KR20210031544A - Method for producing laminate - Google Patents

Abstract

It provides a laminate capable of forming a polarizing film with uniform performance. The manufacturing method of the laminate of the present invention includes a step of heating the resin substrate 11 to a glass transition temperature (Tg) of 15° C. or higher of the resin substrate 11, and a polyvinyl alcohol-based resin layer ( The process of forming 12) is included in this order.

Description

Manufacturing method of laminated body {METHOD FOR PRODUCING LAMINATE}

The present invention relates to a method of manufacturing a laminate. Specifically, it relates to a method for producing a laminate having a resin substrate and a polyvinyl alcohol (PVA)-based resin layer formed on the resin substrate.

A method of obtaining a polarizing film by coating and forming a PVA-based resin layer on a resin substrate and stretching and dyeing the laminate has been proposed (for example, see Patent Document 1 and Patent Document 2). Since a polarizing film having a thin thickness can be obtained from such a method, it is attracting attention because it can contribute to, for example, a thinner image display device. However, in this case, there is a problem that irregularity easily occurs in the performance (specifically, the optical properties of the film thickness and the appearance) of the obtained polarizing film.

Prior art literature

Patent Document 1: Japanese Unexamined Patent Application Publication No. 51-69644

Patent Document 2: Japanese Unexamined Patent Application Publication No. 2001-343521

The present invention was conceived to solve the above problems, and its main purpose is to provide a laminate capable of manufacturing a polarizing film having uniform performance.

The manufacturing method of the laminate of the present invention includes a step of heating a resin substrate to a glass transition temperature (Tg) of -15°C or higher of the resin substrate, and a step of forming a polyvinyl alcohol-based resin layer on the resin substrate in this order. Includes.

In one embodiment, the above-described heating step is performed by unwinding the resin substrate from a resin substrate roll in which an elongated resin substrate is wound in a roll shape.

In one embodiment, the heating step is performed after the storage in the wound state.

In one embodiment, the unwinding process, the heating process, and the polyvinyl alcohol-based resin layer forming process are successively performed.

In one embodiment, the heating step is performed at a glass transition temperature (Tg) of the resin substrate + 15°C or lower.

* In one embodiment, the heating step is carried out while conveying the resin substrate with a conveying roll installed in a heating furnace.

In one embodiment, the shell angle of the conveying roll in the heating furnace is 90° or more.

In one embodiment, the distance between the centers of the conveying rolls in the heating furnace is 2m or less.

In one embodiment, the heating step is performed while conveying the resin substrate with a tenter.

In one embodiment, the shrinkage of the resin substrate by the heating is 3% or less.

In one embodiment, the resin substrate is formed of a polyethylene terephthalate-based resin.

In one embodiment, the resin substrate is stretched in advance.

In one embodiment, the polyvinyl alcohol-based resin layer is formed by applying a coating liquid containing a polyvinyl alcohol-based resin on the resin substrate by a die coating method and drying it.

According to another aspect of the present invention, a method of manufacturing a polarizing film is provided. The manufacturing method of this polarizing film uses the laminated body obtained by the said manufacturing method.

In one embodiment, a process of stretching the laminate is included.

According to another aspect of the present invention, a method of manufacturing a polarizing plate is provided. The manufacturing method of this polarizing plate includes a step of laminating a protective film on the polarizing film obtained by the above manufacturing method.

According to another aspect of the present invention, a stretched laminate is provided. This stretched laminate has a resin substrate and a polyvinyl alcohol-based resin layer formed on the resin substrate. The film thickness irregularity within the size of 200 mm (MD) × 200 mm (TD) of the polyvinyl alcohol-based resin layer is 0.25 μm or less, and 200 mm (MD) × 200 mm (of the polyvinyl alcohol-based resin layer) ( The slow axis fluctuation within the size of TD) is 0.50° or less.

According to another aspect of the present invention, an apparatus for manufacturing a laminate is provided.

In one embodiment, the manufacturing apparatus includes a unwinding means for unwinding the resin substrate from a resin substrate roll in which an elongated resin substrate is wound in a roll shape, and a conveying roll for conveying the elongated resin substrate. A heating furnace for heating the resin substrate to a glass transition temperature (Tg) -15°C or higher of the resin substrate, and a coating means for applying a coating liquid containing a polyvinyl alcohol-based resin on the heated resin substrate.

In one embodiment, the resin substrate is heated while being conveyed by a conveying roll installed in the heating furnace.

In one embodiment, the shell angle of the conveying roll in the heating furnace is 90° or more.

In one embodiment, the distance between the centers of the conveying rolls in the heating furnace is 2m or less.

In one embodiment, the manufacturing apparatus includes a unwinding means for unwinding the resin substrate from a resin substrate roll in which an elongated resin substrate is wound in a roll shape, and a tenter for grasping and conveying both ends of the elongated resin substrate. And a heating means for heating the resin substrate held at both ends of the tenter to a glass transition temperature (Tg) -15°C or higher of the resin substrate and a polyvinyl alcohol-based resin on the heated resin substrate. And an application means for applying a coating liquid to be applied.

