TWI805911B - Polarizing film, polarizing plate, and manufacturing method of the polarizing film - Google Patents

Abstract

The present invention provides a polarizing film in which discoloration of an end portion is suppressed in a high-humidity environment. The polarizing film of the present invention is made of iodine-containing polyvinyl alcohol-based resin film, and when the monomer transmittance is x%, and the orientation function of the polyvinyl alcohol-based resin film is y, the following formula (1 ). y≧-0.06x+2.88 (1)

Description

Polarizing film, polarizing plate, and manufacturing method of the polarizing film

The invention relates to a polarizing film, a polarizing plate and a manufacturing method of the polarizing film.

In a liquid crystal display device which is a typical image display device, polarizing films are arranged on both sides of the liquid crystal cell according to the image forming method. The manufacturing method of polarizing film, for example, has been proposed to have a kind of laminated body that has resin base material and polyvinyl alcohol (PVA) system resin layer stretches and then applies dyeing treatment and obtains the method of polarizing film on resin base material (for example patent document 1). A thinner polarizing film can be obtained by this method, so it can contribute to the thinning of image display devices in recent years and has attracted attention. However, the above-mentioned thin polarizing film has the problem of easy discoloration at the end (especially the end in the width direction) in a high-humidity environment.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2001-343521

This invention is made|formed in order to solve the said conventional subject, Its main object is to provide the polarizing film which suppressed the discoloration of the edge part in a high-humidity environment.

According to one aspect of the present invention, a polarizing film is provided, which is composed of an iodine-containing polyvinyl alcohol-based resin film, and when the monomer transmittance is x%, and the orientation function of the polyvinyl alcohol-based resin film is y , the following formula (1) is satisfied.

y≧-0.06x+2.88 (1)

In one embodiment, the thickness of the polarizing film is 8 μm or less.

In one embodiment, the monomer transmittance of the polarizing film is 41%-43%, and the orientation function of the polyvinyl alcohol-based resin film is 0.30-0.45.

In one embodiment, the monomer transmittance of the above-mentioned polarizing film is greater than 43% and below 45%, and the orientation function of the above-mentioned polyvinyl alcohol-based resin film is 0.20-0.35.

In one embodiment, the monomer transmittance of the above-mentioned polarizing film is greater than 45% and below 47%, and the orientation function of the above-mentioned polyvinyl alcohol-based resin film is 0.15-0.25.

According to another aspect of the present invention, a polarizing plate is provided, which includes the above-mentioned polarizing film and a protective layer disposed on at least one side of the above-mentioned polarizing film.

Yet another aspect of the present invention is to provide a method for manufacturing a polarizing film. The manufacturing method of the polarizing film comprises the steps of: forming a polyvinyl alcohol-based resin layer comprising a halide and a polyvinyl alcohol-based resin on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and, the laminate Sequentially perform air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment. The drying shrinkage treatment is to heat the laminate while transporting it along the long side direction, so as to make it shrink by more than 2% in the width direction; The stretching ratio of the aerial-assisted stretching treatment is 2.6-4.0 times relative to the original length of the laminate, and the ratio of the stretching ratio of the aerial-assisted stretching treatment to the stretching ratio of the underwater stretching treatment is 120%-300%.

In one embodiment, the total magnification of the stretching in the aerial assisted stretching process and the underwater stretching process is 5.0 times or more relative to the original length of the laminated body.

According to the polarizing film of the present invention, by controlling the orientation of the polyvinyl alcohol-based resin layer, it is possible to suppress discoloration of the edge portion under a high-humidity environment.

10: Polarizing film

20: 1st protective layer

30: 2nd protective layer

100a, 100b: polarizer

200: laminated body

R1~R6: conveyor roller

G1~G4: guide roller

Fig. 1A is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention.

Fig. 1B is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing an example of drying shrinkage treatment using a heating roll.

Fig. 3 is a graph showing the relationship between the transmittance of a single substance and the orientation function of a PVA-based resin layer and formula (1).

Fig. 4 is a graph showing the results of discoloration evaluation.

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

A. Polarizing film

The polarizing film of the embodiment of the present invention is made of iodine-containing polyvinyl alcohol (PVA) resin film, and when the monomer transmittance is x%, and the orientation function of the PVA resin film is y, it satisfies the following Formula 1). The polarizing film satisfying the formula (1) has excellent single transmittance, and can suppress discoloration of the end portion under a high-humidity environment. In addition, it is preferable that the above-mentioned y further satisfies the following formula (2) from the viewpoint of securing a practically sufficient single-body transmittance.

y≧-0.06x+2.88 (1)

y≦-0.06x+3.40 (2)

The polarizing film is composed of an iodine-containing PVA-based resin film as described above. Examples of PVA-based resins include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. 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 the PVA-based resin is usually 85 mol %-100 mol %, preferably 95.0 mol %-99.95 mol %, more preferably 99.0 mol %-99.93 mol %. The degree of saponification can be obtained in accordance with JIS K 6726-1994. A polarizing film excellent in durability can be obtained by using a PVA-based resin having such a degree of saponification. When the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to 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 obtained according to JIS K 6726-1994.

