TW201536528A - Manufacturing method of extended laminate body and extended laminate body, and method of manufacturing polarizing film and polarizing film - Google Patents

Abstract

To provide a method of manufacturing an extended laminate body of polarizing film capable of inhibiting the transmissivity variations. The manufacturing method of extended laminate body according to this invention comprises: a step of producing a laminate body by forming a polyvinyl alcohol-based resin layer on an elongated thermoplastic resin substrate; and a step of producing an extended laminate body by performing aerial extension while conveying the laminate body in the longitudinal direction. The polyvinyl alcohol-based resin layer of the extended laminate body has a thickness of 15[mu]m or less, and the polyvinyl alcohol-based resin layer has a difference between the maximum and minimum of front-side birefringence [Delta]nxy is 0.6*10<SP>-3</SP> or less in the width direction.

Description

Manufacturing method of extended laminated body and extended laminated body, and manufacturing method of polarizing film and polarizing film Field of invention

The present invention relates to a method for producing an extended laminate, an extended laminate obtained by the production method, a method for producing a polarizing film, and a polarizing film produced by the method.

Background of the invention

A liquid crystal display device of a representative image display device is often provided with a polarizing film on both sides of a unit cell due to an image forming method. In recent years, due to the expectation of film formation of a polarizing film, there has been proposed a method in which, for example, a laminate of a specific thermoplastic resin substrate and a polyvinyl alcohol-based resin layer is air-extended and dyed, and then subjected to an aqueous solution of boric acid. A method of obtaining a polarizing film by stretching (for example, JP-A-2012-73580). However, the polarizing film produced by such a manufacturing method has a case where the transmittance is uneven.

Summary of invention

According to an embodiment of the present invention, there can be provided a method for producing an extended laminate which can obtain a polarizing film having a suppressed penetration rate.

The method for producing an extended laminated body of the present invention comprises the steps of: forming a laminated body by forming a polyvinyl alcohol-based resin layer on a long-length thermoplastic resin substrate; and performing the air-extension while transporting the laminated body in the longitudinal direction And the steps of making an extended laminate. The thickness of the polyvinyl alcohol-based resin layer in the extended laminated body is 15 μm or less, and the difference between the maximum value and the minimum value of the birefringence Δn _xy in the front direction of the polyvinyl alcohol-based resin layer is 0.6 × 10 ^{-3 .} the following.

In one embodiment, the air extension includes a hot rolling extension step of extending the circumferential speed difference between the hot rolls, and the temperature difference in the width direction of the hot roll is 3 ° C or lower.

In one embodiment, the temperature of the hot roll is 120 ° C or higher.

In one embodiment, the heating of the hot roll is performed by passing a heat medium through a pipe in the hot roll, and includes passing a heat medium through a spiral pipe, and the spiral pipe is disposed inscribed in a peripheral portion of the roll. .

In one embodiment, the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium is 2 times/min or more.

According to another aspect of the invention, an extended laminate can be provided. The extended laminate can be produced by the above manufacturing method.

According to still another aspect of the present invention, a method of producing a polarizing film can be provided. The method for producing the polarizing film includes a step of dyeing the extended laminate.

In one embodiment, the method for producing the polarizing film further comprises extending the extended laminate in an aqueous boric acid solution after the dyeing step. The steps.

According to still another aspect of the present invention, a polarizing film can be provided. The polarizing film can be produced by the above-described production method and has a thickness of 10 μm or less.

According to the present invention, the birefringence Δn _xy of the polyvinyl alcohol (PVA)-based resin layer of the extended laminated body of the intermediate body of the thin (for example, 10 μm or less) polarizing film can be maximized and minimized in the width direction. The extended laminated body is produced in a manner of a difference of 0.6 × 10 ^-3 or less, whereby the variation in the transmittance of the extended laminated body after dyeing can be suppressed. As a result, the variation in the transmittance of the obtained polarizing film can be suppressed. In one embodiment, the difference in the width direction of the birefringence Δn _xy (the difference between the maximum value and the minimum value in the width direction) can be adjusted by setting the temperature variation in the width direction of the hot roll used in the air to a predetermined value or less. control.

1, 2‧‧‧ rolls

9‧‧‧ oven

10‧‧‧Layer

10’‧‧‧Extended laminate

11‧‧‧ thermoplastic resin substrate

11'‧‧‧Resin substrate

12‧‧‧Polyvinyl alcohol (PVA) resin layer

12'‧‧‧ polarizing film

13‧‧‧Adhesive layer

14‧‧‧Parts

15‧‧‧ adhesive layer

16‧‧‧Optical functional film

16'‧‧‧2nd optical functional film

100‧‧‧Optical film laminate

101‧‧‧Spiral Department

110‧‧‧ boric acid aqueous bath

111, 112‧‧‧ rolls

120‧‧‧Aqueous bath of dichroic substance (iodine) and potassium iodide

121, 122‧‧‧ rolls

130‧‧‧Aqueous bath of boric acid and potassium iodide

131, 132‧‧‧ rolls

140‧‧‧ boric acid aqueous bath

141, 142‧‧‧ rolls

150‧‧‧ bath of potassium iodide solution

151, 152‧‧‧ rolls

160‧‧‧Winding Department

200‧‧‧Optical functional film laminate

300‧‧‧Optical functional film laminate

400‧‧‧Optical functional film laminate

Fig. 1 is a partial cross-sectional view showing a laminated body used in a method for producing an extended laminated body according to an embodiment of the present invention.

Fig. 2 is a schematic view showing an example of a block extending step in the method for producing an extended laminated body according to an embodiment of the present invention.

Fig. 3 is a schematic view showing an example of a hot rolling extension step in the method for producing an extended laminated body according to an embodiment of the present invention.

Fig. 4A is a schematic view showing an example of means for controlling the temperature variation in the width direction of the hot roll in the hot rolling extending step.

Fig. 4B is a schematic view showing another example of means for controlling the temperature variation in the width direction of the hot roll in the hot rolling extending step.

Fig. 5 is a schematic view showing an example of a method for producing a polarizing film of the present invention.

Fig. 6 is a schematic cross-sectional view showing an optical film laminate using a polarizing film obtained by the production method of the present invention, and Fig. 6B is a schematic cross-sectional view showing an optical functional film laminate using the polarizing film.

