the PVA-based resin layer; and the laminated body is stretched and dyed to form the PVA-based resin layer into a polarizing film. In this embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching. And if necessary, the stretching may further include in-air stretching the laminated body at a high temperature (for example, 95°C or above) before stretching in a boric acid aqueous solution. stretch. The obtained laminated body of the resin base material/polarizing film can be used directly (that is, the resin base material can also be used as a protective layer of the polarizing film), or the resin base material can be peeled off from the laminated body of the resin base material/polarizing film and then peeled off. Layer any appropriate protective layer on the surface for later use. Details of the manufacturing method of the polarizing film are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of this publication is used as a reference in this specification.

The manufacturing method of the polarizing film typically includes the following steps: forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin base material to prepare a laminate; and, for the above The laminated body is sequentially subjected to air-assisted stretching treatment, dyeing treatment, water stretching treatment and drying shrinkage treatment. The drying and shrinking treatment is to transport the above-mentioned laminated body in the longitudinal direction while heating it, thereby shrinking it by 2% in the width direction. above. Thereby, a polarizing film with excellent optical properties and suppressed variation in optical properties can be provided. The polarizing film has a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more. That is, by introducing auxiliary stretching, the crystallinity of PVA can be improved even when PVA is coated on a thermoplastic resin, and high optical properties can be achieved. At the same time, improving the orientation of PVA in advance can prevent problems such as the decrease in orientation or dissolution of PVA when immersed in water in the subsequent dyeing step or stretching step, thereby achieving high optical properties. In addition, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain halides, the orientation disorder and decrease in orientation of polyvinyl alcohol molecules can be suppressed. Therefore, the optical properties of the polarizing film obtained by immersing the laminate in a liquid, such as dyeing treatment and water stretching treatment, can be improved. In addition, the optical properties can be improved by shrinking the laminate in the width direction through drying and shrinkage treatment.

B-2.Protective layer

The first protective layer 12 and the second protective layer 13 are each formed of any appropriate thin film that can be used as a protective layer of the polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetylcellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, and polyamide-based resins. Imine-based, polyether-based, polystyrene-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based and acetate-based transparent resins, etc. Furthermore, thermosetting resins such as (meth)acrylic-based, urethane-based, (meth)acrylic-urethane-based, epoxy-based, and polysiloxane-based resins, or ultraviolet curable resins can also be cited. Other examples include glassy polymers such as siloxane polymers. Furthermore, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted acyl imine group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, for example Examples include resin compositions having an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extruded product of the above-mentioned resin composition. In one embodiment, the protective layer (especially the protective layer on the viewing side) contains a TAC-based resin. By using TAC-based resin film as a protective layer, bending durability can be improved.

The polarizing plate with a retardation layer of the present invention is typically arranged on the viewing side of the image display device as will be described later, and the first protective layer 12 is typically arranged on the viewing side. Therefore, the first protective layer 12 can also be applied if necessary. There are surface treatments such as hard coating treatment, anti-reflective treatment, anti-adhesion treatment, and anti-glare treatment. And/or, the first protective layer 12 may also be subjected to processing to improve the visibility when viewed through polarized sunglasses (representatively, imparting (elliptical) polarization function and imparting ultra-high phase difference) as needed. By performing the above processing, excellent visibility can be achieved even when the displayed image is viewed through polarized lenses such as polarized sunglasses. Therefore, the polarizing plate with the retardation layer can also be suitably used in an image display device that can be used outdoors.

The thickness of the first protective layer is preferably 5 μm ~80 μm , more preferably 10 μm ~40 μm , and more preferably 10 μm ~35 μm . In addition, when surface treatment is performed, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

In one embodiment, the second protective layer 13 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0 nm~10 nm, and the phase difference Rth(550) in the thickness direction is -10 nm~+10 nm. In one embodiment, the second protective layer 13 is a retardation layer having any appropriate phase difference value. At this time, the in-plane phase difference Re (550) of the retardation layer is, for example, 110 nm to 150 nm. The thickness of the second protective layer is preferably 5 μm ~80 μm , more preferably 10 μm ~40 μm , and more preferably 10 μm ~30 μm . From the viewpoint of thinning and lightweighting, it is ideal to omit the second protective layer.

B-3. Manufacturing method of polarizing film

The polarizing film can be obtained, for example, by a manufacturing method including the following steps: forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) on one side of a long thermoplastic resin base material to form a laminate. The polyvinyl alcohol-based resin layer Contains halide and polyvinyl alcohol-based resin (PVA-based resin); and, the laminate is sequentially In-air auxiliary stretching treatment, dyeing treatment, water stretching treatment and drying shrinkage treatment. The drying and shrinkage treatment is performed by heating the laminated body while transporting it in the longitudinal direction to shrink it by more than 2% in the width direction. The halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment should be carried out using a heated roller, and the temperature of the heated roller should be 60°C~120°C. The shrinkage rate in the width direction of the laminated body obtained by drying and shrinking treatment is preferably 2% or more. According to the manufacturing method, the polarizing film described in the above item B-1 can be obtained. In particular, a polarizing film with excellent optical properties (typically single transmittance and degree of polarization) and with suppressed variation in optical properties can be obtained by producing a laminate including a PVA-based resin layer containing a halide, The above-mentioned laminated body is stretched through multi-stage stretching including auxiliary stretching in the air and stretching in water, and then the stretched laminated body is heated with a heating roller. Specifically, by using a heating roller in the drying and shrinkage treatment step, the entire laminated body can be uniformly shrunk while conveying the laminated body. This can not only improve the optical properties of the polarizing film obtained, but also stably produce polarizing films with excellent optical properties, and suppress variations in the optical properties of the polarizing film (especially the single transmittance).

B-3-1. Making a laminated body

Any appropriate method may be used as a method of producing a laminate of a thermoplastic resin base material and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried, thereby forming a PVA-based resin layer on the thermoplastic resin base material. As mentioned above, the halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

The coating liquid may be applied by any appropriate method. Examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, blade coating (comma coating, etc.). The coating and drying temperature of the above-mentioned coating liquid is preferably 50°C or above.

The thickness of the PVA resin layer is preferably 3 μm ~40 μm , more preferably 3 μm ~20 μm .

Before forming the PVA-based resin layer, the thermoplastic resin base material may be subjected to surface treatment (such as corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin base material. By performing the above-described treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.

B-3-1-1. Thermoplastic resin base material

The thickness of the thermoplastic resin substrate is preferably 20 μm ~300 μm , more preferably 50 μm ~200 μm . If it is less than 20 μm , it may be difficult to form a PVA-based resin layer. If it is larger than 300 μm , for example, when the thermoplastic resin base material is stretched in water as described later, it may take a long time to absorb water and may cause an excessive load on the stretching.

The water absorption rate of the thermoplastic resin base material is preferably above 0.2%, more preferably above 0.3%. The thermoplastic resin substrate absorbs water, and the water acts as a plasticizer to plasticize it. As a result, the tensile stress can be significantly reduced, allowing high-rate stretching. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent disadvantages such as deterioration of the appearance of the resulting polarizing film due to significant reduction in dimensional stability of the thermoplastic resin base material during production. It can also prevent the base material from breaking when it extends in water, or the PVA resin layer from peeling off the thermoplastic resin base material. condition. In addition, the water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value obtained in accordance with JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin base material is preferably 120°C or lower. By using such a thermoplastic resin base material, the crystallization of the PVA-based resin layer can be suppressed while fully ensuring the extensibility of the laminate. In addition, considering that the thermoplastic resin base material can be plasticized by water and can be stretched well in water, the temperature is preferably 100°C or lower, and more preferably 90°C or lower. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60°C or above. By using such a thermoplastic resin base material, defects such as deformation of the thermoplastic resin base material (such as unevenness, sagging, or wrinkling) can be prevented when coating and drying the coating liquid containing the above-mentioned PVA-based resin. Thus, the laminated body can be produced satisfactorily. In addition, the PVA-based resin layer can be stretched favorably at an appropriate temperature (for example, about 60° C.). In addition, the glass transition temperature of the thermoplastic resin base material can be adjusted, for example, by heating using a crystallized material that can introduce a modifying group into the constituent material. Glass transition temperature (Tg) is a value calculated based on JIS K 7121.