In one embodiment, heating is performed while conveying the resin substrate with the tenter.

According to the present invention, surface irregularities of the resin substrate (eg, a gauge band generated when the resin substrate is wound up) can be alleviated (uniformized) by subjecting the resin substrate to heat treatment at a predetermined temperature or higher. As a result, a PVA-based resin layer excellent in thickness uniformity can be formed on a resin substrate. By performing various treatments on the PVA-based resin layer having excellent uniformity in thickness, there is no fluctuation in performance (specifically, film thickness, optical properties, appearance), and a polarizing film having very excellent uniformity (for example, a liquid crystal television) That satisfies the required quality sufficiently) can be manufactured.

1 is a schematic cross-sectional view of a laminate according to an embodiment of the present invention.
2, (a) and (b) are schematic diagrams illustrating a method of heating a resin substrate according to an embodiment.
3 is a schematic diagram illustrating a method of heating a resin substrate according to another embodiment.
4 is a schematic diagram showing an example of the present invention.
5 is a schematic diagram illustrating a method for evaluating the appearance of a PVA-based resin layer.

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

A. Laminate

1 is a schematic cross-sectional view of a laminate according to an embodiment of the present invention. The laminate 10 can be obtained by forming a polyvinyl alcohol (PVA)-based resin layer 12 on the resin substrate 11.

A-1. Resin base

Typically, the resin substrate has an elongated shape. The thickness of the resin substrate is preferably 20 µm to 300 µm, more preferably 50 µm to 200 µm.

Examples of the resin base material include ester resins such as polyethylene terephthalate resins, cycloolefin resins, olefin resins such as polypropylene, (meth)acrylic resins, polyamide resins, and polycarbonate resins. And copolymer resins of. Preferably, a polyethylene terephthalate-based resin can be used. Among them, an amorphous polyethylene terephthalate resin can be preferably used. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid as a dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol as a glycol.

The glass transition temperature (Tg) of the resin substrate is preferably 170°C or less. By using such a resin substrate, it is possible to stretch the laminate at a temperature at which the crystallization of the PVA-based resin does not proceed rapidly, and troubles caused by the crystallization (e.g., obstructing the orientation of the PVA-based resin layer by stretching) are prevented. Can be suppressed. On the other hand, the glass transition temperature of the resin substrate is preferably 60°C or higher. In addition, the glass transition temperature (Tg) is a value which can be calculated|required according to JIS K 7121.

The resin substrate is molded by any suitable method. Examples of the molding method include a melt extrusion method, a solution casting method (solution casting method), a calender method, and a compression molding method. Among these, the melt extrusion method is preferable.

Surface modification treatment (eg, corona treatment, etc.) may be applied to the surface of the resin substrate, or an inverse adhesive layer may be formed. According to such a treatment, the adhesion between the resin substrate and the PVA-based resin layer can be improved. The surface modification treatment and/or formation of the adhesive layer may be performed before the heat treatment described later, or after the heat treatment. In addition, when stretching to be described later is performed, it may be performed before or after stretching.

In one embodiment, the resin substrate is stretched before heat treatment described later. Any suitable method can be adopted as the stretching method of the resin substrate. Specifically, the fixed end stretching may be sufficient and the free end stretching may be sufficient. Moreover, simultaneous biaxial stretching may be sufficient and sequential biaxial stretching may be sufficient. The stretching of the resin substrate may be performed in one step or in multiple steps. In the case of performing in multiple steps, the draw ratio of the resin substrate described later is the product of the draw ratio of each step. Further, the stretching method is not particularly limited, and may be an air stretching system or an underwater stretching system.

The stretching direction of the resin substrate can be appropriately set. For example, the elongated resin substrate is stretched in the width direction. Specifically, the resin substrate is conveyed in the longitudinal direction, and is stretched in a direction (TD) orthogonal to the conveying direction (MD). In this specification, "orthogonal" also includes a case where it is substantially orthogonal. Here, "substantially orthogonal" includes the case of 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°. By stretching the resin substrate in the width direction (TD), the resin substrate can be effectively used. Further, the thickness of the resin substrate in the TD can be made uniform, and partial film thickness fluctuations described later can be suppressed.

The stretching temperature of the resin substrate can be set to any appropriate value depending on the material for forming the resin substrate, the stretching method, and the like. The stretching temperature is typically Tg-10°C to Tg+80°C with respect to the glass transition temperature (Tg) of the resin substrate. When a polyethylene terephthalate-based resin is used as the material for forming the resin substrate, the stretching temperature is preferably 70°C to 150°C, more preferably 90°C to 130°C.

The draw ratio of the resin substrate is preferably 1.5 times or more with respect to the original length of the resin substrate. By setting it as such a range, partial film thickness fluctuation mentioned later can be suppressed favorably. On the other hand, the draw ratio of the resin substrate is preferably 3.0 times or less with respect to the original length of the resin substrate. By setting it as such a range, occurrence of wrinkles can be satisfactorily suppressed in the heating process mentioned later.

