KR20180018365A - A polarizing film - Google Patents

Abstract

The objective of the present invention is to provide a polarizing film with improved strength under an environment at repeated high and low temperature. The polarizing film is formed of a polyvinyl alcohol-based resin and has a dichroic material, wherein an orientation degree in an azimuth distribution measured by a wide angle X-ray diffraction method is 81.0% or more.

Description

A POLARIZING FILM [0002]

The present invention relates to a polarizing film.

Conventionally, a liquid crystal display device is known as an image display device. The liquid crystal display has a liquid crystal panel and a polarizer provided on both surfaces of the liquid crystal panel. As a polarizer, a polarizing film in which a dichroic dye is adsorbed and oriented on a stretched film obtained by stretching a polyvinyl alcohol (PVA) based resin film is known (for example, Patent Document 1).

[Patent Document 1] Japanese Patent Application Laid-Open No. 2009-098653

In recent years, a liquid crystal display device is required to be reduced in size and thickness in order to reduce the weight thereof, and accordingly, a polarizing film constituting a liquid crystal display device has been studied to be thin. For this reason, a polarizing film having sufficient strength (for example, suppressing cracking of a polarizing film under an environment such as repeating high and low temperatures) even if it is thinned is required.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a polarizing film having enhanced strength under an environment such as high temperature and low temperature.

In order to solve the above problems, a polarizing film of one embodiment of the present invention is a polarizing film having a dichroic substance, which comprises a polyvinyl alcohol-based resin as a forming material, , And an orientation degree in an azimuth distribution is 81.0% or more.

The polarizing film may have a structure in which the ratio of the confinement noncontact portion to the total of the crystal portion, the confinement noncontact portion and the noncontact portion obtained from the spin-spin relaxation time obtained by the pulse NMR ( ¹ H) is not less than 40% and not more than 95% good.

According to the present invention, it is possible to provide a polarizing film having enhanced strength under an environment such as high temperature and low temperature.

1 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate of the first embodiment.
Fig. 2 is a schematic diagram showing the microstructure of the polyvinyl alcohol-based resin of the polarizing film of the first embodiment. Fig.
Fig. 3 is a flowchart showing an example of a method of manufacturing the polarizing film of the first embodiment.
4 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate of the second embodiment.
5 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate of the third embodiment.

Hereinafter, the polarizing film according to the present embodiment will be described with reference to the drawings. On the other hand, in all the drawings below, dimensions, ratios and the like of the respective components are appropriately different in order to make the drawings easy to see.

[First Embodiment]

<Polarizer>

Fig. 1 is a schematic sectional view showing an example of the layer structure of the polarizing plate 1 according to the first embodiment.

The polarizing plate 1 is a polarizing plate having a one-side protective film. The polarizing plate 1 includes a polarizing film 5, a protective film (protective film) 10 positioned on one side of the polarizing film 5, a bonding agent 15).

The polarizing plate 1 of the present embodiment may be a polarizing plate disposed on the visual (front) side of an image display element such as a liquid crystal cell when incorporated in an image display device such as a liquid crystal display device, For example, a backlight side of a liquid crystal display). Conventionally, it is known that a polarizing plate disposed on the viewer side is liable to cause condensation and the like as compared with a polarizing plate disposed on the back side, and thus cracks tend to occur in the polarizing film. According to the polarizing plate 1 of the present embodiment, the occurrence of cracks in the polarizing film 5 can be remarkably suppressed.

<Polarizing Film>

The polarizing film 5 is made of a polyvinyl alcohol-based resin and is dyed with a dichroic substance (dichroism pigment). As the polyvinyl alcohol-based resin, a polyvinyl alcohol resin or a polyvinyl alcohol resin derivative is used. Hereinafter, polyvinyl alcohol is referred to as PVA in the present specification.

Examples of the PVA resin derivative include polyvinylformal, polyvinyl acetal, polyvinyl butyral, and modified products thereof. Examples of the modifier include the above-described PVA resin derivatives, modified with an olefin such as ethylene or propylene, an alkyl ester of an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or crotonic acid or an unsaturated carboxylic acid, .

The PVA resin is a crystalline polymer. When the PVA resin is dyed with a dichroic substance, a complex composed of a dichroic substance and a PVA resin is formed near the crystal of the PVA resin. Since this complex is stable and easy to align, it contributes to improvement of the polarization performance when the polarizing film is formed.

In the present specification, the term &quot; orientation &quot; means that molecular chains of the PVA-based resin are arranged in one direction. Further, the molecular chain is oriented in the stretching direction of the PVA-based resin. The orientation direction of the molecular chains is the absorption axis direction in the polarizing film (5).

The average degree of polymerization of the PVA resin as a material for forming the polarizing film 5 is preferably 100 to 10,000, more preferably 1,500 to 8,000, and still more preferably 2,000 to 5,000. The average degree of polymerization of the PVA resin can be determined in accordance with JIS K 6726 (1994).

The saponification degree of the PVA resin is preferably 85 mol% or more, more preferably 90 mol% or more, and still more preferably 99 mol% or more. On the other hand, the degree of saponification of the PVA resin is preferably less than 100 mol%, and may be less than 99.9 mol%.

When the degree of saponification of the PVA resin is 85 mol% or more, the degree of crystallization of the obtained polarizing film becomes high, and the degree of orientation is easily increased.

On the other hand, if the degree of saponification of the PVA resin is less than 100 mol%, the dyeing speed of the PVA resin is sufficiently fast. Thereby, a polarizing film having sufficient polarization performance even in a short time can be obtained.

Examples of the dichroic substance used for dyeing the PVA resin of the present embodiment include dichroic substances known as coloring matters for polarizing films, and iodine is preferable.

Hereinafter, the description will be limited to the case where iodine is used as the dichroic substance. An iodine solution is preferably used for dyeing the PVA resin according to the present embodiment, and an iodine aqueous solution is preferably used.

As the iodine aqueous solution, an iodine and an aqueous solution containing iodide ions dissolved in iodide as a dissolution aid are used.

As the iodide, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide or titanium iodide is preferable and potassium iodide is more preferable.

The polarizing film (5) may contain a plasticizer within a range not to impair the effect of the present invention. Examples of the plasticizer include condensates of polyols or polyols such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The content of the plasticizer in the polarizing film (5) is not particularly limited, but is preferably 20% by mass or less, and more preferably 10% by mass or less. When the content of the plasticizer is 20 mass% or less, the degree of orientation of the obtained polarizing film tends to be high. From the viewpoint of improving the degree of orientation, if the strength of the stretching apparatus permits, the content of the plasticizer is preferably substantially 0% by mass, and a plasticizer may not be added. The content of the plasticizer is substantially 0 mass% in this specification, for example, 1 mass% or less.

The degree of alignment of the polarizing film 5 is represented by the degree of orientation of the polarizing film 5. The degree of orientation of the polarizing film 5 of the present embodiment is 81.0% or more, and preferably 81.5% or more. If the degree of orientation of the polarizing film 5 is 81.0% or more, the cause is unclear, but the occurrence rate of cracking of the polarizing film can be remarkably suppressed even in an environment where repetition of high temperature and low temperature is repeated.

In this specification, the degree of orientation of the polarizing film 5 can be measured by the wide-angle X-ray diffraction method (WAXD), and specifically, it can be measured by the method described in the section of Examples described later.

In the PVA-based resin as a material for forming the polarizing film 5, there exist crystal portions and non-crystal portions. Recent advances in analytical techniques have revealed that there is a part called the constraint declassified state, which is an intermediate state between decision-making and non-governmental organizations. It is considered that the molecular chains are not constrained in comparison with the crystal unit. Further, it is considered that the constraint nonconformation part is in a state in which the molecular chain is not elongated as compared with the noncrystal part and the crystal is slightly loosened.