The PVA-based resin preferably includes PVA-based resin modified with acetoacetyl. as long as the Composition, a polarizing film with desired mechanical strength can be obtained. When the whole PVA-based resin is 100% by weight, the blending amount of the PVA-based resin modified with acetoacetyl group is preferably 5% by weight to 20% by weight, more preferably 8% by weight to 12% by weight. As long as the blending amount is within the above range, a polarizing film with more excellent mechanical strength can be obtained.

The thickness of the polarizing film is preferably less than 8 μm, preferably less than 7 μm, more preferably less than 5 μm, and most preferably less than 3 μm. The lower limit of the thickness of the polarizing film may be 1 μm in one embodiment, and may be 2 μm in another embodiment. The above-mentioned thickness can be realized by producing a polarizing film using, for example, a laminate of a thermoplastic resin substrate and a PVA-based resin layer coated and formed on the thermoplastic resin substrate, as will be described later.

The polarizing film should exhibit absorption dichroism at any wavelength between 380nm and 780nm. The single transmittance of the polarizing film is preferably above 40.0%, more preferably above 41.0%. The upper limit of the single transmittance may be 49.0%, for example. In one embodiment, the single transmittance of the polarizing film is 40.0% to 47.0%. The degree of polarization of the polarizing film is preferably above 99.0%, more preferably above 99.4%. The upper limit of the degree of polarization may be, for example, 99.999%. In one embodiment, the degree of polarization of the polarizing film is 99.0% to 99.9%. In addition, the single transmittance represents the Y value obtained by measuring with an ultraviolet-visible spectrophotometer and correcting the light sensitivity. In addition, the single-body transmittance is the value when the refractive index of one surface of a polarizing plate was converted into 1.50, and the refractive index of the other surface was converted into 1.53. The representative degree of polarization is based on the parallel transmittance Tp and cross transmittance Tc obtained by measuring with an ultraviolet-visible spectrophotometer and correcting the sensitivity, and obtained through the following formula.

Degree of polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In the PVA-based resin film constituting the polarizing film, the PVA-based resin is oriented along the direction of the absorption axis. Generally, the single transmittance of a polarizing film is negatively correlated with the orientation of the PVA-based resin film constituting the polarizing film, which means that once the orientation of the PVA-based resin film increases, the single transmittance tends to decrease. In this regard, the balance of the monomer transmittance of the polarizing film of the present invention and the orientation of the PVA-based resin film is improved. Compared with the conventional polarizing film, the orientation of the PVA-based resin film can be affected without reducing the monomer transmittance. promote. Since the orientation of the PVA-based resin film constituting the polarizing film is improved, it is possible to suppress iodine from the end Partial dissolution, the result can suitably suppress fading.

In one embodiment, the single transmittance of the polarizing film is 41%-43%, and the orientation function of the PVA-based resin film constituting the polarizing film is preferably 0.30-0.45, more preferably 0.35-0.45.

In another embodiment, the single transmittance of the polarizing film is greater than 43% and below 45%, and the orientation function of the PVA-based resin film constituting the polarizing film is preferably 0.20-0.35, more preferably 0.25-0.35.

In yet another embodiment, the single transmittance of the polarizing film is greater than 45% and below 47%, and the orientation function of the PVA-based resin film constituting the polarizing film is preferably 0.15-0.25, more preferably 0.18-0.25.

The orientation function (y) is obtained, for example, by attenuated total reflection (ATR: attenuated total reflection) measurement using a Fourier transform infrared spectrophotometer (FT-IR) and using polarized light as measurement light. Specifically, the measurement was carried out in a state where the extending direction of the polarizing film was parallel and perpendicular to the polarization direction of the measurement light, and the intensity at 2941 cm ⁻¹ of the obtained absorbance spectrum was used for calculation according to the following formula. Here, the intensity I is the value of 2941cm ^-1 /3330cm ^-1 with 3330cm ^-1 as the reference peak. In addition, when y=1, it is fully oriented, and when y=0, it is random. Also, we think that the peak at 2941 cm ^-1 is caused by the vibration absorption of the PVA main chain (-CH ₂ -) in the polarizing film.

y=(3<cos ² θ >-1)/2=(1-D)/[c(2D+1)]=-2×(1-D)/(2D+1)

However, when c=(3cos ² β-1)/2, 2941cm ^-1 vibration, β=90°.

