TWI669543B - Polarizing film, polarizing plate and method for producing polarizing film - Google Patents

Abstract

The invention provides a polarizing plate having a thin polarizing film (thickness ≦ 10 μm), which can suppress light leakage when mounted on a display device. In addition, a method for producing a polarizing film is provided, which is a method for producing a polarizing film having a thickness of 10 μm or less, a swing of an absorption axis in a plane of 0.2 ° or less, and the following step (1). This step (1) is a step of preparing a base film, which is a long base film containing a thermoplastic resin, and a standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the base film in the MD direction. 0.80 μm or less, and after Fourier transform of the aforementioned waveform, the standard deviation σ 2 calculated from the waveform of the thickness obtained by inverse Fourier transform of the spectrum of the region with a wavenumber of 1/3 (1 / m) or more is 0.65 μm or less.

Description

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

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

The polarizing plate is widely used as a supplying element for polarized light in a liquid crystal display device and as a detecting element for polarized light. The polarizing plate is mainly used for a polarizing film made of a polyvinyl alcohol resin, and a protective film made of triethyl cellulose and the like is pasted through a bonding agent. The expansion of mobile devices such as computers and mobile phones, as well as the expansion of large TVs, requires thinner and lighter polarizers.

Conventional polarizing films are produced by stretching and dyeing the embryonic film of polyvinyl alcohol resin (typically about 75 to 30 μm in thickness), and the thickness of the stretched film is generally about 30 to 12 μm. In order to make the film thinner, if the embryonic membrane of the polyvinyl alcohol-based resin is 30 μm or less, there is a problem in productivity such that the membrane is easily broken during stretching.

Therefore, in order to respond to the reduction in thickness of a polarizing plate, a method of applying a coating solution containing a polyvinyl alcohol resin on a base film has been proposed. Such as In this method, a coating film containing a polyvinyl alcohol resin is coated on a substrate film to form a polyvinyl alcohol resin layer to obtain a laminated film. The laminated film is subjected to extension and dyeing treatment to polymerize the laminated film. The vinyl alcohol-based resin layer gives a polarizing function to obtain a polarizing film. (Patent Documents 1 and 2).

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2011-150313

[Patent Document 2] Japanese Patent Laid-Open No. 2012-159778

As described above, the method of manufacturing a polarizing plate by applying a coating solution containing a polyvinyl alcohol-based resin to a polarizing film can relatively easily achieve thinning of the polarizing plate. However, when the polarizing plate manufactured by the above method is mounted on a liquid crystal display device, light leakage occurs, and there is a problem that high contrast cannot be obtained.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a polarizing plate, which is a polarizing plate having a thin polarizing film (thickness ≦ 10 μm), and can suppress light leakage when such a polarizing plate is mounted on a display device. , And further provides a method for manufacturing such a polarizing film and a polarizing plate.

The present invention includes the following.

[1] A polarizing film having a thickness of 10 μm or less and a swing of an absorption axis in a plane of 0.2 ° or less.

[2] A polarizing plate obtained by bonding a protective film to the polarizing film described in [1].

[3] A display device having the polarizing film according to [1] or [2].

[4] A method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film with a thickness of 10 μm or less and an in-plane absorption axis swing of 0.2 ° or less, which includes the following steps (1) to (5): (1) A step of preparing a base film, which is a long base film containing a thermoplastic resin, and a standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the base film in the MD direction and the thickness of the base film The ratio of d (σ 1 / d) is 9.0 × 10 ^-3 or less, and after the aforementioned waveform is Fourier transformed, the inverse Fourier transformation is performed on the spectrum of a region with a wavenumber of 1/3 (1 / m) or more. The ratio of the standard deviation σ 2 calculated from the thickness waveform to the thickness d of the base film (σ 2 / d) is 8.0 × 10 ^-3 or less; (2) at least one side of the base film is coated with polyethylene Alcohol-based resin coating liquid, after preparing a coating film, drying the coating film, thereby forming a polyvinyl alcohol-based resin layer to obtain a laminated film; (3) uniaxially stretching the laminated film to obtain an extended film (4) a step of dyeing the stretched film to obtain a polarizing laminated film; (5) peeling the base film from the polarizing laminated film A step of polarizing film obtained.

[5] A method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film having a thickness of 10 μm or less and an in-plane absorption axis swing of 0.2 ° or less, which includes the following steps (1) to (5): (1) A step of preparing a base film, which is a long base film containing a thermoplastic resin, and a standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the base film in the MD direction is 0.80 μm In the following, the standard deviation σ 2 calculated from the waveform of the thickness obtained by inverse Fourier transforming the spectrum of a region with a wavenumber of 1/3 (1 / m) or more after the aforementioned waveform is Fourier transformed is 0.65 μm or less; (2) Applying a coating solution containing a polyvinyl alcohol-based resin on at least one side of the substrate film to obtain a coating film, and then drying the coating film, thereby forming a polyvinyl alcohol-based resin layer to obtain a laminated film. Steps; (3) a step of uniaxially stretching the aforementioned laminated film to obtain a stretched film; (4) a step of dyeing the aforementioned stretched film to obtain a polarizing laminated film; (5) a step of peeling a base from the aforementioned polarizing laminated film Material film to obtain a polarizing film.

[6] The method for producing a polarizing film according to [4] or [5], further comprising a step of laminating a protective film on the polarizing film in the polarizing laminated film through an adhesive or an adhesive.

[7] The method for producing a polarizing film according to [4] or [5], wherein the base film prepared in step (1) is a base film formed by melt extrusion.

[8] The method for producing a polarizing film according to the item [4], wherein the thickness of the substrate film prepared in step (1) is 5 to 300 μm.

[9] The method for producing a polarizing film according to the item [5], wherein the thickness of the substrate film prepared in step (1) is 20 to 150 μm.

[10] The method for producing a polarizing film according to [4] or [5], wherein the base film prepared in step (1) is a base film containing a polyolefin-based resin.

According to the method of the present invention, a polarizing plate capable of suppressing light leakage when mounted on a display device can be provided, and a display device incorporating such a polarizing plate can achieve high contrast.

1‧‧‧TD direction

2‧‧‧MD direction

3‧‧‧ polarizing film

4‧‧‧ substrate film

5‧‧‧Polarized laminated film

6‧‧‧ Absorption axis

7‧‧‧dotted arrow

8‧‧‧ protective film

9‧‧‧ The polarizing plate of the present invention

10‧‧‧ LCD cell

11‧‧‧ backlight unit

12‧‧‧ LCD display device

Fig. 1 is a diagram for explaining a method for measuring the swing of the absorption axis.

Fig. 2 is a schematic diagram showing an example of a layer configuration of a polarizing plate of the present invention.

FIG. 3 is a schematic diagram showing an example of a layer configuration of a display device of the present invention.

The polarizing film of the present invention can be produced according to the steps including the following steps (1) to (5). Each step is explained in order.

(1) A step of preparing a base film, which is a long base film containing a thermoplastic resin, and a standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the base film in the MD direction is 0.80 μm In the following, the standard deviation σ 2 calculated from the waveform of the thickness obtained by inverse Fourier transforming the spectrum of a region with a wavenumber of 1/3 (1 / m) or more after the aforementioned waveform is Fourier transformed is 0.65 μm or less; (2) a step of applying a coating solution containing a polyvinyl alcohol resin to at least one side of the substrate film, preparing a coating film, and drying the coating film, thereby forming a polyvinyl alcohol resin layer to obtain a laminated film (3) a step of uniaxially stretching the aforementioned laminated film to obtain an extended film; (4) a step of dyeing the stretched film to obtain a polarizing laminated film; (5) a step of obtaining a polarizing film by peeling the base film from the polarizing laminated film.

Moreover, the polarizing film of this invention can also be manufactured by the process containing the following process (1)-(5).

(1) A step of preparing a base film, which is a long base film containing a thermoplastic resin, and the standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the base film in the MD direction and the base material The ratio (σ 1 / d) of the thickness d of the film is 9.0 × 10 ^-3 or less, and after the aforementioned waveform is Fourier-transformed, inverse Fourier transform is performed from the spectrum of a region with a wavenumber of 1/3 (1 / m) or more. The ratio of the standard deviation σ 2 calculated from the converted thickness waveform to the thickness d of the substrate film (σ 2 / d) is 8.0 × 10 ^-3 or less; (2) coating on at least one side of the substrate film A coating liquid containing a polyvinyl alcohol-based resin, after the coating film is prepared, and the coating film is dried, thereby forming a polyvinyl alcohol-based resin layer to obtain a laminated film; (3) uniaxially stretching the laminated film to A step of obtaining a stretched film; (4) a step of dyeing the stretched film to obtain a polarizing laminated film; and (5) a step of obtaining a polarizing film by peeling a base film from the polarizing laminated film.

[step 1)]

In step (1), a substrate film is prepared. The substrate film is a long substrate film containing a thermoplastic resin, and the thickness of the substrate film is measured from the MD direction. The calculated standard deviation σ 1 is 0.80 μm or less, and the waveform obtained by inverse Fourier transform of the spectrum of the region with a wavenumber of 1/3 (1 / m) or more is obtained after Fourier transform of the aforementioned waveform. The calculated standard deviation σ 2 is 0.65 μm or less.

The substrate film prepared in step (1) may be a long substrate film containing a thermoplastic resin. The standard deviation σ 1 calculated from the waveform obtained by measuring the thickness of the substrate film in the MD direction and the thickness of the substrate film The ratio of d (σ 1 / d) is 9.0 × 10 ^-3 or less, and after the aforementioned waveform is Fourier transformed, the inverse Fourier transformation is performed on the spectrum of a region with a wavenumber of 1/3 (1 / m) or more. The ratio (σ 2 / d) of the standard deviation σ 2 calculated from the thickness waveform to the thickness d of the substrate film is 8.0 × 10 ^-3 or less.