It is considered that the optical characteristics of the polarizing film 5 are likely to be stabilized under a high temperature or high temperature and high humidity environment when the amount of the constraining nonconjugator is large in the PVA resin as a material for forming the polarizing film 5. If the amount of the confinement noncontact portion is large in the PVA resin as a material for forming the polarizing film 5, the strength of the polarizing film 5 is likely to increase under high temperature or high temperature and high humidity environments.

The reason why the optical characteristic is stable is that when the iodine is introduced into the confinement noncrystal portion and the PVA and iodine are complex formed thereon, the molecular chains are harder to move than the noncrystal portion originally. Therefore, It is thought that the resistance is strong.

The reason for the increase in the strength of the polarizing film is that iodine is introduced into the confinement confinement portion which is a portion in which the PVA molecular chains are slightly loosened from the crystal portion and PVA-iodine complex is formed, This is probably due to the increase in the intensity of the polarizing film as iodine is caught.

In the polarizing film 5 of the present embodiment, the ratio of the confinement noncontact portion to the total of the crystal portion, the confinement noncontact portion and the noncontact portion is preferably more than 20%, more preferably not less than 30%, more preferably not less than 40% Is more preferable. The upper limit of the constraint non-confinement is not particularly limited, but it may be 95% or less.

In the present specification, the ratio of the constraint non-blocking portion is calculated from the spin-spin relaxation time obtained by the pulse NMR ( ¹ H) measurement according to the description of the embodiment to be described later.

It is known that crystals of PVA have a folded structure in which polymer chains are repeatedly folded and formed. The determination of this folded structure is generally called a lamellar type crystal.

Fig. 2 is a schematic diagram showing the microstructure of the PVA-based resin of the polarizing film 5. Fig.

In Fig. 2, a part of the polymer chain constituting the lamellar crystal is shown. The lamellar crystal (crystal of PVA) 50 has a folded structure in which the polymer chain 51 is folded back in the width direction. In the lamellar crystal (crystal of PVA) 50, the folded structure is continuously formed repeatedly in the depth direction.

The crystal size of the lamellar type crystal 50 can be adjusted by the thermal history of the PVA type resin as described later.

In the stretching direction (absorption axis direction) of the polarizing film 5 of the present embodiment, the distance Wa between the lamellar crystals is preferably 7.0 nm or more and 30.0 nm or less. The distance Wb between the lamellar crystals is preferably 1.0 nm or more and 10.0 nm or less in a direction (transmission axis direction) perpendicular to the stretching direction of the polarizing film 5 of the present embodiment.

In the present specification, the distance between the lamellar crystals adopts a value measured from an incineration (small angle) X-ray scattering method (SAXS) according to the description of the embodiment to be described later.

The thickness of the polarizing film 5 of the present embodiment is preferably 30 占 퐉 or less, more preferably 20 占 퐉 or less. In order to thin the polarizing plate, the thickness of the polarizing film 5 is more preferably 10 m or less, particularly preferably 8 m or less. The thickness of the polarizing film is preferably 2 mu m or more. According to the present embodiment, since the intensity per unit film thickness can be increased, a polarizing film having a thin shape and excellent strength can be obtained.

The polarization performance of the polarizing film 5 of the present embodiment will be described. In this specification, the polarization performance of the polarizing film is evaluated by two parameters called &quot; visual sensitivity-corrected single transmittance (Ty) &quot; and &quot; visual sensitivity correction polarization degree (Py) Ty and Py are the transmittance and the degree of polarization, respectively, in the visible region (wavelength 380 to 780 nm) corrected so that the weight around 550 nm, which has the highest sensitivity of the human eye, is maximized. Since light having a wavelength of less than 380 nm can not be seen by human eyes, Ty and Py are not considered.

The T i of the polarizing film 5 is preferably 40% or more and 47% or less, more preferably 41% or more and 45% or less. When the Ty of the polarizing film 5 is 40% or more, the balance between Ty and Py becomes better. When the Ty of the polarizing film 5 is 47% or less, Py becomes sufficiently high, the luminance of the image display device becomes sufficiently high, and the display quality becomes sufficiently high. On the other hand, when the Ty of the polarizing film 5 is less than 40%, the input power of the image display apparatus can be increased in order to sufficiently increase the brightness of the image display apparatus.

The Py of the polarizing film 5 is preferably 99.9% or more, more preferably 99.95% or more, and may be 99.99% or more.

In the present specification, Ty and Py of the polarizing film 5 are measured using a spectrophotometer ("V7100" manufactured by Nihon Bunko K.K.) having an integrating sphere (integrating sphere).

The polarizing film 5 preferably has a stuck strength per unit thickness of 6.0 g / m or more. If the sticking strength per unit thickness of the polarizing film 5 is 6.0 g / 탆 or more, the occurrence rate of the cracking of the polarizing film 5 can be remarkably suppressed even under an environment of repeating high temperature and low temperature.

In this specification, the sticking strength per unit thickness of the polarizing film 5 is obtained by performing the following sticking test. The sticking test was carried out by using a test piece (polarizing film (5)) on a small table tester ("EZ Test (registered trademark)" manufactured by Shimadzu Seisakusho Co., Ltd.) equipped with a sticking jig having a diameter of 1 mm and a radius of curvature of 0.5R ) Is fixed. The piercing test is performed under the condition of a temperature of 23 占 占 폚 and at a threshing speed of 0.33 cm / sec. The striking strength was determined by performing a stabbing test on 10 test pieces. The strength of the stamper when the test piece was torn in the direction of the transmission axis of Fig. 2 was taken as the average of four values excluding the top three and the bottom three. By dividing the average value by the film thickness of the test piece, the sticking strength per unit film thickness is obtained.

<Protection film>

The protective film 10 is bonded to one side of the polarizing film 5 via a bonding agent 15, as shown in Fig. The protective film 10 is made of a thermoplastic resin having translucency. Further, it is preferable that the protective film 10 be formed of an optically transparent thermoplastic resin.

Examples of the thermoplastic resin include a polyolefin resin such as a chain polyolefin resin (polypropylene resin) and a cyclic polyolefin resin (norbornene resin); a cellulose ester resin such as cellulose triacetate and cellulose diacetate; Ester resins, polycarbonate resins, (meth) acrylic resins, polystyrene resins, and mixtures and copolymers thereof.

The protective film 10 may be a film having optical functions such as a retardation film and a brightness enhancement film. The protective film 10 is obtained, for example, by stretching (uniaxially stretching or biaxially stretching) a film made of a thermoplastic resin. When the protective film 10 is a phase difference film, a phase difference film having an arbitrary retardation given to the above-mentioned film can be obtained by forming a liquid crystal layer or the like on the obtained film.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer is formed on the surface of the protective film 10 opposite to the polarizing film 5 It is possible. The protective film 10 may contain one or more additives such as a lubricant, a plasticizer, a dispersant, a heat stabilizer, an ultraviolet absorber, an infrared absorber, an antistatic agent and an antioxidant.

The thickness of the protective film 10 is preferably 90 占 퐉 or less, more preferably 50 占 퐉 or less, and still more preferably 30 占 퐉 or less, from the viewpoint of thinning of the polarizing plate. The thickness of the protective film 10 is usually 5 占 퐉 or more from the viewpoints of mechanical strength and handleability.

<Bonding agent (adhesive or pressure-sensitive adhesive)>

The bonding agent 15 is positioned between the polarizing film 5 and the protective film 10 as shown in Fig. The bonding agent 15 forms a layer for adhering and fixing the protective film 10 to one surface of the polarizing film 5. As the bonding agent 15, an adhesive or a pressure-sensitive adhesive may be employed.

When an adhesive is used as the bonding agent 15, an adhesive to be used includes an active energy ray-curable adhesive containing a curable compound which is cured by irradiation of active energy rays such as ultraviolet rays, visible rays, electron beams and X rays, an adhesive such as a PVA- Based adhesive in which the component is dissolved or dispersed in water. As the active energy ray curable adhesive, an active energy ray curable adhesive composition comprising a cationic polymerizable curable compound and a radical polymerizable curable compound or both is preferable from the standpoint of exhibiting good adhesiveness.