A-2. Winding and storage

In one embodiment, the elongated resin substrate is wound in a roll shape. When the resin substrate is molded, a partial variation in the film thickness may occur, and if the resin substrate is wound in this state, irregularities may occur in the resin substrate. The winding tension is typically 60N/m∼150N/m (unit: N/m is the tension per unit width and length). The wound resin substrate (resin substrate roll) can be stored (left) in a wound state for any suitable period until it is used in the next step. For example, after molding the resin substrate, in the case where the PVA-based resin layer is not continuously formed (cannot be), the resin substrate is stored in a wound state. When this storage period is prolonged (e.g., 3 days or more), the occurrence of irregularities (the degree of irregularities, the number of irregularities) becomes remarkable, and there is a tendency that the film thickness fluctuation occurs in the resulting PVA-based resin layer (laminate). . Therefore, the longer the storage period of the resin base roll, the more remarkably the effect of the heat treatment described later can be obtained. In addition, the resin-based roll can be stored under any suitable atmosphere. The storage temperature is, for example, 15°C to 35°C. Relative humidity is, for example, 40%RH to 80%RH.

A-3. heating

The resin substrate is heated. Specifically, the resin substrate is heated by hot air, an infrared heater, a roll heater, or the like. The heating temperature is the glass transition temperature (Tg) of the resin substrate -15°C or higher, preferably Tg-10°C or higher, and more preferably Tg-5°C or higher. In the case of using a polyethylene terephthalate-based resin as the material for forming the resin substrate, the heating temperature is preferably 68°C or higher. By heating the resin substrate at such a temperature, it is possible to alleviate (uniform) the surface irregularities of the resin substrate. As a result, a PVA-based resin layer to be described later can be formed satisfactorily, and a PVA-based resin layer excellent in thickness uniformity can be formed. On the other hand, the heating temperature is preferably (Tg)+15°C or less, more preferably Tg+10°C or less. In the case of using a polyethylene terephthalate-based resin as the material for forming the resin substrate, the heating temperature is preferably 80°C or less. By heating the resin substrate at this temperature, the occurrence of wrinkles (heat wrinkles) can be satisfactorily suppressed.

The heating time is preferably 70 seconds to 150 seconds, more preferably 75 seconds to 100 seconds.

The resin substrate can shrink by heating. For example, when the resin substrate is stretched in the width direction before heating, the resin substrate may shrink (TD shrink) in the width direction by heating. The shrinkage (TD shrinkage) of the resin substrate is preferably 3% or less, more preferably 2% or less, and particularly preferably 1.5% or less. Within this range, occurrence of wrinkles is suppressed and an excellent appearance can be obtained. In addition, the TD contraction rate is calculated by the following equation.

TD shrinkage rate (%) = {1-(the width of the resin substrate after heating (W ₁ )/the width of the resin substrate before heating (W ₀ ))}×100

In one embodiment, the resin substrate is heated while being conveyed. As described above, when the resin substrate is wound in a roll shape, it is preferable to heat-treat the resin substrate unwound from the resin substrate roll. Examples of the heating method include a method of conveying a resin substrate with a conveying roll installed in a heating furnace, and a method of heating while conveying the resin substrate with a tenter. According to the former, the enlargement of equipment can be suppressed. According to the latter, the occurrence of wrinkles can be suppressed very well.

A specific example in the case of using a conveying roll is shown in Figs. 2(a) and 2(b). In the illustrated example, the resin substrate 11 is heated by conveying the resin substrate 11 in the longitudinal direction by the pre-rolls R2 to R5 provided in the oven A. From the viewpoint of production speed, it is preferable to install four or more pre-rolls in the oven as in the illustrated example.

The shell angle of the pre-roll in the oven is preferably 90° or more. In the example shown in Fig. 2(a), the foam angle θ of the pre-rolls R2 and R5 is set to 90°, and the foam angle θ of the pre-rolls R3 and R4 is set to 180°. In the example shown in Fig. 2(b), the foam angle θ of the pre-rolls R2 to R5 is set to 90°. By setting it as such a shell, shrinkage of the resin substrate can be suppressed and the occurrence of wrinkles can be suppressed. In addition, the shell angle is a straight line connecting the center point of the pre-roll and the starting point of contact between the resin substrate and the pre-roll when viewed as a cross section perpendicular to the axial direction, and the center point of the pre-roll and the resin substrate and the pre-roll. It is the angle formed by the straight line connecting the contact end point. The pre-roll spacing (distance between the centers of the rolls) in the oven is preferably 2 m or less. In addition, it is preferable that the distance between two free rolls (between R1-R2 and between R5-R6 in the illustrated example) that is installed across the entrance to the oven is also 2m or less. By setting it as such an interval, shrinkage of the resin substrate can be suppressed and the occurrence of wrinkles can be suppressed. In addition, in this embodiment, the shrinkage of the resin substrate may be related to the stretching ratio, heating temperature, and the like of the resin substrate.