(Base film)

The resin forming the base film preferably contains a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, elongation, and the like. Examples of the thermoplastic resin include cellulose ester resins such as cellulose triacetate; polyester resins; polyether fluorene resins; polyfluorene resins; polycarbonate resins; polyamine resins; polyfluorene Imine resins; polyolefin resins such as chain polyolefin resins, cyclic polyolefin resins (norbornene resins, etc.); (meth) acrylic resins; polyarylate resins; Styrene-based resin; polyvinyl alcohol-based resin, etc. In this specification, a general term for (meth) acrylic resin-based methacrylic resin and acrylic resin.

The cellulose ester resin is an ester of cellulose and a fatty acid. Examples of the cellulose ester-based resins include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Among these, cellulose triacetate is preferred. Many types of cellulose triacetate products are sold, which is advantageous in terms of easy availability and cost. As for any of the commercially available products of cellulose triacetate, for example, "Fujitac (registered trademark) TD80" (manufactured by Fuji Film (stock)), "Fujitac (registered trademark) TD80UF" (Fuji Film (stock) )), `` Fujitac (registered trademark) TD80UZ '' (Fuji Film (stock) system), `` Fujitac (registered trademark) TD40UZ '' (Fuji Film (stock) system), `` KC8UX2M '' (Konica Minolta Opto (share) system) , "KC4UY" (made by Konica Minolta Opto (shares)), etc.

In addition to the homopolymer of a polyethylene resin, a polypropylene resin, etc., a chain polyolefin resin is a copolymer which consists of 2 or more types of chain olefins, for example.

Cyclic polyolefin resin is a general term for a resin polymerized by using a cyclic olefin as a polymerization unit. Examples of the resin include JP-A No. 1-240517, JP-A No. 3-14882, and JP-A No. 3-122137. And other recorded resins. Examples of the cyclic polyolefin resin include ring-opening polymers of cyclic olefins, ring-opening copolymers of cyclic olefins, addition polymers of cyclic olefins, and cyclic olefins and chain olefins such as ethylene and propylene. Copolymers (typically random copolymers), graft polymers modified with unsaturated carboxylic acids or derivatives thereof, and hydrides thereof. Among them, cyclic olefins are preferably norbornene-based resins obtained by polymerizing norbornene-based monomers such as norbornene or polycyclic norbornene-based monomers.

There are various commercially available cyclic polyolefin resins. As for any of commercially available products of cyclic polyolefin resins, for example, "Topas (registered trademark)" (available from TOPAS ADVANCED POLYMERS GmbH, available from Polyplastics (stock)), "Arton (registered trademark)" ) "(JSR (share) system)," ZEONOR (registered trademark) "(Japan Zeon (share) system)," ZEONEX (registered trademark) "(Japan Zeon (system))," Apel (registered trademark) "( Mitsui Chemicals Co., Ltd.).

Any (meth) acrylic resin can be used as the (meth) acrylic resin. Examples include poly (meth) acrylates such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic copolymer, methyl methacrylate- (meth) acrylate copolymer, methyl Methyl acrylate-acrylate- (meth) acrylic acid copolymer, methyl (meth) acrylate-styrene copolymer (MS resin, etc.), polymers having alicyclic hydrocarbon groups (e.g. methyl methacrylate-methyl Cyclohexyl acrylate copolymer, methyl methacrylate-norbornyl (meth) acrylate copolymer, etc.). Poly (meth) acrylates such as poly (meth) acrylates having an alkyl moiety having a carbon number of 1 to 6 can be preferably used, and more preferably, methyl methacrylate can be used as a main component. (50 to 100% by weight, preferably 70 to 100% by weight) a methyl methacrylate resin.

In view of the excellent stretchability of the laminated film of the laminated polyvinyl alcohol resin layer, the base film preferably contains a group selected from the group consisting of a cellulose ester resin, a polyolefin resin, and a (meth) acrylic resin. At least one kind of resin. Among them, it is easy to adjust the phase transition temperature. The base film is preferably a chain-like polyolefin resin, and a polypropylene resin containing a polypropylene resin (a homopolymer of propylene, a polypropylene resin, and a copolymer mainly composed of propylene). Materials), or polyethylene resins (polyethylene resins of homopolymers of ethylene, with ethylene as the Copolymers of the host, etc.) are more preferred.

There are many cases where the chain polyolefin resin has crystallinity, and the melting point Tm of the polypropylene resin of the homopolymer of propylene is about 150 to 180 ° C. In the case of a polyethylene resin which is a homopolymer of ethylene, the melting point Tm varies depending on the density and the like, but the melting point Tm is probably in the range of 100 to 140 ° C. Then, a polypropylene resin obtained by copolymerizing other types of monomers such as ethylene based on propylene can obtain a copolymer having a melting point lower than the melting point of a homopolymer of propylene. In this way, the phase transition temperature of the polypropylene resin can be controlled by adjusting the presence or absence of the copolymerization component or the type or content of the copolymerization component.

Examples of other types of monopolymers that can be copolymerized with propylene include ethylene, α-olefin, and the like. The α-olefin is preferably an α-olefin having 4 or more carbon atoms, and more preferably an α-olefin having 4 to 10 carbon atoms. The α-olefins having 4 to 10 carbon atoms may be linear monoolefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, etc .; Branched monoolefins such as 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, and the like; vinyl cyclohexane and the like. The copolymer of propylene and other monomers copolymerizable with polypropylene may be a random copolymer or a block copolymer. In addition, the content rate of the constituent units derived from the other monomers in the copolymer is determined according to the method described on page 616 of the "Polymer Analysis Handbook" (1995, issued by Kii Kokuya Bookstore), and can be measured based on infrared (IR) spectra. Seeking.

The polypropylene resin is preferably a homopolymer of propylene, a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, or a propylene-ethylene-1-butene random copolymer.

The three-dimensional regularity of the polypropylene resin is preferably the same row or the opposite row. The substrate film containing a resin layer composed of polypropylene resins having three-dimensional regularity in the same row or in the opposite row has good operability and excellent mechanical strength in a high-temperature environment.

In addition to the above-mentioned thermoplastic resin, the base film may be added with additives. Examples of the additive system include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, anti-colorants, flame retardants, nucleating agents, antistatic agents, pigments, and colorants.

The content of the thermoplastic resin in the substrate film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, and still more preferably 60 to 98% by weight.

When the content of the thermoplastic resin in the base film is less than 50% by weight, the transparency of the thermoplastic resin may not be sufficiently developed.

The thickness of the base film is preferably from 1 to 500 μm, more preferably from 5 to 300 μm, more preferably from 10 to 200 μm, and even more preferably from 20 to 150 μm from the point of workability such as strength and operability.

The base film used in the production of the polarizing film of the present invention may be a single-layer film composed of a single layer or a multilayer film composed of a plurality of layers. The meaning of imparting crack resistance in the extension step of the subsequent step is preferably using a multilayer film. (Reference: Japanese Patent Application Publication No. 2013-101241)

The long substrate film prepared in step (1) has a standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the substrate film in the MD (Machine Direction) direction to be 0.80 μm or less, and the aforementioned waveform is subjected to After the Fourier transform, the spectrum from the region with a wavenumber of 1/3 (1 / m) or more The standard deviation σ 2 calculated from the thickness waveform obtained by inverse Fourier transform is 0.65 μm or less.

In the measurement of the thickness of the base film, the measurement position of the TD (Transverse Direction) direction in the base film is arbitrary, but it is generally measured at the midpoint of the base film.

From the viewpoint of reliability of the values of the standard deviation σ1 and the standard deviation σ2, the length in the MD direction in the long substrate film is preferably 10 m or more, and more preferably 100 m or more. In addition, if the length of the actual long substrate film is considered, the length in the MD direction is generally 10,000 m or less.

In the present invention, it is necessary to measure thickness unevenness with a wavenumber of 1 / 3m ^-1 or more, that is, thickness unevenness with a period of 3m or less. Therefore, from the viewpoint of reliability of the values of the standard deviation σ1 and the standard deviation σ2, the interval between the thickness data acquisition positions is generally 50 cm or less, and preferably 5 cm or less. The interval between thickness data acquisition positions is generally 1 cm or more.

In the state of fixed measurement device, while continuously measuring the thickness while conveying the long substrate film, the conveyance of the substrate film can be appropriately selected in accordance with the cycle of obtaining thickness data by the measuring device to meet the interval of obtaining the thickness data. speed. For example, when the cycle of measuring thickness data by the measuring device is a 1 second cycle, the conveying speed of the substrate film is preferably 3 m / min. Or less.

The method for measuring the thickness of the film is only a method capable of measuring the thickness displacement of 0.1 μm or less, but a method using laser or infrared light is preferable, and a method using laser is more preferable.

The base film which satisfies the above-mentioned standard deviation σ1 and standard deviation σ2 can be manufactured, for example, as follows.

When a multilayer film is used as the substrate film, the substrate film can be produced by a coextrusion molding method (also referred to as a coextrusion casting method), an extrusion lamination method, or the like. It is preferable to form by a co-extrusion molding method (co-extrusion casting method) from the viewpoint of productivity and cost. The co-extrusion molding system is equipped with a necessary number of extruders, and is connected to one T-die device by each extruder. The T-die is laminated into a film from the state of the resin, and the roll is cooled. A method for cooling and solidifying to produce a multilayer film.

Specifically, as an example of a method for manufacturing a multi-layered base film by a co-extrusion molding method, a method for manufacturing a base film made of three layers of polypropylene-based resin is described below.

Each of the three extruders was heated to about 200 to 300 ° C, and a polypropylene resin was supplied to each of the extruders. The polypropylene resin is melt-kneaded by the screw of each extruder, melted and co-extruded from a T-die, and then contacted with a cooling roller by various means to cool it to produce a multilayer base film.