The active energy ray curable adhesive may further include either or both of a cationic polymerization initiator and a radical polymerization initiator for initiating the curing reaction of the curable compound.

When an adhesive is used as the bonding agent 15, an adhesive containing a cationically polymerizable curable compound is preferably used for the bonding agent 15 in view of good adhesiveness.

When an adhesive is used as the bonding agent 15, the thickness of the bonding agent 15 is preferably 0.001 to 5 mu m, more preferably 0.01 to 3 mu m, and further preferably 0.1 to 1.5 mu m.

When a pressure-sensitive adhesive is used as the bonding agent 15, a pressure-sensitive adhesive to be used is preferably a pressure-sensitive adhesive which is a base polymer, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound, Sensitive adhesive composition. It is also possible to use a pressure-sensitive adhesive containing fine particles to exhibit light scattering properties.

When a pressure-sensitive adhesive is used as the bonding agent 15, the thickness of the bonding agent 15 is preferably 1 to 40 占 퐉, more preferably 3 to 25 占 퐉.

The polarizing plate 1 of the present embodiment is composed of a polarizing film 5, a bonding agent 15 and a protective film 10. The polarizing plate 1 includes a polarizing film 5, a bonding agent 15, 10) may be further provided. Examples of the other optical layers include a reflective polarizing film that transmits polarized light of a certain kind and reflects polarized light exhibiting a property opposite to that of the polarized light, a film having an antireflection function having a concavo-convex shape on the surface, A reflection film having a reflection function on the surface, a transflective film having a reflection function and a transmission function, and a viewing angle compensation film.

&Lt; Polarizing Film Production Method >

Next, a method of manufacturing the polarizing film 5 of the present embodiment will be described.

3 is a flow chart showing an example of a method of manufacturing the polarizing film 5. The method for producing the polarizing film 5 of the present embodiment is characterized in that a step of forming a PVA resin layer (hereinafter referred to as step S1), a drawing step (hereinafter referred to as step S2), a dyeing step (hereinafter referred to as step S3) And a crosslinking step (hereinafter referred to as step S4).

(Step S1)

In step S1 of the present embodiment, a resin layer (PVA resin layer) made of PVA resin is formed on at least one surface of a base film. Thus, a laminated film comprising the base film and the PVA-based resin layer is formed.

As shown in Fig. 3, step S1 of the present embodiment includes a coating step S11 (hereinafter referred to as step S11) for coating a base film with a PVA type resin solution and a drying step S12 for drying the PVA type resin solution S12).

(Step S11)

In step S11 of the present embodiment, an aqueous solution containing a PVA resin is applied to at least one surface of the base film while conveying the strip-like base film in the longitudinal direction to form a coating layer.

The base film coated with the aqueous solution containing the PVA resin suppresses the breakage of the PVA resin layer when the PVA resin layer is thinned by stretching the PVA resin layer in step S2 described later. The base film may be peeled from the polarizing film 5 after the polarizing film 5 is formed on the surface, or may be used as a protective film without being peeled off.

The base film may be composed of a thermoplastic resin and is preferably composed of a thermoplastic resin excellent in transparency, mechanical strength, heat stability, stretchability, and the like. Specific examples of such a thermoplastic resin include polyolefin resins such as a chain polyolefin resin and a cyclic polyolefin resin (norbornene resin and the like), a polyester resin, a (meth) acrylic resin, a cellulose triacetate, a cellulose diacetate Based resin, polyvinyl acetate-based resin, polyarylate-based resin, polystyrene-based resin, polyether sulfone-based resin, polysulfone-based resin, polyamide-based resin, polyimide-based resin Resins, or mixtures or copolymers thereof.

The base film may be a single layer structure composed of one resin layer made of one kind of thermoplastic resin or two or more kinds of thermoplastic resins, or a multilayer structure in which a plurality of resin layers made of one kind or two or more kinds of thermoplastic resins are laminated. It is preferable that the base film is made of a resin that can be stretched at a stretching temperature suitable for stretching the PVA resin layer in step S2 described later.

The base film may contain an additive. Specific examples of the additive include an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a release agent, a coloring inhibitor, a flame retardant, a nucleating agent, an antistatic agent, a pigment, and a colorant.

The thickness of the base film is preferably 1 to 500 占 퐉, more preferably 1 to 300 占 퐉, further preferably 5 to 200 占 퐉, and particularly preferably 5 to 150 占 퐉. When the thickness of the base film is within the above range, the mechanical strength of the base film becomes high and the base film becomes easy to handle.

The aqueous solution containing the PVA resin may contain an additive such as a solvent other than water, a plasticizer and a surfactant if necessary. Examples of solvents other than water include organic solvents having compatibility with water such as methanol, ethanol, propanol, and alcohols typified by polyhydric alcohols (preferably, glycerin).

The initial water content of the coating layer composed of the aqueous solution containing the PVA resin is preferably a value exceeding 30 mass%. When the initial water content of the coating layer exceeds 30 mass%, the aqueous solution containing the PVA resin becomes a uniform solution, and unintentional crystallization can be suppressed before S12 described later.

The initial water content of the coating layer is preferably 40 mass% or more, and more preferably 50 mass% or more. Thus, in step S11 of the present embodiment, it is easy to handle an aqueous solution containing PVA resin.

The method of coating the aqueous solution on the base film may be carried out by a roll coating method such as a wire bar coating method, a reverse coating method and a gravure coating method, a die coating method, a comma coating method, a lip coating method, a spin coating method, , Dipping method, spraying method and the like.

The coating layer may be formed on only one side of the base film or on both sides.

Prior to step S11 of the present embodiment, in order to improve the adhesion between the base film and the PVA resin layer, at least the surface of the base film on the side where the coating layer is formed is subjected to corona treatment, plasma treatment, flame treatment May be performed. For the same reason, the coating layer may be formed on the base film through a primer layer or the like.

(Step S12)

In step S12 of the present embodiment, water is removed from the coating layer having a moisture content exceeding 30 mass% to form a PVA-based resin layer. Drying of the coating layer (removal of water) can be performed by heating, but drying by reduced pressure or the like may be used in combination. Examples of the heating method include a method in which a substrate film is brought into contact with a heated roll (hot roll), a method in which hot air is blown, and a combination of these methods.

The drying temperature in step S12 of the present embodiment is, for example, in the range of 50 to 200 DEG C, preferably in the range of 60 to 150 DEG C.

In step S12 of the present embodiment, water is removed from the coated layer on the base film, and the coated layer is dried until a desired moisture content is reached, thereby forming a PVA-based resin layer on the base film. Hereinafter, the moisture content of the coating layer immediately before the step S12 is referred to as &quot; initial moisture content W1 &quot;. The moisture content of the PVA resin layer obtained in step S12 is referred to as &quot; final moisture content W2 &quot;.

In step S12 of the present embodiment, it is important to appropriately adjust the removal rate of water when the water content of the coating layer is 30 mass% or the average removal rate of water when the water content is close to 30 mass%.

Here, the "water removal rate" means a decrease in water content (mass%) of the coating layer per unit time (sec), and the unit is mass% / second. Further, the "moisture content of the coating layer is about 30 mass%" means that the water content of the coating layer is between 30 and 10 mass%. Hereinafter, the water removal rate when the moisture content of the coating layer is 30 mass% is referred to as &quot; removal rate V (30) &quot;. The average removal rate of water when the water content of the coating layer is in the range of 30 to 10 mass% is referred to as &quot; average removal rate Vave (30-10) &quot;.

In step S12 of the present embodiment, either or both of the removal rate V (30) and the average removal rate Vave (30-10) is set in the range of 0.01 to 1.8 mass% / second. The crystal size of the PVA is reduced by drying the coating layer so that either or both of the removal rate V 30 and the average removal rate Vave 30-10 is in the above range, The distance Wb can be shortened, and the distribution of the fine crystal can be obtained. As a result, in the polarizing film 5, the ratio of the confinement noncontact portion to the total of the crystal portion, the confinement noncontact portion, and the noncontact portion can be increased.

