TW201829153A - 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 stretched laminated body, stretched laminated body, and manufacturing method of polarizing film        Field of invention    

The present invention relates to a method for manufacturing an extended laminated body, an extended laminated body obtained by the manufacturing method, a manufacturing method of a polarizing film, and a polarizing film obtained by the manufacturing method.

    Background of the invention    

The liquid crystal display device of a typical image display device is often provided with polarizing films on both sides of the unit cell due to its image formation method. In recent years, due to the expectation of thinning of polarizing films, the following methods have been proposed: for example, the laminate of a specific thermoplastic resin substrate and a polyvinyl alcohol resin layer is subjected to aerial stretching and dyeing, and then carried out in a boric acid aqueous solution. The method of extending | stretching and obtaining a polarizing film (for example, Unexamined-Japanese-Patent No. 2012-73580). However, there may be cases where the transmittance of the polarizing film produced by such a manufacturing method varies.

    Summary of invention    

According to an embodiment of the present invention, a method for manufacturing an extended laminated body capable of obtaining a polarizing film with suppressed transmittance variation can be provided.

The manufacturing method of the stretched laminated body of the present invention includes: a step of forming a laminated body by forming a polyvinyl alcohol resin layer on a long thermoplastic resin substrate; and carrying out the aerial stretching while conveying the laminated body in the longitudinal direction. The steps of making an extended laminate. Extending the polyvinyl alcohol resin layer thickness of the laminate in 15μm or less and the birefringence △ n _xy polyvinyl alcohol-based resin layer of the front direction in the width direction of the difference between the maximum and minimum values of 0.6 × 10 ^{- 3} or less.

In one embodiment, the above-mentioned air stretching includes a hot rolling stretching step. The hot rolling stretching step is performed by a circumferential speed difference between hot rolling rolls, and a temperature variation in a width direction of the hot rolling rolls 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 the heat medium through a spiral pipe. The spiral pipe is arranged to be inscribed in the outer periphery of the roll. .

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

According to another aspect of the present invention, an extended laminated body can be provided. This extended laminated body can be manufactured by the said manufacturing method.

According to another aspect of the present invention, a method for manufacturing a polarizing film can be provided. The manufacturing method of this polarizing film includes the process of dyeing the said stretched laminated body.

In one embodiment, the method for manufacturing the polarizing film further includes a step of stretching the stretched laminate in a boric acid aqueous solution after the dyeing step.

According to another aspect of the present invention, a polarizing film can be provided. The polarizing film can be manufactured by the above manufacturing method, and its thickness is 10 μm or less.

According to the present invention, the birefringence △ n _xy in the front direction of the polyvinyl alcohol (PVA) -based resin layer of the stretched laminated body of a thin (for example, 10 μm or less) polarizing film intermediate body can be made to have a maximum value and a minimum value in the width direction The extension laminated body is manufactured in a manner that the difference is 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, variations in the transmittance of the obtained polarizing film can be suppressed. In one embodiment, the _{variation 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 below a predetermined value by adjusting the temperature variation in the width direction of the hot-rolled roll used in the air To control.

1, 2‧‧‧ rolls

9‧‧‧ Oven

10‧‧‧ laminated body

10’‧‧‧extended laminate

11‧‧‧ thermoplastic resin substrate

11’‧‧‧ resin substrate

12‧‧‧Polyvinyl alcohol (PVA) resin layer

12’‧‧‧ polarizing film

13‧‧‧Adhesive layer

14‧‧‧ spacer

15‧‧‧ Adhesive layer

16‧‧‧ Optical Functional Film

16’‧‧‧The second optical function film

100‧‧‧ Optical film laminate

101‧‧‧ Swing Out

110‧‧‧boric acid aqueous bath

111, 112‧‧‧ roll

120‧‧‧ Dichroic (Iodine) and potassium iodide solution

121, 122‧‧‧ rolls

130‧‧‧ Boric acid and potassium iodide aqueous bath

131, 132‧‧‧ rolls

140‧‧‧boric acid aqueous bath

141, 142‧‧‧roller

150‧‧‧potassium iodide bath

151, 152‧‧‧ rolls

160‧‧‧ Take-up Department

200‧‧‧ Optical Functional Film Laminate

300‧‧‧ Optical Functional Film Laminate

400‧‧‧ Optical Functional Film Laminate

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

FIG. 2 is a schematic diagram showing an example of a block extension step in a method for manufacturing an extended laminated body according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing an example of a hot-rolled stretching step in a method for manufacturing an extended laminated body according to an embodiment of the present invention.

FIG. 4A is a schematic diagram showing an example of a means for controlling the temperature variation in the width direction of the hot roll during the hot rolling elongation step.

FIG. 4B is a schematic diagram showing another example of a means for controlling the temperature variation in the width direction of the hot roll during the hot rolling elongation step.

FIG. 5 is a schematic diagram showing an example of a method for manufacturing a polarizing film of the present invention.

In FIG. 6, FIG. 6A is a schematic cross-sectional view of an optical film laminate using a polarizing film produced by the manufacturing method of the present invention, and FIG. 6B is a schematic cross-sectional view of an optical functional film laminate using this polarizing film.