Any appropriate thermoplastic resin can be used as the constituent material of the thermoplastic resin base material. Examples of the thermoplastic resin include ester-based resins such as polyethylene terephthalate-based resins, cyclic olefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and Copolymer resins, etc. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are more preferred.

In one embodiment, it is preferable to use amorphous (non-crystallized) ) Polyethylene terephthalate resin. Among them, amorphous (difficult to crystallize) polyethylene terephthalate-based resin is particularly suitable. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, or copolymers further containing cyclohexane. Dimethanol or diethylene glycol as a copolymer of glycol.

In a preferred embodiment, the thermoplastic resin base material is composed of polyethylene terephthalate resin having an isophthalic acid unit. This is because this thermoplastic resin base material has extremely excellent elongation and can suppress crystallization during elongation. We speculate that this is caused by introducing isophthalic acid units to impart huge flexibility to the main chain. Polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit relative to the total of all repeating units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more. This is because a thermoplastic resin base material with extremely excellent elongation can be obtained. On the other hand, the content ratio of isophthalic acid units is preferably 20 mol% or less, more preferably 10 mol% or less based on the total of all repeating units. By setting the content ratio to the above-described content ratio, the degree of crystallization can be favorably increased in the drying and shrinkage treatment described below.

The thermoplastic resin base material may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, it extends along the transverse direction of the long thermoplastic resin base material. The lateral direction is preferably a direction orthogonal to the extension direction of the laminate described below. In addition, the term "orthogonal" in this specification also includes the case of being substantially orthogonal. Here, the so-called "substantially orthogonal" includes the case of 90°±5.0°, and is preferably 90°±3.0°, and more preferably 90°±1.0°.

The elongation temperature of the thermoplastic resin substrate relative to the glass transition The transfer temperature (Tg) should be Tg-10℃~Tg+50℃. The elongation ratio of the thermoplastic resin base material is preferably 1.5 times to 3.0 times.

The thermoplastic resin base material may be extended by any appropriate method. Specifically, it can be a fixed end extension or a free end extension. The extension method can be dry or wet. The stretching of the thermoplastic resin substrate can be performed in one stage or in multiple stages. When it is carried out in multiple stages, the above-mentioned stretching ratio is the product of the stretching ratios in each stage.

B-3-1-2. Coating liquid

The coating liquid system contains a halide and a PVA-based resin as mentioned above. The above-mentioned coating liquid is a solution in which the above-mentioned halide and the above-mentioned PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, ethylidene Amines such as diamine and diethylenetriamine. These may be used alone or in combination of two or more. Of these, water is the best. The PVA resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. As long as the resin concentration is the above, a uniform coating film that adheres closely to the thermoplastic resin base material can be formed. The halide content in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin.

Additives may also be blended into the coating liquid. Examples of additives include plasticizers, surfactants, etc. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerol. Examples of the surfactant include nonionic surfactants. These can be used in order to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

Any appropriate resin can be used as the above-mentioned PVA-based resin. Can Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification is determined in accordance with JIS K 6726-1994. By using a PVA-based resin having the above saponification degree, a polarizing film excellent in durability can be obtained. When the degree of saponification is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000~10000, preferably 1200~4500, more preferably 1500~4300. In addition, the average degree of polymerization can be determined in accordance with JIS K 6726-1994.

Any appropriate halide may be used as the above-mentioned halide. Examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferred.

The amount of halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of PVA resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of PVA resin. If the amount of the halide is greater than 20 parts by weight relative to 100 parts by weight of the PVA resin, the halide may overflow and the polarizing film finally obtained may become white and turbid.

Generally speaking, when the PVA resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA resin layer will become higher. However, if the stretched PVA resin layer is immersed in a water-containing liquid, there will be polyethylene The orientation of alcohol molecules is disordered and the orientation is reduced. Especially for thermoplastic resins When the laminate of the base material and the PVA-based resin layer is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material, the orientation degree tends to decrease. Significantly. For example, the stretching of a PVA film monomer in boric acid water is generally performed at 60°C. On the other hand, the stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is carried out at 70°C. The temperature before and after is a higher temperature. At this time, the directionality of PVA at the initial stage of extension will decrease before it rises due to extension in water. In this regard, after preparing a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin base material, the laminate is stretched at high temperature in the air (auxiliary stretching) before stretching in boric acid water, thereby promoting the post-auxiliary stretching. Crystallization of the PVA-based resin in the PVA-based resin layer of the laminate. As a result, when the PVA-based resin layer is immersed in a liquid, the orientation disorder and decrease in orientation of polyvinyl alcohol molecules can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristics of the polarizing film obtained through the processing steps of immersing the laminate in a liquid, such as dyeing processing and water stretching processing, can be improved.

B-3-2. Aerial auxiliary extended processing

In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and boric acid water stretching is chosen. For example, in the two-stage stretching method, by introducing auxiliary stretching, the crystallization of the thermoplastic resin base material can be suppressed while stretching, thereby solving the problem of reduced ductility caused by excessive crystallization of the thermoplastic resin base material during the subsequent boric acid water stretching. problem, so that the laminated body can be stretched at a higher magnification. In addition, when coating PVA-based resin on a thermoplastic resin base material, in order to suppress glass transfer of the thermoplastic resin base material Due to the influence of temperature, the coating temperature must be lower than when PVA-based resin is coated on a general metal roller. As a result, the crystallization of PVA-based resin becomes relatively low and sufficient optical properties cannot be obtained. In this regard, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be improved even when the PVA-based resin is coated on the thermoplastic resin, and high optical properties can be achieved. In addition, by improving the orientation of the PVA resin in advance, problems such as the decrease in orientation or dissolution of the PVA resin when immersed in water in the subsequent dyeing step or stretching step can be achieved, thereby achieving high optical properties.

The stretching method of aerial auxiliary stretching can be fixed-end stretching (such as stretching using a tenter stretching machine), or free-end stretching (such as uniaxial stretching of the laminate through rollers with different peripheral speeds). ), but in order to obtain high optical properties, free end extension can be actively used. In one embodiment, the in-air stretching process includes a heating roller stretching step in which the above-mentioned laminated body is conveyed in the longitudinal direction and stretched using the difference in circumferential speed between the heating rollers. The air stretching process typically includes a zone stretching step and a heated roller stretching step. In addition, the order of the area extending step and the heating roller extending step is not limited. The area extending step may be performed first, or the heating roller extending step may be performed first. The region extension step can also be omitted. In one embodiment, the area stretching step and the heating roller stretching step are performed sequentially. In another embodiment, the ends of the film are held in a tenter stretcher and the film is stretched by increasing the distance between the tenters in the traveling direction (the increase in the distance between the tenters is the stretch ratio). At this time, the distance of the tenter in the width direction (perpendicular direction with respect to the traveling direction) is set so as to be arbitrarily close. Preferably, the extension magnification relative to the direction of travel can be set to utilize the extension of the free end for approach. When the free end is extended, it is calculated based on the shrinkage rate in the width direction = (1/extension ratio) ^1/2 .

Aerial assisted extension can be performed in one stage or in multiple stages. When it is carried out in multiple stages, the extension ratio is the product of the extension ratios of each stage. The extension direction of the auxiliary extension in the air should be roughly the same as the extension direction of the extension in the water.

The extension ratio of auxiliary extension in the air should be 2.0 times to 3.5 times. When combining the auxiliary extension in the air and the extension in water, the maximum extension ratio is preferably 5.0 times or more relative to the original length of the laminated body, preferably 5.5 times or more, and more preferably 6.0 times or more. The "maximum elongation ratio" in this specification means the elongation ratio just before the laminated body breaks, and is a value that is 0.2 lower than the value after confirming the elongation ratio at which the laminated body breaks.

The stretching temperature of the in-air auxiliary stretching can be set to any appropriate value according to the forming material of the thermoplastic resin base material, stretching method, etc. The extension temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin base material, more preferably above the glass transition temperature (Tg) of the thermoplastic resin base material + 10°C, and especially above Tg + 15°C. On the other hand, the upper limit of the extension temperature is preferably 170°C. By stretching at such a temperature, the rapid progression of crystallization of the PVA-based resin can be suppressed, thereby suppressing problems caused by the crystallization (for example, obstruction of the orientation of the PVA-based resin layer due to stretching). The crystallization index of the PVA resin after air-assisted stretching is preferably 1.3~1.8, more preferably 1.4~1.7. The crystallization index of PVA resin can be measured using a Fourier transform infrared spectrophotometer and the ATR method. Specifically, the measurement is performed using polarized light as the measurement light, and the crystallization index is calculated according to the following formula using the intensities of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum.

