KR20220093005A - Method for producing laminate - Google Patents

Abstract

A laminate capable of forming a polarizing film having uniform performance is provided. 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 ( 12) is included in this order.

Description

Method for manufacturing a laminate {METHOD FOR PRODUCING LAMINATE}

The present invention relates to a method for manufacturing a laminate. Specifically, it relates to a method for manufacturing 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 (see, for example, Patent Document 1 and Patent Document 2). Since a polarizing film with a thin thickness can be obtained from this method, attention is paid to, for example, in that it can contribute to thickness reduction of an image display apparatus. However, in this case, there is a problem that irregularity easily occurs in the performance (specifically, film thickness, optical properties, and appearance) of the resulting polarizing film.

Patent Document 1: Japanese Patent Laid-Open No. 51-69644 Patent Document 2: Japanese Patent Laid-Open No. 2001-343521

The present invention has been devised to solve the above-mentioned problems, and its main purpose is to provide a laminate capable of manufacturing a polarizing film having uniform performance.

In the method for manufacturing a laminate of the present invention, 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 are performed in this order include

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

In one embodiment, the heating process is performed after storage in the rolled up state.

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

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

* In one embodiment, the heating step is performed while conveying the resin substrate by a conveying roll installed in a heating furnace.

In one embodiment, the envelope 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 2 m or less.

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

In one embodiment, the shrinkage rate 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 solution including a polyvinyl alcohol-based resin on the resin substrate by a die coating method and drying.

According to another aspect of the present invention, a method for 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, the process of extending|stretching the said laminated body is included.

According to another aspect of the present invention, a method for manufacturing a polarizing plate is provided. The manufacturing method of this polarizing plate includes the process of laminating|stacking a protective film on the polarizing film obtained by the said 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 the polyvinyl alcohol-based resin layer is 200 mm (MD) × 200 mm ( The slow-axis variation 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 is provided with an unwinding means for unwinding the resin substrate from a resin substrate roll on which the elongated resin substrate is wound in a roll shape, and a conveying roll for transporting the elongated resin substrate, A heating furnace for heating the resin substrate to a glass transition temperature (Tg) of -15°C or higher of the resin substrate, and a coating means for applying a coating solution 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 envelope 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 2 m or less.

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

In one embodiment, the resin substrate is heated while being conveyed by the tenter.

According to the present invention, it is possible to relieve (uniform) the surface unevenness of the resin substrate (eg, a gauge band generated when the resin substrate is wound) by subjecting the resin substrate to heat treatment at a predetermined temperature or higher. As a result, it is possible to form a PVA-based resin layer excellent in thickness uniformity on the resin substrate. By subjecting the PVA-based resin layer excellent in thickness uniformity to various treatments, there is no variation in performance (specifically, film thickness, optical properties, and appearance), and a polarizing film excellent in uniformity (e.g., for liquid crystal televisions) sufficiently satisfying the required quality) 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 views 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.
It is a schematic diagram explaining the evaluation method of the external appearance of a PVA-type 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 the polyvinyl alcohol (PVA)-based resin layer 12 on the resin substrate 11 .

A-1. resin substrate

The resin substrate is typically elongated. The thickness of the resin substrate is preferably 20 µm to 300 µm, more preferably 50 µm to 200 µm.

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

The glass transition temperature (Tg) of the resin substrate is preferably 170°C or less. By using such a resin base material, it is possible to stretch the laminate at a temperature at which crystallization of the PVA-based resin does not proceed rapidly, and troubles due to the crystallization (eg, hindering the orientation of the PVA-based resin layer due to 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, a glass transition temperature (Tg) is a value which can be calculated|required according to JISK7121.

The resin substrate is molded by any suitable method. As a shaping|molding method, the melt extrusion method, the solution casting method (solution casting method), the calendering method, the compression molding method etc. are mentioned, for example. Among these, the melt extrusion method is preferable.

A surface modification treatment (eg, corona treatment, etc.) may be performed on the surface of the resin substrate, or an anti-adhesive layer may be formed. According to such a process, the adhesiveness of a resin base material and a PVA-type resin layer can be improved. The surface modification treatment and/or formation of the easy-adhesive layer may be performed before the below-mentioned heat treatment, or may be performed after the heat treatment. Moreover, when performing the extending|stretching mentioned later, you may carry out before the extending|stretching, and you may carry out after extending|stretching.