In FIG. 7, FIGS. 7A and 7B are schematic cross-sectional views of an optically functional thin film laminated body of another embodiment using a polarizing film produced by the manufacturing method of the present invention, respectively.

    Forms used to implement the invention    

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

    A. Manufacturing method of extended laminated body    

The manufacturing method of the stretched laminated body of the present invention includes: a step of forming a laminated body by forming a polyvinyl alcohol resin layer on a long thermoplastic resin base material; and carrying the laminated body in the air while conveying it in the longitudinal direction. Extending to make an extended laminate. Each step will be described below.

A-1. Production steps of laminated body

FIG. 1 is a partial cross-sectional view of a laminated body that can be used in a method for manufacturing an extended laminated body according to an embodiment of the present invention. The laminated body 10 includes a thermoplastic resin substrate 11 and a polyvinyl alcohol (PVA) -based resin layer 12. The laminated body 10 can be produced by forming a 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 adopted. The PVA-based resin substrate 11 is desirably coated with a coating solution containing a PVA-based resin and dried to form a PVA-based resin layer 12.

As a material for forming the thermoplastic resin substrate, any appropriate thermoplastic resin can be adopted. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, and polymers Carbonate resins and copolymer resins thereof. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate-based resin is suitably used. Among them, an amorphous (hardly crystallizable) polyethylene terephthalate-based resin is particularly suitable. Specific examples of the amorphous polyethylene terephthalate resin include copolymers containing isophthalic acid as a dicarboxylic acid and copolymers containing cyclohexanedimethanol as a glycol. Thing.

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

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

The thermoplastic resin substrate may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, the thermoplastic resin substrate is in a state of being stretched in the lateral direction in a long strip. The lateral direction is preferably a direction orthogonal to the extending direction of the laminated body described later. In this specification, "orthogonal" also includes the case of being substantially orthogonal. Here, the “substantially orthogonal” includes a case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.

Relative to the glass transition temperature (Tg), the extension temperature of the thermoplastic resin substrate is preferably Tg-10 ° C ~ Tg + 50 ° C. The stretch ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

As a method for extending the thermoplastic resin substrate, any appropriate method can be adopted. Specifically, it may be a fixed end extension or a free end extension. The extension method can be dry or wet. The thermoplastic resin substrate can be extended in one stage or in multiple stages. When carried out in multiple stages, the above-mentioned extension magnification is the product of the extension magnifications in each stage.

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

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10,000, ideally 1200 to 4500, and more preferably 1500 to 4,300. The average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

The coating liquid is typically a solution in which the PVA-based resin is dissolved in a solvent. As for the solvent, polyhydric alcohols such as water, dimethylarsine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and trimethylolpropane can be mentioned. , Ethylene diamine, diethylene triamine and other amines. These can be used alone or in combination of two or more. Of these, water is ideal. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. As long as it is such a resin concentration, a uniform coating film which adheres to a thermoplastic resin substrate can be formed.

Additives can also be added to the coating solution. As for the additives, examples thereof include plasticizers and surfactants. As the plasticizer, a polyhydric alcohol such as ethylene glycol or glycerin may be mentioned. In terms of surfactants, non-ionic surfactants can be mentioned. These can be used for the purpose of further improving the uniformity, dyeability, and extensibility of the PVA-based resin layer obtained.

The coating liquid may be applied by any appropriate method. For example, a roll coating method, a spin coating method, a wire rod coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (such as a notched wheel coating method) and the like.

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 3 μm to 25 μm, and more preferably 5 μm to 20 μm.

Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (such as corona treatment), 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, any appropriate functional layer may be formed on the side of the thermoplastic resin base material 11 on which the PVA-based resin layer 12 is not formed. In a preferred embodiment, the functional layer has heat resistance. By having heat resistance, for example, even if a temperature higher than the glass transition temperature of the thermoplastic resin substrate is added to the laminate in the hot-rolling stretching step described later, the laminate (thermoplastic resin substrate) can be prevented from sticking to Roller 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 structure, excellent anti-caking properties can be achieved, and further, manufacturing efficiency can be improved. In addition, it has excellent antistatic properties. As the antistatic layer, any appropriate structure can be adopted. A typical example of the conductive material is a polythiophene-based polymer (for example, poly (ethylene dioxythiophene)). As the binder resin, for example, a resin that has both adhesion and flexibility with a thermoplastic resin substrate and is soluble or dispersible in an aqueous solvent can be used. Specific examples include polyurethane resins. The thickness of the antistatic layer is preferably 0.1 μm to 10 μm. The surface resistance value of the antistatic layer is preferably less than 10 × 10 ¹³ Ω / □. The surface arithmetic average roughness Ra of the antistatic layer is preferably 10 nm to 100 nm.