The reason why a dense crystal structure can be formed by adjusting one or both of the removal rate V (30) and the average removal rate Vave (30-10) within the above range is presumed as follows.

When the moisture content of the coating layer is 30 mass% or the vicinity thereof, it is considered that crystal nuclei composed of a PVA-based resin start to be generated in the coating layer. It is considered that this is because it is more stable to form crystal nuclei composed of a PVA-based resin and crystallize from a moisture content of about 30 mass%. At this time, it is considered that when either or both of the removal rate V (30) and the average removal rate Vave (30-10) is within the above range, enough crystal nuclei composed of the PVA-based resin are generated. It is considered that by forming a large number of crystal nuclei composed of a PVA-based resin, the density of crystals in the PVA-based resin layer becomes high and a denser crystal structure is formed.

On the other hand, in the region where the water content of the coating layer exceeds 30% by mass, the PVA resin is uniformly dissolved in water, and the state (solution) in which the molecular chains of the PVA resin are uniformly present is considered to be stable . In fact, in a region where the water content exceeds 30 mass%, stable crystal nuclei of a critical size or more are hardly generated.

As described above, the crystal nucleus of the PVA-based resin starts to form when the water content of the coating layer is reduced to about 30 mass%, and the water content of the coating layer is also in the range of 30 to 10 mass%. On the other hand, when the moisture content of the coating layer is less than 10 mass%, stable crystal nuclei of a critical size or more are difficult to be generated. This is presumably because the water content of both coatings in the coating layer is so small that the mobility of the molecular chain of the PVA-based resin is lowered.

In the step S12 of the present embodiment, at least the average removal rate Vave (30-10) is set to 0.01 to 1.8% by mass / second because the crystal nuclei can be generated in a sufficient amount over the entire water content range in which crystal nucleation occurs. , And it is more preferable to adjust both the removal rate V (30) and the average removal rate Vave (30-10) within the range of 0.01 to 1.8 mass% / second. Thereby, a sufficient number of crystal nuclei composed of the PVA-based resin can be generated.

The upper limit value of either or both of the removal rate V (30) and the average removal rate Vave (30-10) is preferably 1.65 mass% / second or less, more preferably 1.5 mass% / second or less. Thereby, the density of crystal nuclei made of the PVA-based resin in the PVA-based resin layer can be further increased.

If the density of the crystal nucleus made of the PVA-based resin in the PVA-based resin layer is too high in step S3 to be described later, the dyeing efficiency may be lowered. If the lower limit value of either or both of the removal rate V (30) and the average removal rate Vave (30-10) is 0.01% by mass / second or more, the density of the crystal nucleus made of the PVA resin in the PVA- And the dyeing efficiency in step S3 can be kept sufficiently high.

The lower limit of the removal rate V (30) and / or the average removal rate Vave (30-10) is preferably 0.15 mass% / second or more, more preferably 0.5 mass% / second or more. As a result, the dyeing efficiency in step S3 described later can be kept sufficiently high, and the productivity of the polarizing film 5 can be increased.

As a method for lowering the removal rate V (30) and / or the average removal rate Vave (30-10) to fall within the above range, the following methods can be mentioned. Such a method includes, for example, a method of lowering the surface temperature of the heated roll when the heated roll is used in step S12. As another method, when hot air is used in step S12, either one or both of the temperature and wind speed of the hot air may be lowered. Also, the humidity of the environment in which the step S12 is performed may be increased.

In the step S12 of the present embodiment, from the viewpoint of productivity, it is preferable to enhance the drying speed of the water by increasing the drying condition in the region where the water content of the coating layer greatly exceeds 30 mass%. However, in the operation of the facility used in step S12 of the present embodiment, it is difficult to make the water removal rate abruptly slow at the moment when the water content of the coating layer becomes 30 mass%. Therefore, it is preferable to set the removal rate V (30) and the average removal rate Vave (30-10) to be in the range of 30% or more, because the removal rate of the water before the water content of the coating layer reaches 30% It is easy to adjust to within.

In the step S12 of the present embodiment, when the coating layer is dried from the initial moisture content W1 to the final moisture content W2, if the drying is carried out under constant drying conditions at all times, the temperature of the coating layer gradually increases and the removal rate of water There is a tendency to rise significantly. Therefore, in order to set the removal rate V (30) and / or the average removal rate Vave (30-10) to fall within the above range, the drying conditions are not made constant during the step S12, .

Next, a method of measuring the removal rate V (30) will be described. The removal rate V (30) can be calculated from the decrease curve of the water content (fitting curve) obtained by plotting the water content of the coating layer with respect to the elapsed time since the start of step S12. When the measurement interval of the water content of the coating layer is sufficiently narrow and is a continuous measurement value, the removal rate V (30) can be obtained from the differential value at the time when the water content of the coating layer is 30 mass%. However, in actual measurement, it is difficult to obtain a continuous measurement value, and in many cases, a measurement value with a sufficiently narrow measurement interval can not be obtained. Therefore, in this case, the average value of the water content in the predetermined period including the time point when the water content of the coating layer is 30 mass% is adopted as the removal rate V (30). In the production method of the present embodiment, the "predetermined period including the time when the water content is 30 mass%" is the "period when the water content is 32 mass% to 28 mass%". The removal rate V (30) is calculated based on the fitting curve according to the following equation [a].

Removal rate V (30) = (32-28) [mass%] / time required for water content to be from 32 mass% to 28 mass% [sec]

In order to accurately calculate the removal rate of water when acquiring the fitting curve, the measured value of the water content may be obtained at an interval of about 2% by mass.

On the other hand, the average removal rate Vave (30-10) is obtained in the same manner as the removal rate V (30). The average removal speed Vave (30-10) is calculated based on the fitting curve according to the following equation [b].

Average removal rate Vave (30-10) = (30-10) [mass%] / (time required for water content to become 10 mass% from 30 mass%) [

In the present specification, a base film having a coating layer formed on at least one side thereof is sometimes referred to as a &quot; laminated film &quot;. The final water content of the PVA resin layer in the thus obtained laminated film is preferably 0.15% or more, more preferably 0.30% or more, and may be 0.40% or more. The upper limit value is not particularly limited, but may be 10% or less.

The reason why the final water content of the PVA resin layer is important will be described by way of example. For example, when the coating layer having the same moisture content before drying is dried at the same time, when the final water content of the resulting PVA resin layer is high, the coating layer can be relatively gently dried as compared with the case where the final water content is low . Thereby, the distance between crystals of the lamellar crystal 50 in the PVA resin layer can be made small, and a lot of fine crystal nuclei are formed.

On the other hand, when the final water content of the obtained PVA resin layer is low, the PVA resin layer is rapidly dried as compared with the case where the final water content is high. As a result, the distance between crystals of the lamellar crystal 50 in the PVA resin layer is large, and coarse crystals are formed in a small number.

The reason for this difference can be considered as the following model. First, when dried rapidly, the difference in temperature distribution in the coating layer becomes large. Therefore, it is considered that the formation amount of very fine crystal nuclei is very small. Thereafter, as the coating layer is dried and the concentration of the PVA resin is increased, the initially formed fine crystal nuclei are preferentially grown, so that it is considered that coarse crystals are formed in a small number.

On the other hand, in the case of gentle drying, the difference in temperature distribution in the coating layer becomes small. Therefore, it is considered that the formation amount of very fine crystal nuclei is very early. Thereafter, as the coating layer is dried and the concentration of the PVA resin is increased, the number of fine crystal nuclei formed at the beginning is large, and it is considered that the crystal nuclei are hardly increased finally.