Crystallization index = (I _C /I _R )

However, I _C : the intensity at 1141 cm ^-1 when measurement light is incident and measurement is performed, and _IR : the intensity at 1440 cm ^-1 when measurement light is incident and measurement is performed.

B-3-3. Insolubilization treatment

If necessary, insolubilization treatment may be performed after the air-assisted extension treatment and before the water extension treatment or dyeing treatment. The above-mentioned insolubilization treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing insolubilization treatment, the PVA-based resin layer can be given water resistance and prevent the PVA from being reduced in orientation when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insoluble bath (boric acid aqueous solution) should be 20℃~50℃.

B-3-4. Dyeing treatment

The above dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, this is performed by adsorbing iodine to the PVA-based resin layer. Examples of the adsorption method include: a method of immersing the PVA-based resin layer (laminated body) in a dyeing liquid containing iodine, a method of applying the dyeing liquid on the PVA-based resin layer, and a method of spraying the dyeing liquid onto the PVA Methods on the resin layer, etc. A method of immersing the laminated body in a dyeing liquid (dyeing bath) is preferred. Because it can adsorb iodine well.

The above-mentioned dyeing solution is preferably an iodine aqueous solution. The blending amount of iodine is preferably 0.05 to 0.5 parts by weight relative to 100 parts by weight of water. In order to improve the solubility of iodine in water, it is advisable to mix iodide into the iodine aqueous solution. Iodide can be cited For example: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Among these, potassium iodide is preferred. The blending amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight relative to 100 parts by weight of water. In order to inhibit the dissolution of PVA-based resin, the liquid temperature of the dyeing solution during dyeing should be 20℃~50℃. When the PVA-based resin layer is immersed in the dyeing liquid, in order to ensure the transmittance of the PVA-based resin layer, the immersion time is preferably 5 seconds to 5 minutes, and 30 seconds to 90 seconds is better.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the final polarizing film has a single transmittance of 48% or more and a polarization degree of 85% or more. The dyeing conditions are preferably to use an iodine aqueous solution as the dyeing solution, and the content ratio of iodine and potassium iodide in the iodine aqueous solution is set to 1:5~1:20. The content ratio of iodine and potassium iodide in the iodine aqueous solution should be 1:5~1:10. Thereby, a polarizing film having the above-mentioned optical properties can be obtained.

When the laminate is immersed in a treatment bath containing boric acid (typically an insolubilization treatment) and then followed by a dyeing treatment, the boric acid contained in the treatment bath will be mixed into the dyeing bath, and the boric acid concentration of the dyeing bath will decrease. As time passes, the dyeability may become unstable. In order to suppress the destabilization of dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight relative to 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight based on 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath mixed with boric acid in advance. In this way, the boric acid mixing in the above treatment bath can be reduced. Ratio of change in boric acid concentration when entering the dye bath. The amount of boric acid blended into the dyeing bath in advance (that is, the content of boric acid not derived from the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight relative to 100 parts by weight of water, and more preferably 0.5 parts by weight. ~1.5 parts by weight.

B-3-5. Cross-linking treatment

If necessary, cross-linking treatment is performed after the dyeing treatment and before the water extension treatment. The above-mentioned cross-linking treatment can typically be performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing cross-linking treatment, water resistance can be imparted to the PVA-based resin layer to prevent the PVA from being reduced in orientation when it is immersed in high-temperature water during subsequent water stretching. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Furthermore, when performing cross-linking treatment after the above-mentioned dyeing treatment, it is preferable to further blend iodide. By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) should be 20℃~50℃.

B-3-6. Extension treatment in water

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. Through the water stretching treatment, it is possible to stretch at a temperature lower than the glass transition temperature of the above-mentioned thermoplastic resin base material or PVA-based resin layer (typically about 80°C), thereby suppressing the crystallization of the PVA-based resin layer. Perform high-magnification extension. As a result, a polarizing film with excellent optical properties can be produced.

The laminate may be extended by any appropriate method. Specifically, it can be a fixed end extension or a free end extension (for example A method of uniaxially extending the laminate through rollers with different peripheral speeds). It is better to choose free end extension. The extension of the laminated body can be carried out in one stage or in multiple stages. When the process is carried out in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios in each stage.

The underwater stretching is preferably performed by immersing the laminate in a boric acid aqueous solution (boric acid underwater stretching). By using a boric acid aqueous solution as a stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding the tension during stretching and water resistance that is insoluble in water. Specifically, boric acid will generate tetrahydroxyborate anions in aqueous solution and can cross-link with PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be given rigidity and water resistance, and can be stretched well, thereby producing a polarizing film with excellent optical properties.

The above boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water that is a solvent. The boric acid concentration is preferably 1 to 10 parts by weight relative to 100 parts by weight of water, more preferably 2.5 to 6 parts by weight, especially 3 to 5 parts by weight. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed and a polarizing film with higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. in a solvent can also be used.

It is suitable to mix iodide into the above extension bath (boric acid aqueous solution). By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight relative to 100 parts by weight of water, and more preferably 0.5 to 8 parts by weight.

The extension temperature (liquid temperature of the extension bath) should be 40℃~85℃. The preferred temperature is 60℃~75℃. As long as the temperature is as described above, dissolution of the PVA-based resin layer can be suppressed and high-magnification elongation can be achieved. Specifically, as mentioned above, considering the relationship between the formation of the PVA-based resin layer and the formation of the PVA-based resin layer, the glass transition temperature (Tg) of the thermoplastic resin base material is preferably 60° C. or higher. At this time, if the stretching temperature is lower than 40° C., even if it is considered to plasticize the thermoplastic resin base material with water, it may not be able to be stretched satisfactorily. On the other hand, the higher the temperature of the extension bath, the higher the solubility of the PVA-based resin layer, and excellent optical properties may not be obtained. The immersion time of the laminate in the extension bath is preferably 15 seconds to 5 minutes.

The extension ratio for extending in water is preferably 1.5 times or more, preferably 3.0 times or more. The total extension ratio of the laminated body is preferably 5.0 times or more, more preferably 5.5 times or more relative to the original length of the laminated body. By achieving such a high stretching ratio, a polarizing film with extremely excellent optical properties can be produced. The high stretching ratio can be achieved by using a water stretching method (boric acid water stretching).

B-3-7. Drying and shrinkage treatment

The above-mentioned drying and shrinkage treatment can be performed by regional heating in which the entire region is heated, or by heating a transport roller (so-called use of a heating roller) (heated roller drying method). It is better to use both. By drying using a heating roller, heat curling of the laminate can be effectively suppressed and a polarizing film with excellent appearance can be produced. Specifically, by drying the laminated body along a heating roller, the crystallization of the thermoplastic resin base material can be effectively promoted and the degree of crystallization can be increased, even at a relatively low drying temperature. It can still effectively increase the degree of crystallization of thermoplastic resin substrates. As a result, the rigidity of the thermoplastic resin base material increases and becomes a state that can withstand shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. again, By using a heating roller, the laminated body can be dried while maintaining a flat state, thereby suppressing not only the occurrence of curls but also the occurrence of wrinkles. At this time, the laminated body can be shrunk in the width direction through drying and shrinkage treatment to improve the optical properties. This is because it can effectively improve the orientation of PVA and PVA/iodine complexes. The shrinkage rate in the width direction of the laminate obtained by drying and shrinking treatment is preferably 1% to 10%, more preferably 2% to 8%, especially 4% to 6%. By using a heated roller, the laminated body can be continuously shrunk in the width direction while being conveyed, thereby achieving high productivity.

FIG. 3 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminated body 200 is dried while being conveyed using the conveyance rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveying rollers R1 to R6 are arranged to alternately and continuously heat the surface of the PVA resin layer and the thermoplastic resin base material. However, for example, the conveying rollers R1 to R6 may also be arranged to continuously heat only the laminated body 200 One side (such as the thermoplastic resin base material side).