A-2. Aerial extension steps

The aerial stretching step includes a hot-rolling stretching step. The hot-rolling stretching step is performed by conveying the laminated body in the longitudinal direction thereof by a peripheral speed difference between the hot rolling rolls. The aerial stretching step includes a block stretching step and a hot rolling stretching step. 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 stretching step and the hot rolling stretching step are sequentially performed. The block extension step and hot-rolled extension step in this embodiment will be described below, and then the characteristic parts of the entire aerial extension step will be described.

A-2-1. Block extension steps

In the block extension step, two rolls are separately arranged, and a heating block is set between the two rolls, and the laminated body is extended in the heating block. Fig. 2 is a schematic diagram showing an example of a block extension step, (a) is a diagram seen from the front, and (b) is a diagram seen from above. In the example shown in the figure, roll pairs 1, 1 and roll pairs 2, 2 are provided at predetermined intervals in the conveyance direction (MD) of the laminate, and the laminate 10 is sandwiched by each roll pair. Roll 1 and roll 2 rotate at different peripheral speeds, and the peripheral speed of roll 2 on the downstream side is set to be greater than that of roll 1 on the upstream side.

For the heating block (heating means) provided between the two rolls, any appropriate means can be adopted. In the example shown in the figure, an oven 9 is provided between the rolls 1 and 2. The elongation temperature is below 100 ° C, and preferably below 95 ° C. On the other hand, the elongation temperature is preferably 70 ° C or higher. The extension temperature (temperature of the laminated body) in the block extension step can be confirmed using, for example, a temperature measurement sticker or a thermocouple.

Roll 1 and Roll 2 are set such that the distance between extensions L ₁ and the width of the laminate (prior to the block extension instant) W is ideally to satisfy the relationship of L ₁ /W≧0.3, and more preferably 0.4 ≦ L ₁ / W The relationship is ≦ 2.0. By satisfying this relationship, a free-end extension can be achieved. Free end extension usually refers to an extension method that extends in only one direction. If the laminated body is extended in a certain direction, the laminated body will shrink in a direction that is slightly orthogonal to the extending direction. The method of extending without suppressing the shrinkage is called free end extension. In this specification, the "distance between extensions" refers to a distance at which additional tension can be maintained by the difference in peripheral speed between the rolls. In addition, it is a distance that can be maintained to be heated at the predetermined extension temperature. For example, in the example shown in the figure, the length in the conveying direction of the oven 9 corresponds to the inter-extension distance L ₁ .

The width W of the laminated body is 500 mm to 6000 mm, preferably 1000 mm to 5000 mm.

Relative to the original length of the multilayer body, the extension ratio of the block extension is preferably 1.1 times to 3.0 times, and more preferably 1.3 times to 2.0 times.

As described above, by performing free-end extension at a predetermined temperature, it is possible to suppress shrinkage and simultaneously improve the orientation of the PVA-based resin. By improving the orientation of the PVA-based resin, the orientation of the PVA-based resin can be improved even after being stretched in boric acid water in a method for manufacturing a polarizing film described later. Specifically, it is presumed that the orientation of the PVA-based resin is improved in advance through this step, so that the PVA-based resin and boric acid are easily cross-linked when the boric acid is stretched, and the stretching is carried out under the condition that the boric acid becomes a node, so that the PVA is stretched 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 elongation step

In the hot rolling stretching step, a plurality of (representatively at least three) hot rolling rolls each capable of temperature control are used, and the hot rolling rolls are arranged in line along the conveying direction of the laminated body 10. The laminated body 10 in contact with the hot roll is conveyed by the rotation of a plurality of hot rolls, and at the same time, the laminated body 10 is extended by the peripheral speed difference of the plurality of hot rolls. Fig. 3 is a schematic view showing an example of a hot rolling elongation step. In the example shown in the figure, the first roll R1 to the seventh roll R7, each of which can be temperature-controlled, are provided at predetermined intervals 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 the laminated body from being attached. In the example shown in the figure, one side of the laminated body 10 (for example, the PVA-based resin layer 12 side) is in contact with 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 thermoplastic resin substrate 11 side) is conveyed in contact with the even-numbered rolls (the second roll R2, the fourth roll R4, and the sixth roll R6). The first to fifth rolls R1 to R5 can be heated to a predetermined temperature and used as hot rolls, so that the laminated body 10 can be heated from both the upper side and the lower side.

The temperature of the hot roll is preferably 120 ° C or higher, and more preferably 125 ° C to 150 ° C. By heating the laminate at this temperature, the crystallinity of the PVA-based resin can be improved. In addition, the block extensions can be combined according to the needs, which can further improve the crystallinity of PVA-based resins. By improving the crystallinity, it is possible to prevent the PVA-based resin layer from being dissolved in water and lower the orientation during water stretching described later. Thus, a polarizing film having excellent optical characteristics can be produced.

The temperature of each hot roll can 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 region and gradually decrease from the intermediate region toward the downstream side. In the example shown in the figure, the sixth and seventh rolls R6 and R7 can be set to any appropriate temperature. For example, the laminated body can be cooled below the glass transition temperature (Tg) of the laminated body. Cooling in this way can suppress the occurrence of creases (for example, in a jagged state) in the laminated body. The temperature of the cooling roller is, for example, 30 ° C to 50 ° C. The ambient temperature (the ambient temperature of the hot rolling extension interval) in the hot rolling elongation step is, for example, 40 ° C to 60 ° C.