A specific example in the case of using a tenter is shown in FIG. 3. In the illustrated example, both ends of the resin substrate 11 (on a line orthogonal to the conveying direction) are held by the clips 21 and 21 on the left and right of the tenter, and the heating zone is conveyed at a predetermined speed in the longitudinal direction to convey the resin. The substrate 11 is heating. The distance between clips in the conveyance direction (the distance between adjacent clip ends) is preferably 20 mm or less, more preferably 10 mm or less. The clip width is preferably 20 mm or more, more preferably 30 mm or more. In this embodiment, the TD contraction of the resin substrate can be controlled by adjusting the distance between the left and right clips, for example. Specifically, when the distance between the left and right clips is moved without changing, the TD contraction rate becomes substantially 0%. Conversely, by increasing the distance between the left and right clips, the resin substrate can be TD stretched. The rate of change in TD of the resin substrate is preferably 1.00 times or more, more preferably 1.00 times to 1.10 times. In addition, the TD change rate is calculated by the following equation.

TD change rate (times) = width of resin substrate after heating (W ₁ )/width of resin substrate before heating (W ₀ )

A-4. Formation of PVA-based resin layer

Any suitable resin can be employed as the PVA-based resin for forming the PVA-based resin layer. For example, polyvinyl alcohol and an ethylene vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene vinyl alcohol copolymer can be obtained by saponifying the ethylene vinyl acetate copolymer. The degree of sensitivity of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. Sensitivity can be obtained according to JIS K 6726-1994. By using a PVA-based resin having such a sensitivity, a polarizing film excellent in durability can be obtained. If the sensitivity is too high, there is a risk of 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 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

The PVA-based resin layer is preferably formed by applying a coating liquid containing a PVA-based resin on a resin substrate and drying it. The coating liquid is typically a solution obtained by dissolving the PVA-based resin in a solvent. As a solvent, for example, water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylprolitone, various glycols, polyhydric alcohols such as trimethylolpropane, amines such as ethylenediamine and diethylenetriamine Can be used. These may be used alone or in combination of two or more. Among these, water is preferable. The concentration of the PVA resin in the solution is preferably 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the resin substrate.

The coating liquid may contain an additive. As an additive, a plasticizer, a surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As a surfactant, a nonionic surfactant is mentioned, for example. These are used for the purpose of further improving the uniformity, dyeing property, and stretchability of the obtained PVA-based resin layer. Moreover, as an additive, a fast adhesive component is mentioned, for example. By using the adhesive component, the adhesion between the resin substrate and the PVA-based resin layer can be improved. As a result, for example, troubles such as peeling of the PVA-based resin layer from the resin substrate can be suppressed, and dyeing and stretching in water described later can be satisfactorily performed. As the fast adhesion component, for example, a modified PVA such as acetoacetyl modified PVA can be used.

Any suitable method can be adopted as a method of applying the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (coma coating method, etc.) may be mentioned.

In one embodiment, a die coating method is employed. In the die coating method, since the coating liquid is applied by making the gap between the resin substrate and the die (eg, fountain die, slot die) constant, a coating film having very excellent thickness uniformity can be obtained. On the other hand, when unevenness occurs in the resin substrate, the distance between the resin substrate and the die lip is not uniform, making it difficult to form a uniform coating film. Therefore, in the case of employing the die coating method, the effect of the heat treatment can be remarkably obtained.

The coating solution is applied so that the thickness of the dried PVA-based resin layer is preferably 3 µm to 40 µm, more preferably 3 µm to 20 µm. The coating/drying temperature of the coating liquid is preferably 50°C or higher.

Preferably, after the heating, a PVA-based resin layer is continuously formed. For example, after heating, a PVA-based resin layer is formed on the resin substrate without winding up the resin substrate. This is because the effect of the heating can be obtained well.

Further, before forming the PVA-based resin layer, an undercoat layer (primer layer) may be formed in advance on the side where the PVA-based resin layer of the resin substrate is formed. The material constituting the primer layer is not particularly limited as long as it is a material that exhibits some degree of strong adhesion to both the resin substrate and the PVA-based resin layer. For example, a thermoplastic resin excellent in transparency, thermal stability, stretchability, and the like can be used. Examples of the thermoplastic resin include acrylic resins, polyolefin resins, polyester resins, polyvinyl alcohol resins, or mixtures thereof.

A-5. Other

In one embodiment, unwinding of the resin substrate from the resin substrate roll (unwinding process), heating of the resin substrate (heating process), and formation of a PVA-based resin layer (PVA-based resin layer forming process) are successively performed. According to such an embodiment, the effect of the heat treatment can be obtained satisfactorily. As a specific example of this embodiment, as shown in FIG. 4, a form in which the elongated resin substrate is unwound in a series of lines for conveying, and heating and PVA-based resin layer formation steps are sequentially performed. In the laminate manufacturing apparatus 100 shown in FIG. 4, the unwinding roll 40 for unwinding the resin substrate 11 from the resin substrate roll 30, a heating device 50 for heating the resin substrate 11, and a resin. A coating device 60 for applying a coating liquid containing the PVA-based resin to the surface of the substrate 11, a drying device 70 for drying the applied coating liquid, and a winding roll for winding the laminate 10 ( 80) is provided. In addition, the laminate manufacturing apparatus 100 is provided with a plurality of conveying rolls 90.