θ: The angle of the molecular chain relative to the direction of extension

β: The angle of the transition dipole moment relative to the molecular chain axis

D=(I _⊥ )/(I _// )(At this time, the more oriented the PVA molecule is, the larger the D will be)

I _⊥ : Measure the absorption intensity when the polarization direction of light is perpendicular to the extension direction of the polarizing film

I _// : Measure the absorption intensity when the polarization direction of light is parallel to the extension direction of the polarizing film

B. Polarizer

1A and 1B are schematic cross-sectional views of a polarizing plate according to an embodiment of the present invention, respectively. The polarizing plate 100 a shown in FIG. 1A includes a polarizing film 10 and a first protection layer 20 disposed on one side of the polarizing film 10 . The polarizing plate 100 b shown in FIG. 1B includes: a polarizing film 10 , a first protective layer 20 disposed on one side of the polarizing film 10 , and a second protective layer 30 disposed on the other side of the polarizing film 10 . The polarizing film 10 is the polarizing film described in item A. One of the first protective layer and the second protective layer may be a thermoplastic resin substrate used to manufacture a polarizing film. The manufacturing method of the polarizing film will be described in detail in item C.

The first and second protective layers are formed of any appropriate thin film that can be used as a protective layer of a polarizing film. Specific examples of the material used as the main component of the film include: cellulose-based resins such as cellulose triacetate (TAC); polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyamide-based resins, etc. Imine-based, polyether-based, polystyrene-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based and acetate-based transparent resins, etc. Further, thermosetting resins such as (meth)acrylic, urethane, (meth)acrylate urethane, epoxy, and silicone, or ultraviolet curable resins are also mentioned. Other examples include glassy polymers such as siloxane polymers. Furthermore, a polymer film described in JP-A-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 imide 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, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extruded product of the above-mentioned resin composition.

When the polarizing plate is applied to an image display device, the thickness of the protective layer (outer protective layer) disposed on the side opposite to the display panel is typically not more than 300 μm, preferably not more than 100 μm, more preferably 5 μm to 80 μm, more preferably 10μm~60μm. In addition, when surface treatment is applied, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

When the polarizer is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having any appropriate retardation value. At this time, the in-plane retardation Re(550) of the retardation layer is, for example, 110 nm to 150 nm. "Re(550)" is the in-plane retardation measured with light with a wavelength of 550nm at 23°C, and can be obtained by the formula: Re=(nx-ny)×d. Here, "nx" is the refractive index in the direction where the in-plane refractive index becomes the largest (that is, the direction of the slow axis), and "ny" is the refractive index in the direction that is perpendicular to the slow axis in the plane (that is, the direction of the fast axis) , "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

C. Manufacturing method of polarizing film

A method for manufacturing a polarizing film according to an embodiment of the present invention includes the following steps: forming a PVA-based resin layer on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and sequentially performing aerial assisted stretching on the laminate Treatment, dyeing treatment and water extension treatment. Preferably, the manufacturing method of the polarizing film includes the following steps: forming a PVA-based resin layer on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and sequentially performing aerial assisted stretching and dyeing on the laminate treatment, underwater stretching treatment, and drying shrinkage treatment. The dry shrinkage treatment is to heat the laminate while transporting it in the longitudinal direction, thereby shrinking it by 2% or more in the width direction. In the manufacturing method of this embodiment, the stretching ratio of the air-assisted stretching process is 2.6 to 4.0 times the original length of the laminate. Also, the ratio of the stretching ratio of the air-assisted stretching treatment to the stretching ratio of the underwater stretching treatment is 120% to 300%. Preferably, the total extension ratio of the aerial-assisted stretching treatment and the underwater stretching treatment (the product of the stretching ratio of the aerial-assisted stretching and the stretching ratio of the underwater stretching, hereinafter also referred to as the "total stretching ratio") relative to the original length of the laminated body is More than 5.0 times. According to the manufacturing method of this embodiment, the polarizing film described in A term can be obtained suitably.

One of the characteristics of the above-mentioned manufacturing method can be cited: while ensuring the total stretching ratio sufficient to impart good optical properties to the polarizing film, the ratio of the aerial assisted stretching treatment in the combination of the aerial assisted stretching treatment and the underwater stretching treatment is increased. When stretching in water, in the thickness direction of the PVA resin layer Variations in the degree of orientation tend to occur, for example, the degree of orientation of the PVA-based resin layer tends to be lower on the side of the thermoplastic resin substrate than on the exposed side. On the other hand, by increasing the stretching ratio of the in-air assisted stretching, the laminate can be subjected to underwater stretching while the PVA-based resin is highly and uniformly oriented. As a result, even in the case of lowering the stretching ratio of the underwater stretching treatment, a sufficient total stretching ratio can be ensured, and as a result, the variation in the degree of orientation in the thickness direction can be suppressed and the overall uniformity of the PVA-based resin layer can be obtained without impairing the optical characteristics. Polarizing film with enhanced orientation.