The temperature of the coextruded molten sheet-like polypropylene-based resin multilayer film (hereinafter, sometimes referred to as a molten multilayer film) is preferably about 250 to 300 ° C, and more preferably 260 to 290 ° C. If the temperature of the molten multilayer film is lower than 250 ° C, the melt-kneading state of the polypropylene resin in the extruder is insufficient, and the appearance of the obtained film may be extremely deteriorated, and the thickness accuracy of the film in the TD direction may be deteriorated . Further, if the temperature of the molten multilayer film is lower than 250 ° C, the obtained multilayer film may become poor in transparency. In addition, if the temperature exceeds 300 ° C, degradation or decomposition of the polypropylene-based resin is likely to occur, and bubbles or carbides are generated in the sheet. Further, because of the The viscosity of the resin is significantly reduced, so that the molten multilayer film cannot be cooled and solidified stably, and the thickness accuracy of the obtained film may be deteriorated.

The three extruders can be single-shaft extruders or two-shaft extruders, and the extruders may not be uniform. In addition, according to the composition ratio of each layer in the base film, by selecting each size of three extruders, it can also be manufactured with a stable extrusion amount on the equipment. Each resin melt-kneaded with each extruder is supplied to a supply block or a conversion connector through a temperature-adjusted single tube called a connector. These can be selected according to the type of T-shaped pattern. When there is one path in the T-shaped mold, the resin is arranged in the supply block in advance according to the resin composition of the multilayer film and supplied to the T-shaped mold. On the other hand, when there is a device with multiple flow paths in a T-shaped die called a multi-manifold, each resin layer is laminated directly in front of the lip portion of the T-shaped die, so the path from each extruder is converted by a connector. , Connected to each path in the T-shaped pattern according to the film configuration.

At this time, the pressure in each extruder is preferably a variable value within 0.5 MPa. When the pressure fluctuation value exceeds 0.5 MPa, the flow rate of the resin from the T-shaped mold changes, so the thickness accuracy in the MD direction of the obtained film may be deteriorated, especially the thickness fluctuation in a cycle of 3 m or more is likely to increase. .

In addition, from the viewpoint of suppressing the extrusion variation of each resin constituting the multilayer film, a gear pump can be installed between each extruder and the T-die through a connector to stabilize the pressure in each extruder and supply the resin to T font.

Further, the leaf-type filter removes the acrylic resin The foreign matter contained in it is preferable. The number of leaf disc filters and the filtering area per one can be arbitrarily selected according to the viscosity and extrusion amount (flow rate) of the molten resin and the heat resistance of the resin. From the viewpoint of reducing the amount of foreign matter that is drawn into the film and improving the quality of the film, it is preferable to use a filter with a foreign matter size of 10 μm or less whose capture rate of foreign matter is 98% or more. A filter having a foreign matter collection rate of 98% or more and a foreign matter size of 5 μm or less is more preferable, and a filter using a foreign matter collection rate of 98% or more and a foreign matter size of 3 μm or less is more preferable. The installation position of the leaf disc filter is in the order of an extruder, a gear pump, a leaf disc filter, and a T-die, and it is preferable from the viewpoint of stable removal of foreign matter.

The molten multilayer film is then brought into contact with a metal cooling roll (also called a chill roller or a casting roll), and is cooled in close contact with the cooling roll to obtain a multilayer film containing a polypropylene resin (hereinafter, sometimes referred to as a multilayer film). . In this case, the method of adhering the cooling roll may affect the transparency. Adhesion to the cooling roller can be implemented according to a conventional method, for example: a method in which static electricity can be imparted to a molten multilayer film, and the surface state is cooled by a cooling roller that is in close contact with a mirror surface; the molten multilayer film is in a mirror state on the surface state Method for sandwiching a cooling roll with an elastically deformable metal roll (also known as a contact roll) or a metal belt whose surface state is a mirror to make it close to the cooling roll for cooling; contacting the molten multilayer film with the cooling roll In some cases, the cooling method is to make the air blown from the air chamber close to the cooling roller, but from the viewpoint of productivity and quality, the molten multilayer film is tightly cooled by the air blown from the air chamber. The method of cooling by roller is preferable.

Fused multilayer film by air blowing from an air chamber The method of cooling by adhering to the cooling roller is to make the molten multilayer film extruded from the T-shaped die contact the cooling roller, and then blow the air through the air chamber toward the cooling roller through the molten multilayer film to thereby melt the molten film. The multilayer film is in close contact with the cooling roll. As the air chamber, a commercially available one can be used. The blown-out air is sucked in, for example, by a blower (blower) or the like through a high-performance air filter (HEPA Filter: High Efficiency Particulate Air Filter). It is preferable that the air chamber has a pressurized state of 50 to 300 Pa. It is better to be in a pressurized state of 100 to 200 Pa. When the pressure in the air chamber is higher than 300Pa, the pressure applied to the molten multilayer film is too large, and the thickness of the multilayer film obtained from the vibration of the molten multilayer film is greatly deteriorated. In particular, the thickness variation in a cycle of 3m or less Has a tendency to become larger. In addition, when the pressure in the air chamber is less than 50 Pa, the wind pressure applied to the molten multilayer film becomes small and the adhesion to the cooling roller is insufficient, so the haze of the multilayer film increases, and depending on the situation, the density of the cooling roller may be The thickness of the multilayer film is uneven, and the depth of the multilayer film is different. The appearance is deteriorated, and the thickness accuracy is greatly deteriorated.

The cooling roller used in the above three types is preferably one whose surface temperature is adjusted to 10 to 60 ° C, for example. If the surface temperature of the cooling roller exceeds 60 ° C, it takes time to cool and solidify the molten multilayer film, so the crystalline component in the propylene resin constituting the molten multilayer film may grow and the transparency of the obtained multilayer film may be deteriorated. On the other hand, if the surface temperature of the cooling roller is lower than 10 ° C, dew on the surface of the cooling roller and water droplets adhere, the appearance of the obtained multilayer film may deteriorate.

The processing speed when manufacturing a multilayer film containing a polypropylene-based resin layer depends on the time required to cool and solidify the polypropylene-based resin in the molten multilayer film. Regarding the processing speed, if the diameter of the cooling roll used becomes larger, the distance between the molten multilayer film and the cooling roll becomes longer, so that the multilayer film can be manufactured at a higher speed. Specifically, use 600mm When a metal cooling roll is used to produce a multilayer film containing a transparent acrylic resin layer with a haze value of 20% or less, the processing speed is about 20 to 40 m / min. When the processing speed is lower than 20m / min., The thickness of the film in the MD direction is likely to be uneven, and the thickness variation in a cycle of 3m or less is likely to become large. When the processing speed is higher than 40 m / min., Although the crystallization proceeds uniformly, the crystallization speed becomes slower and the haze becomes higher, and the transparency of the multilayer film may be deteriorated.

As described above, the optimal conditions for the temperature of the molten multilayer film, the pressure in the air chamber, the temperature of the cooling roller, and the processing speed are appropriately selected, thereby obtaining a multilayer substrate film with excellent film thickness accuracy.

Furthermore, in order to improve the adhesion with the polyvinyl alcohol-based resin layer, the obtained substrate film may be subjected to corona treatment, plasma treatment, or flame treatment on the surface on the side where the polyvinyl alcohol-based resin layer is formed. Wait.

The ratio σ 1 / d of the standard deviation σ 1 to the thickness d of the base film is 9.0 × 10 ^-3 or less, and the ratio σ 2 / d of the standard deviation σ 2 to the thickness d of the base film is 8.0 × 10. A base film of ^-3 or less can be produced in the same manner as a base film that satisfies the above-mentioned standard deviation σ 1 and standard deviation σ 2. When σ 1 / d and σ 2 / d satisfy the above ranges, the polarizing film of the present invention can be manufactured because of the thickness of the base film, regardless of the thickness of the substrate film, and thus it is preferable.

[Step (2)]

Step (2) is to coat at least one side of the substrate film with polyethylene A coating liquid of an alcohol-based resin to obtain a coating film. Then, the coating film is dried to form a polyvinyl alcohol-based resin layer.

(Coating liquid containing polyvinyl alcohol resin)

The coating liquid is preferably a polyvinyl alcohol-based resin solution obtained by dissolving a powder of the polyvinyl alcohol-based resin in a good solvent (for example, water). Examples of the polyvinyl alcohol-based resin include a polyvinyl alcohol resin and a derivative thereof. In addition to polyvinyl alcohol resin derivatives such as polyvinyl formaldehyde and polyvinyl acetal, for example, polyvinyl alcohol resins can be modified with olefins such as ethylene and propylene; acrylic acid, methacrylic acid, and crotonic acid Modified with unsaturated carboxylic acids; Modified with alkyl esters of unsaturated carboxylic acids; Modified with acrylamide. The modification ratio is preferably less than 30 mole%, and more preferably less than 10 mole%. When the modification exceeds 30 mol%, it is difficult to adsorb dichroic pigments, resulting in an unfavorable situation in which the polarization performance becomes low. Among the above-mentioned polyvinyl alcohol-based resins, polyvinyl alcohol resins are preferably used.

The average degree of polymerization of the polyvinyl alcohol resin is preferably in the range of 100 to 10,000, more preferably in the range of 1,000 to 10,000, even more preferably in the range of 1500 to 8000, and most preferably in the range of 2000 to 5000. The average degree of polymerization can be determined in accordance with the method specified in JIS K 6726-1994 "Test Method for Polyvinyl Alcohol". When the average polymerization degree is less than 100, it is difficult to obtain better polarizing performance, and when it exceeds 10,000, the solubility to the solvent is deteriorated, and it is difficult to form a polyvinyl alcohol-based resin layer.

The polyvinyl alcohol-based resin is preferably a saponified product of a polyvinyl acetate-based resin. The range of saponification degree is more than 80 mol%, further It is more than 90 mol%, especially more than 94 mol%. If the degree of saponification is too low, the water resistance or moist heat resistance of the polarizing laminated film or the formation of a polarizing plate will be insufficient. It may be completely saponified (those having a saponification degree of 100 mol%), but if the saponification degree is too high, the dyeing speed will be slowed down, and the manufacturing time will be lengthened in order to obtain sufficient polarizing performance, depending on the circumstances. A polarizing film having sufficient polarization performance was obtained. Therefore, the saponification degree is preferably 99.5 mol% or less, further preferably 99.0 mol% or less.