B. Stretched laminate

The stretched laminate of the present invention is produced by stretching the laminate. In one embodiment, the stretched laminate is produced by stretching the laminate at a draw ratio of 1.5 times or more and 3.0 times or less in an aerial stretching method. Details of the stretching method of the laminate are as described later. In the stretched laminate, the variation in the film thickness within the size of 200 mm (MD) x 200 mm (TD) of the PVA-based resin layer is preferably 0.25 µm or less, more preferably 0.20 µm or less. In the stretched laminate, the variation of the slow axis within the size of 200 mm (MD) × 200 mm (TD) of the PVA-based resin layer is preferably 0.50° or less, more preferably 0.30° or less, particularly preferably 0.25° or less. to be.

C. Polarizing film

The polarizing film of the present invention is produced by subjecting the PVA-based resin layer of the laminate to a polarizing film.

The treatment for forming the polarizing film includes, for example, dyeing treatment, stretching treatment, insolubilization treatment, crosslinking treatment, washing treatment, and drying treatment. These treatments can be appropriately selected according to the purpose. In addition, the processing order, processing timing, processing number, and the like can be appropriately set. Hereinafter, each process is demonstrated.

(Dye treatment)

The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic material. Preferably, it is carried out by adsorbing a dichroic substance to the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (laminate) in a dye containing a dichroic substance, a method of applying the dye to a PVA-based resin layer, and spraying the dye to the PVA-based resin layer. And how to do it. Preferably, it is a method of immersing the laminate in a dyeing solution. This is because the dichroic substance can be satisfactorily adsorbed.

Examples of the dichroic material include iodine and organic dyes. These may be used alone or in combination of two or more. The dichroic material is preferably iodine. When iodine is used as the dichroic substance, the dyeing solution is preferably an aqueous iodine solution. The blending amount of iodine is preferably 0.05 parts by weight to 5.0 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to blend iodide in an aqueous solution of iodine. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like. Among these, potassium iodide is preferred. The blending amount of iodide is preferably 0.3 parts by weight to 15 parts by weight based on 100 parts by weight of water.

When dyeing the dyeing solution, the temperature of the liquid is preferably 20°C to 40°C. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 10 seconds to 300 seconds. Under such conditions, the dichroic material can be sufficiently adsorbed to the PVA-based resin layer. Moreover, dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or single transmittance of the polarizing film which can be finally obtained becomes 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 so that the single transmittance of the polarizing film that can be obtained is about 40%.

(Stretching treatment)

Any suitable method can be adopted as the layered product stretching method. Specifically, it may be a fixed end stretching (for example, a method using a tenter stretching machine) or a free end stretching (for example, a method of uniaxial stretching between rolls having different circumferential speeds through a laminate). Moreover, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) may be sufficient, or sequential biaxial stretching may be sufficient. The stretching of the laminate may be performed in one step or in multiple steps. In the case of performing in multiple steps, the draw ratio (maximum draw ratio) of the laminate to be described later is the product of the draw ratio at each step.

The stretching treatment may be an underwater stretching method performed while the laminate is immersed in a stretching bath, or an air stretching method may be used. Preferably, the underwater stretching treatment is performed at least once, and more preferably, the underwater stretching treatment and the aerial stretching treatment are combined. According to the underwater stretching, the resin substrate or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically about 80° C.), and the PVA-based resin layer can be stretched at a high magnification while suppressing its crystallization. As a result, a polarizing film having excellent optical properties (eg, degree of polarization) can be manufactured.

Any suitable direction can be selected as the stretching direction of the laminate. In one embodiment, the elongated laminate is stretched in the longitudinal direction. Specifically, the laminate is conveyed in the longitudinal direction, and it is the conveying direction (MD). In another embodiment, the elongated laminate is stretched in the width direction. Specifically, it is the direction (TD) which conveys a laminated body in the longitudinal direction and is orthogonal to the conveyance direction (MD).

The stretching temperature of the laminate can be set to any appropriate value depending on the material for forming the resin substrate, the stretching method, and the like. When the aerial stretching method is employed, the stretching temperature is preferably at least the glass transition temperature (Tg) of the resin substrate, more preferably the glass transition temperature (Tg) of the resin substrate (Tg) + 10°C or higher, particularly preferably Tg+ It is more than 15℃. On the other hand, the stretching temperature of the laminate is preferably 170°C or less. By stretching at such a temperature, it is possible to suppress rapid progress of crystallization of the PVA-based resin, thereby suppressing troubles caused by the crystallization (for example, disturbing the orientation of the PVA-based resin layer due to stretching).

When an underwater stretching system is employed as the stretching system, the liquid temperature of the stretching bath is preferably 40°C to 85°C, more preferably 50°C to 85°C. At such a temperature, stretching can be performed at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is less than 40° C., there is a fear that the stretching may not be satisfactory even in consideration of plasticization of the resin substrate by water. On the other hand, as the temperature of the stretching bath increases, the solubility of the PVA-based resin layer increases, and there is a fear that excellent optical properties cannot be obtained.