In Fig. 7, Fig. 7A and Fig. 7B are schematic cross-sectional views showing an optical function film laminate in another embodiment using a polarizing film obtained by the production method of the present invention.

Form for implementing the invention

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited by the embodiments.

A. Manufacturing method of extended laminated body

The method for producing an extended laminate of the present invention comprises the steps of: forming a layered body on a long-shaped thermoplastic resin substrate to form a layered body; and transporting the layered body in the longitudinal direction The step of extending to make an extended laminate. Hereinafter, each step will be described.

A-1. Steps for making a laminate

Fig. 1 is a partial cross-sectional view showing a laminated body which can be used in a method for producing an extended laminated body according to an embodiment of the present invention. The laminated body 10 has a thermoplastic resin base material 11 and a polyvinyl alcohol (PVA)-based resin layer 12. The laminated body 10 can be produced by forming the PVA-based resin layer 12 on a long thermoplastic resin substrate. As a method of forming the PVA-based resin layer 12, any appropriate method can be employed. It is preferable to apply a PVA-based resin to the PVA-based resin substrate 11 The coating liquid is dried and formed to form the PVA-based resin layer 12.

As the material for forming the thermoplastic resin substrate, any appropriate thermoplastic resin can be used. Examples of the thermoplastic resin include an ester resin such as a polyethylene terephthalate resin, a cycloolefin resin such as a norbornene resin, an olefin resin such as polypropylene, a polyamine resin, and a poly A carbonate resin, a copolymer resin or the like. Among these, it is desirable to reduce the terpene-based resin or the amorphous polyethylene terephthalate resin.

In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is suitably used. Among them, an amorphous (hard to crystallize) polyethylene terephthalate resin is particularly suitable. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer containing isophthalic acid as a dicarboxylic acid and copolymerization of cyclohexane dimethanol as a glycol. Things.

The thickness of the thermoplastic resin substrate before stretching is preferably from 20 μm to 300 μm, more preferably from 50 μm to 200 μm. If it is less than 20 μm, it is difficult to form a PVA-based resin layer. If it exceeds 300 μm, there is a need for a large load for the extension.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 170 ° C or lower, more preferably 120 ° C or lower, more preferably 80 ° C or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is desirably 60 ° C or higher. Further, the glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

The thermoplastic resin substrate can be extended in advance (before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin substrate is stretched in the lateral direction. The transverse ideal is the extension of the laminated body described later. The direction in which the directions are orthogonal. However, in the present specification, "orthogonal" also includes the case of being substantially orthogonal. Here, "substantially orthogonal" includes 90° ± 5.0°, desirably 90° ± 3.0°, more desirably 90° ± 1.0°.

The elongation temperature of the thermoplastic resin substrate is desirably from Tg - 10 ° C to Tg + 50 ° C with respect to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin substrate is desirably 1.5 times to 3.0 times.

As a method of extending the thermoplastic resin substrate, any appropriate method can be employed. Specifically, it may be a fixed end extension or a free end extension. The extension mode can be dry or wet. The extension of the thermoplastic resin substrate can be carried out in one stage or in multiple stages. When the multi-stage is performed, the above stretching ratio is the product of the stretching ratio of each stage.

As the PVA-based resin forming the PVA-based resin layer, any appropriate resin can be used. For example, polyvinyl alcohol, ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually from 85 mol% to 100 mol%, preferably from 95.0 mol% to 99.95 mol%, more preferably from 99.0 mol% to 99.93 mol%. The degree of saponification can be determined in accordance with JIS K 6726-1994. By using such a saponification degree PVA-based resin, a polarizing film excellent in durability can be obtained. When the degree of saponification is too high, there is a gelatinization.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually from 1000 to 10,000, preferably from 1200 to 4500, and more preferably from 1,500 to 4,300. However, the average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

The coating liquid is typically a solution in which a solvent of the above PVA resin is dissolved in a solvent. Examples of the solvent include polyols such as water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and trimethylolpropane. An amine such as ethylene diamine or diethylene triamine. These may be used alone or in combination of two or more. In these, water is ideal. The PVA-based resin concentration of the solution is preferably from 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. As long as it is such a resin concentration, a uniform coating film adhered to the thermoplastic resin substrate can be formed.

The additive may also be blended in the coating liquid. As the additive, a plasticizer, a surfactant, or the like can be mentioned. The plasticizer may, for example, be a polyol such as ethylene glycol or glycerin. As the surfactant, a nonionic surfactant can be mentioned. These can be used for the purpose of further improving the uniformity, dyeability and extensibility of the obtained PVA-based resin layer.

The coating method of the coating liquid can be any appropriate method. For example, roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (corner coating, etc.).

The drying temperature of the coating liquid is preferably 50 ° C or higher.

The thickness of the PVA-based resin layer before stretching is preferably from 3 μm to 25 μm, more preferably from 5 μm to 20 μm.

The thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment or the like) before the formation of the PVA-based resin layer, or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such a treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

Although not shown, it may be in the shape of the thermoplastic resin substrate 11 Any suitable functional layer is formed on the side of the PVA-based resin layer 12. In a preferred embodiment, the functional layer has heat resistance. By providing heat resistance, for example, even if a temperature higher than the glass transition temperature of the thermoplastic resin substrate is applied to the laminate in the hot rolling extension step described later, the laminate (thermoplastic resin substrate) can be prevented from adhering to the heat. Rolls for excellent anti-caking properties.

The functional layer may be, for example, an antistatic layer containing a conductive material and a binder resin. With such a configuration, excellent anti-caking property can be achieved, and manufacturing efficiency can be improved. Also, it has excellent antistatic properties. As the antistatic layer, any appropriate configuration can be employed. As a representative example of the conductive material, a polythiophene-based polymer (for example, polyethylene dioxythiophene) can be mentioned. For the binder resin, for example, a resin which has both adhesion to the thermoplastic resin substrate and flexibility and which can be dissolved or dispersed in an aqueous solvent can be used. As a specific example, a polyurethane resin can be mentioned. The thickness of the antistatic layer is desirably 0.1 μm to 10 μm. The surface resistance value of the antistatic layer is desirably less than 10 × 10 ¹³ Ω / □. The surface arithmetic mean roughness Ra of the antistatic layer is desirably 10 nm to 100 nm.