In the example shown in the figure, 7 rolls are used. However, it is not necessary to say clearly that various conditions such as the total number of rolls used, the number of hot rolls and / or cooling rolls, and the arrangement order of the hot rolls and / or cooling rolls can be appropriate change.

In the hot-rolling stretching step, tension is applied to the laminated body 10 based on the peripheral speed difference between the adjacent rollers in the above-mentioned roll groups R1 to R7, so that the laminated body 10 is uniaxially extended in the longitudinal direction. More specifically, the stretching is performed by increasing the peripheral speed of the roll closer to the downstream side. In the hot rolling elongation step, for example, it is desirable to further extend the laminated body that has been extended by 1.2 times to 1.5 times in the block by 1.1 times to 3.0 times.

A-2-3. Overall air extension step

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

In the present invention, the difference between the maximum value and the minimum value of the birefringence Δn _xy in the width direction of the PVA-based resin layer in the obtained extended laminated body (hereinafter also referred to as the birefringence difference) is 0.6. × 10 ^-3 or less, and preferably 0.4 × 10 ^-3 or less, and more preferably 0.2 × 10 ^-3 or less, for aerial stretching. The birefringence Δn _xy is obtained by the formula: Δn _xy = n _x -n _y . Here, n _x is a refractive index in a direction in which the refractive index in the plane is the maximum (that is, a 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 the birefringence within the above-mentioned range, the variation of the transmittance (represented by unit transmittance) of the polarizing film obtained by using the stretched laminate can be significantly controlled. That is, if the birefringence of the PVA-based resin layer is changed, the crystal state of the PVA-based resin will change, and the dyeability in the dyeing step described later will also change (specifically, the larger the Δn, the lower the dyeability ). As a result, the variation in the birefringence in the width direction of the PVA-based resin layer is large, and the variation in the transmittance in the width direction of the obtained polarizing film is increased. Therefore, by controlling the variation of the birefringence below a predetermined value, the variation of the transmittance of the polarizing film can be significantly suppressed. This will be explained in detail below.

Display unevenness is recognized due to uneven brightness of the liquid crystal display device. Conversely, as long as the luminance unevenness is below a predetermined value, the viewer cannot recognize display unevenness. Here, it is known that if the luminance deviation ΔL * is x and the display unevenness is y, the relationship can be approximated to the first-order function of the following formula (1) No. 4798 "Relevant Research on Evaluation Methods of Glass Quality Based on Vision", Takizawa Shin).

y = 2.75x-1.54 ... (1) From the expression (1), if x (that is, ΔL *) is lower than 0.56, then y = 0, it can be said that the display unevenness becomes invisible. Here, when two polarizing plates are arranged so that their absorption axes are parallel to each other, the luminance L * of the liquid crystal display device is represented by L * _// , and the characteristics of the polarizing plate are represented by the unit transmittance (when a polarizing plate is used). Transmittance) Y value: Ts. The unit transmittance of the polarizing plate was changed over a wide range to investigate the correlation between L * _// and Ts, and the result confirmed that the brightness difference ΔL * _// and the unit transmittance difference △ Ts can be expressed by (2) First degree function representation.

△ L * _// = 1.289 × △ Ts ... (2) As can be seen from the formula (2), in order to make the brightness difference L * _// (corresponding to L *) lower than the threshold of the display unevenness that cannot be seen 0.56, △ Ts should be less than 0.43.

On the other hand, the present inventors have also found that in the stretched laminate used to make a thin (for example, 10 μm or less) polarizing film, the transmittance of the polarizing film may change due to the birefringence of the PVA-based resin layer, and From the results of the trial and error method of the experiment, it was confirmed that there is a correlation shown in the following formula (3) between the variation of the birefringence Δn _xy of the PVA-based resin layer and the variation ΔTs of the cell transmittance.

△ Ts = 9.53 × 10 ^-5 × (△ n _xy variation) ² + 117 × (△ n _xy variation) ... (3) From the formula (3), the PVA-based resin layer in the obtained extended laminate is obtained. When the birefringence Δn _{xy has} an unevenness of 0.6 × 10 ^-3 or less to perform air stretching, △ Ts can be made to 0.43 or less, and as a result, display unevenness can no longer be visually recognized.

In addition, the present inventors have found that the above-mentioned desired birefringence variation can be achieved in the PVA-based resin layer of the obtained stretched laminate by specifically controlling the conditions of hot rolling stretching in the aerial stretching step. Specifically, 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), the above-mentioned desired birefringence variation can be achieved. In more detail, the results of the trial and error method found that there is a correlation between the temperature variation in the width direction of the hot roll and the birefringence Δn _xy as shown in the following formula (4).