In the case of employing the underwater stretching method, it is preferable to immerse the laminate in an aqueous boric acid solution to stretch (stretching in boric acid in water). By using the aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted to the PVA-based resin layer with rigidity to withstand the tension required at the time of stretching, and water resistance that is not dissolved in water. Specifically, a tetrahydroxyborate anion can be generated in an aqueous silver boric acid solution and crosslinked by hydrogen bonding with a PVA-based resin. As a result, rigidity and water resistance are imparted to the PVA-based resin layer, so that it can be stretched satisfactorily, thereby producing a polarizing film having excellent optical properties.

The aqueous boric acid solution can be obtained by dissolving boric acid and/or boric acid salt in water, which is preferably a solvent. The boric acid concentration is preferably 1 to 10 parts by weight based on 100 parts by weight of water. When the boric acid concentration is 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or boric acid salt, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, and the like in a solvent may also be used.

Preferably, iodide is blended in the stretching bath (aqueous boric acid solution). By blending iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight and more preferably 0.5 parts by weight to 8 parts by weight based on 100 parts by weight of water.

The immersion time of the layered product in the stretching bath is preferably 15 seconds to 5 minutes.

The elongation rate (maximum draw ratio) of the laminate is typically 4.0 times or more and preferably 5.0 times or more with respect to the original length of the laminate. Such a high draw ratio can be achieved, for example, by employing an underwater stretching method (boric acid underwater stretching). In addition, in the present specification, the "maximum draw ratio" means a draw ratio just before the laminate is broken, and refers to a value that is 0.2 less than the value after confirming the draw ratio at which the separate laminate breaks.

Preferably, the underwater stretching treatment is performed after the dyeing treatment.

(Insolubilization treatment)

The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. In particular, in the case of employing an underwater stretching method, water resistance can be imparted to the PVA-based resin layer by performing an insolubilization treatment. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight based on 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous boric acid solution) is preferably 20°C to 50°C. Preferably, the insolubilization treatment is performed after fabrication of the laminate and before dyeing treatment or underwater stretching treatment.

(Crosslinking processing)

The crosslinking treatment is typically 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 crosslinking treatment. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight based on 100 parts by weight of water. Further, when crosslinking treatment is performed after the dyeing treatment, it is more preferable to blend iodide. By blending iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 to 5 parts by weight based on 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. Preferably, the crosslinking treatment is carried out before the underwater stretching treatment. In a preferred embodiment, dyeing treatment, crosslinking treatment and underwater stretching treatment are performed in this order.

(Cleaning treatment)

The washing treatment is typically performed by immersing a PVA-based resin layer in an aqueous potassium iodide solution.

(Dry processing)

The drying temperature in the drying treatment is preferably 30°C to 100°C.

The obtained polarizing film is substantially a PVA-based resin film in which a dichroic substance is adsorbed and oriented. The thickness of the polarizing film is preferably 15 µm or less, more preferably 10 µm or less, still more preferably 7 µm or less, and particularly preferably 5 µm or less. Such a polarizing film can suppress the occurrence of cracks and the like in an environmental test (eg, 80° C. environmental test). On the other hand, the thickness of the polarizing film is preferably 0.5 µm or more, more preferably 1.0 µm or more. Such a polarizing film may be very excellent in transportability at the time of manufacture or the like.

The polarizing film preferably exhibits absorption dichroism at a wavelength of 380 nm to 780 nm. It is preferable that the polarization film has a polarization degree of 99.9% or more at a single transmittance of 42% or more.

D. Polarizer

The polarizing plate of the present invention has the polarizing film. Preferably, the polarizing plate has the polarizing film and a protective film disposed on at least one side of the polarizing film. As this protective film, the said resin base material may be used as it is, and a film different from the said resin base material may be used. Examples of the material for forming the protective film include cellulose resins such as (meth)acrylic resin, diacetyl cellulose, and triacetyl cellulose, cycloolefin resins, olefin resins such as polypropylene, and esters such as polyethylene terephthalate resins. Resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. The thickness of the protective film is preferably 10 µm to 100 µm.

As described above, in one embodiment, the resin substrate may be used as a protective film without being peeled off from the polarizing film. In another embodiment, the resin substrate is peeled from the polarizing film and another film is laminated. The protective film may be laminated to the polarizing film through an adhesive layer, or may be laminated in close contact (without passing through an adhesive layer). The adhesive layer is typically formed of an adhesive or pressure-sensitive adhesive. According to the present invention, since a polarizing film having very excellent thickness uniformity can be obtained, lamination of the protective film to the polarizing film can be performed satisfactorily.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited to these examples.

[Example 1-1]

(Manufacturing of laminate)

It is composed of amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) having an absorption rate of 0.75% and a glass transition temperature (Tg) of 75°C, and TD stretched 2.0 times at 115°C in advance. It was stored for 30 days in an environment of 25°C and a relative humidity of 60% RH in a wound state as a resin base roll wound in a roll shape at /m.