A-2. Aerial extension steps

The aerial stretching step includes a hot rolling extending step of extending the laminated body toward the longitudinal direction thereof by the circumferential speed difference between the hot rolling rolls. The aerial extension step represents a step of extending the block and a step of hot rolling. However, the order of the block extension step and the hot rolling extension step is not limited, and the block extension step may be performed first, or the hot rolling extension step may be performed first. The block extension step can also be omitted. In one embodiment, the block extension step and the hot rolling extension step are sequentially performed. The following describes the embodiment The block extension step and the hot rolling extension step are followed by a description of the features of the overall air extension step.

A-2-1. Block extension step

In the block extending step, two rolls are separated and a heating block is disposed between the two rolls, and the laminated body is extended in the heating block. Fig. 2 is a schematic view showing an example of a step of extending a block, (a) is a view seen from the front, and (b) is a view seen from above. In the illustrated example, the pair of rolls 1, 1 and the pair of rolls 2, 2 are provided at a predetermined interval in the conveying direction (MD) of the laminated body, and the laminated body 10 is held by each pair of rolls. The roll 1 and the roll 2 are rotated at different peripheral speeds, and the peripheral speed of the roll 2 on the downstream side is set to be larger than the roll 1 on the upstream side.

Any suitable means can be employed for the heating block (heating means) provided between the above two rolls. In the illustrated example, an oven 9 is provided between the roll 1 and the roll 2. The extension temperature is below 100 ° C, and is desirably below 95 ° C. On the other hand, the stretching temperature is desirably above 70 °C. Further, the extension temperature (temperature of the laminate) in the block extension step can be confirmed, for example, by using a sticker for temperature measurement or a thermocouple.

Roll 1 and roll 2 is set to be based (instant before the block extends) W ₁ over the distance L and a width extending between the laminate L to satisfy the relation _{1 /W≧0.3,} and more desirably satisfy 0.4 ≦ L ₁ / W ≦2.0 relationship. By satisfying this relationship, a free end extension can be achieved. Free end extension generally refers to an extension method that extends only in one direction. When the laminated body is extended in a certain direction, the laminated body is shrunk in a direction orthogonal to the extending direction, and the method of extending without suppressing the shrinkage is referred to as a free end extension. However, in the present specification, the "inter-stretch distance" is a distance at which an additional tension can be maintained by the circumferential speed difference between the rolls. Further, it is also possible to maintain the distance heated to the predetermined extension temperature. For example, in the illustrated example, the length in the conveying direction of the oven 9 corresponds to the inter-stretch distance L ₁ .

The width W of the laminate is 500 mm to 6000 mm, and preferably 1000 mm to 5000 mm.

The stretching ratio of the block extension is preferably 1.1 times to 3.0 times, and preferably 1.3 times to 2.0 times, relative to the original length of the laminated body.

As described above, by performing the free end extension at a predetermined temperature, shrinkage can be suppressed and the alignment of the PVA-based resin can be simultaneously improved. By improving the alignment of the PVA-based resin, the orientation of the PVA-based resin can be improved even after extending in boric acid water in the method for producing a polarizing film described later. Specifically, it is presumed that the orientation of the PVA-based resin is increased in advance by this step, and the PVA-based resin and the boric acid are easily cross-linked when the boric acid is extended in water, and the boronic acid is extended in a state in which the boric acid is in a node, thereby extending the PVA in the boric acid water. The alignment of the resin is also improved. Thus, a polarizing film having excellent optical characteristics can be produced.

A-2-2. Hot rolling extension step

In the hot rolling extending step, a plurality of (representing at least three) hot rolling rolls which are individually temperature controllable are used, and the hot rolling rolls are arranged in series along the conveying direction of the laminated body 10. The laminated body 10 which is in contact with the hot rolling rolls is conveyed by rotation of a plurality of hot rolling rolls, and at the same time, the laminated body 10 is extended by the peripheral speed difference of the plurality of hot rolling rolls. Fig. 3 is a schematic view showing an example of a hot rolling extension step. In the example of the figure, the first roll R1 to the seventh roll which can individually perform temperature control The R7 is provided at a predetermined interval along the conveying direction. The surfaces of the rolls R1 to R7 are subjected to a surface treatment (for example, a plating treatment) for the purpose of preventing adhesion of the laminate. In the example of the drawing, the laminated body 10 is in contact with one side (for example, the PVA-based resin layer 12 side) and the odd-numbered rolls (the first roll R1, the third roll R3, the fifth roll R5, and the seventh roll R7). The other surface (for example, the side of the thermoplastic resin base material 11) is conveyed in contact with the even-numbered rolls (the second roll R2, the fourth roll R4, and the sixth roll R6). Each of the first roll R1 to the fifth roll R5 can be heated to a predetermined temperature to be a hot roll, and the laminated body 10 can be heated from the upper side and the lower side.

The temperature of the hot roll is desirably 120 ° C or higher, and preferably 125 ° C to 150 ° C. By heating the laminate at this temperature, the crystallinity of the PVA resin can be improved. Further, by combining the block extensions according to the demand, the crystallinity of the PVA resin can be further improved. By increasing the crystallinity, the PVA-based resin layer can be prevented from being dissolved in water in the water extension described later, and the alignment property is lowered. Thus, a polarizing film having excellent optical characteristics can be produced.

The temperatures of the individual hot rolls may be the same or different. In one embodiment, the temperatures of the hot rolls are all the same. In other embodiments, the temperature of the hot roll may be set to gradually increase from the upstream side toward the intermediate portion and gradually decrease from the intermediate portion toward the downstream side. In the illustrated example, the sixth and seventh rolls R6 and R7 are set to any appropriate temperature, and for example, the laminated body can be cooled by setting the glass transition temperature (Tg) of the laminate. By performing cooling in this manner, it is possible to suppress the occurrence of scars in the laminated body (for example, in a state in which the fluctuation is in a zigzag shape). The temperature of the cooling roll is, for example, 30 ° C to 50 ° C. The ambient temperature (ambient temperature of the hot rolling extension zone) in the hot rolling extension step is, for example, 40 ° C to 60 ° C.