Drying conditions can be controlled by adjusting the heating temperature of the conveyor roller (temperature of the heating roller), the number of heating rollers, and the contact time with the heating roller. The temperature of the heating roller is preferably 60°C~120°C, more preferably 65°C~100°C, especially 70°C~80°C. The degree of crystallization of the thermoplastic resin can be increased satisfactorily to suppress curling, and at the same time, an optical laminate with extremely excellent durability can be produced. In addition, the temperature of the heating roller can be measured with a contact thermometer. In the example of the drawing, six conveying rollers are provided, but there is no particular restriction as long as the number of conveying rollers is a plurality. The number of conveying rollers is usually 2 to 40, and preferably 4 to 30 are provided. The contact time between the laminated body and the heating roller (total contact time) is 1 second. ~300 seconds is suitable, 1~20 seconds is better, and 1~10 seconds is better.

The heating roller can be installed in a heating furnace (such as an oven) or in a general manufacturing production line (at room temperature). It should be installed in a heating furnace with an air supply mechanism. By combining drying with heated rollers and hot air drying, rapid temperature changes between the heated rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be 30℃~100℃. Moreover, the hot air drying time should be 1 second to 300 seconds. The wind speed of hot air should be about 10m/s~30m/s. In addition, the wind speed is the wind speed in the heating furnace, which can be measured with a mini fan blade type digital anemometer.

B-3-8.Other processing

It is advisable to perform cleaning treatment after stretching in water and before drying and shrinking. The above-described cleaning treatment can typically be performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

C. 1st phase difference layer

The first retardation layer 20 can have any appropriate optical properties and/or mechanical properties according to the purpose. The first phase difference layer 20 typically has a slow axis. In one embodiment, the angle θ formed by the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is 40° to 50°, preferably 42° to 48°, and more preferably about 45° as mentioned above. . As long as the angle θ is within the above range, as described later, by using the first retardation layer as a λ/4 plate, it is possible to obtain a retardation layer having very excellent circular polarization properties (resulting in very excellent anti-reflection properties). Polarizing plate.

The first retardation layer preferably has a refractive index characteristic showing the relationship nx>ny≧nz. The first retardation layer is typically provided to impart anti-reflective properties to the polarizing plate, and in one embodiment can function as a λ/4 plate. At this time, the in-plane phase difference Re (550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm. In addition, "ny=nz" here includes not only the case where ny and nz are exactly the same, but also the case where they are substantially the same. Therefore, ny<nz may be satisfied within the scope that does not impair the effect of the present invention.

The Nz coefficient of the first phase difference layer is preferably 0.9~3, more preferably 0.9~2.5, more preferably 0.9~1.5, and 0.9~1.3 is particularly preferred. By satisfying the above relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, a very excellent reflection hue can be achieved.

The first phase difference layer can exhibit an inverse wavelength dispersion characteristic in which the phase difference value becomes larger with the wavelength of the measurement light. It can also exhibit a normal wavelength dispersion characteristic in which the phase difference value becomes smaller with the wavelength of the measurement light. It can also exhibit a phase difference value that is almost constant. Flat wavelength dispersion characteristics that vary with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits reverse dispersion wavelength characteristics. At this time, Re(450)/Re(550) of the phase difference layer is preferably 0.8 or more and less than 1, and more preferably 0.8 or more and 0.95 or less. With this configuration, very excellent anti-reflection properties can be achieved.

The absolute value of the photoelastic coefficient included in the first phase difference layer is preferably 2×10 ^-11 m ² /N or less, and preferably 2.0×10 ^-13 m ² /N to 1.5× ^{10 -11} m ² /N, and more preferably The resin is 1.0×10 ^-12 m ² /N~1.2×10 ^-11 m ² /N. As long as the absolute value of the photoelastic coefficient is within the above range, the phase difference will not easily change when shrinkage stress occurs during heating. As a result, thermal unevenness of the resulting image display device can be prevented satisfactorily.

The first retardation layer is typically composed of a stretched film of a resin film. In one embodiment, the thickness of the first retardation layer is preferably 70 μm or less, and preferably 45 μm to 60 μm . As long as the thickness of the first retardation layer is within the above range, curling during heating can be satisfactorily suppressed and curling during lamination can be satisfactorily adjusted. Furthermore, as will be described later, in an embodiment in which the first retardation layer is made of a polycarbonate resin film, the thickness of the first retardation layer is preferably 40 μm or less, and preferably 10 μm to 40 μm , and more preferably 10 μm to 40 μm. It is suitable to be 20 μm ~30 μm . The first retardation layer is composed of a polycarbonate resin film having the above thickness, which can suppress the occurrence of curling and can help improve bending durability and reflective hue.

The first retardation layer 20 can be composed of any appropriate resin film that satisfies the above characteristics. Representative examples of the resin include polycarbonate resin, polyester carbonate resin, polyester resin, polyvinyl acetal resin, polyarylate resin, cyclic olefin resin, cellulose resin, Polyvinyl alcohol resin, polyamide resin, polyimide resin, polyether resin, polystyrene resin, acrylic resin. These resins can be used individually or in combination (eg blending, copolymerization). When the first retardation layer is composed of a resin film showing reverse dispersion wavelength characteristics, a polycarbonate resin or a polyester carbonate resin (hereinafter sometimes referred to simply as a polycarbonate resin) can be suitably used.

As long as the effects of the present invention can be obtained, any appropriate polycarbonate resin may be used as the polycarbonate resin. For example, the polycarbonate resin includes a structural unit derived from a fluorine-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from an alicyclic diol, an alicyclic dimethanol, Di, tri or polyethylene glycol, and alkylene glycol Or the structural unit of at least one dihydroxy compound in the group consisting of spiroglycerol. Preferably, the polycarbonate resin contains a structural unit derived from a fluorine-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, a structural unit derived from an alicyclic dimethanol, and/or a structural unit derived from dihydroxy compounds. Structural units derived from tris or polyethylene glycol; more preferably, structural units derived from fluorine dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds and structures derived from di, tri or polyethylene glycol. unit. The polycarbonate resin may also contain structural units derived from other dihydroxy compounds as needed. In addition, details of the polycarbonate-based resin that can be suitably used in the present invention are described in, for example, Japanese Patent Application Laid-Open No. 2014-10291, Japanese Patent Application Laid-Open No. 2014-26266, Japanese Patent Application Laid-Open No. 2015-212816, and Japanese Patent Application Publication 2015. -212817 and Japanese Patent Publication No. 2015-212818, and this specification uses these records as a reference.

The glass transition temperature of the polycarbonate resin is preferably 110°C to 150°C, and preferably 120°C to 140°C. If the glass transition temperature is too low, the heat resistance will tend to deteriorate, which may cause dimensional changes after the film is formed, or may reduce the image quality of the resulting organic EL panel. If the glass transition temperature is too high, the forming stability during film forming may deteriorate, or the transparency of the film may be impaired. In addition, the glass transition temperature can be obtained in accordance with JIS K 7121 (1987).

The molecular weight of the polycarbonate resin can be expressed by reduced viscosity. The specific viscosity is measured using methylene chloride as the solvent, after the polycarbonate concentration is precisely adjusted to 0.6g/dL, and then measured using an Ubbelohde viscosity tube at a temperature of 20.0℃±0.1℃. The lower limit of the reduced viscosity is usually 0.30dL/g, and It is better to use 0.35dL/g or above. The upper limit of the reduced viscosity is usually 1.20dL/g, preferably 1.00dL/g, and 0.80dL/g is better. If the reduced viscosity is less than the aforementioned lower limit, there may be a problem that the mechanical strength of the molded product becomes smaller. On the other hand, if the reduced viscosity is greater than the above-mentioned upper limit, the fluidity during molding will decrease, which may cause problems with lowering productivity or moldability.

A commercially available film can also be used as a polycarbonate resin film. Specific examples of commercially available products include "PURE-ACE WR-S", "PURE-ACE WR-W", and "PURE-ACE WR-M" manufactured by Teijin Co., Ltd., and "NRF" manufactured by Nitto Denko Co., Ltd. ”.