In one embodiment, the resin substrate is stretched before heat treatment to be described later. Any suitable method can be employ|adopted as a extending|stretching method of a resin base material. Specifically, fixed-end stretching may be used or free-end stretching may be sufficient. Moreover, simultaneous biaxial stretching may be sufficient and sequential biaxial stretching may be sufficient as it. Extending|stretching of a resin base material may be performed in one step, and may be performed in multiple steps. When carrying out in multiple steps, the draw ratio of the resin base material mentioned later is the product of the draw ratio of each step. Moreover, an extending|stretching system is not specifically limited, An air extending|stretching system may be sufficient, and an underwater extending|stretching system may be sufficient.

The resin base material extending|stretching direction can be set suitably. For example, an elongate resin base material is extended|stretched in the width direction. Specifically, a resin base material is conveyed in a longitudinal direction, and it extends|stretches in the direction (TD) orthogonal to the conveyance direction (MD). As used herein, the term “orthogonal” includes a case where it is substantially orthogonal. Herein, the term “substantially orthogonal” includes the case of 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°. By extending|stretching a resin base material in the width direction (TD), a resin base material can be utilized effectively. Moreover, the thickness in TD of a resin base material can be made uniform, and the partial film thickness fluctuation|variation mentioned 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 preferably Tg-10°C to Tg+80°C with respect to the glass transition temperature (Tg) of the resin substrate. When using a polyethylene terephthalate-type resin as a forming material of a resin base material, the extending|stretching temperature becomes like this. Preferably it is 70 degreeC - 150 degreeC, More preferably, it is 90 degreeC - 130 degreeC.

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, the 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, wrinkle generation can be suppressed favorably 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, there is a partial variation in the film thickness, and if the film is wound in this state, irregularities may occur in the resin substrate. The winding tension is typically 60N/m to 150N/m (unit: N/m is the tension per unit width and length). The wound resin substrate (resin substrate roll) can be stored (leaved) in a wound state for any suitable period until it is used in the next process. For example, when the PVA-based resin layer is not continuously formed after molding of the resin substrate, the resin substrate is stored in a wound state. When this storage period is prolonged (for example, 3 days or more), the occurrence of irregularities (the degree of irregularities, the number of occurrences of irregularities) becomes significant, and the resulting PVA-based resin layer (laminate) tends to have a film thickness fluctuation. . Therefore, the longer the storage period of the resin base roll, the more remarkable the effect of the heat treatment described later. The resin-based rolls may also be stored under any suitable atmosphere. The storage temperature is, for example, 15°C to 35°C. The 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 (Tg) -15°C or higher, preferably Tg-10°C or higher, more preferably Tg-5°C or higher. When using a polyethylene terephthalate-type resin as a forming material of a resin base material, a heating temperature becomes like this. Preferably it is 68 degreeC or more. By heating the resin substrate to such a temperature, it is possible to relieve (uniform) the surface irregularities of the resin substrate. As a result, the PVA-type resin layer mentioned later can be formed favorably, and the PVA-type resin layer excellent in thickness uniformity can be formed. On the other hand, the heating temperature is preferably (Tg)+15°C or lower, more preferably Tg+10°C or lower. When a polyethylene terephthalate-type resin is used as a forming material of a resin base material, a heating temperature becomes like this. Preferably it is 80 degreeC or less. By heating the resin base material to this temperature, generation|occurrence|production of wrinkles (thermal wrinkles) can be suppressed favorably.

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 contract in the width direction (TD shrinkage) by heating. The shrinkage rate (TD shrinkage rate) of the resin substrate is preferably 3% or less, more preferably 2% or less, particularly preferably 1.5% or less. If it is within such a range, generation|occurrence|production of wrinkles is suppressed and an excellent external appearance can be obtained. In addition, the TD shrinkage rate is calculated by the following formula.