In the example of the figure, seven rolls are used, but it is needless to say that various conditions such as the total number of rolls used, the number of hot rolls and/or chill rolls, the order of hot rolls and/or chill rolls, etc. may be appropriate. change.

In the hot rolling extension step, tension is applied to the laminated body 10 by the circumferential speed difference between the adjacent rolls among the roll groups R1 to R7, and the laminated body 10 is uniaxially extended in the longitudinal direction. More specifically, the elongation is performed by increasing the peripheral speed of the rolls closer to the downstream side. In the hot rolling extension step, for example, the ideal layer is further extended by 1.1 times to 3.0 times by a layer extending 1.2 times to 1.5 times.

A-2-3. Overall flight steps

The stretching ratio by the air extension (hot rolling extension and block extension) is preferably 1.5 times to 4.0 times, and preferably 1.8 times to 3.0 times, relative to the original length of the laminated body. The extension ratio using the air extension is the product of the extension ratio of the block extension and the extension ratio using the hot rolling extension. In the case where the air extension is only for the hot rolling extension, the stretching ratio of the hot rolling extension is within the range as described above.

In the present invention, the difference between the maximum value and the minimum value of the birefringence Δn _xy in the front direction of the PVA-based resin layer in the obtained laminated body in the width direction (hereinafter also referred to as the deviation of birefringence) is 0.6 × It is preferably 10 ^-3 or less, and is preferably in the range of 0.4 × 10 ^-3 or less, more preferably 0.2 × 10 ^-3 or less. Further, the birefringence Δn _xy is obtained by the equation: Δn _xy = n _{x -} n _y . Here, n _x is a refractive index in a direction in which the in-plane refractive index is the maximum value (that is, in the slow axis direction), and n _y is a refractive index in a direction orthogonal to the slow axis in the plane.

By controlling the variation of birefringence to the above range, the transmittance of the polarizing film obtained by using the extended laminated body can be significantly controlled (representatively The difference in the yuan penetration rate). In other words, if the birefringence of the PVA-based resin layer is changed, the crystal state of the PVA-based resin changes, and the dyeability in the dyeing step described later also changes (specifically, Δn becomes large, and dyeability is lowered) . As a result, the birefringence in the width direction of the PVA-based resin layer is largely different, and the transmittance of the obtained polarizing film in the width direction is increased. Therefore, by controlling the variation of birefringence to be lower than a predetermined value, the variation in the transmittance of the polarizing film can be remarkably suppressed. The details will be described below.

The display unevenness is recognized due to the difference in luminance of the liquid crystal display device. Conversely, as long as the luminance difference is below a predetermined value, the visual person cannot recognize the display unevenness. Here, it is known that if the luminance difference ΔL* is x and the display unevenness is y, the relationship can be approximated by the first-order function of the following formula (1) (Tokyo Institute of Technology, 2000 Ph.D. Thesis, No. 4798) No. "Research on the evaluation method of glass quality based on vision", Yu Zexin).

y=2.75x−1.54 (1) From the point of the formula (1), when x (that is, ΔL*) is less than 0.56, y=0, it can be said that the display unevenness cannot be visually observed. Here, when the polarizing plates 2 are arranged in parallel with each other, the luminance L* of the liquid crystal display device is represented by L* _// , and the characteristics of the polarizing plate are the cell transmittance (when the polarizing plate is one piece) Transmittance) Y value: Ts. The unit transmittance of the polarizing plate is changed over a wide range to investigate the correlation between L* _// and Ts. As a result, it is confirmed that the luminance difference ΔL* _{// is} different from the unit transmittance ΔTs by the equation (2). Function representation.

ΔL* _// =1.289×ΔTs (2) It can be seen from the equation (2) that in order to make the luminance difference L* _// (corresponding to L*) lower than 0.56 which becomes a threshold which cannot be visually recognized due to display unevenness, Let ΔTs be lower than 0.43.

On the other hand, the present inventors have found that in the extended laminate for producing a thin (for example, 10 μm or less) polarizing film, the transmittance of the polarizing film may be changed by the birefringence of the PVA-based resin layer, and As a result of the trial and error of the experiment, it was confirmed that there is a correlation relationship between the parameter of the birefringence Δn _xy of the PVA-based resin layer and the parameter ΔTs of the cell transmittance.

ΔTs = 9.53 × 10 ^-5 × (difference of Δn _xy ) ² + 117 × (difference of Δn _xy ) (3) From the viewpoint of the formula (3), the birefringence of the PVA-based resin layer in the obtained extended laminated body When the variation of Δn _xy is in the range of 0.6 × 10 ^-3 or less, the ΔTs can be made 0.43 or less, and as a result, the display unevenness can be prevented from being visually observed.

Further, the inventors of the present invention have found that the above-described desired birefringence unevenness can be achieved in the PVA-based resin layer of the obtained extended laminated body by specifically controlling the conditions of hot rolling elongation in the air extending step. Specifically, the above-described desired birefringence unevenness can be achieved by controlling the temperature variation in the width direction of the hot roll (the difference between the maximum value and the minimum value of the temperature in the width direction). In more detail, as a result of experimental trial and error, it was found that there is a correlation between the temperature difference in the width direction of the hot roll and the birefringence Δn _xy as in the following formula (4).

(The temperature difference in the width direction of the hot roll) = 2770 × {1000 × (the difference of Δn _xy ) ² + (the difference of Δn _xy )} (4) Using the formula (4), the width direction of the hot roll can be controlled. When the temperature is uneven, the difference in the birefringence Δn _xy of the PVA-based resin layer of the obtained stretched laminate is 0.6 × 10 ^-3 or less. Specifically, the temperature variation in the width direction of the hot roll is desirably 3 ° C or less, preferably 2 ° C or less, more preferably 1.5 ° C or less, particularly preferably 1 ° C or less, and most preferably 0.5 ° C or less.