The first retardation layer 20 can be obtained by stretching a film made of the above-mentioned polycarbonate resin, for example. The method of forming a thin film from a polycarbonate-based resin may employ any appropriate molding process. Specific examples include: compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (such as tape casting method), calendering molding method , hot pressing method, etc. Instead, the extrusion molding method or the casting coating method is preferred. This is because it can improve the smoothness of the resulting film, thereby achieving good optical uniformity. The molding conditions can be appropriately set according to the composition or type of the resin used, the desired characteristics of the retardation film, and the like. In addition, as mentioned above, many polycarbonate-based resin film products are sold on the market, so the commercially available films can be directly used for the stretching process.

The thickness of the resin film (unstretched film) can be set to any appropriate value according to the desired thickness of the first retardation layer, desired optical properties, stretching conditions described below, and the like. It is suitable to be 50 μm ~300 μm .

The above-mentioned stretching can adopt any appropriate stretching method and stretching conditions (such as stretching temperature, stretching ratio, stretching direction). Specifically, various stretching methods such as free end extension, fixed end extension, free end contraction, and fixed end contraction can be used individually, or simultaneously or sequentially. Regarding the extension direction, it can also be carried out in various directions or dimensions such as the length direction, the width direction, the thickness direction, and the oblique direction. The stretching temperature is preferably Tg-30°C to Tg+60°C, and preferably Tg-10°C to Tg+50°C relative to the glass transition temperature (Tg) of the resin film.

By appropriately selecting the above-mentioned stretching method and stretching conditions, a retardation film having the above-mentioned desired optical properties (eg, refractive index characteristics, in-plane retardation, Nz coefficient) can be obtained.

In one embodiment, the retardation film can be produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. A specific example of fixed-end uniaxial stretching is a method in which the resin film is moved in the longitudinal direction and simultaneously stretched in the width direction (lateral direction). The extension ratio should be 1.1 times to 3.5 times.

In another embodiment, the retardation film can be produced by continuously extending a long resin film obliquely in a direction making the above-mentioned angle θ with respect to the longitudinal direction. By using diagonal stretching, a long stretched film with an orientation angle of θ (having a slow axis in the direction of angle θ) relative to the long side direction of the film can be obtained. For example, it can be rolled when laminated with a polarizing film. To roll, thus simplifying the manufacturing steps. In addition, the angle θ may be the angle formed by the absorption axis of the polarizing film and the slow axis of the retardation layer in a polarizing plate with a retardation layer. The angle θ is as above, preferably 40°~50°, and preferably 42°~48° °, more preferably about 45°.

A stretching machine used for diagonal stretching can be a tenter-type stretching machine, which adds conveying force at different speeds or a stretching force or pulling force to the transverse direction and/or the longitudinal direction. Stenter-type stretchers include horizontal single-axis stretchers, simultaneous biaxial stretchers, etc. Any appropriate stretcher can be used as long as it can continuously stretch a long resin film diagonally.

By appropriately controlling the left and right speeds in the stretching machine, a retardation layer (essentially a strip-shaped retardation film) having the desired in-plane retardation and a slow axis in the desired direction can be obtained. ).

The stretching temperature of the above-mentioned film will vary depending on the desired in-plane retardation value and thickness of the retardation layer, the type of resin used, the thickness of the film used, the stretching ratio, etc. Specifically, the extension temperature is preferably Tg-30°C to Tg+30°C, more preferably Tg-15°C to Tg+15°C, and most preferably Tg-10°C to Tg+10°C. By extending at the above temperature, the first retardation layer having characteristics suitable for the present invention can be obtained. In addition, Tg is the glass transition temperature of the material constituting the film.

D. 2nd phase difference layer

As mentioned above, the second retardation layer may be a so-called positive C-plate whose refractive index characteristics exhibit the relationship nz>nx=ny. By using the positive C plate as the second retardation layer, oblique reflection can be effectively prevented, and the anti-reflection function can be widened to a wider viewing angle. At this time, the retardation Rth (550) in the thickness direction of the second retardation layer is preferably -50nm~-300nm, more preferably -70nm~-250nm, more preferably -90nm~-200nm, and particularly preferably -100nm~-180nm. Here, "nx=ny" includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the second retardation layer may be less than 10 nm.

The second retardation layer having the refractive index characteristic of nz>nx=ny can be formed of any appropriate material. The second retardation layer is preferably composed of a thin film containing a liquid crystal material fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) capable of vertical alignment can be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the method of forming the liquid crystal compound and the retardation layer include the liquid crystal compound and the method of forming the retardation layer described in paragraphs [0020] to [0028] of Japanese Patent Application Laid-Open No. 2002-333642. At this time, the thickness of the second retardation layer is preferably 0.5 μm ~10 μm , more preferably 0.5 μm ~8 μm , and more preferably 0.5 μm ~5 μm .

E. Conductive layer or isotropic substrate with conductive layer

The conductive layer can be formed by forming a metal oxide film on any appropriate substrate using any appropriate film forming method (such as vacuum evaporation, sputtering, CVD, ion plating, spraying, etc.). Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium tin composite oxide (ITO) is suitable.

When the conductive layer contains metal oxide, the thickness of the conductive layer is preferably 50 nm or less, more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

The conductive layer can be transferred from the above-mentioned base material to the first retardation layer (or the second retardation layer if there is a second retardation layer) to form a single conductive layer. As a constituent layer of a polarizing plate with a retardation layer alone, it can also be laminated on the first retardation layer (or if there is a second retardation layer) in the form of a laminate of a conductive layer and a base material (a base material with a conductive layer) It is the second phase difference layer). It is preferable that the above-mentioned base material is optically isotropic, so the conductive layer can be used as an isotropic base material with a conductive layer for a polarizing plate with a retardation layer.

Any appropriate isotropic base material can be used as the optically isotropic base material (isotropic base material). Examples of materials constituting the isotropic base material include materials having a main skeleton of a resin without a conjugated system, such as norbornene resin or olefin resin, and acrylic resin having a lactone ring or glutaryl ring in the main chain. Materials with cyclic structures such as imine rings, etc. If such a material is used, the phase difference caused by the orientation of molecular chains when forming an isotropic base material can be suppressed to a small size. The thickness of the isotropic substrate is preferably 50 μm or less, and more preferably 35 μm or less. The lower limit of the thickness of the isotropic substrate is, for example, 20 μm .

The conductive layer and/or the conductive layer of the isotropic substrate with the conductive layer can be patterned as needed. Conductive portions and insulating portions can be formed through patterning. As a result, electrodes can be formed. The electrodes may function as touch sensing electrodes for sensing contact with the touch panel. The patterning method may employ any suitable method. Specific examples of the patterning method include wet etching and screen printing.

F.Image display device

The polarizing plate with a retardation layer described in the above items A to E can be applied to an image display device. Therefore, the present invention includes an image display device using the polarizing plate with a retardation layer. Representative examples of image display devices include Liquid crystal display device, electroluminescence (EL) display device (eg, organic EL display device, inorganic EL display device). An image display device according to an embodiment of the present invention is provided with the polarizing plate with a retardation layer described in the above items A to E on its viewing side. A polarizing plate with a retardation layer is laminated so that the retardation layer becomes the image display unit (for example, a liquid crystal unit, an organic EL unit, an inorganic EL unit) side (the polarizing film becomes the viewing side). In one embodiment, the image display device has a curved shape (substantially a curved display screen) and/or is flexible or bendable. In the image display device, the effect of the polarizing plate with a retardation layer of the present invention is more remarkable.

Example

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited by these examples. The measurement method of each characteristic is as follows. In addition, unless otherwise noted, "parts" and "%" in the examples and comparative examples are based on weight.

(1)Thickness

The thickness of 10 μm or less is measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). The thickness greater than 10 μm is measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C").

(2)Monomer transmittance and polarization degree

The polarizing film/protective layer laminate (polarizing plate) used in the examples and comparative examples was measured using an ultraviolet-visible light spectrophotometer (V-7100 manufactured by JASCO Corporation), and the measured single transmittance Ts, parallel The transmittance Tp and the cross transmittance Tc are respectively regarded as Ts, Tp and Tc of the polarizing film. the Ts, Tp, and Tc are Y values measured using the 2-degree field of view (C light source) of JIS Z8701 and corrected for optical efficiency. In addition, the refractive index of the protective layer is 1.50, and the refractive index of the surface of the polarizing film opposite to the protective layer is 1.53.