The so-called saponification degree refers to the ratio of the acetic acid group (acetoxy: -OCOCH ₃ ) contained in the polyvinyl acetate-based resin used as a raw material of the polyvinyl alcohol-based resin to the hydroxyl group by saponification treatment, and the unit ratio (mol%) ) Is defined by the following formula: degree of saponification (mol%) = [(number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetate groups)] × 100.

The higher the degree of saponification is, the more the ratio of the hydroxyl groups is, and therefore it means that the ratio of the acetic acid group that hinders crystallization is small. The degree of saponification can be determined in accordance with the method specified in JIS K 6726-1994 "Test Method for Polyvinyl Alcohol".

Examples of the polyvinyl acetate-based resin other than polyvinyl acetate which is a homopolymer of vinyl acetate include copolymers of other monomers which can be copolymerized with vinyl acetate. Other monosystems that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated acetic acids, acrylamides having ammonium groups, and the like.

As a trade name of any of the commercially available polyvinyl alcohol resins that can be used, for example, "PVA124" (Saponification degree: made by Kuraray) 98.0 to 99.0 mole%), "PVA117" (Saponification degree: 98.0 to 99.0 mole%), "PVA117H" (saponification degree: 99.5 mole% or more), "PVA624" (saponification degree: 95.0 to 96.0 mole%) ), "PVA617" (Saponification degree: 94.5 to 95.5 mole%); "AH-26" (Saponification degree: 97.0 to 98.8 mole%) made by Japan Synthetic Chemical Industry Co., Ltd., "AH-22" (saponification Degree: 97.5 to 98.5 mole%), "NH-18" (degree of saponification: 98.0 to 99.0 mole%), "N-300" (degree of saponification: 98.0 to 99.0 mole%); Japan VAM & POVAL (shares ) "JC-33" (Saponification degree: 99.0 mole% or more), "JM-33" (Saponification degree: 93.5 to 95.5 mole%), "JM-26" (Saponification degree: 95.5 to 97.5 mole) %), "JP-45" (degree of saponification: 86.5 to 89.5 mole%), "JF-17" (degree of saponification: 98.0 to 99.0 mole%), "JF-17L" (degree of saponification: 98.0 to 99.0 mole) Ear%), "JF-20" (Saponification degree: 98.0 to 99.0 mole%), etc.

The coating liquid may contain additives such as a plasticizer and a surfactant, as needed. Examples of the plasticizer include a polyhydric alcohol or a condensate thereof, and specific examples thereof include glycerin, diglycerol, triglycerol, ethylene glycol, propylene glycol, and polyethylene glycol. The blending amount of the additives is preferably 20% by weight or less of the polyvinyl alcohol resin.

(Application of coating liquid and drying of coating film)

The method for applying the coating liquid to the substrate film can be a wire rod coating method; a roll coating method such as reverse coating, gravure coating; a die coating method; a corner wheel coating method; a die Lip coating method; spin coating method; screen coating method; spray coating method; dipping method; spraying method and the like are appropriately selected.

When applying the coating solution on both sides of the substrate film, The methods are applied sequentially one by one, or both sides of the substrate film can be simultaneously applied by dipping or spraying.

The drying temperature and drying time of the coating film (the polyvinyl alcohol-based resin layer before drying) are set in accordance with the type of solvent contained in the coating liquid. The drying temperature is, for example, 50 to 200 ° C, and preferably 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 ° C or higher. The drying time is, for example, 2 to 20 minutes.

The polyvinyl alcohol-based resin layer may be formed on only one side of the base film, or may be formed on both sides. If a polyvinyl alcohol-based resin layer is formed on both sides, in addition to suppressing the warpage of the polarizing laminated film or the production of a polarizing plate, and obtaining one polarizing laminated film to two polarizing films Therefore, it is also advantageous in terms of the production efficiency of the polarizing film.

The thickness of the polyvinyl alcohol-based resin layer in the laminated film is preferably 3 to 30 μm, and more preferably 5 to 20 μm. If it is a polyvinyl alcohol-based resin layer having a thickness within this range, after steps (3) and (4) described later, the dichroic pigment has good dyeability and excellent polarization performance, and a thickness of 10 μm or less can be obtained. Polarizing film. When the thickness of the polyvinyl alcohol-based resin layer exceeds 30 μm, the thickness of the polarizing film may exceed 10 μm. If the thickness of the polyvinyl alcohol-based resin layer is less than 3 μm, the thickness of the polyvinyl alcohol-based resin layer is too thin after stretching, which tends to deteriorate the dyeability.

Before the coating liquid is applied, in order to improve the adhesion between the substrate film and the polyvinyl alcohol resin layer, the surface of the substrate film on the side where the polyvinyl alcohol resin layer is formed may be subjected to corona treatment and plasma treatment. , Flame treatment, etc.

(Primer layer)

Before the coating liquid is applied, in order to improve the adhesion between the base film and the polyvinyl alcohol-based resin layer, a polyvinyl alcohol-based resin layer may be formed on the base film by a primer layer or an adhesive layer.

The primer layer can be formed by applying a coating liquid for forming a primer layer on the surface of a substrate film and then drying it. The coating liquid for forming a primer layer is a component contained in both the base film and the polyvinyl alcohol-based resin layer to exert a certain degree of strong adhesion. The coating liquid for forming a primer layer generally contains a resin component and a solvent that impart such adhesion. The resin component is preferably a thermoplastic resin having excellent transparency, thermal stability, and extensibility, and examples thereof include (meth) acrylic resins and polyvinyl alcohol resins. Among them, a polyvinyl alcohol-based resin that imparts good adhesion is preferred.

Examples of the polyvinyl alcohol-based resin include a polyvinyl alcohol resin and a derivative thereof. Derivatives of polyvinyl alcohol resins are, in addition to polyvinyl formaldehyde, polyvinyl acetal, etc., for example, polyvinyl alcohol resins modified with olefins such as ethylene and propylene; such as acrylic acid, methacrylic acid, and crotonic acid Modified with unsaturated carboxylic acids; Modified with alkyl esters of unsaturated carboxylic acids; Modified with acrylamide. Among the above-mentioned polyvinyl alcohol-based resins, polyvinyl alcohol resins are preferably used.

As the solvent, a general organic solvent or an aqueous solvent capable of dissolving the resin component can be generally used. Solvents are aromatic hydrocarbons such as benzene, toluene, and xylene; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; such as ethyl acetate and isobutyl acetate; such as dichloro Chlorinated hydrocarbons of methane, trichloroethylene, and chloroform; alcohols such as ethanol, 1-propanol, 2-propanol, and 1-butanol. However, if the primer layer is formed from a coating liquid for forming a primer layer containing an organic solvent, the base film may be dissolved. Therefore, the solvent is preferably selected in consideration of the solubility of the base film. If considering the impact on the environment, it is better to use water as the solvent to form the primer layer.

In order to improve the strength of the primer layer, a crosslinking agent may be added to the coating liquid for forming a primer layer. The cross-linking agent is appropriately selected from known ones such as organic and inorganic based on the type of thermoplastic resin used. Examples of the crosslinking agent system include an epoxy-based crosslinking agent, an isocyanate-based crosslinking agent, a dialdehyde-based crosslinking agent, and a metal-based crosslinking agent.

The ratio of the resin component to the crosslinking agent in the coating liquid for forming the primer layer is 100 parts by weight with respect to the resin component, as long as the range from 0.1 to 100 parts by weight of the crosslinking agent depends on the type of the resin component or the type of the crosslinking agent. It may be determined as appropriate, and in particular, it is preferably selected from the range of 0.1 to 50 parts by weight. The solid content of the coating liquid for forming a primer layer is preferably 1 to 25 parts by weight based on 100 parts by weight of the solvent in the coating liquid for forming a primer layer.

The thickness of the primer layer is preferably 0.05 to 1 μm, and more preferably 0.1 to 0.4 μm. If it is thinner than 0.05 μm, the adhesion improvement effect of the base film and the polyvinyl alcohol resin layer is small. If it is thicker than 1 μm, it is not conducive to thinning the polarizing laminated film or polarizing plate.

The method of applying the coating liquid for forming a primer layer to a base film is, for example, the same method as the method of coating a coating liquid containing a polyvinyl alcohol resin. The coating liquid for forming a primer layer is applied on the surface (one or both sides of the base film) on which the coating liquid for forming a polyvinyl alcohol resin layer is applied. From The drying temperature and drying time of the coating layer obtained by the coating liquid for forming a primer layer are set in accordance with the type of the solvent contained in the coating liquid. The drying temperature is, for example, 50 to 200 ° C, and preferably 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 ° C or higher. The drying time is, for example, 30 seconds to 20 minutes.

When a primer layer is provided, the coating order of the base film is not particularly limited. For example, when a polyvinyl alcohol-based resin layer is formed on both sides of the base film, the primer layer can be formed on both sides of the base film. Then, a polyvinyl alcohol-based resin layer is formed on both sides, or a primer layer and a polyvinyl alcohol-based resin layer are sequentially formed on one side of the base film, and then a primer layer is sequentially formed on the other side of the base film. Polyvinyl alcohol resin layer.

[Step (3)]

In step (3), the aforementioned laminated film is uniaxially stretched to obtain an stretched film. The stretch ratio of the laminated film can be appropriately selected according to the desired polarization characteristics, but it is preferably more than 5 times and 17 times less than the original length of the laminated film, and more preferably more than 5 times and 8 times or less. If the stretching ratio is 5 times or less, the polymer chains of the polyvinyl alcohol resin constituting the polyvinyl alcohol resin layer are not sufficiently aligned, so the polarization degree of the polarizing film may not be sufficiently high. On the other hand, if the stretching ratio is When it exceeds 17 times, the film is likely to be cracked during stretching, and the thickness of the stretched film becomes thinner than necessary. At the same time, the workability and handling properties of the subsequent steps may be reduced.