In the means for controlling the temperature variation in the width direction of the hot roll, the circulation path of the heat medium (oil) for heating the rolls is appropriately set, and the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium is appropriately set. (heat medium flow rate / volume of heat medium in the hot roll), and combinations thereof. The circulation path of the heat medium can be configured as shown in Figs. 4A and 4B. The configuration of Fig. 4A is such that a linear pipe is provided in the roll, the heat medium is circulated through the pipe, and the heat medium in the roll is circulated by the pressure caused by the flow. In the configuration of Fig. 4B, a spiral pipe is provided so as to be continuous with the straight pipe of Fig. 4A and attached to the inner circumference of the roll, and the heat medium is circulated through the spiral pipe. It is preferable to constitute the structure as shown in Fig. 4B. Because of the more precise temperature control. 4B, in order to facilitate observation, the spiral piping is described as being located away from the outer peripheral portion of the roll (that is, inside) and is described as being spaced apart by a spiral interval. However, the spiral piping is actually disposed inscribed in the outer circumference of the roll. And set to reduce the spiral spacing as much as possible (as far as possible, there is no gap formed between the spirals). In addition, although not shown in FIG. 4B, the spiral piping discharges the heat medium from the end portion in the width direction of the roll to the outside (the discharged heat medium is circulated by the heat source and returned from the illustrated straight pipe to the inside of the roll). Further, the linear pipe and the spiral pipe may be continuously formed as shown in FIG. 4B, and the linear pipe and the spiral pipe may be formed as individual members (not shown). When the linear pipe and the spiral pipe are each configured as an individual, an opening is provided in a predetermined portion of the spiral pipe, and the linear pipe and the spiral pipe may be connected to each other. The ratio of the volume of the heat medium to the flow rate of the heat medium in the hot roll (the heat medium flow rate/the volume of the heat medium in the hot roll) is preferably 2 times/min or more, more preferably 2 times/minute to 20 times/minute, more preferably 2 times / minute ~ 10 times / minute. And, in the hot roll The heat medium volume refers to the total volume of the heat medium (the unit in the present embodiment is liter) in the flowing hot roll (the piping existing in the hot roll). For example, when the temperature of the hot roll is set to 130 ° C, a spiral pipe as shown in FIG. 4B is provided, so that the temperature of the heat medium becomes 130 ° C and the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium is 10 times. /min, the temperature variation in the width direction of the hot roll can be extremely precisely controlled at about 0.1 °C.

B. Extended laminated body

The extended laminate of the embodiment of the present invention can be obtained by the production method described in the above item A. The extended laminated body is preferably extended from 1.5 times to 4.0 times, and more preferably from 1.8 times to 3.0 times, with respect to the original length of the laminated body as described in the above-mentioned A-2-2 for the stretching ratio of the air extending. By using the extended laminated body obtained by the manufacturing method described in the above item A, for example, the laminated body which has not been extended in the air is extended only by the water which will be described later, and finally, a high stretching ratio can be attained. Specifically, the thermoplastic resin substrate on which the laminate is stretched is stretched while suppressing the alignment. The higher the orientation, the greater the extension tension, the more difficult it is to perform a stable extension or the breaking of the resin substrate, but by the inhibition of the alignment, a higher stretching ratio can be achieved. Thus, a polarizing film having excellent optical characteristics (for example, a degree of polarization) can be produced.

The birefringence Δn _xy in the front direction of the PVA-based resin layer of the laminated body is in the range of 0.6 × 10 ^-3 or less, preferably 0.4 × 10 ^-3 or less, more preferably 0.2 × 10 ^-3 or less in the width direction. . The lower limit of the difference of the birefringence Δn _{xy is} , for example, 0.1 × 10 ^-3 . As long as the birefringence parameter is within this range, as described above, the variation in the transmittance (representing the cell transmittance) of the polarizing film obtained by the extension layering method can be remarkably suppressed.

The thickness of the PVA-based resin layer of the extended laminated body represents the thickness of the polarizing film obtained by the above-mentioned system to a thickness of 10 μm or less. Specifically, the thickness of the PVA-based resin layer of the extended laminated body is 15 μm or less, and preferably 5 μm to 10 μm. According to the present invention, a remarkable effect is exhibited in such a very thin PVA-based resin layer (finally, a polarizing film).

C. How to use

The extended laminate described in the above item B is representative of the manufacture of the polarizing film. Specifically, the extended laminated body can be suitably subjected to a treatment for forming a PVA-based resin layer into a polarizing film. The treatment for forming the polarizing film includes, for example, elongation treatment, dyeing treatment, insolubilization treatment, crosslinking treatment, washing treatment, drying treatment, and the like. However, the number, order, and the like of the processes are not particularly limited.

C-1. Water extension

In a preferred embodiment, the extended laminate is extended in water (extension in boric acid water). Specifically, the water is extended in a direction parallel to the extending direction of the laminated body. By extending in water, it is possible to extend at a temperature lower than the glass transition temperature (represented by about 80 ° C) of the resin substrate and the PVA-based resin layer, and the PVA-based resin layer can be prevented from being crystallized while being oxidized. Extend at high magnification. Thus, a polarizing film having excellent optical characteristics (for example, a degree of polarization) can be produced. In the present specification, the "parallel direction" includes 0 ° ± 5.0 °, and is preferably 0 ° ± 3.0 °, more preferably 0 ° ± 1.0 °.

The extension method of the extended laminated body may employ any appropriate method. Specifically, it may be a fixed end extension or a free end extension. The extending direction of the extended laminated body is substantially the extending direction (longitudinal direction) of the above-described aerial extension. The extension of the extended laminate can be carried out in one stage or in multiple stages.

The extension in water is ideally carried out by immersing the extended laminate in an aqueous solution of boric acid (extension in boric acid water). By using an aqueous boric acid solution as an extension bath, the PVA-based resin layer can be imparted with rigidity to withstand the tension applied during stretching and water resistance to water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and the film can be favorably stretched to produce a polarizing film having excellent optical characteristics (for example, a degree of polarization).

The aqueous boric acid solution is preferably obtained by dissolving boric acid and/or borate in water of a solvent. The boric acid concentration is desirably from 1 part by weight to 10 parts by weight per 100 parts by weight of water. When the concentration of the boric acid is 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having a high characteristic can be produced. Further, in addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal or glutaraldehyde in a solvent may be used.

When a dichroic substance (representatively, iodine) is adsorbed to the PVA-based resin layer in advance by the dyeing treatment described later, the iodide is preferably blended in the stretching bath (boric acid aqueous solution). By mixing the iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. In the case of iodide, there may be mentioned potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, titanium iodide. Wait. Among these, potassium iodide is desirable. The concentration of the iodide is preferably from 0.05 part by weight to 15 parts by weight, more preferably from 0.5 part by weight to 8 parts by weight, per 100 parts by weight of water.