C-1. Fabrication of laminated body

Any appropriate method can be adopted for the method of producing the laminate of the thermoplastic resin base material and the PVA-based resin layer. Preferably, the coating liquid containing PVA-based resin is coated on the surface of the thermoplastic resin substrate and dried, thereby forming a PVA-based resin layer on the thermoplastic resin substrate.

Any appropriate method can be adopted for the coating method of the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (cutting wheel coating, etc.) and the like. The coating and drying temperature of the above-mentioned coating solution is preferably 50°C or higher.

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

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

Any appropriate thermoplastic resin film can be used as the thermoplastic resin substrate. The details of the thermoplastic resin film substrate are described in, for example, JP-A-2012-73580. In this specification, the entire description of the publication is incorporated by reference. It is preferable to use a polyester resin, and it is more preferable to use a polyethylene terephthalate resin.

The coating liquid refers to a solution in which PVA-based resin is dissolved in a solvent. Regarding the PVA-based resin, it is as described in the item A. Examples of the solvent include water, dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, ethylene glycol, and the like. Diamine, Amines such as diethylenetriamine. These can be used individually or in combination of 2 or more types. Among these, the solvent is preferably water.

The concentration of the PVA-based resin in the coating liquid is preferably 3 parts by weight to 20 parts by weight relative to 100 parts by weight of the solvent. As long as it is the above-mentioned resin concentration, a uniform coating film can be formed in close contact with the thermoplastic resin substrate.

The coating liquid preferably further contains a halide. As the halide, any appropriate halide can be used. Examples thereof include iodide and sodium chloride. Examples of iodide include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferable.

The compounding amount of the halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA-based resin. If the blending amount of the halide is more than 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may overflow and the finally obtained polarizing film may become cloudy.

Generally speaking, by stretching the PVA resin layer, the orientation of the polyvinyl alcohol molecules in the PVA resin layer will become higher, but if the stretched PVA resin layer is immersed in a liquid containing water, there will be polyethylene The situation where the alignment of alcohol molecules is disordered and the orientation is reduced. In particular, when stretching a laminate of a thermoplastic resin and a PVA-based resin layer in boric acid water, the above-mentioned degree of orientation tends to decrease when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. Significantly. For example, the stretching of PVA film monomer in boric acid water is generally carried out at 60°C. In contrast, the stretching of the laminate of A-PET (thermoplastic resin substrate) and PVA-based resin layer is at 70°C. The temperature before and after C is higher temperature. At this time, the orientation of the PVA at the beginning of stretching will decrease in the stage before it rises due to stretching in water. In this regard, by making a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and stretching the laminate at a high temperature in air (assisted stretching) before stretching it in boric acid water, it is possible to facilitate post-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 was immersed in the liquid, compared with the case where the PVA-based resin layer did not contain halides, Moreover, it can inhibit the orientation disorder and decrease of orientation of polyvinyl alcohol molecules. Thereby, the optical characteristic of the polarizing film obtained through the process step which immerses a laminated body in liquid, such as a dyeing process and an underwater stretching process, can be improved.

Additives may be further blended in the coating solution. Examples of additives include plasticizers and surfactants. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. The surfactant may, for example, be a nonionic surfactant. These can be used to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

C-2. Air Assisted Extended Processing

In particular, in order to obtain high optical properties, the method of combining dry stretching (assisted stretching) and boric acid underwater stretching is selected as a two-stage stretching method. Like the two-stage stretching method, by introducing auxiliary stretching, stretching can be performed while suppressing crystallization of the thermoplastic resin base material. In addition, when the PVA-based resin is applied to the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature must be higher than that of the general case of applying the PVA-based resin to a metal roller. If it is too low, as a result, the crystallization of the PVA-based resin becomes relatively low, so that sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be improved even when the PVA-based resin is coated on a thermoplastic resin, and high optical characteristics can be achieved. Also, at the same time, improving the orientation of the PVA-based resin in advance prevents problems such as a decrease in the orientation or dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step or stretching step, and achieves high optical characteristics.

The stretching method of aerial auxiliary stretching can be fixed end stretching (such as stretching method using a tenter stretching machine), or free end stretching (such as the method of uniaxial stretching the laminated body through rollers with different peripheral speeds) ), but in order to obtain high optical properties, the free end extension can be actively used. In one embodiment, the in-air auxiliary stretching process includes a heating roll stretching step of stretching the above-mentioned layered product using a peripheral speed difference between the heating rolls while conveying the laminate in the longitudinal direction. The air-assisted stretching process typically includes a zone stretching step and a heated roller stretching step. In addition, the order of the zone stretching step and the heating roller stretching step is not limited, and the zone stretching step or the heating roller stretching step may be performed first. The region extension step can also be omitted. In one embodiment, the region stretching step and the heating roll stretching step are performed sequentially. In another embodiment, the end of the film is held in a tenter stretching machine, and the distance between the tenters is increased in the traveling direction to stretch (the increase in the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (vertical direction with respect to the traveling direction) is set so as to be arbitrarily close. Preferably, it can be set as an extension ratio relative to the flow direction to use the extension of the free end for approaching. When the free end is extended, it is calculated as the shrinkage rate in the width direction = (1/extension ratio) ^1/2 .