Thereafter, the resin substrate was unwound from the resin substrate roll, and heat treatment was performed at 70° C. for 60 seconds while conveying the resin substrate.

Next, corona treatment was performed on one side of the resin substrate. Polyvinyl alcohol (polymerization degree 4200, sensitivity 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl modification degree 4.6%, sensitivity 99.0 mol% or more, manufactured by Japanese Synthetic Chemical Industry Co., Ltd.) An aqueous solution containing “GOHSEFIMER Z200” in a ratio of 9:1 was applied by die coating at 25℃ and dried at 60℃ for 200 seconds to form a PVA-based resin layer with a thickness of 10㎛. Was produced.

(Production of the polarizing film)

The obtained laminate was uniaxially stretched at a free end 2.0 times in the longitudinal direction between rolls having different circumferential speeds in an oven at 115°C (air stretching).

Next, the laminate was immersed for 30 seconds in an insolubilization bath having a liquid temperature of 30°C (a boric acid aqueous solution obtained by blending 3 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilization treatment).

Then, while adjusting the iodine concentration and immersion time so that the single transmittance (Ts) of the polarizing film obtained in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in water at a weight ratio of 1:7) is 40% or less. It was immersed (dyeing treatment).

Subsequently, it was immersed for 30 seconds in a crosslinking bath having a liquid temperature of 30°C (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 3 parts by weight of boric acid) for 100 parts by weight of water (crosslinking treatment).

Thereafter, the laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 70°C (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water), and 2.7 in the longitudinal direction between the rolls having different circumferential speeds. Uniaxial stretching was performed by double (underwater stretching).

Thereafter, the laminate was immersed for 10 seconds in a washing bath having a liquid temperature of 30°C (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water), and then dried for 60 seconds with a warm air at 60°C (washing, Drying process).

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

[Example 1-2]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that the temperature of the heat treatment was set to 75°C.

[Example 1-3]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that the temperature of the heat treatment was set to 80°C.

[Example 1-4]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that the temperature of the heat treatment was set to 90°C.

[Example 1-5]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that the temperature of the heat treatment was set to 100°C.

[Example 2-1]

(Manufacturing of laminate)

A laminate was produced in the same manner as in Example 1-1.

(Formation of a polarizing film)

The obtained laminate was uniaxially stretched at the free end using a tenter stretching machine under heating at 115°C, and stretched in the width direction by 4.0 times (stretching treatment).

Subsequently, the laminate was immersed for 30 seconds in an insolubilization bath having a liquid temperature of 30°C (a boric acid aqueous solution obtained by blending 3 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilization treatment).

Next, the iodine concentration so that the single transmittance (Ts) of the polarizing film obtained in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in water at a weight ratio of 1:7) is 40% or less. , It was immersed while adjusting the immersion time (dyeing treatment).

Subsequently, it was immersed for 30 seconds in a crosslinking bath having a liquid temperature of 30°C (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 3 parts by weight of boric acid) for 100 parts by weight of water (crosslinking treatment).

Thereafter, the laminate was immersed for 10 seconds in a washing bath having a liquid temperature of 30°C (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) and then dried for 60 seconds with a warm air at 60°C (washing, drying fair).

In this way, a 2.5 µm-thick polarizing film was formed on the resin substrate.

[Example 2-2]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 2-1, except that the temperature of the heat treatment was set to 75°C.

[Example 2-3]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 2-1, except that the temperature of the heat treatment was set to 100°C.

[Comparative Example 1-1]

A polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that heat treatment was not performed in the production of the laminate.

[Comparative Example 1-2]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that the temperature of the heat treatment was set to 50°C.

[Comparative Example 1-3]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 1-1, except that the temperature of the heat treatment was set to 55°C.

[Comparative 2-1]

In the production of the laminate, a polarizing film was formed on the resin substrate in the same manner as in Example 2-1, except that the temperature of the heat treatment was set to 55°C.

(evaluation)

The following evaluation was performed about each Example and a comparative example.

1. Film thickness fluctuation

(I) After coating and drying the polyvinyl alcohol aqueous solution (before stretching) and (II) after air stretching, the film thickness of the PVA-based resin layer was measured using “MCPD3000” manufactured by Otsuka Electronics. Cut the part including the defect part (the part with the original gauge band) into a size of 200 mm (MD) × 200 mm (TD) to make a measurement sample, measure the thickness of both MD and TD in-plane at 1 mm pitch, and measure the maximum film of the defect area. The difference between the thickness and the minimum film thickness was evaluated.

2. Slow axis fluctuations and absorption axis fluctuations

(I) the slow axis direction of the PVA-based resin layer after applying and drying the polyvinyl alcohol aqueous solution (before stretching), (II) the slow axis direction of the PVA-based resin layer after air stretching, and (III) the absorption axis direction of the polarizing film. It was measured using “Axoscan”, a product of Axometrics. The portion including the defect portion was cut out to a size of 200 mm (MD) x 200 mm (TD) to obtain a measurement sample, and the difference in the maximum axis direction of the defect portion in the plane was measured. In addition, for (I) and (II), after affixing the PVA-based resin layer to the glass plate through the pressure-sensitive adhesive layer, the resin substrate was peeled off, and the slow axis of the PVA-based resin layer was measured.