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

In one embodiment, the resin substrate is heated while being conveyed. As mentioned above, when a resin base material is wound up in roll shape, it is preferable to heat-process to the resin base material unwound from the resin base material roll. As a heating method, the method of conveying a resin base material with the conveyance roll provided in the heating furnace, for example, the method of heating while conveying a resin base material with a tenter is mentioned. According to the former, the enlargement of an installation can be suppressed. According to the latter, generation|occurrence|production of a wrinkle can be suppressed very favorably.

A specific example in the case of using a conveyance roll is shown in FIG.2(a) and FIG.2(b). In the example of illustration, the resin base material 11 is heated by conveying the resin base material 11 in the longitudinal direction with the prerolls R2 - R5 provided in the oven furnace A. As shown in FIG. From the viewpoint of production speed, it is preferable to install four or more prerolls in the oven furnace as shown in the illustrated example.

The angle of the preroll in the oven is preferably 90° or more. In the example shown in Fig. 2(a), the envelope angle θ of the prerolls R2 and R5 is 90°, and the envelope angle θ of the prerolls R3 and R4 is 180°. In the example shown in FIG.2(b), the envelope angle θ of the prerolls R2 to R5 is set to 90°. By setting it as such a wrapper, the shrinkage|contraction of a resin base material can be suppressed and generation|occurrence|production of wrinkles can be suppressed. In addition, when the preroll is viewed as a cross section perpendicular to the axial direction, the straight line connecting the center point of the preroll and the contact start point between the resin substrate and the preroll, and the center point of the preroll and the resin substrate and the preroll The angle formed by a straight line joining the contact endpoints. The distance between the prerolls in the oven (distance between the centers of the rolls) is preferably 2 m or less. In addition, it is preferable that the distance between the two prerolls (between R1-R2 and R5-R6 in the example shown) installed as if spanning the entrance to the oven is also less than 2m. By setting it as such a space|interval, the shrinkage|contraction of a resin base material can be suppressed and generation|occurrence|production of wrinkles can be suppressed. In addition, in the present embodiment, the shrinkage of the resin substrate may be related to the draw ratio of the resin substrate, the heating temperature, and the like.

A specific example in the case of using a tenter is shown in FIG. In the illustrated example, both ends (on a line orthogonal to the conveying direction) of the resin substrate 11 are respectively gripped by the clips 21 and 21 on the left and right of the tenter, and the heating zone is conveyed in the longitudinal direction at a predetermined speed, whereby the resin The base material 11 is being heated. The distance between clips in the conveying direction (distance between adjacent clip ends) is preferably 20 mm or less, more preferably 10 mm or less. The clip width is preferably at least 20 mm, more preferably at least 30 mm. In this embodiment, the TD shrinkage of the resin substrate can be controlled by, for example, adjusting the distance between the left and right clips. Specifically, when the distance between the left and right clips is moved without changing, the TD shrinkage rate becomes substantially 0%. Conversely, by increasing the distance between the left and right clips, the resin substrate can be TD stretched. The TD change rate 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 formula.

TD change rate (fold) = 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 appropriate 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 are mentioned. Polyvinyl alcohol can be obtained by saponification of polyvinyl acetate. An ethylene vinyl alcohol copolymer can be obtained by saponification of an ethylene vinyl acetate copolymer. The sensitization degree of PVA-type resin is 85 mol% - 100 mol% normally, Preferably it is 95.0 mol% - 99.95 mol%, More preferably, it is 99.0 mol% - 99.93 mol%. The sensitivity can be obtained according to JIS K 6726-1994. A polarizing film excellent in durability can be obtained by using the PVA-type resin of such a sensitization degree. 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 according to 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 calculated|required according to JISK6726-1994.

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 solution is typically a solution in which the PVA-based resin is dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylprolitone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. can be used These can be used individually or in combination of two or more types. Among these, water is preferable. The concentration of the PVA-based 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, a uniform coating film in close contact with the resin substrate can be formed.

The coating liquid may contain an additive. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As surfactant, a nonionic surfactant is mentioned, for example. These are used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer. Moreover, as an additive, an anti-adhesive component is mentioned, for example. By using an easy-adhesive component, the adhesiveness of a resin base material and a PVA-type resin layer can be improved. As a result, for example, troubles, such as peeling of a PVA-type resin layer from a resin base material, can be suppressed, and dyeing and underwater extending|stretching mentioned later can be performed favorably. As an easy-adhesive component, modified PVA, such as acetoacetyl modified PVA, can be used, for example.