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

By means of controlling the temperature variation in the width direction of the hot rolls, for example, the circulation path of the heat medium (oil) for heating the rolls can be appropriately set, and the ratio of the volume of the heat medium to the flow rate of the heat medium in the hot rolls can be appropriately set. (Heat medium flow rate / heat medium volume in hot rolls), and combinations thereof. The circulation path of the heat medium may be configured as shown in Figs. 4A and 4B. The structure of FIG. 4A is such that a linear pipe is provided in the roll to circulate the heat medium through the pipe, and the heat medium in the roll is circulated by the pressure caused by the flow. The structure of FIG. 4B is provided with a spiral piping so as to be continuous with the linear piping of FIG. 4A and attached to the inner periphery of the roll, and the heat medium is circulated through the spiral piping. The structure shown in FIG. 4B is preferable. Because more precise temperature control is possible. In FIG. 4B, for the convenience of observation, the spiral piping is described as being located away from the outer peripheral portion of the roll (that is, the inside) and is spaced apart from each other by spiral intervals. In fact, the spiral piping is arranged to be inscribed in the outer peripheral portion of the roll It is set to reduce the spiral interval as much as possible (so that no gap is formed between the spirals). Although omitted in FIG. 4B, the spiral pipe is extended from the widthwise end of the roll to the outside to discharge the heat medium (the discharged heat medium is circulated by the heat source and returned to the inside of the roll from the straight pipe shown in the figure). In addition, the straight pipe and the spiral pipe may be continuously configured as shown in FIG. 4B, or the straight pipe and the spiral pipe may be configured as separate units (not shown). When the straight piping and the spiral piping are respectively constituted as individual bodies, an opening portion is provided in a predetermined portion of the helical piping, and the linear piping and the helical piping may be connected so as to be connectable. The ratio of the heat medium volume to the heat medium flow rate (heat medium flow rate / heat medium volume in the hot roll) is preferably 2 times / minute or more, more preferably 2 times / minute to 20 times / minute, and more preferably 2 times / minute to 10 times / minute. The volume of the heat medium in the hot roll refers to the total volume of the heat medium in the flowing hot roll (the piping existing in the hot roll) (the unit is liter in this embodiment). For example, when the temperature of the hot roll is set to 130 ° C, a spiral pipe as shown in Fig. 4B is set 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 becomes 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 laminate

The stretched laminated body according to the embodiment of the present invention can be produced by the manufacturing method described in the above item A. As shown in the above section A-2-2 for the extension ratio of air extension, the extension laminate is ideally extended from 1.5 to 4.0 times, and more preferably from 1.8 to 3.0 times, relative to the original length of the laminate. By using the stretched laminated body prepared by the manufacturing method described in the above item A, for example, the laminated body that has not been stretched in the air is only stretched in water as described later, and finally, a higher stretch rate can be achieved. Specifically, the thermoplastic resin base material of the stretched laminate is stretched while suppressing alignment. The higher the alignment, the greater the stretching tension, the more difficult it is to perform stable stretching or the resin substrate is broken, but by suppressing the alignment, a higher stretching ratio can be achieved eventually. Thus, a polarizing film having excellent optical characteristics (for example, polarization degree) can be produced.

The birefringence in the front direction of the PVA-based resin layer of the stretched laminate Δn _{xy has a variation} in the width direction of 0.6 × 10 ^-3 or less, preferably 0.4 × 10 ^-3 or less, and more preferably 0.2 × 10 ^-3 as described above. the following. The lower limit of the birefringence Δn _{xy is} , for example, 0.1 × 10 ^-3 . As long as the birefringence variation is within this range, as described above, the variation in the transmittance (representing the unit transmittance) of the polarizing film obtained by using the extended laminated system can be significantly suppressed.

The thickness of the PVA-based resin layer of the stretched laminated body represents the thickness of the polarizing film prepared above that is 10 μm or less. Specifically, the thickness of the PVA-based resin layer of the stretched laminate is 15 μm or less, and is preferably 5 μm to 10 μm. According to the present invention, a remarkable effect can be exerted in such a thin PVA-based resin layer (finally a polarizing film).

C. How to use

The extended laminated body described in the above item B is representatively available for the manufacture of a polarizing film. Specifically, the stretched laminated body can be appropriately subjected to a treatment for forming a PVA-based resin layer into a polarizing film. Examples of the treatment for forming a polarizing film include an extension treatment, a dyeing treatment, an insolubilization treatment, a crosslinking treatment, a washing treatment, and a drying treatment. However, the number and order of such processes are not particularly limited.

C-1. Extension in water

In a preferred embodiment, the stretched laminate is stretched in water (stretched in boric acid). Specifically, it extends in water in a direction parallel to the extending direction of the laminated body. By stretching in water, it can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C) of the resin substrate and the PVA-based resin layer, and the PVA-based resin layer can be inhibited from crystallization while being stretched. Stretch at high magnification. Thus, a polarizing film having excellent optical characteristics (for example, polarization degree) can be produced. In this specification, the "parallel direction" includes a case of 0 ° ± 5.0 °, preferably 0 ° ± 3.0 °, and more preferably 0 ° ± 1.0 °.

Any appropriate method can be adopted as the method of extending the laminated body. 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 (long side direction) of the above-mentioned aerial extension. The extension of the extension laminate can be performed in one stage or in multiple stages.