The extension of the laminated film may be a longitudinal extension extending in the MD direction, or a lateral extension or an oblique extension extending in the TD direction. The longitudinal stretching method can be exemplified as: stretching between rollers using a roller [side Conveying between two kneading rollers provided with a distance, while longitudinally uniaxially stretching by waiting for the peripheral speed difference between the two kneading rollers], hot roller stretching [by extending on a stretchable surface When a heat roller heated at a desired temperature and a guide roller (also a heat roller) having a higher peripheral speed than the heat roller are passed, when contacting the heat roller in a heating state generated by contact with the heat roller ( On the heat roller) or in the vicinity of the longitudinal uniaxial extension], compression extension, extension with a chuck (clamp), etc., the lateral extension method can be, for example, the tenter method. The stretching treatment may be either a wet stretching method or a dry stretching method (stretching in the air), but the point of selecting the stretching temperature from a wide range is preferably the dry stretching method.

The elongation temperature is set to a temperature that shows the fluidity of the laminated film (polyvinyl alcohol resin layer and the substrate film) to the extent that it can be stretched, preferably the phase transition temperature (melting point or glass transition temperature) of the substrate film The range is from -30 to + 30 ° C, more preferably from -30 ° C to + 5 ° C, and even more preferably from -25 ° C to + 0 ° C. When the substrate film is composed of a plurality of resin layers, the phase transition temperature is the highest phase transition temperature among the phase transition temperatures shown by the plurality of resin layers.

If the elongation temperature is lower than -30 ° C of the phase transfer temperature, it is difficult to achieve a high-rate elongation exceeding 5 times, or the fluidity of the substrate film is too low, and the elongation treatment tends to be difficult. If the elongation temperature exceeds + 30 ° C of the phase transition temperature, the fluidity of the substrate film is too large and the elongation tends to be difficult. Since it is easy to achieve a high elongation ratio of more than 5 times, the elongation temperature is within the above range, and more preferably 120 ° C or more. When the stretching temperature is 120 ° C or higher, the stretching process is usually not difficult even at a high stretching ratio exceeding 5 times.

The heating method of the stretched laminated film is: a zone heating method (for example, a method of heating in an extension section of a heating furnace adjusted to a predetermined temperature by blowing hot air); and stretching by a hot roller At the time, the method of heating the roll itself; the heater heating method (the method of placing infrared heaters, halogen heaters, panel heaters, etc. above and below the laminated film and heating by radiant heat) and the like. In the roll-to-roll stretching method, the zone heating method is preferred from the viewpoint of uniformity of the stretching temperature. At this time, the two kneading rollers can be set in the temperature-adjusted extension section or outside the extension section. However, in order to prevent the laminated film and the kneading roller from adhering, it is better to set them outside the extension section. .

In addition, the so-called extension temperature refers to the ambient temperature in the zone (for example, in a heating furnace) when the zone heating method is used. Even in the heater heating method, the temperature in the furnace refers to the ambient temperature in the furnace. . In addition, when the heat roller is extended, it means the surface temperature of the heat roller.

The stretch of the laminated film is not limited to one stretch, and may be performed in multiple stages. In this case, it is preferable to perform the stretching treatment in such a manner that the entire stage of the stretching treatment is merged and the stretching ratio is more than 5 times.

Before step (3), a preheating step for preheating the laminated film may also be provided. The preheating method can be applied to the same method as the heating method in the elongation treatment. When the stretching method is stretching between rolls, the preheating system can be performed at any time before passing the kneading roll on the upstream side, passing, or passing the latter. When the stretching method is hot roll stretching, the pre-heating is preferably performed at the timing before passing the hot roll. When the extension method is an extension with a chuck, the pre-heating is preferably performed before the width of the chuck is widened. The preheating temperature is preferably in the range of (elongation temperature -50) ° C to (elongation temperature +0) ° C, and the (elongation temperature The range of -40) ° C to (elongation temperature-10) ° C is more preferable.

In addition, after the laminated film is stretched in step (3), a heat fixing treatment step may be provided. The heat-fixing treatment is a treatment in which the end portion of the stretched film is held in a tensioned state by a jig, and heat treatment is performed at a temperature above the crystallization temperature of the polyvinyl alcohol-based resin layer. By this heat setting treatment, crystallization of the polyvinyl alcohol-based resin layer can be promoted. The temperature of the heat fixing treatment is preferably in the range of (elongation temperature -80) ° C to (elongation temperature +0) ° C, and more preferably in the range of (elongation temperature -50) ° C to (elongation temperature +0) ° C.

[Step (4)]

In step (4), the polyvinyl alcohol-based resin layer of the stretched film is dyed with a dichroic dye, and the dichroic dye is adsorbed and aligned to obtain a polarizing laminated film. After this step, a polarizing laminated film having a polarizing film on one or both sides of the substrate film can be obtained.

Examples of the dichroic pigment system include iodine or a dichroic organic dye. Examples of dichroic organic dyes include red BR, red LR, red R, pink LB, ruby red BL, bay red GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy blue RY, and green LG. , Purple LB, Purple B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Bright Red GL, Bright Red KGL, Congo Red, Bright Purple BK, Super Blue G, Super Blue GL, Super Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. The dichroic pigments may be used alone or in combination of two or more.

Dyeing can be achieved by using a solution containing dichroic pigments (dyeing Color solution) by dipping the stretched film. As the dyeing solution, a solution obtained by dissolving the dichroic pigment in a solvent can be used. The solvent of the dyeing solution is generally water, but an organic solvent compatible with water may be added. The concentration of the dichroic pigment in the dyeing solution is preferably 0.010 to 10% by weight, more preferably 0.020 to 7% by weight, and still more preferably 0.025 to 5% by weight.

When iodine is used as a dichroic pigment, the dyeing efficiency can be further improved, so it is better to add iodide to the dyeing solution containing iodine. Examples of the iodide system include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of iodide in the dyeing solution is preferably 0.01 to 20% by weight. Among the iodides, potassium iodide is preferably added. When potassium iodide is added, the ratio of iodine to potassium iodide is based on a weight ratio, preferably in a range of 1: 5 to 1: 100, more preferably in a range of 1: 6 to 1:80, and in a range of 1: 7 to 1:70. The range is even better.

The immersion time of the stretch film in the dyeing solution is generally 15 seconds to 15 minutes, preferably 30 seconds to 3 minutes. The temperature of the dyeing solution is preferably 10 to 60 ° C, and more preferably 20 to 40 ° C.

Furthermore, in the step (4), an additional stretching treatment may be further applied to the stretched film. The implementation mode at this time can be exemplified as follows: 1) In the above step (3), after the extension treatment is performed at a rate lower than the target, in the dyeing process in step (4), the total extension ratio becomes the target magnification. The method of performing the elongation treatment as described above, or the case where the cross-linking treatment is performed after the dyeing treatment is described below. 2) In the above step (3), after the elongation is performed at a lower rate than the target, In the dyeing process in step (4), stretching is performed to the extent that the total stretching magnification does not reach the target magnification, and then the stretching treatment is performed in the cross-linking treatment so that the final total stretching magnification becomes the target magnification. Wait.

The preferred step (4) includes a step of performing a crosslinking treatment after the dyeing treatment.

The crosslinking treatment can be performed by immersing the dyed film in a solution (crosslinking solution) containing a crosslinking agent. As the crosslinking agent, conventionally known substances such as boric acid, a boron compound of borax, glyoxal, glutaraldehyde, and the like can be used.

The crosslinking agent may be used alone or in combination of two or more.

The crosslinking solution is specifically a solution in which a crosslinking agent is dissolved in a solvent. As the solvent, water may be used, and an organic solvent having compatibility with water may be further included. The concentration of the crosslinking agent in the crosslinking solution is preferably 1 to 20% by weight, and more preferably 6 to 15% by weight.

The crosslinking solution may contain iodide. By adding iodide, the in-plane polarizing performance of the polarizing film can be made more uniform. Examples of the iodide system include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of iodide in the crosslinking solution is preferably from 0.05 to 15% by weight, and more preferably from 0.5 to 8% by weight.

The immersion time of the dyed film in the crosslinking solution is generally 15 seconds to 20 minutes, and preferably 30 seconds to 15 minutes. The temperature of the crosslinking solution is preferably 10 to 90 ° C.

Furthermore, the crosslinking treatment can be performed before the dyeing treatment. The cross-linking agent can also be formulated in the dyeing solution, and the dyeing treatment can be performed simultaneously. Moreover, you may perform extension processing in a crosslinking process. The specific aspect of performing the extension treatment in the crosslinking treatment is as described above.

After step (4), it is preferable to perform a washing step (step (4 ')) and a drying step (step (4 ")). Step (4') generally includes a water washing step. The water washing treatment system can be borrowed It is performed by immersing pure water such as ion-exchanged water and distilled water in a polarized laminated film after dyeing or crosslinking treatment. The water washing temperature is generally 3 to 50 ° C, preferably 4 to 20 ° C.

The immersion time in water is generally 2 to 300 seconds, preferably 3 to 240 seconds.

Step (4 ') may be a combination of a water washing step and a washing step using an iodide solution. In addition, the washing liquid used in the water washing step and / or the washing treatment with the iodide solution may suitably contain a liquid alcohol such as methanol, ethanol, isopropanol, butanol, and propanol in addition to water. .

Step (4 ") can be any suitable method such as natural drying, air drying, and heating drying. For example, when heating and drying, the drying temperature is generally 20 to 95 ° C, and the drying time is generally 1 to 15 minutes. The obtained polarizing laminated film system can be used directly as a polarizing element or as an intermediate for producing a polarizing plate containing a polarizing film and a protective film.

The thickness of the polarizing film included in the polarizing laminated film is 10 μm or less, and preferably 7 μm or less. By setting the thickness of the polarizing film to 10 μm or less, a thin polarizing laminated film can be formed.