3. Appearance

(I) PVA-based resin layer after applying and drying a polyvinyl alcohol aqueous solution (before stretching)

(II) The appearance of the PVA-based resin layer and (III) polarizing film after aerial stretching was visually observed.

Regarding (I) and (II), as shown in Fig. 5(a), a commercially available polarizing plate was superimposed on each of the top and bottom of the laminate (sample), and light was irradiated from the bottom and observed with the naked eye from the top. At that time, the two polarizing plates were arranged so that their absorption axes were orthogonal to each other, and the stretching direction of the laminate and the absorption axes of the lower polarizing plates were arranged to be orthogonal.

Regarding (III), as shown in Fig. 5(b), a commercially available polarizing plate was superimposed under the laminate (sample), light was irradiated from the bottom, and visually observed from above. At that time, it was arrange|positioned so that the absorption axis of the polarizing film of a laminated body and the absorption axis of the lower polarizing plate might be orthogonal to each other.

In addition, the evaluation criteria shown in Table 1 are as follows.

○: Changes in defects cannot be recognized

×: Changes in defects can be visually recognized

4. Polarization

Using a spectrophotometer (manufactured by Murakami Color Co., Ltd., product name “Dot-41”), the single transmittance (Ts), parallel transmittance (Tp), and orthogonal transmittance (Tc) of the polarizing film were measured, and the degree of polarization (P) was obtained by the following equation. . In addition, these transmittances are Y values measured by a 2-degree field of view (C light source) of JIS Z 8701 and corrected for visibility.

Polarization degree (P)={(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In the examples, fluctuations in the film thickness of the PVA-based resin layer and fluctuations in slow axis and absorption axis were suppressed at all times. The appearance was also excellent. In addition, in Examples 1-5 and 2-3, occurrence of wrinkles was visually confirmed. This can be considered to be due to thermal wrinkles generated on the resin substrate by heat treatment.

[Industrial availability]

The polarizing film of the present invention can be most suitably used, for example, in an image display device. Specifically, it is suitably used for liquid crystal panels such as liquid crystal televisions, liquid crystal displays, mobile phones, digital cameras, camcorders, portable game machines, car navigation machines, copiers, printers, fax machines, watches, microwave ovens, and anti-reflection plates for organic EL devices. .

10: laminate
11: resin substrate
12: polyvinyl alcohol (PVA)-based resin layer

Claims (15)

A unwinding step of unwinding the resin substrate from the resin substrate roll in which the elongated resin substrate is wound in a roll shape, and
A step of heating the unwound resin substrate to a glass transition temperature (Tg) of -15°C or higher of the resin substrate, and
A step of performing corona treatment on the surface of the resin substrate, and
A coating liquid containing polyvinyl alcohol-based resin is applied on the corona-treated resin substrate to form a coating film, and the coating film is dried without stretching the resin substrate on which the coating film is formed to form a polyvinyl alcohol-based resin layer Forming process
A method for producing a laminate comprising in this order. The method of claim 1,
The production method, wherein a heating step is performed after storage in the wound state. The method according to claim 1 or 2,
The manufacturing method, wherein the unwinding step, the heating step, the corona treatment, and the polyvinyl alcohol-based resin layer forming step are successively performed. The method according to any one of claims 1 to 3,
The manufacturing method, wherein the heating step is performed at a glass transition temperature (Tg) of the resin substrate + 15°C or lower. The method according to any one of claims 1 to 4,
A manufacturing method, wherein the heating step is carried out while conveying the resin substrate with a conveying roll installed in a heating furnace. The method of claim 5,
The manufacturing method, wherein the foam angle of the conveying roll in the heating furnace is 90° or more. The method according to claim 5 or 6,
The manufacturing method, wherein the distance between the centers of the conveying rolls in the heating furnace is 2 m or less. The method according to any one of claims 1 to 4,
A manufacturing method, wherein the heating step is performed while conveying the resin substrate with a tenter. The method according to any one of claims 1 to 8,
The production method, wherein the shrinkage of the resin substrate by the heating is 3% or less. The method according to any one of claims 1 to 9,
The production method, wherein the resin substrate is formed of a polyethylene terephthalate-based resin. The method according to any one of claims 1 to 10,
The production method in which the resin substrate has been previously stretched. The method according to any one of claims 1 to 11,
The production method, wherein the polyvinyl alcohol-based resin layer is formed by applying a coating liquid containing a polyvinyl alcohol-based resin on a resin substrate by a die coating method and drying it. A method for producing a polarizing film using the laminate obtained by the production method according to any one of claims 1 to 12. The method of claim 13,
A manufacturing method comprising the step of stretching the stretched body. A method for manufacturing a polarizing plate, including a step of laminating a protective film on the polarizing film obtained by the manufacturing method according to claim 13 or 14.

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