In the coating layer having a small film thickness, the temperature distribution and the concentration distribution of the PVA resin tend to decrease in the film thickness direction. Therefore, the smaller the coating thickness of the coating layer, the more easily crystals of PVA having a smaller size are easily produced, and the degree of orientation is likely to be improved. In addition, as the thickness of the coating layer is smaller, crystals of PVA having a smaller size are more likely to be generated, and the ratio of the constraining portion to the total of the crystal portion, the confinement non-confinement portion and the non-confinement portion can be increased.

In the present invention, the moisture content of the final PVA-based resin layer is determined by a dry weight method and a value obtained from a calibration curve obtained in an infrared multi-component system, in accordance with the examples of later-described examples.

A polarizing film having a high degree of orientation can be obtained by adjusting the water content in the step S12 of the PVA resin layer even if the degree of saponification of the PVA resin is relatively low (for example, less than 99.9 mol%). In addition, it is possible to increase the ratio of the constraint noncontiguous portion to the total of the decision portion, the constraint noncontiguous portion, and the noncontiguous portion. This makes it possible to obtain a polarizing film having high optical characteristics and high strength even in an environment where repetition of high temperature and low temperature is repeated.

(Step S2)

In step S2 of the present embodiment, the laminated film obtained in step S1 is stretched while being transported in the longitudinal direction. By stretching the laminated film, a stretched film obtained by laminating a stretched base film on which a base film is stretched and a resin film on which a PVA resin layer is stretched can be obtained. Step S2 of the present embodiment is advantageous in that it is easy to obtain a polarizing film of a thin film.

The stretching treatment in step S2 of the present embodiment is, for example, uniaxial stretching.

The stretch magnification of the laminated film in step S2 of the present embodiment can be appropriately selected in accordance with the desired polarization performance and the thickness of the lamellar crystal. The stretching magnification of the laminated film is preferably 1.1 times or more and 17 times or less, more preferably 1.5 times or more and 8 times or less, with respect to the original length of the laminated film. When the stretching magnification of the laminated film is 17 times or less, the film is hardly broken at the time of stretching. When the stretching magnification of the laminated film is 17 times or less, the stretched film is sufficiently thick, so that it is easy to process in a subsequent process and is easy to handle.

The stretching process in step S2 of the present embodiment is not limited to one stage but may be multistage. When the stretching process is a multi-stage process, all of the stretching processes may be performed continuously before the step S3 of the subsequent stage, and the stretching process of the second and subsequent stages may be performed simultaneously with either or both of the steps S3 and S4. In the case of performing the stretching treatment in such a multi-stage, it is preferable to perform the stretching treatment such that the stretching magnification ratio of all the stretching processes combined is more than four times the original length of the laminated film.

The stretching process in step S2 of the present embodiment may be vertical stretching in which the laminated film is stretched in the longitudinal direction of the film (film transport direction), transverse stretching in stretching in the film width direction, Or the like may be used. Examples of the longitudinal stretching method include roll-to-roll stretching using a roll, compression stretching, and stretching using a chuck. Examples of the transverse stretching method include a tenter method and the like.

Any of the wet drawing method and the dry drawing method can be adopted as the drawing process in the step S2 of the present embodiment, but it is preferable to use the dry drawing method. Thereby, the stretching temperature of the laminated film can be selected within a wide range.

The stretching temperature of the laminated film of the present embodiment is set to be equal to or higher than the temperature at which the entire PVA resin layer and the substrate film exhibit fluidity to such an extent that stretching is possible. The stretching temperature of the laminated film is preferably in the range of -30 캜 to + 30 캜, more preferably in the range of -30 캜 to + 5 캜, with respect to the phase transition temperature (melting point or glass transition temperature) of the base film , More preferably in the range of -25 DEG C to +0 DEG C. In the case where the base film is composed of a plurality of resin layers, the phase transition temperature means the highest phase transition temperature among the phase transition temperatures indicated by the plurality of resin layers.

If the stretching temperature of the laminated film is higher than -30 캜 with respect to the phase transition temperature of the base film, the laminated film tends to be stretched more than 4 times the original length of the laminated film. If the stretching temperature of the laminated film is higher than -30 캜 based on the phase transition temperature of the base film, the fluidity of the base film becomes sufficiently high, and the laminated film tends to be easily stretched.

On the other hand, if the stretching temperature of the laminated film is lower than +30 占 폚 with respect to the phase transition temperature of the base film, the fluidity of the base film becomes sufficiently low, and the laminated film tends to be easily stretched.

It is more preferable that the stretching temperature of the laminated film is within the above range and is 120 DEG C or more. Thereby, it is easy to stretch the laminated film so that it exceeds 4 times the original length of the laminated film.

The stretching temperature of the laminated film is particularly preferably 120 ° C or more and 170 ° C or less. Thereby, it is possible to suppress the growth of the lamellar crystal 50 (see Fig. 2) in the PVA-based resin layer due to the heat at the time of stretching. Thereby, the lamellar crystals 50 in the PVA resin layer can be made smaller, and the distance between crystals can be shortened. As a result, a dense crystal distribution can be maintained in the PVA resin layer.

Examples of the method of heating the laminated film in the stretching process in step S2 of the present embodiment include a method of heating in a stretching zone such as a heating furnace in which hot air is blown and adjusted to a predetermined temperature (hereinafter, zone heating method) . When the laminated film is stretched using a roll, the laminated film may be heated by heating the roll itself. As another heating method of the laminated film in the case of stretching the laminated film using a roll, there is a method of heating the laminated film by means of radiant heat by providing a heater such as an infrared heater, a halogen heater or a panel heater on the top and bottom of the laminated film Hereinafter, the heater heating method is used. In the case of using the inter-roll stretching as the stretching process in step S2 of the present embodiment, the zone heating method is preferable as the heating method of the laminated film from the viewpoint of the uniformity of the stretching temperature.

On the other hand, in the case of the zone heating method, the drawing temperature means the atmosphere temperature in the zone (for example, in a heating furnace). In the case of heating in the furnace in the heater heating method, the drawing temperature means the atmospheric temperature in the furnace. Further, in the case of the method of heating the roll itself, the stretching temperature means the surface temperature of the roll.

Between steps S1 and S2 of the present embodiment, a preheating process for preheating the laminated film may be performed. The preheating method of the laminated film is the same as the above-mentioned heating method.

The preheating temperature of the laminated film is preferably in the range of -50 占 폚 to 占 0 占 폚 with respect to the stretching temperature of the laminated film, and more preferably in the range of -40 占 폚 to -10 占 폚.

Between step S2 and step S3 of the present embodiment, the stretched film may be subjected to heat fixing treatment. In the heat-setting treatment of the stretched film, heat treatment is performed at a temperature not lower than the crystallization temperature of the PVA-based resin while keeping the end portion of the stretched film in a state of being gripped by a clip. By this heat setting treatment, the crystallization of the resin film in the stretched film is promoted.

The temperature of the heat-setting treatment of the stretched film is preferably in the range of -0 to -80 캜 with respect to the stretching temperature of the laminated film, and more preferably in the range of -0 캜 to -50 캜.

(Step S3)

In step S3 of the present embodiment, the resin film in the stretched film is dyed with iodine, which is a dichroic substance, and adsorbed and aligned.

In step S3 of the present embodiment, the resin film is dyed with iodine by immersing the drawn film in a solution containing iodine (hereinafter, a dyeing aqueous solution).

As the dyeing aqueous solution, a solution in which iodine is dissolved in a solvent can be used. As the solvent, water is preferable, but an organic solvent compatible with water may be further added to water. The concentration of iodine in the dyeing aqueous solution is preferably 0.01 to 10% by mass, and more preferably 0.02 to 7% by mass.

In order to improve the dyeing efficiency of the resin film, it is preferable to add iodide to the dyeing aqueous solution. Examples of the iodide 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 the iodide in the dyeing aqueous solution is preferably 0.01 to 20% by mass. Among iodides, it is preferable to add potassium iodide. When potassium iodide is added, the ratio of iodine to potassium iodide is preferably 1: 5 to 1: 100, more preferably 1: 6 to 1:80, in mass ratio.