The extension in water is preferably performed by immersing the extension laminate in an aqueous solution of boric acid (extension in boric acid). By using an aqueous boric acid solution as the extension bath, the PVA-based resin layer can be provided with rigidity capable of withstanding the tension applied during extension and water-insolubility which is insoluble in water. Specifically, boric acid can generate a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and further, it can be stretched well, and a polarizing film having excellent optical characteristics (for example, polarization degree) can be produced.

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

By the dyeing process described later, when a dichroic substance (representatively iodine) is adsorbed on the PVA-based resin layer in advance, an iodide is preferably blended in the extension bath (aqueous boric acid solution). By blending iodide, the elution of iodine which has been adsorbed on the PVA-based resin layer can be suppressed. In the case of iodide, examples include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Wait. Among these, potassium iodide is desirable. The concentration of iodide is preferably 0.05 to 15 parts by weight, and more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of water.

The extension temperature (liquid temperature of the extension bath) in water is preferably 40 ° C to 85 ° C, and more preferably 50 ° C to 85 ° C. As long as it is at this temperature, it is possible to perform high-rate stretching while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ° C or higher from the relationship with the formation of the PVA-based resin layer. At this time, once the elongation temperature is lower than 40 ° C, even if the plasticization of the thermoplastic resin substrate using water is considered, there is a possibility 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 there is a possibility that excellent optical characteristics cannot be obtained. The immersion time of the extension laminate in the extension bath is preferably 15 seconds to 5 minutes.

By combining the above-mentioned thermoplastic resin substrate with elongation in water (boric acid elongation in water), a high magnification extension can be performed, and a polarizing film having excellent optical characteristics (for example, polarization degree) can be produced. Specifically, the maximum extension 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 laminate (including the extension ratio of the extension laminate). In this specification, the "maximum extension ratio" refers to the extension ratio immediately before the extension laminate is broken, and is a value which is 0.2 lower than the value after confirming the extension ratio of the extension laminate. However, the maximum stretching ratio of the laminated body using the thermoplastic resin substrate may be higher in the case of stretching in water than in the case of stretching only in the air.

C-2. Other

The dyeing process mentioned above represents a process of dyeing a PVA-based resin layer with a dichroic substance. Ideally, it is performed by adsorbing a dichroic substance to a PVA-based resin layer. The adsorption method includes, for example, a method of dipping a PVA-based resin layer (extended laminate) in a dichroic substance-containing dyeing solution, a method of applying the dyeing solution to a PVA-based resin layer, and spraying the dyeing solution to Method of PVA-based resin layer and the like. Ideally, it is a method of immersing the stretched laminate in a dyeing solution containing a dichroic substance. Because it can adsorb dichroic materials well.

Examples of the dichroic material include iodine and dichroic dyes. Ideally, it is iodine. When iodine is used as the dichroic substance, the dyeing solution is an iodine aqueous solution. The blending amount of iodine is preferably 0.1 to 0.5 parts by weight relative to 100 parts by weight of water. In order to improve the solubility of iodine with respect to water, it is suitable to mix iodide with an iodine solution. Specific examples of the iodide are as described above. With respect to 100 parts by weight of water, the blending amount of iodide is preferably 0.02 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, and even more preferably 0.7 to 3.5 parts by weight. In order to suppress the dissolution of the PVA-based resin, the temperature of the dyeing liquid during dyeing is preferably 20 ° C to 50 ° C. When the PVA-based resin layer is immersed in the dyeing liquid, in order to ensure the transmittance of the PVA-based resin layer, the immersion time is preferably 5 seconds to 5 minutes. In addition, the dyeing conditions (concentration, liquid temperature, and immersion time) can be set such that the polarization degree or cell transmittance of the polarizing film finally produced is within a predetermined range. In one embodiment, the immersion time is set so that the polarization degree 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 performed before the above-mentioned water stretching.

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

The above-mentioned crosslinking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By performing a crosslinking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is desirably 1 to 4 parts by weight relative to 100 parts by weight of water. When the crosslinking treatment is performed after the dyeing treatment, it is preferable to further mix iodide. By blending iodide, elution of iodine that has been adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20 ° C to 50 ° C. Ideally, the crosslinking treatment is preferably performed before the above-mentioned water stretching. In an ideal embodiment, the dyeing treatment, the cross-linking treatment, and the elongation in water should be sequentially performed.

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

FIG. 5 is a schematic view showing an example of a method for manufacturing a polarizing film. The extended laminated body 10 ′ is spun out from the spin-out portion 101, immersed in a boric acid aqueous bath 110 through rolls 111 and 112 (insolubilization treatment), and immersed in a dichroic substance (iodine) and potassium iodide through rolls 121 and 122. Aqueous solution bath 120 (dyeing treatment). Next, the rollers 131 and 132 were immersed in an aqueous bath 130 of boric acid and potassium iodide (crosslinking treatment). Then, the stretched laminated body 10 'is immersed in a boric acid aqueous solution bath 140 and simultaneously stretched (stretched in water) by applying tension to the longitudinal direction (long-side direction) with rollers 141 and 142 having different speed ratios. The stretched laminate 10 'extended in water is immersed in a potassium iodide aqueous bath 150 (washing treatment) by rollers 151 and 152, and is then subjected to a drying treatment (not shown). Thereafter, the extended laminated body 10 'is wound up by the winding unit 160.