[Step (5)]

Step (5) is a step of peeling the base film from the polarizing laminated film. After this step (5), a polarizing film without a base film on the polarizing film can be obtained. When the polarizing laminated film has polarizing films on both sides of the base film, in step (5), two polarizing films can be obtained from one polarizing laminated film. The method for peeling and removing the base film is not particularly limited, and it can be peeled in the same manner as the peeling step of a separation film (release film) performed by a general polarizer with an adhesive.

In addition, before peeling the base film, a protective film may be laminated on the polarizing film of the polarizing laminated film with an adhesive or an adhesive. When a base film is peeled from a laminated body in which a protective film is laminated on a polarizing film of a polarizing laminated film, a polarizing plate having a polarizing film and a protective film can be obtained.

(Protective film)

Examples of protective films include polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.), cyclic polyolefin resins (norbornene resins, etc.); such as cellulose triacetate, and fibers Cellulose ester resin of cellulose diacetate; Polyester resin of polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate; Polycarbonate resin; ( (Meth) acrylic resin; or a film made of a mixture, copolymer, or the like.

The protective film may be a protective film that also has optical functions such as a retardation film and a brightness enhancement film. For example, a resin film made of the above-mentioned material is stretched (uniaxially stretched or biaxially stretched, etc.), or a liquid crystal layer is formed on the film, etc., and a retardation film having an arbitrary retardation value can be formed.

In the protective film, the bonding surface with the polarizing film is on the opposite side Optical layers such as hard coatings, anti-glare layers, and anti-reflection layers can also be formed on the surface. The method for forming such an optical layer on the surface of the protective film is not particularly limited, and a known method can be applied. The optical layer may be formed on the protective film in advance, or may be formed after the protective film is bonded to the polarizing laminated film.

When a protective film is attached to the polarizing film, in order to improve the adhesion with the polarizing film, the bonding surface of the protective film and the polarizing film can be previously treated with plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) ) Treatment, saponification treatment and other surface treatment (easy to follow treatment). Among them, plasma treatment, corona treatment or saponification treatment is preferred. For example, when the protective film is composed of a cyclic polyolefin resin, a plasma treatment or a corona treatment is generally performed. In the case of a cellulose ester resin, saponification is generally performed. The saponification treatment may be, for example, a method of immersion in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

The thickness of the protective film is preferably thin. If it is too thin, the strength is reduced and the processability is poor. On the other hand, if it is too thick, problems such as a decrease in transparency and a long curing time required after bonding may occur. Therefore, the thickness of the protective film is preferably 90 μm or less, more preferably 5 to 60 μm, and still more preferably 5 to 50 μm. From the viewpoint of thinning the polarizing plate, the total thickness of the polarizing film and the protective film is preferably 100 μm or less, more preferably 90 μm or less, and even more preferably 80 μm or less.

(Adhesive)

As the adhesive system, an aqueous adhesive or a photocurable adhesive can be used. The aqueous adhesive system may be, for example, an adhesive composed of an aqueous solution of a polyvinyl alcohol resin. Agents, aqueous two-liquid urethane-based emulsion adhesives, and the like. In particular, when using a cellulose ester-based resin film with a surface treatment (hydrophilization treatment) such as saponification treatment as the protective film, it is preferable to use an aqueous adhesive composed of a polyvinyl alcohol-based resin aqueous solution.

Polyvinyl alcohol resin is a vinyl alcohol homopolymer obtained by saponifying a polyvinyl acetate homopolymer of polyvinyl acetate, and a copolymer of vinyl acetate and other monomers copolymerizable therewith may be used. The polyvinyl alcohol-based copolymer obtained by the saponification treatment or a modified polyvinyl alcohol-based polymer having a partially modified hydroxyl group and the like. The aqueous adhesive may contain additives such as polyaldehyde, water-soluble epoxy compound, melamine-based compound, zirconia compound, and zinc compound. The thickness of the adhesive layer obtained from the aqueous adhesive is generally 1 μm or less.

The water-based adhesive is applied to the polarizing film and / or the protective film of the polarizing laminated film, and the two films are bonded by the adhesive layer. Therefore, two films can be laminated. The coating method of the water-based adhesive (the same applies to the photocurable adhesive) is not particularly limited, and a casting method, a wire rod coating method, a gravure coating method, a notch wheel coating method, a doctor blade method, a die coating method, Conventionally known methods such as a dip coating method and a spray method.

When an aqueous adhesive is used, it is preferable to perform a drying step for drying the film in order to remove the water contained in the aqueous adhesive after performing the above-mentioned bonding. Drying can be performed by introducing a polarizing film with a protective film bonded thereto into a drying furnace. The drying temperature (temperature of the drying furnace) is preferably 30 to 90 ° C. If it does not reach 30 ° C, the protective film tends to be easily peeled from the polarizing film. Again, several If the drying temperature exceeds 90 ° C, the polarization performance of the polarizing film may be deteriorated due to heat. The drying time is generally 10 to 1000 seconds. From the viewpoint of productivity, it is preferably 60 to 750 seconds, and more preferably 150 to 600 seconds.

After drying, it can be hardened at room temperature or slightly higher, for example, at a temperature of 20 to 45 ° C for 12 to 600 hours. The hardening temperature is generally set below the drying temperature.

The photocurable adhesive is an adhesive that is cured by irradiating active energy rays such as ultraviolet rays. Examples of the photocurable adhesive system include an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, an adhesive containing a binder resin, and a photoreactive crosslinker. Examples of the polymerizable compound system include photopolymerizable monomers such as epoxy-based monomers, acrylic monomers, and urethane-based monomers, and oligomers derived from photopolymerizable monomers. The photopolymerization initiator is a compound capable of generating active species such as neutral radicals, anionic radicals, and cationic radicals by irradiation of active energy rays such as ultraviolet rays. The photocurable adhesive containing a polymerizable compound and a photopolymerization initiator is preferably an adhesive containing a photocurable epoxy-based monomer and a photocationic polymerization initiator.

When using a photocurable adhesive, after bonding the above-mentioned polarizing film and protective film, a drying step is performed as necessary (when the photocurable adhesive contains a solvent, etc.), and then the photocurable is adhered by irradiating active energy rays.剂 curing。 Agent hardening. The light source of the active energy line is preferably a light source with a luminous distribution below a wavelength of 400 nm. Low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black lights, microwave-excited mercury lamps, metal halide lamps, etc. are preferred. .

The light irradiation intensity of the photocurable adhesive is appropriately determined depending on the composition of the photocurable adhesive. The irradiation intensity in the wavelength region effective for the activation of the polymerization initiator is set to 0.1 to 6000 mW / cm ² . good. When the irradiation intensity of 0.1mW / cm ² or more, the reaction time is unduly prolonged, is 6000mW / cm ² or less, self-heating and light-curing adhesive radiated light due to the heat generation during the curing of the photocurable adhesive There is less risk of yellowing or deterioration of the polarizing film.

The light irradiation time for the photocurable adhesive is appropriately determined depending on the composition of the photocurable adhesive. The cumulative light amount shown by the product of the above-mentioned irradiation intensity and irradiation time is preferably set to be 10 to 10,000 mJ / cm ² . . Integrated light quantity is 10 mJ / cm ² or more, derived from a polymerization initiator of a sufficient amount of the active species generating curing reaction more reliably performed, when is 10000mJ / cm ² or less, the irradiation time may be too long and will not maintain good productivity .

Furthermore, the thickness of the adhesive layer after irradiation with active energy rays is generally 0.001 to 5 μm, preferably 0.01 to 2 μm, and more preferably 0.01 to 1 μm.

(Adhesive)

Adhesives that can be used for the adhesion of protective films are generally composed of acrylic resin, styrene resin, silicone resin, etc. as the matrix polymer, and then added such as isocyanate compound, epoxy compound, aziridine compound It is composed of an adhesive composition of a crosslinking agent. It may further contain fine particles as an adhesive exhibiting light scattering properties.

The thickness of the adhesive layer formed from the adhesive composition is generally 1 to 40 μm, but in the range of characteristics that do not impair processability and durability, it is preferable to apply a thin layer, and more preferably 3 to 25 μm. The thickness of 3 to 25 μm has good processability and is suitable for suppressing the dimensional change of the polarizing film. If the adhesive layer is less than 1 μm, the adhesiveness is reduced, and if it exceeds 40 μm, it is easy to cause bad situations such as bleeding of the adhesive from the end of the polarizing plate. The method for attaching a protective film to a polarizing film of a polarizing laminated film by an adhesive is that after an adhesive layer is provided on the protective film surface, the polarizing film can be attached, or after an adhesive layer is provided on the polarizing film surface. , And then attach the protective film.

The method for forming the adhesive layer is not particularly limited. An adhesive composition containing various components including the matrix polymer described above can be applied to the protective film surface or the polarizing film surface, and dried to form an adhesive layer, and then bonded. The protective film and the polarizing film can also be formed on the separation film (release film) after the adhesive layer is formed, and then the adhesive layer is transferred to the protective film surface or the polarizing film surface, and then the protective film and the polarizing film are bonded. When the adhesive layer is formed on the protective film surface or the polarizing film surface, surface treatment, corona treatment, etc. may be applied to the protective film surface or the polarizing film surface, or one or both sides of the adhesive layer as required.

(Polarizing film or polarizing plate)

The swing of the absorption axis in the plane of the polarizing film or polarizing plate obtained from the steps containing steps (1) to (5) above is 0.2 ° or less. Further, the standard deviation of the absorption axis in such a plane is preferably 0.04 ° or less. However, in the case of a polarizing laminated film having polarizing films on both sides of the base film, generally, the absorption axes of the polarizing films are about the same, but on at least one side, as long as the absorption axis has a swing It is sufficient that it is 0.2 ° or less, and the swing of the absorption axis is preferably 0.2 ° or less even on either side.