The temperature of the dyeing aqueous solution is preferably from 10 to 60 캜, more preferably from 20 to 40 캜.

(Step S4)

In step S4 of the present embodiment, a resin film (hereinafter referred to as a dyed film) dyed with a dichroic substance is immersed in a cross-linking solution containing a cross-linking agent. At this time, the resin film may be stretched in the longitudinal direction in the cross-linking solution.

Examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. The crosslinking agent may be used alone or in combination of two or more.

As the solvent of the crosslinking solution, water may be used, but an organic solvent which is compatible with water may be further contained. The concentration of the crosslinking agent in the crosslinking solution is preferably 0.2 to 20% by mass, and more preferably 0.5 to 10% by mass.

The crosslinking solution may further contain iodide. By adding iodide, the polarization performance in the plane of the polarizing film 5 can be made more uniform. Specific examples of the iodide are the same as described above. The concentration of iodide in the crosslinking solution is preferably 0.05 to 15% by mass, and more preferably 0.5 to 8% by mass. The temperature of the crosslinking solution is preferably 1 to 90 占 폚.

On the other hand, step S4 of the present embodiment may be performed simultaneously with step S3 of the present embodiment by blending the cross-linking agent in the dyeing aqueous solution.

The treatment of immersing the dye film in the crosslinking solution may be carried out two or more times by using two or more kinds of crosslinking solutions having different compositions.

After the step S4 of the present embodiment, it is preferable to perform the washing treatment and the drying treatment on the dye film (hereinafter referred to as the crosslinked film) after the crosslink treatment.

The washing treatment of the crosslinked film includes a water washing treatment. In the water washing treatment of the crosslinked film, a crosslinked film is immersed in pure water such as ion-exchanged water and distilled water. The temperature of the water washing treatment of the crosslinked film is preferably 3 to 50 占 폚, more preferably 4 to 20 占 폚.

The washing treatment of the crosslinked film may be a combination of a water washing treatment and a washing treatment with an iodide solution.

As the drying treatment to be carried out after the washing treatment of the crosslinked film, any appropriate method such as natural drying, air drying, heating drying and the like can be adopted. For example, in the case of heat drying, the drying temperature of the crosslinked film is preferably 20 to 95 ° C.

The polarizing film 5 can be obtained by peeling the stretched base film from the resin film after crosslinking, after the step S4 of the present embodiment, or after the washing treatment and the drying treatment which are carried out if necessary. The method for peeling the stretched base film is not particularly limited, and conventionally known methods can be used.

By carrying out the above steps, the polarizing film 5 can be produced. The polarizing plate 1 shown in Fig. 1 can be manufactured by bonding the protective film 10 to one side of the polarizing film 5 via the bonding agent 15. [

According to the polarizing film 5 of the present embodiment, by adjusting the degree of orientation of the polarizing film 5 and the content ratio of the confinement confinement portion, the occurrence of cracks in the polarizing film 5 can be suppressed . According to the present embodiment, the durability against cracking per unit film thickness of the polarizing film 5 can be enhanced. Therefore, the polarizing film 5 of the present embodiment can attain both thinning and improved durability against cracks.

The degree of orientation of the polarizing film 5 and the content ratio of the confinement non-confinement portion can be adjusted by the thermal history in the manufacturing process. More specifically, the degree of orientation of the polarizing film 5 and the content ratio of the constraint non-confinement portion can be adjusted by the moisture content in the drying process of the PVA-based resin layer during the production process.

According to this embodiment, a dense crystal structure can be formed by adjusting the degree of saponification of the PVA resin to a relatively low degree (for example, less than 99.9 mol%) by the thermal history in the production process. As a result, the polarizing film 5 having a high polarization performance and a high degree of orientation can be obtained.

[Second Embodiment]

4 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate 2 of the second embodiment.

The polarizing plate 2 of the present embodiment differs from the first embodiment in that a protective film 10 is formed on both sides of the polarizing film 5 in comparison with the first embodiment. In the meantime, the same constituent elements as those of the above-described embodiment are denoted by the same reference numerals, and a description thereof will be omitted.

The polarizing plate 2 includes a polarizing film 5 and a protective film 10 positioned on both sides of the polarizing film 5 and a bonding agent 15 bonded to the polarizing film 5 and the respective protective films 10 . In the present embodiment, the pair of protective films 10 formed on both surfaces of the polarizing film 5 have the same constitution, but they may be protective films made of different kinds of resins or protective films having different thicknesses . Similarly, the bonding agent 15 for bonding the pair of protective films 10 to the polarizing film 5 may be a bonding agent of a different kind.

[Third embodiment]

5 is a schematic cross-sectional view showing an example of the layer configuration of the polarizing plate 3 of the third embodiment. In the meantime, the same constituent elements as those of the above-described embodiment are denoted by the same reference numerals, and a description thereof will be omitted.

The polarizing plate 3 of the present embodiment includes a polarizing film 5 and an adhesive layer 16 laminated on one side of the polarizing film 5. The adhesive layer 16 is used for bonding the polarizing plate 3 to another member (for example, a liquid crystal cell in the case of applying to a liquid crystal display device). On the other hand, in the polarizing plate 3 of the present embodiment, the adhesive layer 16 is formed on only one side of the polarizing film 5, but it may be formed on both sides.

While the preferred embodiments of the present invention have been described with reference to the accompanying drawings, it is needless to say that the present invention is not limited to these examples. Various shapes and combinations of the constituent members shown in the above-described examples are merely examples, and can be variously changed based on design requirements and the like without departing from the gist of the present invention.

[Example]

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.

(Measurement of Moisture Content of Coating Layer)

For measurement of the water content of the coating layer, an infrared multi-component "IRMA-5162S" manufactured by Kabushiki Kaisha Shino was used.

First, 10 film samples with different water ratios were prepared. As the film sample, a film having a coating layer formed by coating an aqueous solution containing PVA on the same base film as used in each of the Examples and Comparative Examples was used. This aqueous solution contains only water as a volatile component.

Next, the water content of these samples was measured according to the following formula [c] (dry weight method). Specifically, for each of the 10 film samples, the following measurements (i), (ii) and (iii) were performed in order, and the water content of each film sample was determined according to the following equation [c].

(I) - [(i)] - [100] ... [c] [i]

(I): the mass of the film sample (before the drying treatment) is measured

(Ii): The mass of the film sample after drying at 105 DEG C for 2 hours was measured

(Iii): peeling off the coating layer, and measuring the mass of the remaining base film

Apart from this measurement, the intensity of infrared absorption from water in these samples was measured using the infrared multi-component system described above. Then, the corresponding relationship between the measured value of the water content by the dry weight method and the intensity of the infrared absorption was plotted and approximated by a linear equation to prepare a calibration curve.

Next, the water content of the coating layer in each of the examples and the comparative examples was calculated by substituting the measured value by the infrared multi-component system into the linear equation of the calibration curve.

[Measurement of polarization degree]

For the polarizing plate having the obtained double-sided protective film, Ty and Py were measured using a spectrophotometer ("V7100" manufactured by Nihon Bunko K.K.) having an integrating sphere. In this measurement, a polarizing plate having a double-side protective film was set so that incident light was irradiated to the polarizing film side.

[Measurement of size of lamellar crystal (SAXS)]

The size of the lamellar crystal of the polarizing film was determined by through-passing of SAXS (Small Angle X-ray Scattering).

First, a plurality of rectangular films having long sides in the MD direction of the polarizing film were cut out. A plurality of the cut films were stacked and fixed so that their MDs were parallel to each other, and this was used as a measurement sample. The thickness of the measurement sample was about 0.05 mm. The following X-ray output conditions were used to irradiate one surface of the sample for measurement from the direction perpendicular to the surface of the sample for measurement by the following incineration X-ray scattering apparatus, A scattering image was captured.