C. Polarizing film

As described above, a polarizing film can be formed on the resin substrate by performing the above-mentioned processes on the stretched laminate of the present invention. This polarizing film is substantially a PVA-based resin film that adsorbs and aligns a dichroic substance. The thickness of the polarizing film is preferably 10 μm or less, more preferably 7 μm or less, and even 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 ideally exhibits absorption dichroism at any of the wavelengths from 380nm to 780nm. The unit transmittance of the polarizing film is preferably 40.0% or more, more preferably 41.0% or more, and even more preferably 42.0% or more. The degree of polarization of the polarizing film is preferably 99.8% or more, more preferably 99.9% or more, and even more preferably 99.95% or more.

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

D. Optical film laminate and optical functional film laminate

The polarizing film can be used for an optical film laminate and / or an optically functional film laminate. FIG. 6A is a schematic cross-sectional view of an optical thin film laminated body capable of using a polarizing film, and FIG. 6B is a schematic cross-sectional view of an optical functional thin film laminated body capable of using a polarizing film. The optical film laminate 100 includes 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 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 this order. In these embodiments, the resin substrate is not peeled off from the obtained polarizing film 12 'and is used directly as an optical member. The resin base material 11 'functions as, for example, a protective film for the polarizing film 12'.

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

The laminated layers of the respective layers constituting the optical film laminated body or the optical functional film laminated body are not limited to the illustrated examples, and any appropriate adhesive layer or adhesive layer can be used. The adhesive layer may be formed of an acrylic adhesive. The adhesive layer may be formed of a vinyl alcohol-based adhesive. The optical functional film can function as, for example, a polarizing film protective film, a retardation film, and the like.

    Examples    

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

(1) Thickness

The multilayer system was measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). The PVA-based resin layer of the stretched laminate was measured at 100 mm intervals along the width direction of the stretched laminate using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD3000").

(2) Glass transition temperature (Tg)

The measurement was performed in accordance with JIS K 7121.

(3) Roll temperature variation

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

(4) Birefringence

The PVA-based resin layer was transferred to the adhesive-attached glass having no retardation at a portion of the thickness measured in the above (1), and the front retardation was measured using KOBRA-WPR manufactured by Oji Instruments Co., Ltd. The birefringence was calculated by dividing the obtained frontal retardation value by the thickness of the PVA-based resin layer obtained in (1) above. Let the difference between the calculated maximum and minimum values of birefringence be uneven.

(5) the unit penetration rate is uneven

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

(6) Display unevenness

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

[Example 1]

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

Corona treatment was performed on one surface of the thermoplastic resin substrate (treatment conditions: 55 W‧min / m ² ), and the corona-treated surface was coated with polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 Mo) at 60 ° C. Ear%) 90 parts by weight and acetamidine modified PVA (degree of polymerization 1200, acetamidine modification 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 performed to form a PVA-based resin layer having a thickness of 11 µm to prepare a laminate.

The obtained laminated body is sandwiched between a pair of rollers provided at an inlet and an outlet of a temperature-adjustable oven, and the peripheral speed difference between the rollers is extended by 1.5 times in the longitudinal direction (block extension step). The laminated body extended by the block is further extended 1.3 times between a plurality of rolls which have been heated to 130 ° C. (hot rolling stretching step). In this way, aerial extension of the laminate is performed at a total extension ratio of 2.0 times. The roll is provided with a spiral pipe as shown in FIG. 4B, and a heat medium is passed 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 heat medium volume to the heat medium flow rate (heat medium flow / heat medium volume in the hot roll) is 10 times / minute. The temperature variation (the difference between the maximum value and the minimum value) in the width direction of the roll was 0.1 ° C. The _unevenness in the width direction of the birefringence Δn _xy in the front direction of the PVA-based resin layer of the obtained extended laminated body (2500 mm in width) was 0.13 × 10 ^-3 . The central value of the birefringence Δn _xy is 16.6 × 10 ^-3 .

Next, the extended laminated body was immersed in an insolubilization bath (aqueous boric acid solution prepared by mixing 4 parts by weight of boric acid with 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 dyeing bath at a liquid temperature of 30 ° C. In this example, as the dyeing bath system, an iodine aqueous solution obtained by mixing 0.2 parts by weight of iodine and 1.0 part by weight of potassium iodide with respect to 100 parts by weight of water was used to immerse the extended laminate in the dyeing bath for 60 seconds ( Staining).

Then, the extended laminated body was immersed in a cross-linking bath at a liquid temperature of 30 ° C (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with 100 parts by weight of water) (crosslinking deal with).

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

Thereafter, the stretched laminate was immersed in a washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 30 ° C (washing treatment).

In this way, a 5 μm thick polarizing film was formed on a thermoplastic resin substrate.