Aerial assisted extension can be performed in one phase or in multiple phases. When it is carried out in multiple stages, the extension ratio is the product of the extension ratios of each stage. The direction of extension in aerial auxiliary extension should be approximately the same as that of underwater extension.

The extension magnification of aerial auxiliary extension is, for example, 2.6 times to 4.0 times, preferably 2.8 times to 3.8 times, more preferably 3.0 times to 3.6 times. As long as the stretching ratio of the aerial auxiliary stretching is within the above range, the PVA-based resin layer can be highly and uniformly oriented, and the orientation of the PVA-based resin layer after underwater stretching can be improved.

The stretching temperature of the air-assisted stretching can be set to any appropriate value according to the forming material and stretching method of the thermoplastic resin substrate. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, and more preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, especially preferably above Tg+15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. Stretching at the above temperature suppresses the rapid progress of crystallization of the PVA-based resin, thereby suppressing disadvantages caused by the crystallization (for example, disturbance of the orientation of the PVA-based resin layer by stretching).

C-3. Insoluble treatment, dyeing treatment and cross-linking treatment

Insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment or dyeing treatment as necessary. The above-mentioned insolubilization treatment is typically carried out by immersing the PVA-based resin layer in a boric acid aqueous solution. The above-mentioned dyeing treatment is representatively carried out by dyeing the PVA-based resin layer with iodine. After the dyeing treatment and before the stretching treatment in water, a crosslinking treatment is performed as necessary. The above-mentioned cross-linking treatment can be represented by using The PVA-based resin layer is dipped in a boric acid aqueous solution. Details of insolubilization treatment, dyeing treatment, and crosslinking treatment are described in, for example, JP-A-2012-73580 (above).

C-4. Extended treatment in water

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. By stretching in water, it can be stretched at a temperature lower than the glass transition temperature (typically about 80°C) of the above-mentioned thermoplastic resin substrate or PVA-based resin layer, and can suppress the crystallization of the PVA-based resin layer at the same time Make an extension. As a result, a polarizing film with excellent optical properties can be produced.

Any appropriate method can be used for the stretching method of the laminate. Specifically, it may be a fixed end extension, or a free end extension (for example, a method of uniaxially extending a laminate through rollers with different circumferential speeds). Preferably a free end extension is selected. The extension of the laminate may be performed in one step or in multiple steps. When it is carried out in multiple stages, the total extension ratio is the product of the extension ratios of each stage.

The underwater stretching is preferably carried out by immersing the laminate in an aqueous solution of boric acid (boric acid underwater stretching). By using an aqueous solution of boric acid as a stretching bath, the PVA-based resin layer can be given rigidity capable of withstanding tension during stretching and water resistance insoluble in water. Specifically, boric acid generates tetrahydroxyboric acid anion in aqueous solution, which can cross-link with PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and good stretching can be performed, 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 which is a solvent. The concentration of boric acid relative to 100 parts by weight of water is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, particularly preferably 3 to 5 parts by weight. By setting the concentration of boric acid 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. Moreover, the aqueous solution which melt|dissolved boron compound, such as borax, glyoxal, glutaraldehyde, etc. in a solvent other than boric acid or borate, can also be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C~85°C, more preferably 60°C~75°C. As long as it is the above-mentioned temperature, the dissolution of the PVA-based resin layer can be suppressed, and at the same time, high-magnification stretching can be achieved. Specifically, as described above, considering the relationship with 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 considering plasticizing the thermoplastic resin substrate with water, it may not be possible to stretch well. On the other hand, the higher the temperature of the stretching bath is, the higher the solubility of the PVA-based resin layer will be, and it may not be possible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio of underwater stretching is preferably 1.3 times to 2.3 times, more preferably 1.4 times to 2.1 times, more preferably 1.5 times to 1.9 times. As long as the stretching ratio of underwater stretching is within the above range, when combined with aerial auxiliary stretching, the total stretching ratio can be set within a desired range, and at the same time, the overall orientation of the PVA-based resin layer can be improved. As a result, a polarizing film having excellent optical characteristics and in which discoloration of the end portion is suppressed can be obtained.

In general, the extension ratio of aerial auxiliary extension is greater than that of underwater extension. The ratio of the stretching magnification of aerial assisted stretching to that of underwater stretching (stretching magnification of aerial assisted stretching/stretching magnification of underwater stretching) should be 120%~300%, preferably 140%~260%, 160%~230 % better. By setting this ratio, the total stretch ratio can be set within a desired range, and the orientation of the entire PVA-based resin layer can be improved. As a result, a polarizing film having excellent optical characteristics and in which discoloration of the end portion is suppressed can be obtained.