The degree of polarization P was calculated from the obtained Tp and Tc using the following formula.

Polarization P(%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In addition, a spectrophotometer such as LPF-200 manufactured by Otsuka Electronics Co., Ltd. can also be used to perform equivalent measurements. As an example, V-7100 and LPF-200 were used to measure Samples 1 to 3 of polarizing plates having the same structure as the following examples, and the measured single transmittance Ts and polarization degree P were measured. The measured values are listed in Table 1. As shown in Table 1, the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 is less than 0.1%. It can be seen that no matter when using any spectrophotometer, Obtain equivalent measurement results.

In addition, for example, when a polarizing plate with anti-glare (AG) surface treatment or an adhesive with diffusion properties is used as the measurement object, different measurement results will be obtained depending on the spectrophotometer. However, in this case, by Using the measurement values obtained when measuring the same polarizing plate with each spectrophotometer as the basis for numerical conversion, the difference in measurement values obtained by the spectrophotometers can be compensated.

(3) The optical properties of long polarizing films vary

From the polarizing plates used in Examples and Comparative Examples, measurement samples were cut out at five positions at equal intervals in the width direction, and then the monomers at the center of each of the five measurement samples were measured in the same manner as in (2) above. Transmittance. Next, the difference between the maximum value and the minimum value among the individual transmittances measured at each measurement position was calculated, and this value was used as the optical characteristic variation of the long polarizing film.

(4) The optical properties of flake polarizing films vary

A measurement sample of 100 mm × 100 mm was cut out from the polarizing plate used in the Example and Comparative Example, and the optical characteristic variation of the sheet-shaped polarizing plate (50 cm ² ) was determined. Specifically, the monomer transmittance is measured in the same manner as in (2) above, at a total of 5 locations from the midpoint of each of the four sides of the measurement sample, including a position about 1.5cm to 2.0cm inward and the central part. Next, the difference between the maximum value and the minimum value among the individual transmittances measured at each measurement position was calculated, and this value was used as the optical property variation of the sheet-shaped polarizing film.

(5)Warpage

The polarizing plate with a retardation layer obtained in the Example and the Comparative Example was cut into a size of 110 mm×60 mm. At this time, the polarizing film is cut so that the absorption axis direction is the long side direction. The cut polarizing plate with the retardation layer was bonded to a glass plate with a size of 120 mm × 70 mm and a thickness of 0.2 mm through an adhesive to prepare a test sample. The test sample was put into a heating oven maintained at 85°C for 24 hours, and the amount of warpage was measured after taking it out. After placing the test sample on a flat surface with the glass plate down, take the height of the highest part from the flat surface as the amount of warpage.

(6)Bending durability

The polarizing plates with retardation layers obtained in the Examples and Comparative Examples were cut into Cut to size 50mm×100mm. At this time, the polarizing film is cut with the absorption axis direction as the short side direction. Using a folding endurance testing machine (manufactured by YUASA, CL09 type-D01) equipped with a constant temperature and humidity chamber, the cut polarizing plate with a retardation layer was subjected to a bending test under the conditions of 20°C and 50%RH. Specifically, the polarizing plate with the retardation layer is repeatedly bent in a direction parallel to the absorption axis direction with the retardation layer side as the outer side, and the measurement is performed until cracks, peeling, or film breakage that cause poor image display occur. The number of bends is evaluated based on the following criteria (bending diameter: 2mmφ).

<Evaluation criteria>

Less than 10,000 times: bad

More than 10,000 times and less than 30,000 times: good

More than 30,000 times: Excellent

(7)Elastic coefficient

The film to be measured was formed into a tensile test dumbbell-shaped piece with a parallel portion width of 10 mm and a length of 40 mm in accordance with JIS K6734:2000, and then a tensile test was performed in accordance with JIS K7161:1994 to determine the tensile elastic coefficient. Here, the length direction is usually consistent with the extending direction of the polarizing film.

[Example 1]

1. Make polarizing film

The thermoplastic resin base material is a long amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm ) with a water absorption rate of 0.75% and a Tg of approximately 75°C. And corona treatment is applied to one side of the resin substrate.

Mix polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetate-acetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) at a ratio of 9:1. 13 parts by weight of potassium iodide was added to 100 parts by weight of PVA-based resin (trade name "GOHSEFIMER Z410") and dissolved in water to prepare a PVA aqueous solution (coating liquid).

The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm , thereby producing a laminate.

The obtained laminate was uniaxially extended at the free end 2.4 times in the longitudinal direction (long side direction) between rollers with different peripheral speeds in an oven at 130°C (air-assisted stretching treatment).

Next, the laminated body was immersed in an insolubilization bath (a boric acid aqueous solution in which 4 parts by weight of boric acid was mixed with 100 parts by weight of water) having a liquid temperature of 40°C for 30 seconds (insolubilization treatment).

Next, while adjusting the concentration of a dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) with a liquid temperature of 30° C., the concentration of the finally obtained polarizing film is uniform. When the body transmittance (Ts) reaches 48% or more, immerse it in it for 60 seconds (dyeing treatment).

Next, it was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) with a liquid temperature of 40° C. for 30 seconds (crosslinking treatment) ).

Then, while the laminated body was immersed in a boric acid aqueous solution with a liquid temperature of 70° C. (boric acid concentration 4.0% by weight), it was uniaxially stretched in the longitudinal direction (longitudinal direction) between rollers with different circumferential speeds so that the total stretch was The magnification is up to 5.5 times (extension treatment in water).

Thereafter, the laminated body was immersed in a cleaning bath with a liquid temperature of 20° C. (relative to water 100 parts by weight, an aqueous solution obtained by mixing 4 parts by weight of potassium iodide) (washing treatment).

Thereafter, it was dried in an oven maintained at 90° C. while keeping the surface temperature in contact with a SUS heated roller kept at 75° C. for about 2 seconds (drying shrinkage treatment). The laminate was subjected to drying and shrinkage treatment, and the shrinkage rate in the width direction was 5.2%.

Through the above procedures, a polarizing film with a thickness of 5.0 μm was formed on the resin substrate.

2. Make polarizing plates

On the surface of the polarizing film obtained above (the side opposite to the resin base material), a cycloolefin-based film (thickness: 28 μm , elastic coefficient: 2100MPa) as a protective layer. Specifically, the hardening adhesive is applied to a total thickness of 1.0 μm and bonded using a roller. Thereafter, UV light is irradiated from the protective layer side to harden the adhesive. Next, both ends were cut, and the resin base material was peeled off to obtain a long polarizing plate (width: 1300 mm) having a structure of protective layer/adhesive layer/polarizing film. The single transmittance of the polarizing plate (essentially a polarizing film) is 48.48%, and the polarization degree is 87.036%. Moreover, the optical properties of the strip-shaped polarizing film vary by 0.58%, while the optical properties of the flake-shaped polarizing film vary by 0.14%.

3. Preparation of retardation film constituting the retardation layer

3-1. Polymerization of polyester carbonate resin

Polymerization was performed using a batch polymerization device consisting of two vertical reactors equipped with stirring blades and a reflux cooler controlled to 100°C. Feed in 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), and spiroglycerol (SPG) 42.28 parts by mass (0.139 mol), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC) and 1.19×10 ^-2 parts by mass (6.78×10 ^-5 mol) of calcium acetate monohydrate as a catalyst. After the reactor was replaced with nitrogen under reduced pressure, it was heated with a heating medium, and stirring was started when the internal temperature reached 100°C. The internal temperature was brought to 220°C 40 minutes after the start of the temperature rise, and the temperature was controlled to be maintained while simultaneously starting to reduce the pressure so that it reached 13.3 kPa 90 minutes after reaching 220°C. The phenol vapor generated by the polymerization reaction is introduced into a reflux cooler at 100°C, so that a small amount of monomer components contained in the phenol vapor is returned to the reactor, and the uncondensed phenol vapor is introduced into a condenser at 45°C for recovery. After introducing nitrogen into the first reactor and temporarily returning it to atmospheric pressure, the oligomerized reaction liquid in the first reactor is moved to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and after 50 minutes, the internal temperature was set to 240°C and the pressure was set to 0.2 kPa. Thereafter, polymerization is performed until a predetermined stirring power is reached. At the time point when the predetermined power is reached, nitrogen is introduced into the reactor to restore the pressure, the generated polyester carbonate resin is extruded into water, and the bundles are cut to obtain pellets.