The extension temperature in the water extension (liquid temperature of the extension bath) is preferably from 40 ° C to 85 ° C, preferably from 50 ° C to 85 ° C. At this temperature, it is possible to suppress the dissolution of the PVA-based resin layer while performing high-rate stretching. specific As described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ° C or more from the relationship with the PVA resin layer. At this time, once the elongation temperature is lower than 40 ° C, even if plasticization of the thermoplastic resin substrate using water is considered, there is still a problem that the elongation cannot be performed well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and the inability to obtain excellent optical characteristics. The immersion time of the extended laminate in the extension bath is preferably from 15 seconds to 5 minutes.

By combining the above thermoplastic resin substrate with water extension (boric acid water extension), high-magnification stretching can be performed and a polarizing film having excellent optical characteristics (for example, polarization degree) can be produced. Specifically, the maximum stretching ratio is preferably 5.0 times or more, more preferably 5.5 times or more, and more preferably 6.0 times or more with respect to the original length of the laminated body (the stretching ratio of the extended laminated body). In the present specification, the "maximum stretching ratio" is the value of the stretching ratio before the breaking of the laminated layer, and the value of the stretching ratio of the extended laminated body is further reduced by 0.2. However, the maximum stretching ratio of the laminate using the above thermoplastic resin substrate may be such that the person extending through the water is higher than the one extending only in the air.

C-2. Other

The above dyeing treatment represents a treatment in which a PVA-based resin layer is dyed with a dichroic substance. It is desirable to carry out the adsorption of the dichroic substance to the PVA-based resin layer. The adsorption method includes, for example, a method of immersing a PVA-based resin layer (extended laminate) in a dye solution containing a dichroic material, a method of applying the dye solution to a PVA-based resin layer, and spraying the dye solution to A method of a PVA-based resin layer or the like. Ideally, the extended laminate is immersed in a dye containing a dichroic substance. Liquid method. Because of the good adsorption of dichroic substances.

The dichroic substance may, for example, be iodine or a dichroic dye. Ideal for iodine. When iodine is used as the dichroic substance, the above dyeing liquid is an aqueous iodine solution. The blending amount of iodine is preferably from 0.1 part by weight to 0.5 part by weight based on 100 parts by weight of water. In order to increase the solubility of iodine relative to water, it is preferred to incorporate iodide in an aqueous iodine solution. Specific examples of the iodide are as described above. The amount of the iodide blended is preferably from 0.02 part by weight to 20 parts by weight, more preferably from 0.1 part by weight to 10 parts by weight, even more preferably from 0.7 part by weight to 3.5 parts by weight, per 100 parts by weight of water. In order to suppress the dissolution of the PVA-based resin, the liquid temperature of the dyeing liquid at the time of dyeing is preferably from 20 ° C to 50 ° C. When the PVA-based resin layer is immersed in the dyeing liquid, the immersion time is preferably 5 seconds to 5 minutes in order to secure the transmittance of the PVA-based resin layer. Further, the dyeing conditions (concentration, liquid temperature, immersion time) can be set such that the degree of polarization or the cell transmittance of the polarizing film finally obtained is within a predetermined range. In one embodiment, the immersion time is set such that the degree of polarization of the obtained polarizing film is 99.98% or more. In another embodiment, the immersion time is set such that the unit transmittance of the obtained polarizing film is 40% to 44%.

Ideally, the dyeing treatment is preferably carried out before the extension of the above water.

The above insolubilization treatment is performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Water resistance can be imparted to the PVA-based resin layer by performing insolubilization treatment. The concentration of the aqueous boric acid solution is desirably from 1 part by weight to 4 parts by weight based on 100 parts by weight of water. The liquid temperature of the insolubilizing bath (aqueous boric acid solution) is desirably 20 ° C to 50 ° C. Ideally, the insolubilization treatment is preferably carried out before the above water extension or the above dyeing treatment.

The above cross-linking treatment represents the upper layer by dipping the PVA-based resin layer The stain is applied to an aqueous solution of boric acid. Water resistance can be imparted to the PVA-based resin layer by performing the crosslinking treatment. The concentration of the aqueous boric acid solution is desirably from 1 part by weight to 4 parts by weight based on 100 parts by weight of water. Further, when the crosslinking treatment is carried out after the above dyeing treatment, it is preferred to further incorporate an iodide. By mixing the iodide, iodine elution which has been adsorbed to the PVA-based resin layer can be suppressed. The blending amount of the iodide is preferably from 1 part by weight to 5 parts by weight per 100 parts by weight of the water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is desirably 20 ° C to 50 ° C. Ideally, the crosslinking treatment is preferably carried out before the extension of the above water. In a preferred embodiment, dyeing, cross-linking, and water extension are preferred.

The above washing treatment is performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide. The drying temperature in the above drying treatment is desirably from 30 ° C to 100 ° C.

Fig. 5 is a schematic view showing an example of a method of producing a polarizing film. The extended laminated body 10' is unscrewed from the unwinding portion 101, immersed in the boric acid aqueous solution bath 110 by the rolls 111 and 112 (insolubilization treatment), and immersed in the dichroic substance (iodine) and potassium iodide by the rolls 121 and 122. In the aqueous bath 120 (dyeing treatment). Then, the rolls 131 and 132 are immersed in the aqueous bath 130 of boric acid and potassium iodide (crosslinking treatment). Then, the extended laminated body 10' is immersed in the boric acid aqueous solution bath 140, and simultaneously stretched in the longitudinal direction (longitudinal direction) by the rolls 141 and 142 having different speed ratios (water extending). The extended laminated body 10' extended in water is immersed in the potassium iodide aqueous solution bath 150 by the rolls 151 and 152 (washing treatment), and then subjected to a drying treatment (not shown). Thereafter, the extended laminated body 10' is taken up by the winding unit 160.