Incinerating X-ray scattering device: &quot; NANO-Viewer &quot; manufactured by Rigaku Kabushiki Kaisha

X-ray output conditions: Cu target, 40 kV, 20 mA

(Sector (q) - intensity in the MD direction and TD direction) in the MD direction and in the TD direction by sector averaging the range of +/- 10 degrees from the respective azimuth angles with respect to the MD direction and TD direction of the polarizing film from the obtained incidence angle X- Distribution). The uncompensated sector profile refers to a sector profile before background correction is performed.

Next, measurement was performed under the same conditions except that the measurement sample was removed from the optical axis of the X-ray to calculate the background of the sector profile. After the transmittance correction of the background is performed, the background is removed from the unmodified sector profile to obtain a sector profile after background correction (hereinafter simply referred to as a "sector profile").

The distances Wa and Wb between the lamella type crystals were calculated from the scattering vectors qa and qb of the peak top in the curves obtained by multiplying the sector profiles in the MD and TD directions by q2 according to the following formulas (D1) and (D2) .

Wa = 2 pi / qa ... (D1)

Wb = 2? / Qb ... (D2)

&Lt; Example 1 >

(1) Formation of primer layer

PVA powder ("Z-200" manufactured by Nippon Gosei Chemical Industry Co., Ltd., average degree of polymerization: 1100, degree of saponification: 99.5 mol%) was dissolved in hot water at 95 ° C to prepare a PVA aqueous solution having a concentration of 3% by mass. The obtained aqueous solution was mixed with 5 parts by mass of a crosslinking agent (&quot; Sumirez Resin (registered trademark) 650 &quot; manufactured by Daoka Kagaku Kogyo K.K.) per 6 parts by mass of the PVA powder to obtain a coating solution.

Next, an unoriented polypropylene (PP) film (melting point: 163 占 폚) having a thickness of 90 占 퐉 was prepared as a base film, and corona treatment was performed on one surface thereof. The above coating liquid was coated on the surface of the substrate film subjected to the corona treatment using a small-diameter gravure coater. The obtained coating film was dried at 80 占 폚 for 10 minutes to form a primer layer having a thickness of 0.2 占 퐉.

(2) Fabrication of laminated film (step S1)

PVA powder ("PVA 124" manufactured by Kabushiki Kaisha Kurara Co., Ltd., average degree of polymerization: 2400, degree of saponification: 98.0 to 99.0 mol%) was dissolved in hot water at 95 ° C to prepare a PVA aqueous solution having a concentration of 7.5% by mass. The surface of the primer layer of the base film having the primer layer prepared in the above (1) was coated with the PVA aqueous solution using a die coater to form a coating layer having a thickness of 130 탆 (step S11).

Thereafter, hot air at 85 캜 was blown to dry the coating layer (step S12). At this time, while the moisture content of the coating layer during drying was monitored by the above infrared multi-component system, drying was continued while gradually decreasing the wind speed of the hot air, and when the water content of the PVA resin layer reached 0.58 mass% A laminated film composed of a base film / primer layer / PVA resin layer was obtained. In the step S12 of Example 1, the removal rate V (30) was set in the range of 0.01 to 1.8 mass% / second. Also, the average removal rate Vave (30-10) was set in the range of 0.01 to 1.8 mass% / second. The thickness of the PVA resin layer was 9.3 탆.

(3) Production of stretched film (step S2)

The laminated film produced in (2) above was subjected to free uniaxial stretching at a temperature of 150 占 폚 to the original length of the laminated film by 5.3 times using a longitudinal uniaxial stretching apparatus of a floating type to obtain a stretched film. The thickness of the resin film on the stretched film was 5.1 mu m.

(4) Production of a Dyeing Film (Step S3)

First, a dyeing aqueous solution at 30 DEG C containing 0.6 part by mass of iodine and 5.0 parts by mass of potassium iodide per 100 parts by mass of water was prepared. Next, the stretched film prepared in the above (3) was immersed in the dyeing aqueous solution, and the stretched film was dyed with iodine to obtain a dyed film. The immersion time of the stretched film was set so that the stretched film was stained experimentally in advance with iodine and the visibility-corrected single-layer transmittance (Ty) of the obtained film was about 41.5%.

After the dyeing treatment of the stretched film, the obtained dyeing film was washed with pure water at 10 占 폚, and the excess dyeing solution was washed away.

(5) Preparation of crosslinked film (step S4)

First, a crosslinking bath at 78 占 폚 (hereinafter referred to as crosslinking bath (1)) containing 9.0 parts by mass of boric acid per 100 parts by mass of water was prepared. Separately from the crosslinking bath 1, a crosslinking bath at 70 占 폚 (hereinafter referred to as crosslinking bath 2) containing 5.0 parts by mass of boric acid and 4.4 parts by mass of potassium iodide per 100 parts by mass of water was prepared. Subsequently, the dyed film prepared in (4) above was immersed in the crosslinking bath 1 for 180 seconds. Subsequently, the dyed film immersed in the crosslinking bath 1 was immersed in the crosslinking bath 2 for 90 seconds to obtain a crosslinked film.

(6) Cleaning and Drying of the Crosslinked Film

The crosslinked film prepared in the above (5) was immersed in pure water at 10 캜 for about 10 seconds, and immediately thereafter, the water adhering to the surface of the crosslinked film was removed by using an air blower. A crosslinked film was put in an oven at 65 캜 for 240 seconds to obtain a polarizing laminated film in which a polarizing film was laminated on the stretched substrate film.

(7) Production of a polarizing plate having a protective film (joining step, peeling step)

On the polarizing film in the polarizing laminated film produced in (6) above, a coating film composed of an ultraviolet curable adhesive (KR-75T, a cationic polymerizable curing compound manufactured by ADEKA Corporation) was formed. Through this coating film, a protective film (a transparent protective film made of cycloolefin resin ("Zeonoa (registered trademark)" having a thickness of 23 mu m made by Nippon Zeon Co., Ltd.) was bonded to the polarizing laminated film.

Subsequently, the coating film was cured by irradiating ultraviolet rays to the coating film using a high-pressure mercury lamp to obtain an adhesive layer, and a polarizing laminated film having a protective film was produced. Thereafter, the stretched base film was peeled off from the polarizing laminated film having the obtained protective film to obtain a polarizing plate having a one-side protective film.

Thereafter, a coating film was formed on the surface opposite to the protective film of the polarizing plate having the single-sided protective film by using the above-mentioned ultraviolet curable adhesive. The same protective film as the one side of the protective film was bonded to the polarizing plate having the one side surface protective film through the coating film.

Subsequently, the coated film was cured by irradiating ultraviolet rays to the coated film using a high-pressure mercury lamp to obtain an adhesive layer, and a polarizing plate having a double-side protective film was produced.

The polarizing plate having the obtained double-side protective film had 41.7% of Ty and a visual sensitivity correction degree of polarization Py of 99.995%. The inter-crystal distance Wa in the stretching direction (absorption axis direction) of the polarizing film was 16.4 nm. The inter-crystal distance Wb in the direction (transmission axis direction) perpendicular to the stretching direction of the polarizing film was 2.8 nm.

<Evaluation>

[Measurement of sting intensity]

The sticking strength of the polarizing film was determined by conducting the following piercing test. The results are shown in Table 1.

The sticking test was carried out in the same manner as in Test piece (from a polarizing laminated film) to a small desk tester ("EZ Test (registered trademark)" manufactured by Shimadzu Seisakusho Co., Ltd.) equipped with a sticking jig having a diameter of 1 mm and a radius of curvature of 0.5R Polarizing film on which a base film was peeled) was fixed. The measurement was conducted under the conditions of a temperature of 23 占 占 폚 and at a threshing speed of 0.33 cm / sec. The stab intensity measured in the stabbing test was the average of four stabbings excluding the top three and the bottom three of the strength of the test piece when it was torn in the direction of the transmission axis by performing a stab test on the ten test pieces. The average value was divided by the film thickness of the test piece to determine the stuck strength per unit film thickness.