The swing of the absorption axis in the plane will be described with reference to FIG. 1. First, MD direction 2 in FIG. 1 is set as 0 ° as a reference. Then, an angle formed between the MD direction 2 and the absorption axis 6 is determined. However, the angle formed is the smaller of the angles formed by the MD direction 2 and the absorption axis 6 (the angle indicated by θ in the first figure), and the absorption axis is viewed from the direction of the dotted arrow 7 in the figure. At 6 o'clock, the angle of counterclockwise rotation is taken as the positive angle, and the angle of clockwise rotation is taken as the negative angle for the MD direction. However, the positive and negative angles are arbitrary, and either direction can be set to be positive. When the polarizing film is further laminated on the surface of the substrate film 4 on which the polarizing film 3 is not laminated in the first figure (on both sides of the substrate film) The same applies to the case where a polarizing film is laminated. Then, the swing of the absorption axis in the plane refers to the absolute value of the difference between the maximum value and the minimum value of the absorption axis angle in the plane measured by the above method. The amplitude of the in-plane absorption axis can be measured, for example, in the plane of the polarizing laminated film obtained in step (4) or in the plane of the polarizing film of the present invention obtained in step (5) at two or more different planes. To find the angle.

From the viewpoint of value reliability, the number of measurement points of the absorption axis angle is preferably 40 or more, and generally 100 or less is sufficient. Furthermore, in order to further improve the reliability of the value, the measurement of the absorption axis angle is preferably distributed uniformly in the aforementioned film surface. When a polarizing laminated film having polarizing films on both sides of the base film, as described above, generally, the absorption axes of the polarizing films are almost the same, so the angle of absorption axis of the polarizing laminated film can be regarded as the absorption axis of each polarizing film .

The structure of the polarizing plate in which the protective film was bonded to the polarizing film of this invention is demonstrated. FIG. 2 shows a polarizing plate having a protective film 8 on both sides of the polarizing film 3.

The polarizing film of the present invention or the polarizing plate of the present invention can be suitably incorporated in a display device. Examples of the display device include a liquid crystal display device and an organic EL display device. FIG. 3 (a) shows a liquid crystal display device 12 having the polarizing plate 9, the liquid crystal cell 10, the polarizing plate 91, and the backlight unit 11 of the present invention in this order. FIG. 3 (b) shows a liquid crystal display device 12 having a polarizing plate 91, a liquid crystal cell 10, a polarizing plate 9, and a backlight unit 11 in this order. The polarizing plate 91 may be the polarizing plate of the present invention, or may be a known polarizing plate. That is, the liquid crystal display device has one pair of polarizing plates, and at least one of the polarizing plates is the polarizing plate of the present invention. Furthermore, a polarizing film 3 may be used instead of the polarizing plate 9.

[Example]

Examples are given below to further explain the present invention, but the present invention is not limited to these examples.

<Example 1>

(1) Production of substrate film A

A propylene / ethylene random copolymer ("Sumitomo Nobrene W151" made by Sumitomo Chemical Co., Ltd., melting point Tm = 138 ° C) containing a propylene / ethylene random copolymer containing about 5 wt% ethylene units is provided with propylene on both sides A three-layer long substrate film A consisting of a resin layer made of a homopolymer ("Sumitomo NobreneFX80 E 4" manufactured by Sumitomo Chemical Co., Ltd., melting point Tm = 163 ° C), using multilayer extrusion The molding machine is manufactured by coextrusion.

At this time, the resin temperature of each layer is heated to 50 mm at 280 ° C. The extruder was melt-kneaded, and then extruded from a 600 mm wide T-die in a molten state to obtain a molten multilayer film. Such a molten multilayer film is cooled by a cooling roller adjusted to 25 ° C. to form a multilayer base film.

The total thickness of the base film A is about 90 μm, and the thickness ratio (FLX80E4 / W151 / FLX80E4) of each layer is 3/4/3.

[Measurement of thickness unevenness in the MD direction of the base film A]

With the Keyence Laser Tester L T9010, the thickness of the substrate film A with a length of 300 mm in the TD direction and 200 m in the MD direction was continuously measured within 200 m in the MD direction. The measurement of the time when the thickness unevenness in the MD direction is measured is 4096 points sampled at 1 second intervals (measured at 2.5m / minute conveyance, so it is 1 second × (4096-1) × 2.5m / minute ÷ 60 Seconds / minutes = 170.625m, taking thickness unevenness data of 170.625m). From the obtained thickness unevenness waveform, the standard deviation σ 1 was calculated to be 0.63.

[Fourier transform]

The data thus taken is subjected to a high-speed Fourier transform (FFT) process. At this time, if the length (m) of the film is obtained by the variable in the MD direction, the intensity distribution of the wave number (1 / m) is obtained by FFT processing.

[Wave number separation, inverse Fourier transform, and calculation of thickness unevenness]

For the Fourier transform intensity distribution data, the corresponding wave number has not reached The spectral intensity of 112 points at 1/3 (1 / m) is only multiplied by 4096 points of intensity data obtained by 0 to perform inverse Fourier transform. From the obtained waveform of thickness unevenness, the standard deviation σ 2 was calculated to be 0.59.

[Calculation of the ratio of standard deviation to thickness]

Divide the average thickness d of the base film A by the values of the standard deviation σ 1 and the standard deviation σ 2 to calculate the ratios of the standard deviation to the thickness σ 1 / d and σ 2 / d, which are 7.07 × 10 ^-3 and 6.62 × 10 ^-3 . The average thickness d of the base film A is an average value of all measured values of the thickness of the base film when the thickness unevenness measurement in the MD direction is performed.

(2) Formation of primer layer

Polyvinyl alcohol powder ("Z-200" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization 1100, average saponification degree 99.5 mole%) was dissolved in hot water at 95 ° C to prepare polyethylene having a concentration of 3% by weight Alcohol solution. 5 parts by weight of a crosslinking agent ("Sumirez Resin (registered trademark) 650" manufactured by Sumitomo Chemical Co., Ltd.) was mixed with 6 parts by weight of the polyvinyl alcohol powder in the obtained aqueous solution. The obtained mixed aqueous solution was applied to the corona-treated surface of the above-mentioned base film A having been subjected to corona treatment by a microgravure coater, and dried at 80 ° C. for 10 minutes to form a primer layer. Then, the same treatment was performed on the side opposite to the primer layer of the base film A to obtain the base film A with the primer layer formed on both sides. The thickness of the primer layer is 0.5 μm in each case.

(3) Formation of polyvinyl alcohol resin layer

Polyvinyl alcohol powder ("PVA124" by Kuraray Co., Ltd., average degree of polymerization of 2400, average degree of saponification 98.0 to 99.0 mole%) was dissolved in hot water at 95 ° C to prepare an 8% by weight polyvinyl alcohol aqueous solution. The obtained aqueous solution was coated on the primer layer by a mold lip coater, and dried at 80 ° C., 2 minutes: 70 ° C., 2 minutes, and then at 60 ° C., 4 minutes, thereby preparing Laminated film with a three-layer structure consisting of base film A / primer layer / polyvinyl alcohol resin layer. Then, the same treatment was performed on the side opposite to the polyvinyl alcohol-based resin layer of this base film A to obtain a laminated film having a polyvinyl alcohol-based resin layer formed on both sides. The thickness of the polyvinyl alcohol-based resin layer was 9.2 μm and 9.5 μm, respectively.

(4) Production of stretch film

The free-standing longitudinal uniaxial stretching of the laminated film at a stretching temperature of 160 ° C. was 5.3 times to obtain a stretched film.

(Dyeing step)

Thereafter, the stretched film was dipped in a dyeing solution 1 of a mixed aqueous solution of iodine and potassium iodide at 30 ° C for about 180 seconds to dye, and then the excess iodine solution was rinsed with pure water at 10 ° C. Then, it was immersed in the crosslinking solution 1 of a boric acid aqueous solution at 78 ° C for 120 seconds. Then, it was immersed in the 70 degreeC crosslinking solution 2 containing boric acid and potassium iodide for 60 seconds. Thereafter, it was washed with pure water at 10 ° C for 10 seconds, and finally dried at 80 ° C for 300 seconds. A polarizing film is formed from the polyvinyl alcohol-based resin layer by the above steps to obtain a polarizing laminated film. The mixing ratio of each solution is as follows. The thickness of each polarizing film was 6.8 μm.

<Dyeing Solution 1>

Water: 100 parts by weight

Iodine: 0.6 parts by weight

Potassium iodide: 10 parts by weight

<Crosslinking Solution 1>

Water: 100 parts by weight

Boric acid: 10.4 parts by weight

<Crosslinking Solution 2>

Water: 100 parts by weight

Boric acid: 5.7 parts by weight

Potassium iodide: 12 parts by weight

(5) Evaluation test of polarizing laminated film

With respect to the polarized laminated film obtained by the above method, the absorption axis was measured by a retardation film / optical material detection device (trade name "RETS") made by Otsuka Electronics Co., Ltd. First, the center of the TD direction of the produced polarizing multilayer film is taken as a center, and a range of 480 mm is adopted, and a range of 480 mm wide is divided at 10 mm intervals. The absorption axis of the polarizing multilayer film is measured for a total of 49 points. The standard deviation is calculated from these 49-point absorption axes. The absolute value of the difference between the maximum value and the minimum value of the angle of the absorption axis in the plane is taken as the swing of the absorption axis. Furthermore, the polarizing laminated film supplied to the measurement is a polarizing film provided on both sides of the base film, but the angle of absorption axis at each measurement point is almost the same for each polarizing film, so the absorption axis of the polarizing laminated film can be set. Angles Angle of absorption axis of light film.

The standard deviation of the absorption axis of the polarizing laminated film was calculated from the obtained data to be 0.021 °. That is, the standard deviation of the absorption axis of each polarizing film is also 0.021 °. The swing of the absorption axis of each polarizing film is 0.12 °. If the standard deviation of the absorption axis of the polarizing film is less than 0.04 °, and the swing of the absorption axis of the polarizing film is less than 0.2 °, it can be judged that the in-plane uniformity of the absorption axis is good.

<Example 2>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 0.77 and a standard deviation σ 2 of 0.61 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.027 °, and the swing of the absorption axis was 0.11 °.