The total elongation ratio of air-assisted elongation treatment and water elongation treatment is as mentioned above, relative to the original length of the laminated body, it should be more than 5.0 times, more preferably 5.2 times to 7.0 times, more preferably 5.5 times to 6.5 times. By achieving such a high elongation ratio, a polarizing film with extremely excellent optical characteristics can be manufactured.

C-5. Drying shrinkage treatment

The above-mentioned drying shrinkage treatment can be performed by heating the entire area by heating the region, or by heating the conveying roller (using a so-called heating roller) (heating roller drying method). It is preferable to use both. By drying with a heating roller, the heat curl of the laminate can be effectively suppressed, and the Polarizing film with excellent appearance. Specifically, by drying the laminated body along the heating roll, the crystallization of the above-mentioned thermoplastic resin substrate can be effectively promoted to increase the degree of crystallization, even at a relatively low drying temperature, It can still increase the crystallinity of thermoplastic resin substrates well. As a result, the rigidity of the thermoplastic resin substrate is increased to be able to withstand shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling (warping). In addition, since the layered body can be dried while maintaining a flat state by using the heating roller, not only the occurrence of curl but also wrinkling can be suppressed. At this time, the laminated body can shrink in the width direction through drying shrinkage treatment, so as to improve the optical properties. It is because it can effectively improve the orientation of PVA and PVA/iodine complexes. The shrinkage rate in the width direction of the laminate under drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and especially preferably 4% to 6%.

Fig. 2 is a schematic view showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminated body 200 is dried while being conveyed by conveying rollers R1 to R6 and guide rollers G1 to G4 heated to a predetermined temperature. In the example shown in the drawing, the transfer rollers R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but for example, the transfer rollers R1 to R6 may be arranged so as to continuously heat only the laminated body 200 One of the sides (such as thermoplastic resin substrate side).

The drying conditions can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of the heating roller and the contact time with the heating roller, etc. The temperature of the heating roller is preferably 60°C~120°C, more preferably 65°C~100°C, especially 70°C~80°C. It can increase the degree of crystallization of thermoplastic resin well to suppress curling well, and at the same time, it can produce an optical laminate with excellent durability. In addition, the temperature of the heating roller can be measured with a contact thermometer. In the illustrated example, six conveyance rollers are provided, but there is no particular limitation as long as there are plural conveyance rollers. The number of conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, preferably 1 to 20 seconds, more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven), or it can be installed in a general production line (at room temperature). It should be installed in a heating furnace with an air supply mechanism. By combining drying with heating rollers and hot air drying, rapid temperature changes between heating rollers can be suppressed, and the width direction can be easily controlled. shrink. 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 the hot air should be around 10m/s~30m/s. In addition, the wind speed refers to the wind speed in the heating furnace, which can be measured by a mini fan-type digital anemometer.

C-6. Washing treatment

It is preferable to carry out the washing treatment after the stretching treatment in water and before the drying shrinkage treatment. Typically, the cleaning treatment described above can be performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

In the manner described above, a laminate of the thermoplastic resin substrate and the polarizing film (PVA-based resin layer) can be obtained. The laminate can be used as a polarizing plate without peeling off the thermoplastic resin substrate. In this case, the thermoplastic resin substrate can function as a protective layer of the polarizing film. As an alternative, the first resin film is pasted on the surface of the polarizing film of the laminate through any appropriate adhesive layer, and then the thermoplastic resin substrate is peeled off, thereby making a film with [the first protective layer (the first resin film) )/Polarizing film] is composed of a laminate and used as a polarizing plate. And, it is also possible to bond the second resin film on the surface of the polarizing film of the laminated body through any appropriate adhesive layer to make a protective layer with [the first protective layer (thermoplastic resin substrate or the first resin film)/polarizing film/the first 2. A polarizing plate composed of a protective layer (second resin film)].

Example

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

(1) Thickness

Measurement was performed using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000").

(2) Monomer transmittance

For the laminate (polarizing plate) of the polarizing film/protective layer obtained in Examples and Comparative Examples, the single transmittance (Ts) was measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation "V-7100"), and its Ts as polarizing film. Single transmittance is measured by JIS Z8701 2-degree field of view (C light source) and visual sensitivity Correct the resulting Y value.