Next, the surface of the polarizing film of the obtained laminated body was coated with a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd. under the trade name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3% by weight), and bonded as described above, and adhered. Triethyl cellulose cellulose film (Konica Minolta, trade name "KC4UY", thickness: 40 μm) was heated in an oven maintained at 60 ° C for 5 minutes to produce an optically functional film laminate having a polarizing film with a thickness of 5 μm (Polarizing plate). Then, the thermoplastic resin substrate was peeled off to obtain a polarizing plate having a protective film on one side.

The transmittance (unit transmittance) of the obtained polarizing plate was 42.6%. The variation of the unit transmission rate (the difference between the maximum value and the minimum value) is 0.02%. In addition, as a result of observing the display unevenness of the obtained polarizing plate in the manner (6), no display unevenness was found.

[Example 2]

In the air stretching step, a stretched laminate was produced in the same manner as in Example 1 except that the ratio of the heat medium volume to the heat medium flow rate in the hot roll was 5 times / minute. The temperature variation in the width direction of the roll was 1.4 ° C., and the birefringence Δn _xy variation in the PVA-based resin layer of the obtained stretched laminate was 0.36 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminated body 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]

In the air stretching step, a stretched laminate was produced in the same manner as in Example 1 except that the ratio of the heat medium volume to the heat medium flow rate in the hot roll was 2.5 times / minute. The temperature variation in the width direction of the roll was 2.7 ° C, and the birefringence Δn _xy variation in the PVA-based resin layer of the obtained stretched laminate was 0.58 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminated body 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]

In the air stretching step, a stretched laminate was produced in the same manner as in Example 1 except that the ratio of the heat medium volume to the heat medium flow rate in the hot roll was 0.5 times / minute. The temperature variation in the width direction of the roll was 4.5 ° C, and the birefringence Δn _xy variation in the PVA-based resin layer of the obtained stretched laminate was 1.0 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminated body 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 stretching 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 volume of the heat medium in the hot roll to the flow rate of the heat medium is 0.5 times / minute. Except for this, an extended laminated body was produced in the same manner as in Example 1. The temperature variation in the width direction of the roll was 3.9 ° C, and the birefringence Δn _xy variation in the PVA-based resin layer of the obtained stretched laminate was 0.80 × 10 ^-3 . A polarizing plate was produced in the same manner as in Example 1 except that the extended laminated body was used. The obtained polarizing plate was provided in the same evaluation as in Example 1. The results are shown in Table 1.

[Evaluation]

As is clear from Table 1, by reducing the birefringence Δn _xy variation of the PVA-based resin layer of the extended laminated body, the variation of the cell transmittance of the obtained polarizing plate can be reduced. As a result, display unevenness can be reduced. In addition, as can be understood from Table 1, the variation of the birefringence can be controlled by adjusting the variation of the temperature of the hot roll during the hot roll stretching in the air stretching.

    Industrial availability    

The stretched laminate of the present invention is suitable for use in the manufacture of a polarizing film. The prepared polarizing film can suppress variations in transmittance, and is suitable for use in, for example, a liquid crystal panel or an organic EL panel.

Claims (9)

A method for manufacturing an extended laminate, comprising the steps of: forming a polyvinyl alcohol-based resin layer on a long thermoplastic resin substrate to produce a laminate; and carrying out the laminate while conveying it in the longitudinal direction. The step of making an extended laminate by aerial stretching; the above-mentioned aerial extension includes block extension and hot rolling extension. The thickness of the polyvinyl alcohol resin layer in the extended laminate is 15 μm or less, and the front direction of the polyvinyl alcohol resin layer is The difference between the maximum value and the minimum value of the birefringence Δn _xy in the width direction is 0.6 × 10 ^-3 or less.     For example, the manufacturing method of the stretched laminated body according to claim 1, wherein the above-mentioned air stretching includes a hot rolling stretching step, and the hot rolling stretching step is extended by the peripheral speed difference between the hot rolls, and the temperature in the width direction of the hot rolls is uneven. Below 3 ° C.         The method for manufacturing an extended laminated body according to claim 2, wherein the temperature of the aforementioned hot roll is 120 ° C or higher.         The method for manufacturing an extended laminated body according to claim 2, wherein the heating of the aforementioned hot roll is performed by passing a heat medium through a pipe in the hot roll, and the method includes passing the heat medium through a spiral configured to be inscribed in the outer periphery of the roll. Like piping.         For example, the method for manufacturing an extended laminated body according to claim 4, wherein the ratio of the volume of the heat medium in the hot roll to the flow rate of the heat medium is 2 times / minute or more.         An extended laminated body is manufactured by the manufacturing method as claimed in claim 1.         A method for manufacturing a polarizing film, comprising the step of dyeing an extended multilayer body as claimed in claim 6.         For example, the method for manufacturing a polarizing film according to claim 7, further comprising a step of stretching the stretched laminate in a boric acid aqueous solution after the aforementioned dyeing step.         A polarizing film is manufactured by the manufacturing method as claimed in claim 8 and has a thickness of 10 μm or less.