3-2. Preparation of retardation film

The obtained polyester carbonate resin (pellets) was vacuum-dried at 80°C for 5 hours, and then dried using a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-type die (wide 200mm, set temperature: 250℃), cooling roller (set temperature: 120~130℃) and film forming device of the winding machine to produce a long resin film with a thickness of 130 μm . The obtained long-shaped resin film was stretched while adjusting it to obtain a predetermined phase difference, and a phase difference film with a thickness of 48 μm was obtained. The stretching conditions are along the width direction, the stretching temperature is 143°C, and the stretching ratio is 2.8 times. The Re(550) of the obtained retardation film was 141 nm, Re(450)/Re(550) was 0.86, and the Nz coefficient was 1.12.

4. Make a polarizing plate with a phase difference layer

The retardation film obtained in 3. above was bonded to the surface of the polarizing film of the polarizing plate obtained in 2. above through an acrylic adhesive (thickness: 5 μm ). At this time, they are bonded so that the absorption axis of the polarizing film and the slow axis of the retardation film form an angle of 45°. In the above manner, a polarizing plate with a retardation layer composed of a protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer is obtained. The total thickness of the obtained polarizing plate with a retardation layer was 87 μm . The obtained polarizing plate with a retardation layer was used for the evaluation of the above (5) and (6). The amount of warpage is 3.4mm. The results are listed in Table 2.

[Example 2-1]

1. Make polarizing film

A polarizing film with a thickness of 5 μm was formed on the resin substrate in the same manner as in Example 1.

2. Make polarizing plates

A triacetylcellulose (TAC) film with a hard coating layer (hard coating thickness 7 μm , TAC thickness 25 μm , elastic coefficient: 3600MPa) was used as the protective layer, except that it was produced in the same manner as in Example 1 A polarizing plate composed of a protective layer/adhesive layer/polarizing film is produced.

3. Preparation of retardation film constituting the retardation layer

Polyester carbonate resin (pellets) were obtained in the same manner as in Example 1 except that 0.7 parts by mass of PMMA was melt-kneaded, and vacuum dried at 80° C. for 5 hours, using a single-screw extruder (Toshiba). Made by a machinery company, cylinder set temperature: 250°C), T-shaped mold (width 200mm, set temperature: 250°C), cooling roller (set temperature: 120~130°C) and film forming device of the winding machine, are produced A long strip of resin film with a thickness of 105 μm . The obtained long resin film was stretched 2.8 times in the width direction at 138° C. while adjusting it to obtain a predetermined phase difference, thereby obtaining a phase difference film with a thickness of 38 μm . Re(550) of the obtained retardation film was 144 nm, and Re(450)/Re(550) was 0.86.

4. Make a polarizing plate with a phase difference layer

The retardation film obtained in 3. above was bonded to the surface of the polarizing film of the polarizing plate obtained in 2. above through an acrylic adhesive (thickness: 5 μm ). At this time, they are bonded so that the absorption axis of the polarizing film and the slow axis of the retardation film form an angle of 45°. In the above manner, a polarizing plate with a retardation layer composed of a protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer is obtained. The total thickness of the obtained polarizing plate with a retardation layer was 81 μm . The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are listed in Table 2.

[Example 2-2]

A long polyester carbonate resin film with a thickness of 105 μm obtained in the same manner as in Example 2-1 was adjusted to obtain a predetermined phase difference while extending in the width direction to obtain a phase difference with a thickness of 38 μm . film. The Re(550) of the obtained retardation film was 140 nm.

Except using the above-mentioned retardation film as the retardation layer, a polarizing plate with a retardation layer having a composition of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained in the same manner as in Example 2-1. . The total thickness of the obtained polarizing plate with a retardation layer was 81 μm . The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are listed in Table 2.

[Example 2-3]

A long polyester carbonate resin film with a thickness of 105 μm obtained in the same manner as in Example 2-1 was adjusted to obtain a predetermined phase difference while extending in the width direction to obtain a phase difference with a thickness of 38 μm . film. Re(550) of the obtained retardation film was 149 nm.

Except using the above-mentioned retardation film as the retardation layer, a polarizing plate with a retardation layer having a composition of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained in the same manner as in Example 2-1. . The total thickness of the obtained polarizing plate with a retardation layer was 81 μm . The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are listed in Table 2.

[Example 3]

The polycarbonate resin film obtained in the same manner as in Example 1 was stretched obliquely in accordance with the method of Example 2 of Japanese Patent Application Laid-Open No. 2014-194483, to obtain a retardation film with a thickness of 58 μm . The Re(550) of the obtained retardation film was 144 nm, the Re(450)/Re(550) was 0.86, the Nz coefficient was 1.21, and the orientation angle (the direction of the slow axis) was 45° relative to the long direction. The retardation film and the polarizing plate of Example 1 were laminated in a roll-to-roll manner through an acrylic adhesive (thickness 5 μm ) to obtain a protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer. A polarizing plate with a retardation layer. The total thickness of the obtained polarizing plate with the retardation layer was 97 μm . The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage is 4.1mm. The results are listed in Table 2.

[Comparative example 1]

1. Make polarizers

A polyvinyl alcohol-based resin film with an average polymerization degree of 2,400, a saponification degree of 99.9 mol%, and a thickness of 30 μm was prepared. While dipping the polyvinyl alcohol film in a swelling bath (water bath) at 20°C for 30 seconds between rollers with different peripheral speed ratios to swell it, extend it 2.4 times in the conveying direction (swelling step), and then immerse it in a swelling bath (water bath) at 20°C for 30 seconds. ℃ dyeing bath (iodine concentration is 0.03% by weight and potassium iodide concentration is 0.3% by weight), immersed and dyed in such a way that the monomer transmittance after final extension becomes the desired value, while using the original polyvinyl alcohol The film (a polyvinyl alcohol film that is not stretched in the conveying direction at all) is extended in the conveying direction 3.7 times as a reference (dyeing step). The soaking time at this time is about 60 seconds. Next, the dyed polyvinyl alcohol film was immersed in a 40° C. cross-linking bath (an aqueous solution with a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight) and was transported along the original polyvinyl alcohol film as a basis. The direction is extended until 4.2 times (cross-linking step). The obtained polyvinyl alcohol film was then immersed in a stretching bath at 64°C (an aqueous solution with a boric acid concentration of 4.0% by weight and a potassium iodide concentration of 5.0% by weight) for 50 seconds, and was extended along the conveying direction based on the original polyvinyl alcohol film. After reaching 6.0 times (extension step), it was immersed in a 20°C cleaning bath (an aqueous solution with a potassium iodide concentration of 3.0% by weight) for 5 seconds (washing step). The washed polyvinyl alcohol film was dried at 30° C. for 2 minutes to prepare a polarizer (thickness: 12 μm ).

2. Make polarizing plates

The following aqueous solution is used as the adhesive: a polyvinyl alcohol resin containing acetyl acetyl groups (average degree of polymerization 1,200, degree of saponification 98.5 mol%, degree of acetyl acetyl group 5 mol%) and hydroxymethylmelamine . This adhesive was used so that the thickness of the adhesive layer was 0.1 μm , and a triacetylcellulose (TAC) film with a hard coat layer (hard coat thickness 7 μm ) was bonded to one side of the polarizer obtained above using a roll laminator. m, TAC thickness 25 μm , elastic coefficient: 3600MPa), and laminate a TAC film with a thickness of 25 μm on the other side of the polarizer, and then heat and dry it in an oven (temperature: 60°C, time: 5 minutes) , and a polarizing plate having the structure of protective layer 1 (thickness 32 μm )/adhesive layer/polarizer/adhesive layer/protective layer 2 was produced.

3. Make a polarizing plate with a phase difference layer

Laminate the retardation film on the surface of the protective layer 2 of the polarizing plate obtained in 2. above in the same manner as in Example 1 to produce a protective layer 1/adhesive layer/polarizer/adhesive layer/protective layer 2/adhesive layer. A polarizing plate with a retardation layer composed of an agent layer/retardation layer. The total thickness of the obtained polarizing plate with a retardation layer was 122 μm . The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage is 5.3mm.