C. Polarizing film

As described above, by performing the above respective treatments on the extended laminate of the present invention, a polarizing film can be formed on the resin substrate. The polarizing film is substantially a PVA-based resin film in which a dichroic substance is adsorbed and aligned. The thickness of the polarizing film is preferably 10 μm or less, more preferably 7 μm or less, and still more preferably 5 μm or less. On the other hand, the thickness of the polarizing film is preferably 0.5 μm or more, and more preferably 1.5 μm or more. The polarizing film desirably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The unit transmittance of the polarizing film is desirably 40.0% or more, more preferably 41.0% or more, and still more desirably 42.0% or more. The degree of polarization of the polarizing film is preferably 99.8% or more, more preferably 99.9% or more, still more preferably 99.95% or more.

As a method of using the above polarizing film, any appropriate method can be employed. Specifically, it may be used in a state of being integrated with the resin substrate, or may be used by transferring the resin substrate to another member.

D. Optical film laminate and optical functional film laminate

The above polarizing film can be used for an optical film laminate and/or an optical functional film laminate. 6A is a schematic cross-sectional view of an optical film laminate using a polarizing film, and FIG. 6B is a schematic cross-sectional view of an optical functional film laminate using a polarizing film. The optical film laminate 100 has a resin substrate 11', a polarizing film 12', an adhesive layer 13, and a spacer 14 in this order. The optical functional film laminate 200 sequentially includes a resin substrate 11', a polarizing film 12', an adhesive layer 15, an optical functional film 16, an adhesive layer 13, and a spacer 14. In the above embodiments, the resin substrate is not peeled off from the obtained polarizing film 12' and used as an optical member. The resin substrate 11' is protected, for example, as a polarizing film 12'. The membrane functions.

7A and 7B are schematic cross-sectional views showing an optical functional film laminate of another embodiment. The optical functional film laminate 300 has a spacer 14, an adhesive layer 13, a polarizing film 12', an adhesive layer 15, and an optical functional film 16, in this order. In the optical function film laminate 400, the optical function film laminate 300 is added, and the second optical function film 16' is provided between the polarizer film 12' and the spacer 14 with the adhesive layer 13. In these embodiments, the resin substrate has been removed.

The laminate of the respective layers constituting the optical film laminate or the optical functional film laminate is not limited to the illustrated examples, and any appropriate adhesive layer or adhesive layer can be used. The adhesive layer is representative of an acrylic adhesive. Subsequent to the agent layer, a vinyl alcohol-based adhesive can be formed. The optical functional film functions as a polarizing film protective film, a retardation film, or the like, for example.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the examples. Further, the measurement method of each characteristic is as follows.

(1) Thickness

The measurement was performed using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C") for the laminated system. The PVA-based resin layer of the extended laminated body was measured at an interval of 100 mm in the width direction of the extended laminated body using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD3000").

(2) Glass transition temperature (Tg)

The measurement was carried out in accordance with JIS K 7121.

(3) Roll temperature variation

The measurement was carried out using a contact thermometer at intervals of 100 mm along the width direction of the rolls. Let the difference between the maximum value and the minimum value of the measured value be a difference.

(4) Birefringence staggered

The PVA-based resin layer was transferred to the adhesive glass having no phase difference by the above-mentioned (1) thickness measurement, and the front phase difference was measured using KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd. The obtained front surface retardation value was divided by the thickness of the PVA-based resin layer obtained in the above (1) to calculate birefringence. Let the difference between the maximum and minimum values of the calculated birefringence be staggered.

(5) The unit penetration rate is uneven

The cell transmittance Ts of the polarizing plates obtained in the examples and the comparative examples was measured at intervals of 100 mm in the width direction of the polarizing film using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). Let the difference between the maximum value and the minimum value of the measured value be a difference. Further, the cell transmittance Ts is measured by a 2 degree field of view (C light source) of JIS Z 8701 and the Y value of the optical performance correction has been performed.

(6) Display unevenness

The polarizing plates obtained in the examples and the comparative examples were cut into two pieces in a size of 200 mm × 300 mm. The state in which the absorption axes of the two polarizing plates are parallel to each other and the state in which they are orthogonal to each other are overlapped, and the overlapping polarizing plates are respectively placed on the backlight (5000 cd) to visually confirm the display unevenness. The case where the display unevenness was not visually observed in any of the parallel state and the orthogonal state was evaluated as ○, and in the case where at least one of the parallel state and the orthogonal state was visually displayed as the display unevenness, it was evaluated as ×.

[Example 1]

As the thermoplastic resin substrate, an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a long water absorption ratio of 0.75% and a Tg of 75° C. was used.

One side of the thermoplastic resin substrate was subjected to corona treatment (treatment condition: 55 W ‧ min/m ² ), and the corona treated surface was coated with polyvinyl alcohol at a temperature of 60 ° C (degree of polymerization 4200, degree of saponification 99.2 m) Ear %) 90 parts by weight and acetonitrile-based modified PVA (degree of polymerization: 1200, ethylene-sulfonate-based modification degree: 4.6%, saponification degree: 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200" ” 10 parts by weight of an aqueous solution and drying were carried out to form a PVA-based resin layer having a thickness of 11 μm to prepare a laminate.

The obtained laminate was sandwiched between pairs of rolls which were respectively provided at the inlet and the outlet of the temperature-adjustable oven, and had a peripheral speed difference between the rolls, and extended 1.5 times in the longitudinal direction (block extension step). The layered body extending through the block was further extended by 1.3 times between a plurality of rolls heated to 130 ° C (hot rolling extension step). In this way, the airborne extension of the laminate is carried out at a total extension ratio of 2.0 times. Further, a spiral pipe as shown in Fig. 4B is provided on the roll, and the heat medium is circulated through the pipe to heat the roll. The volume of the heat medium in the hot roll is 40 liters, and the flow rate of the heat medium is 400 liters/minute, so the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium (the flow rate of the heat medium / the volume of the heat medium in the hot roll) is 10 times / min. The temperature variation in the width direction of the rolls (the difference between the maximum value and the minimum value) was 0.1 °C. The birefringence Δn _xy of the PVA-based resin layer of the obtained extended laminated body (width: 2,500 mm) in the front direction was 0.13 × 10 ^-3 in the width direction. The center value of the birefringence Δn _xy is 16.6 × 10 ^-3 .