(3) Orientation function (y) of PVA-based resin layer

For the polarizing films obtained in Examples and Comparative Examples, using a Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name: "Frontier"), using polarized infrared rays as measurement light, the surface of the polarizing film was measured. Attenuated total reflection (ATR: attenuated total reflection) measurement. Germanium was used as the microcrystal system for bonding the polarizing film, and the incident angle of the measurement light was set at 45°. The calculation of the orientation function is carried out according to the following procedure. The polarized infrared ray (measurement light) to be incident is set as polarized light (s-polarized light) vibrating parallel to the surface of the sample on which the germanium crystal is attached. Measure individual absorbance spectra in vertical (⊥) and parallel (//) configurations. From the obtained absorbance spectrum, (2941 cm ^-1 intensity) I was calculated with reference to (3330 cm ^-1 intensity). I _⊥ is obtained from the absorbance spectrum (2941cm ^-1 intensity)/(3330cm ^-1 intensity) obtained when the extending direction of the polarizing film is arranged perpendicular to the polarization direction of the measuring light (⊥). Also, I _// is obtained from the absorbance spectrum obtained when the extending direction of the polarizing film is arranged in parallel (//) to the polarization direction of the measurement light (intensity at 2941cm ^-1 )/(intensity at 3330cm ^-1 ). Here, (intensity at 2941cm ^-1 ) is the absorbance ^at the bottom of the absorbance spectrum at 2941cm -1 when 2770cm ^-1 and 2990cm ^-1 are taken as baselines, and (intensity at 3330cm ^-1 ) is when 2990cm ^-1 and 3650cm ^-1 are taken as baselines The absorbance of 3330cm ^-1 . Use the obtained I _⊥ and I _// to calculate the orientation function y according to formula 1. In addition, when y=1, it is fully oriented, and when y=0, it is random. Also, it is estimated that the peak at 2941 cm ^-1 is the absorption due to the vibration of the main chain (-CH ₂ -) of PVA in the polarizing film. Also, it is estimated that the peak at 3330 cm ^-1 is the absorption due to the vibration of the hydroxyl group of PVA.

(Formula 1) y=(3<cos2θ>-1)/2=(1-D)/[c(2D+1)]

y=-2×(1-D)/(2D+1)。 However, with c=(3cos ² β-1)/2, when using 2941cm ^-1 as above, β=90°

y=-2×(1-D)/(2D+1).

θ: The angle of the molecular chain relative to the direction of extension

β: The angle of the transition dipole moment relative to the molecular chain axis

D=(I _⊥ )/(I _// )

I _⊥ : Measure the absorption intensity when the polarization direction of light is perpendicular to the extension direction of the polarizing film

I _// : Measure the absorption intensity when the polarization direction of light is parallel to the extension direction of the polarizing film

[Example 1]

The thermoplastic resin substrate is a long amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100μm) with a Tg of about 75°C, and corona treatment is applied to one side of the resin substrate .

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

The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin substrate 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 stretched to 3.0 times in the longitudinal direction (longitudinal direction) in an oven at 130° C. (in-air assisted stretching treatment).

Next, the laminate was immersed in an insoluble bath (an aqueous solution of boric acid obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insoluble treatment).

Next, adjust the concentration in 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) at a liquid temperature of 30° C. while dipping in it for 60 seconds, so that the final The single transmittance (Ts) of the polarizing film was 45.1% (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) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). ).

Then, the laminate was immersed in a boric acid aqueous solution (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70°C, while uniaxially stretching in the longitudinal direction (longitudinal direction) between rollers with different circumferential speeds. So that the total elongation ratio reaches 5.5 times (in water elongation treatment: the elongation ratio of underwater elongation treatment is 1.83 times).

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

Thereafter, while drying in an oven maintained at approximately 90°C, the contact surface temperature was maintained at approximately 75°C with a heating roller made of SUS (drying shrinkage treatment). The shrinkage rate in the width direction of the laminate under drying shrinkage treatment is 2%.

According to the above method, a polarizing film with a thickness of about 5 μm was formed on the resin substrate to obtain a polarizing plate having a composition of resin substrate/polarizing film.

Then, a cycloolefin-based film (manufactured by ZEON Japan, ZF-12, 23 μm) was bonded to the surface of the obtained polarizing film (the surface opposite to the resin substrate) as a protective substrate through an ultraviolet curable adhesive. Specifically, it is applied so that the total thickness of the hardening adhesive becomes about 1.0 μm, and they are bonded together using a rolling mill. Thereafter, UV light was irradiated from the side of the cycloolefin-based film to harden the adhesive. Next, the resin substrate was peeled off to obtain a polarizing plate having a composition of cycloolefin-based film (protective substrate)/polarizing film.

[Example 2]

A polarizing plate was produced in the same manner as in Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contacting with the treatment solution was 41.9%.

[Example 3]

A polarizing plate was produced in the same manner as in Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contacting with the treatment solution was 45.3%.

[Example 4]

A polarizing plate was produced in the same manner as in Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contacting with the treatment solution was 43.8%.

[Comparative example 1]

The concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contact with the treatment solution was 41.8%, and the stretching ratio of the aerial auxiliary stretching treatment was set to 2.4 times, and the stretching ratio of the underwater stretching treatment was set to 41.8%. A polarizing plate was produced in the same manner as in Example 1 except that the ratio was set to 2.3 times (the total stretching ratio was 5.5 times).