[Comparative example 2]

1. Make polarizers

A polarizer (thickness: 12 μm ) was produced in the same manner as Comparative Example 1.

2. Make polarizing plates

In the same manner as Comparative Example 1, a polarizing plate having a structure of protective layer 1 (thickness 32 μm )/adhesive layer/polarizer/adhesive layer/protective layer 2 (thickness 25 μm ) was produced.

3. Make the first directionally solidified layer and the second directionally solidified layer that constitute the retardation layer.

10 g of polymerizable liquid crystal showing a nematic liquid crystal phase (manufactured by BASF Co., Ltd.: trade name "Paliocolor LC242", represented by the following formula) and a photopolymerization initiator (manufactured by BASF Co., Ltd.: trade name "IRGACURE") for the polymerizable liquid crystal compound were mixed 907″) 3 g was dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

Wipe the surface of polyethylene terephthalate (PET) film (thickness 38 μm ) with a wiping cloth and perform orientation treatment. The direction of the orientation treatment is set to be 15° relative to the absorption axis direction of the polarizer when viewed from the viewing side when attached to the polarizing plate. The above-mentioned liquid crystal coating liquid was applied to the orientation-treated surface using a bar coater, and the liquid crystal compound was oriented by heating and drying at 90° C. for 2 minutes. A metal halide lamp is used to irradiate the liquid crystal layer formed in the above manner with light of 1 mJ/cm ² to harden the liquid crystal layer, thereby forming a liquid crystal orientation solidified layer A on the PET film. The thickness of the liquid crystal orientation solidified layer A is 2.5 μm , and the in-plane phase difference Re (550) is 270 nm. Furthermore, the liquid crystal alignment solidified layer A has a refractive index distribution of nx>ny=nz.

Change the coating thickness and set the orientation treatment direction to be 75° relative to the absorption axis direction of the polarizer when viewed from the viewing side. In addition, form the liquid crystal orientation solidified layer B on the PET film in the same manner as above. . The thickness of the liquid crystal orientation solidified layer B is 1.5 μm , and the in-plane phase difference Re (550) is 140 nm. Furthermore, the liquid crystal alignment solidified layer B has a refractive index distribution of nx>ny=nz. Moreover, Re(450)/Re(550) of the liquid crystal alignment solidified layers A and B was 1.11.

4. Make a polarizing plate with a phase difference layer

On the surface of the protective layer 2 side of the polarizing plate obtained in the above 2., the liquid crystal orientation solidified layer A and the liquid crystal orientation solidified layer B obtained in the above 3. are sequentially transferred. At this time, transfer is performed so that the angle between the absorption axis of the polarizer and the slow axis of the orientationally solidified layer A becomes 15° and the angle between the absorption axis of the polarizer and the slow axis of the orientationally solidified layer B becomes 75° ( fit). In addition, each transfer (bonding) is performed through an ultraviolet curable adhesive (thickness: 1 μm ). In the above manner, a retardation phase having a composition of protective layer 1/adhesive layer/polarizer/adhesive layer/protective layer 2/adhesive layer/retardation layer (first orientationally solidified layer/adhesive layer/second orientationally solidified layer) is obtained. Differential layer of polarizing plate. The total thickness of the obtained polarizing plate with a retardation layer was 75 μm . The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The results are listed in Table 2.

[Comparative example 3]

The procedure was carried out in the same manner as in Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating liquid), the stretching ratio of the air-assisted stretching process was set to 1.8 times, and a heating roller was not used in the drying shrinkage process. An attempt was made to make a polarizing film, but the PVA-based resin layer dissolved during the dyeing process and water stretching process, and the polarizing film could not be made. Therefore, it is also impossible to produce a polarizing plate with a retardation layer.

[evaluate]

After comparing the Examples with the Comparative Examples, it is obvious that the polarizing film of the Examples of the present invention has good optical properties and can significantly suppress warpage after the heating test. In addition, the polycarbonate resin is thinned to less than 40 μm , the layer thickness of the polarizing plate is set to less than 85 μm , and a base material with an elastic coefficient of more than 3000MPa is used, preferably a TAC film as a protective layer. This can further improve the bending characteristics.

industrial availability

The polarizing plate with a retardation layer of the present invention can be suitably used as a circular polarizing plate for liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

10:Polarizing plate

11:Polarizing film

12: 1st protective layer

13: 2nd protective layer

20: Phase difference layer (first phase difference layer)

100: Polarizing plate with phase difference layer

Claims (13)

A method of manufacturing a polarizing plate with a retardation layer. The polarizing plate with a retardation layer has a polarizing plate and a retardation layer. The polarizing plate includes a polarizing film and a protective layer located on at least one side of the polarizing film, and the polarizing plate The film is composed of a polyvinyl alcohol-based resin film containing dichroic substances. Its thickness is 8 μm or less, the monomer transmittance is more than 48%, and the polarization degree is more than 85%. The retardation layer has Re (550) is 100nm~190nm, Re(450)/Re(550) is 0.8 or more and less than 1; and the angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40°~50°; the manufacturing method The method includes the following steps: forming a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and polyvinyl alcohol-based resin on one side of a long thermoplastic resin base material to form a laminate; and sequentially The polarizing film is obtained by performing air-assisted stretching treatment, dyeing treatment, water stretching treatment and drying shrinkage treatment. The drying shrinkage treatment is to heat the laminate while transporting it in the longitudinal direction, thereby shrinking it in the width direction. More than 2%. As claimed in claim 1, the method for manufacturing a polarizing plate with a retardation layer, wherein the protective layer is composed of a base material with an elastic coefficient of 3000 MPa or more. The method for manufacturing a polarizing plate with a retardation layer according to claim 1 or 2, wherein the total thickness of the polarizing plate with a retardation layer is 90 μm or less, The front reflection hue of the polarizing plate with a retardation layer is 3.5 or less, and the protective layer is composed of a resin film with an elastic coefficient of 3000 MPa or more. The method for manufacturing a polarizing plate with a retardation layer according to claim 1 or 2, wherein the protective layer is composed of a triacetylcellulose resin film. The method for manufacturing a polarizing plate with a retardation layer according to claim 1 or 2, wherein the retardation layer is composed of a polycarbonate resin film. The method of manufacturing a polarizing plate with a retardation layer according to claim 1 or 2, wherein the retardation layer is composed of a polycarbonate resin film having a thickness of 40 μm or less. The method for manufacturing a polarizing plate with a retardation layer according to claim 1 or 2, wherein the difference between the maximum value and the minimum value of the single transmittance of the polarizing film in an area of 50 cm ² is less than 0.5%. The manufacturing method of a polarizing plate with a retardation layer as claimed in claim 1 or 2, wherein the width of the polarizing film is more than 1000 mm, and the difference between the maximum value and the minimum value of the single transmittance at a position along the width direction is 1 %the following. The method for manufacturing a polarizing plate with a retardation layer according to claim 1 or 2, wherein the single transmittance of the polarizing film is 50% or less, and the polarization degree is 92% or less. For example, the polarizing plate with a retardation layer according to claim 1 or 2 A manufacturing method, wherein the aforementioned polarizing plate with a retardation layer further has another retardation layer outside the aforementioned retardation layer, and the refractive index characteristics of the other retardation layer show the relationship nz>nx=ny; and, the The manufacturing method includes the following steps: arranging the other phase difference layer outside the aforementioned phase difference layer. The method for manufacturing a polarizing plate with a retardation layer as claimed in claim 1 or 2, wherein the polarizing plate with a retardation layer further has a conductive layer or an isotropic base material with a conductive layer outside the retardation layer; Furthermore, the manufacturing method includes the following steps: arranging the conductive layer or the isotropic base material with the conductive layer outside the retardation layer. The method for manufacturing a polarizing plate with a retardation layer as claimed in claim 1 or 2, wherein the polarizing plate with a retardation layer is in the shape of a strip; and the manufacturing method includes the following steps: stacking the strips in a roll-to-roll manner A long strip-shaped polarizing film with an absorption axis in the direction and a long strip-shaped retardation layer. The aforementioned phase difference layer is an oblique extension with a slow axis in a direction at an angle of 40°~50° with respect to the long strip direction. film. The method for manufacturing a polarizing plate with a retardation layer as claimed in claim 12 includes the following steps: winding the long strip of polarizing plate with a retardation layer into a roll.

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