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

Next, the iodine concentration and the immersion time were adjusted so that the transmittance of the obtained polarizing film was 42.6%, and the stretched laminate was immersed in a dye bath having a liquid temperature of 30 °C. In the present embodiment, as the dyeing bath, an aqueous iodine solution obtained by blending 0.2 part by weight of iodine with 1.0 part by weight of potassium iodide with respect to 100 parts by weight of water is used, and the extended layered body is immersed in the dyeing bath for 60 seconds ( Dyeing treatment).

Further, the extended laminated body was immersed in a crosslinking bath having a liquid temperature of 30 ° C (mixed with 3 parts by weight of potassium iodide and 3 parts by weight of boric acid aqueous solution of boric acid obtained by mixing 100 parts by weight of water) for 30 seconds (crosslinking) deal with).

Then, the extended laminated body is immersed in a boric acid aqueous solution (mixing 5 parts by weight of potassium iodide and 4 parts by weight of boric acid aqueous solution of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 70 ° C, and simultaneously varying at a peripheral speed. The rolls were uniaxially stretched (water extending) in the longitudinal direction (longitudinal direction) so that the total stretch ratio was 5.5 times.

Thereafter, the extended laminated body was immersed in a washing bath at a liquid temperature of 30 ° C (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) (washing treatment).

In this way, a polarizing film having a thickness of 5 μm was formed on the thermoplastic resin substrate.

Then, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Co., Ltd., trade name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3% by weight) was applied to the surface of the polarizing film of the obtained laminate. And bonding a triacetonitrile cellulose film (manufactured by Konica Minolta Co., Ltd., trade name "KC4UY", thickness: 40 μm), and heating it in an oven maintained at 60 ° C for 5 minutes to prepare an optical functional film having a polarizing film having a thickness of 5 μm. Laminated body (polarizer). Next, the thermoplastic resin substrate is peeled off to obtain a polarizing plate having a protective film.

The transmittance (cell transmittance) of the obtained polarizing plate was 42.6%. The difference in cell transmittance (the difference between the maximum and minimum values) is 0.02%. Further, as a result of observing the display unevenness of the obtained polarizing plate by the above (6), no unevenness was observed.

[Embodiment 2]

An extended laminate was produced in the same manner as in Example 1 except that the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium was 5 times/min. The temperature variation in the width direction of the roll was 1.4 ° C, and the birefringence Δn _xy of the PVA-based resin layer of the obtained extended laminated body was 0.36 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminate was used. The obtained polarizing plate was provided in the same evaluation as in Example 1. The results are shown in Table 1.

[Example 3]

An extended laminate was produced in the same manner as in Example 1 except that the ratio of the volume of the heat medium to the flow rate of the heat medium in the hot roll was 2.5 times/min. The temperature variation in the width direction of the rolls was 2.7 ° C, and the birefringence Δn _xy of the PVA-based resin layer of the obtained extended laminated body was 0.58 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminate was used. The obtained polarizing plate was provided in the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 1]

An extended laminated body was produced in the same manner as in Example 1 except that the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium was 0.5 times/min. The temperature variation in the width direction of the rolls was 4.5 ° C, and the birefringence Δn _xy of the PVA-based resin layer of the obtained extended laminated body was 1.0 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminate was used. The obtained polarizing plate was provided in the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]

In the air extending step, a linear pipe as shown in FIG. 4A is provided, and the roll is heated by passing the heat medium through the pipe, and the ratio of the heat medium volume to the heat medium flow rate in the hot roll is 0.5 times/min. An extended laminate was produced in the same manner as in Example 1 except the above. The temperature variation in the width direction of the roll was 3.9 ° C, and the birefringence Δn _xy of the PVA-based resin layer of the obtained laminated body was 0.80 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminate was used. The obtained polarizing plate was provided in the same evaluation as in Example 1. The results are shown in Table 1.

[assessment]

As is clear from Table 1, it is possible to reduce the variation in the cell transmittance of the obtained polarizing plate by reducing the birefringence Δn _xy stagger of the PVA-based resin layer of the extended laminated body. The result is reduced display unevenness. Further, as is apparent from Table 1, the difference in birefringence can be controlled by adjusting the temperature variation of the hot roll extending by the hot roll in the air extension.

Industrial availability

The extended laminate of the present invention is suitable for use in the production of a polarizing film. The polarizing film obtained can suppress variations in transmittance, and can be suitably used, for example, for a liquid crystal panel or an organic EL panel.

10‧‧‧Layer

10’‧‧‧Extended laminate

11‧‧‧ thermoplastic resin substrate

12‧‧‧Polyvinyl alcohol (PVA) resin layer

R1~R7‧‧‧ Roller

MD‧‧‧layer transport direction

Claims (9)

A method for producing an extended laminate comprising the steps of forming a polyvinyl alcohol-based resin layer on a long-length thermoplastic resin substrate to form a laminate; and carrying the laminate while transporting it in the longitudinal direction a step of forming an extended laminate in the air; the thickness of the polyvinyl alcohol-based resin layer in the extended laminate is 15 μm or less, and the birefringence Δn _xy in the front direction of the polyvinyl alcohol-based resin layer is the maximum in the width direction The difference from the minimum value is 0.6 × 10 ^-3 or less. The method of manufacturing an extended laminate according to claim 1, wherein the aerial extension comprises a hot rolling extension step of extending by a circumferential speed difference between the hot rolls, and a temperature difference in a width direction of the hot roll Below 3 °C. The method for producing an extended laminate according to claim 2, wherein the temperature of the hot roll is 120 ° C or higher. The method for producing an extended laminate according to claim 2, wherein the heating of the hot roll is performed by passing a heat medium through a pipe in the hot roll and including passing the heat medium through a spiral pipe, the spiral pipe system being configured It is inscribed in the outer peripheral part of the roll. The method for producing an extended laminate of claim 4, wherein a ratio of a volume of the heat medium to a flow rate of the heat medium in the hot roll is 2 times/min or more. An extended laminate is produced by the manufacturing method of claim 1. A method for producing a polarizing film comprising the step of dyeing an extended laminate according to claim 6. The method for producing a polarizing film according to claim 7, further comprising the step of extending the stretched laminate in an aqueous boric acid solution after the dyeing step. A polarizing film manufactured by the manufacturing method of claim 8 and having a thickness of 10 μm or less.