[Measurement of orientation degree (WAXD)]

The degree of orientation of the polarizing film was determined by the through-angle method of Wide Angle X-ray Diffraction (WAXD). The results are shown in Table 1.

The same measurement sample as the SAXS measurement described above was used. The following X-ray diffraction apparatus was used to irradiate one surface of the measurement sample with X-rays from the direction perpendicular to the surface of the sample for measurement under the following X-ray output conditions, and the diffraction image in the transmission method was picked up .

X-ray diffractometer: &quot; NANO-Viewer &quot; manufactured by Rigaku Co.,

X-ray output conditions: Cu target, 40 kV, 20 mA

From the obtained diffraction image, an unmodified azimuth distribution curve (azimuth angle (beta angle) - intensity distribution curve) was calculated by annular integration in the range of 2? = 19.5 to 20.5 for a peak near the diffraction angle 2? . The uncorrected azimuth distribution curve refers to an azimuth distribution curve before background correction is performed.

Next, measurement was carried out under the same conditions except that the measurement sample was removed from the optical axis of the X-ray to calculate the background of the azimuth distribution curve. After the background is corrected for transmittance, the background is removed from the above-mentioned unmodified azimuth distribution curve to obtain an azimuth distribution curve after the background correction (hereinafter simply referred to as "azimuth distribution curve").

The peak in this azimuth distribution curve is an orientation peak. In this measurement, the MD of the sample for measurement was set in the vertical direction, and the angle of beta at the maximum intensity of the orientation peak appearing in the horizontal direction was 0 DEG. The? -Angle (0 ° and 180 °) at the maximum intensity of the orientation peak is derived from the MD oriented component of the polarizing film. From the obtained azimuth distribution curve, the degree of orientation was determined according to the following formula (C).

Orientation (%) = (360-W) / 360 ... (C)

In the formula (C), W is the sum of the total peak width at which the integral value becomes 50% when the integral value of the entire peak of the azimuth distribution curve is 100%, and the total peak width is obtained for all the orientation peaks. The center position (°) in the entire peak width agrees with the beta angle (°) in which the peak indicates the maximum intensity.

[Determination part, quantitative determination of constraint noncontiguous part and noncontact part (pulse NMR)]

The amounts of the crystalline portion A1 of the polarizing film, the confinement non-confinement portion A2 and the non-crystal portion A3 were determined by pulse NMR ( ¹ H), respectively. The results are shown in Table 1.

First, about 50 mg of the polarizing film cut to a size of about 5 mm x 5 mm was poured into an NMR tube together with 1 mL of heavy water, and immersed in heavy water. The NMR tube was heated in a hot water bath at 60 DEG C for 1 hour and then left at room temperature for 24 hours. The spin-spin relaxation time (T2) of the obtained sample was measured by using the pulsed NMR under the following conditions.

[Condition]

Pulse NMR apparatus: "minispec mq20" manufactured by Bruker BioSpin Co., Ltd.

Pulse series: Solid echo method

Pulse width: 2.8 μsec

Pulse repetition time: 1 second

Accumulation count: 256 times

Measuring temperature: 30 ° C

The free induction decay (FID) signal obtained by the pulse NMR measurement is fitted to the following equation (E) by the linear least squares method to obtain A1, A2, and A3 from the difference in relaxation time of each component, (%) Of the respective components with respect to the total (A1 + A2 + A3).

[Confirmation of occurrence of crack (heat shock test)]

First, the side of the protective film on one side of the polarizing plate having the double-sided protective film was corona treated. Next, a laminate having a pressure-sensitive adhesive between the pair of separate films was prepared, the separate film on one side of the laminate was peeled off, and the exposed pressure-sensitive adhesive was adhered to the corona-treated surface of the polarizing plate having the double- .

Next, a polarizing plate having a pressure-sensitive adhesive double-side protective film was cut from the side of the separate film using a super cutter (&quot; PNI-600 &quot; manufactured by Ogino Seiki Seisakusho Co., Ltd.) to obtain test pieces. The obtained test piece had a size of 120 mm in the stretching direction and 70 mm in the direction perpendicular to the stretching direction of the polarizing plate having a double-side protective film.

Next, the separator film was removed from the test piece, and the resultant was adhered to a glass plate ("Eagle XG" manufactured by Corning Incorporated) with a roller. The test piece on the glass plate was allowed to stand at -35 占 폚 for 30 minutes and then at 85 占 폚 for 30 minutes. A heat shock test (hereinafter referred to as HS test) was performed by repeating this operation for one cycle for 400 cycles on the test piece. Every 100 cycles, the appearance of the polarizing film in the test piece was confirmed by visual observation and using a digital microscope (&quot; VHX-500 &quot;, manufactured by Gibbs Co., Ltd.).

In the above test, it was judged NG when a crack of 1 mm or more occurred in the polarizing film in the test piece. On the other hand, when the polarizing film in the test piece did not crack at least 1 mm, it was judged OK. The results are shown in Table 1.

&Lt; Example 2 >

The same procedure as in Example 1 was carried out except that the moisture content in the drying step was adjusted as shown in Table 1 by adjusting the time for allowing hot air to flow. The moisture content of the PVA-based resin layer in the laminated film obtained in the step S12 was 0.35 mass%. In step S12 of Example 2, the removal rate V (30) was set in the range of 0.01 to 1.8 mass% / second. Also, the average removal rate Vave (30-10) was set in the range of 0.01 to 1.8 mass% / second. The thickness of the PVA resin layer was about 9.3 탆.

The obtained polarizing plate having a double-side protective film had 41.7% of Ty and 99.995% of Py. The inter-crystal distance Wa in the stretching direction (absorption axis direction) of the polarizing film was 16.1 nm. The inter-crystal distance Wb in the direction (transmission axis direction) perpendicular to the stretching direction of the polarizing film was 2.7 nm.

&Lt; Comparative Example 1 &

The same procedure as in Example 1 was carried out except that the moisture content in the drying step was adjusted as shown in Table 1 by adjusting the time for allowing hot air to flow. The moisture content of the PVA-based resin layer in the laminated film obtained in the step S12 was 0.14% by mass. In addition, in step S12 of Comparative Example 1, the removal rate V (30) was out of the range of 0.01 to 1.8 mass% / second. In addition, the average removal rate Vave (30-10) was out of the range of 0.01 to 1.8 mass% / second. The thickness of the PVA resin layer was about 9.3 탆.

The obtained polarizing plate having the double-side protective film had 41.5% of Ty and 99.997% of Py. The inter-crystal distance Wa in the stretching direction (absorption axis direction) of the polarizing film was 16.3 nm. The inter-crystal distance Wb in the direction (transmission axis direction) perpendicular to the stretching direction of the polarizing film was 2.7 nm.

[Table 1]

Table 1 shows the results of confirmation of the PVA crack at the stuck strength and the cold / heat impact test. The higher degree of orientation and the greater number of constraint fixes were good results in stab strength and PVA crack testing. From these results, it was confirmed that the polarizer was superior in strength to the case where the orientation degree was high and the amount of the constraint noncrystalline portion was large.

On the other hand, in the polarizing plate having the double-side protective film of Comparative Example 1 in which the degree of orientation was less than 81.0%, cracks were generated in the HS test.

In view of the above, the present invention has proved to be useful.

1, 2, 3: polarizer
5: polarizing film
10: protective film (protective film)
50: lamellar crystal (crystal of polyvinyl alcohol)
Wa: distance between crystals (absorption axis direction)
Wb: distance between crystals (transmission axis direction)

Claims (2)

As a polarizing film having a polyvinyl alcohol-based resin as a forming material and having a dichroic substance,
Wherein the orientation degree in the azimuthal distribution measured by a wide angle X-ray diffraction method is 81.0% or more. The method according to claim 1, characterized in that the ratio of the confinement non-confinement portion to the total of the crystal portion, the confinement non-confinement portion and the non-confinement portion obtained from the spin-spin relaxation time obtained by the pulse NMR ( ¹ H) is 40% .

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