[Comparative example 2]

A polarizing plate was produced in the same manner as in Comparative Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contacting with the treatment solution was 42.7%.

[Comparative example 3]

A polarizing plate was produced in the same manner as in Comparative Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contacting with the treatment liquid became 43.8%.

[Comparative example 4]

A polarizing plate was produced in the same manner as in Comparative Example 1 except that the concentration of the dyeing bath was adjusted so that the single transmittance of the polarizing film before contacting with the treatment liquid became 45.0%.

Table 1 and Figure 3 show the single transmittance of the polarizing plate (polarizing film) obtained in the above-mentioned examples and comparative examples, the orientation function of the PVA-based resin layer and the relationship between these values and formula (1).

"Evaluation of discoloration at the ends in the width direction"

The polarizing plates obtained in Examples and Comparative Examples were cut into rectangular shapes, and glycerin was applied to the entire periphery. Next, the polarizing plate was placed under the conditions of 65° C. and 90% RH for 72 hours. Next, the presence or absence of discoloration was confirmed with an optical microscope about both ends in the width direction (direction perpendicular to the MD direction) of the polarizing film, and the length of the discolored portion was measured. In addition, the length of the longest discolored portion was defined as the discolored length, and the average value of the discolored lengths at both ends was determined as the discolored amount (μm). For each polarizing plate, the relationship between the single transmittance (Ts) and the amount of discoloration is shown in FIG. 4 .

As can be clearly seen in Figure 4, if the polarizing plate (polarizing film) of the embodiment with the same monomer transmittance is compared with the polarizing plate (polarizing film) of the comparative example, the fading of the end portion of the polarizing film of the embodiment is less suppressed. As shown in Table 1, we speculate that compared with the polarizing plate of the comparative example with the same monomer transmittance, the orientation of the PVA-based resin layer (polarizing film) of the polarizing plate of the example is higher, and as a result, iodine is less likely to occur. Dissolution situation.

Industrial availability

The polarizing film of the present invention can be applied to liquid crystal display devices.

10: Polarizing film

20: 1st protective layer

100a: Polarizing plate

Claims (7)

A kind of polarizing film is made of iodine-containing polyvinyl alcohol-based resin film, and when the monomer transmittance is x%, and the orientation function of the polyvinyl alcohol-based resin film is y, the following formula (1) is satisfied : y≧-0.06x+2.88 (1); i) The monomer transmittance of the polarizing film is greater than 43% and less than 45%, the degree of polarization is more than 99.4%, and the orientation function of the polyvinyl alcohol-based resin film is 0.20 ~0.35; or ii) the monomer transmittance of the polarizing film is greater than 45% and below 47%, and the orientation function of the polyvinyl alcohol-based resin film is 0.15~0.25. The polarizing film according to claim 1, which has a thickness of 8 μm or less. A polarizing plate, comprising: the polarizing film according to claim 1 or 2 and a protective layer disposed on at least one side of the polarizing film. A method for producing a polarizing film, the polarizing film is composed of an iodine-containing polyvinyl alcohol-based resin film, and when the monomer transmittance is x%, and the orientation function of the polyvinyl alcohol-based resin film is y, it satisfies The following formula (1): y≧-0.06x+2.88 (1); the production method includes the following steps: forming polyvinyl alcohol containing halides and polyvinyl alcohol resin on one side of the elongated thermoplastic resin substrate A resin layer is used to make a laminate; and the laminate is sequentially subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment. The drying shrinkage treatment is to transport the laminate along the longitudinal direction. Heating, thereby causing it to shrink by more than 2% in the width direction; the elongation ratio of the air-assisted stretching treatment is 2.8 to 3.8 times the original length of the laminate, and The ratio of the stretching ratio of the air-assisted stretching treatment to the stretching ratio of the underwater stretching treatment is 120%-300%. The manufacturing method according to claim 4, wherein the total extension ratio of the above-mentioned air-assisted stretching treatment and the aforementioned underwater stretching treatment is 5.0 times or more relative to the original length of the above-mentioned laminate. The method for manufacturing a polarizing film according to claim 4 or 5, which is a method for manufacturing a polarizing film with a thickness of 8 μm or less. The method for manufacturing a polarizing film as claimed in item 4 or 5, which is a method of manufacturing the following polarizing film: the transmittance of the monomer is 41%~43%, and the orientation function of the polyvinyl alcohol-based resin film is 0.30~0.45 polarized light Film; a polarizing film with a monomer transmittance greater than 43% and less than 45%, the polyvinyl alcohol-based resin film having an orientation function of 0.20 to 0.35; or a monomer transmittance greater than 45% and less than 47%, the aforementioned polyethylene Alcohol-based resin film with an orientation function of 0.15~0.25 for polarizing film.

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