<Example 3>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 0.78 and a standard deviation σ 2 of 0.63 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.033 °, and the swing of the absorption axis was 0.13 °.

<Example 4>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 0.67 and a standard deviation σ 2 of 0.66 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.041 °, and the swing of the absorption axis was 0.14 °.

<Example 5>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 0.73 and a standard deviation σ 2 of 0.69 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.046 °, and the swing of the absorption axis was 0.16 °.

<Example 6>

(1) Preparation of substrate film B

As the base material film B, an unstretched polyethylene terephthalate film ("Ofan" made by OJK) was used.

[Measurement of thickness unevenness in the MD direction of the base film B]

The thickness of the substrate film B with a length of 640 mm in the TD direction and a length of 131 m in the MD direction was continuously measured by a laser measuring instrument L T9010 of Keyence. When measuring the thickness unevenness in the MD direction, the data is taken by sampling 512 points at 1 second intervals (measured at 2.5m / minute conveyance, so it is 1 second × (512-1) × 2 · 5m / minute ÷ 60 Seconds / minutes = 21.292m, taking thickness unevenness data of 21.292m).

From the obtained thickness unevenness waveform, the standard deviation σ 1 was calculated and found to be 1.79.

[Fourier transform, wave number separation and inverse Fourier transform, and calculation of thickness unevenness]

Apply fast Fourier transform (FFT) to the thickness unevenness data taken Management. Then, the intensity distribution data obtained by performing Fourier transform, the intensity data corresponding to 7 points whose wave number does not reach 1/3 (1 / m) is only multiplied by 0, and 512 points are obtained by inverse Fourier transform. From the obtained waveform of the thickness unevenness, the standard deviation σ 2 was calculated to be 1.68.

[standard deviation Calculation of thickness ratio]

Divide the average thickness d of the base film B by the values of the standard deviation σ 1 and the standard deviation σ 2 to calculate the ratios of the standard deviation to the thickness σ 1 / d and σ 2 / d, which are 7.97 × 10 ^-3 and 7.48 × 10 ^-3 .

(2) Formation of primer layer

As in Example 1, a corona treatment was applied to one side of the substrate film B, and a primer layer was formed on the corona treated surface. The thickness of the primer layer was 0.5 μm.

(3) Formation of polyvinyl alcohol resin layer

In the same manner as in Example 1, a polyvinyl alcohol-based resin layer was formed on the primer layer, and a laminated film having a three-layer structure composed of a base film B / primer layer / polyvinyl alcohol-based resin layer was produced. The thickness of the polyvinyl alcohol-based resin layer was 5.1 μm.

(4) Production of stretch film

The free-standing longitudinal uniaxial stretching of the laminated film at a stretching temperature of 90 ° C. was 1.8 times to obtain a stretched film.

(Dyeing step)

The stretched film was immersed in a crosslinking solution 3 of a boric acid aqueous solution at 30 ° C for 30 seconds. Next, immerse the dyeing solution 2 in a mixed aqueous solution of iodine and potassium iodide at 30 ° C for about 120 seconds to dye, and then rinse the excess iodine solution with pure water at 7 ° C. Then, it was immersed in the crosslinking solution 4 containing a boric acid and potassium iodide in a 40 ° C aqueous solution for 120 seconds. Then, it was immersed in a cross-linking solution 5 containing boric acid and potassium iodide at 75 ° C. for 60 seconds, and the free-end longitudinal uniaxial stretching was simultaneously performed so that the stretching ratio became 3.0 times (total stretching ratio: 5.4 times). Thereafter, it was washed with an aqueous potassium iodide solution (mixed with 4.9 parts by weight of potassium iodide with respect to 100 parts by weight of water) at 7 ° C for 5 seconds, and finally dried at 60 ° C for 180 seconds. By the above steps, a polarizing film is formed from the polyvinyl alcohol-based resin layer to obtain a polarizing laminated film. The mixing ratio of each solution is as follows. The thickness of the polarizing film was 3.7 μm.

<Dyeing Solution 2>

Water: 100 parts by weight

Iodine: 0.59 parts by weight

Potassium iodide: 1.6 parts by weight

<Crosslinking Solution 3>

Water: 100 parts by weight

Boric acid: 3.0 parts by weight

<Crosslinking solution 4>

Water: 100 parts by weight

Boric acid: 3.0 parts by weight

Potassium iodide: 3.1 parts by weight

<Crosslinking solution 5>

Water: 100 parts by weight

Boric acid: 4.0 parts by weight

Potassium iodide: 5.0 parts by weight

(5) Evaluation test of polarizing laminated film

With respect to the polarized laminated film obtained by the above method, the absorption axis was measured using a retardation film / optical material detection device (trade name "RETS") made by Otsuka Electronics Co., Ltd. First, with the center of the TD direction of the polarizing laminated film produced as a center, a range of 110 mm was taken, and the 110 mm wide range was divided at 10 mm intervals. The absorption axis of the polarizing laminated film was measured for a total of 11 points. The standard deviation is calculated from these absorption axes at 11 points. In addition, the absolute value of the difference between the maximum value and the minimum value of the in-plane absorption axis angle is used as the swing of the absorption axis.

The standard deviation of the absorption axis of the polarizing laminated film was calculated from the obtained data to be 0.063 °. That is, the standard deviation of the absorption axis of the polarizing film is 0.063 °. The swing of the absorption axis of the polarizing film is 0.18 °.

<Comparative example 1>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 0.77 and a standard deviation σ 2 of 0.72 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.064 °, and the swing of the absorption axis was 0.26 °.

<Comparative example 2>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 0.97 and a standard deviation σ 2 of 0.84 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.072 °, and the swing of the absorption axis was 0.24 °.

<Comparative example 3>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 1.17 and a standard deviation σ 2 of 0.95 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.080 °, and the swing of the absorption axis was 0.27 °.

<Comparative Example 4>

A polarizing laminated film was obtained in the same manner as in Example 1 except that the base film A having a standard deviation σ 1 of 1.26 and a standard deviation σ 2 of 1.13 was used. As a result of the evaluation, the standard deviation of the absorption axis was 0.142 °, and the swing of the absorption axis was 0.57 °.

The above results are shown in Table 1.

In Table 1, when the swing of the absorption axis is 0.13 ° or less, it is judged as ◎, when the swing of the absorption axis exceeds 0.13 ° and 0.2 ° or less, it is judged as ○, and when the swing of the absorption axis exceeds 0.2 °, it is judged as ×. From Table 1, the swing range of the absorption axis of the polarizing film system obtained in Examples 1 to 6 is 0.2 ° or less, and the contrast of the liquid crystal display device incorporating such a polarizing plate will be improved.

[Industrial availability]

According to the present invention, a polarizing plate having excellent absorption axis accuracy can be provided, and a display device incorporating such a polarizing plate can achieve high contrast.

Claims (7)

A manufacturing method of a polarizing film is a manufacturing method of a polarizing film with a thickness of 10 μm or less and an in-plane absorption axis swing of 0.2 or less. The method includes the following steps (1) to (5): (1) preparing a substrate In the film step, the base film is a long base film containing a thermoplastic resin, and the ratio of the standard deviation σ 1 calculated from the waveform obtained by measuring the thickness of the base film in the MD direction to the thickness d of the base film (σ 1 / d) is 9.0 × 10 ^-3 or less, and after the aforementioned waveform is Fourier-transformed, the thickness is obtained by inverse Fourier-transformation of the spectrum of a region with a wavenumber of 1/3 (1 / m) or more. The ratio (σ 2 / d) of the calculated standard deviation σ 2 to the thickness d of the base film is 8.0 × 10 ^-3 or less; (2) at least one side of the base film is coated with a polyvinyl alcohol-based resin After the coating liquid is prepared, the coating film is dried, thereby forming a polyvinyl alcohol resin layer to obtain a laminated film; (3) a step of uniaxially stretching the laminated film to obtain an extended film; (4) the step of dyeing the stretched film to obtain a polarizing laminated film; (5) peeling the base film from the polarizing laminated film to The step of polarizing film. A manufacturing method of a polarizing film is a manufacturing method of a polarizing film with a thickness of 10 μm or less and an in-plane absorption axis swing of 0.2 or less. The method includes the following steps (1) to (5): (1) preparing a substrate In the film step, the base film is a long base film containing a thermoplastic resin, and a standard deviation σ 1 calculated from a waveform obtained by measuring the thickness of the base film in the MD direction is 0.80 μm or less, and the aforementioned waveform is After Fourier transform, the standard deviation σ 2 calculated from the waveform of the thickness obtained by inverse Fourier transform of the spectrum of a region with a wavenumber of 1/3 (1 / m) or more is 0.65 μm or less; (2) Based on the aforementioned basis A step of applying a coating solution containing a polyvinyl alcohol-based resin to at least one side of the material film to prepare a coating film and drying the coating film, thereby forming a polyvinyl alcohol-based resin layer to obtain a laminated film; (3) A step of uniaxially stretching the aforementioned laminated film to obtain a stretched film; (4) a step of dyeing the aforementioned stretched film to obtain a polarizing laminated film; (5) obtaining a polarized light by peeling the base film from the aforementioned polarizing laminated film Film step. The method for manufacturing a polarizing film according to item 1 or 2 of the scope of the patent application, which includes the step of laminating a protective film on the polarizing film in the aforementioned polarizing laminated film through an adhesive or an adhesive. The method for manufacturing a polarizing film according to item 1 or 2 of the scope of the patent application, wherein the base film prepared in step (1) is a base film formed by melt extrusion. The method for manufacturing a polarizing film according to item 1 of the scope of patent application, wherein the thickness of the substrate film prepared in step (1) is 5 to 300 μm. The method for manufacturing a polarizing film according to item 2 of the scope of patent application, wherein the thickness of the substrate film prepared in step (1) is 20 to 150 μm. The method for manufacturing a polarizing film according to item 1 or 2 of the scope of the patent application, wherein the substrate film prepared in step (1) is a substrate film containing a polyolefin resin.