Any suitable method can be employ|adopted as a coating method of a 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.) etc. are mentioned.

In one embodiment, a die coating method is employed. In the die coating method, the coating liquid is applied with a constant gap between the resin substrate and the die (eg, a fountain die, a slot die), so that a coating film having very good 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, when the die coating method is employed, the effect of the heat treatment can be remarkably obtained.

The coating solution is applied so that the thickness of the PVA-based resin layer after drying 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, the PVA-based resin layer is continuously formed after the heating. For example, the PVA-based resin layer is formed on the resin substrate without winding the resin substrate after heating. It is because the effect by the said heating can be acquired well.

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

A-5. Etc

In one embodiment, the unwinding of the resin substrate from the resin substrate roll (unwinding process), heating (heating process) of the resin substrate, and formation of the 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 favorably. As a specific example of this Example, as shown in FIG. 4, the form which unwinds the elongate resin base material with a series of lines conveying, and performs heating and PVA system resin layer formation process sequentially is mentioned. In the laminate manufacturing apparatus 100 shown in FIG. 4, the unwinding roll 40 which unwinds the resin base material 11 from the resin base roll 30, the heating apparatus 50 which heats the resin base material 11, and resin A coating device 60 for applying the 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 equipped with the some conveyance roll 90. As shown in FIG.

B. Stretched Laminate

The stretched laminate of the present invention is produced by stretching the laminate. In one embodiment, the stretched laminate is manufactured 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. The detail of the extending|stretching method of a laminated body is as mentioned later. In the stretched laminate, the film thickness fluctuation 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 slow axis fluctuation within the size of 200 mm (MD) x 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 this invention is produced by giving the process for making the PVA-type resin layer of the said laminated body into a polarizing film.

Examples of the treatment for forming the polarizing film include 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 time, number of times of processing, etc. 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 substance. Preferably, it is carried out by adsorbing a dichroic substance to a PVA-type resin layer. As the adsorption method, for example, a method of immersing a PVA-based resin layer (laminate) in a dyeing solution containing a dichroic substance, a method of coating the dyeing solution on a PVA-based resin layer, and spraying the dyeing solution on a PVA-based resin layer how to do it, etc. Preferably, it is a method of immersing the laminate in a dyeing solution. It is because a dichroic substance can be adsorb|sucked favorably.

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

The temperature of the liquid at the time of dyeing the dyeing solution 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, it is possible to sufficiently adsorb the dichroic material 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 finally obtained polarizing film may become a predetermined range. In one embodiment, the immersion time is set so that the degree of polarization of the polarizing film obtainable is 99.98% or more. In another embodiment, the immersion time is set so that the single transmittance of the obtainable polarizing film is about 40%.

(Stretching treatment)

Any suitable method can be employ|adopted as a laminated body extending|stretching method. Specifically, fixed-end stretching (eg, a method using a tenter stretching machine) or free-end stretching (eg, a method of uniaxial stretching between rolls having different peripheral speeds through a laminate) may be used. Moreover, simultaneous biaxial stretching (for example, the method using a simultaneous biaxial stretching machine) may be sufficient, and biaxial stretching may be used sequentially. Extending|stretching of a laminated body may be performed in one step, and may be performed in multiple steps. When carrying out in multiple steps, the draw ratio (maximum draw ratio) of the laminated body mentioned later is the product of the draw ratios of each step.

The stretching treatment may be an underwater stretching system performed while immersing the laminate in a stretching bath, or an air stretching system may be used. Preferably, the underwater stretching treatment is performed at least once, and more preferably, the underwater stretching treatment and the air 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, it is possible to manufacture a polarizing film having excellent optical properties (eg, polarization degree).

Any suitable direction can be selected as a laminated body extending|stretching direction. In one embodiment, the elongated laminate is stretched in the longitudinal direction. Specifically, a laminate is conveyed in a longitudinal direction, and it is the conveyance 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 a longitudinal direction and orthogonal to the conveyance direction MD.

The stretching temperature of the laminate can be set to any appropriate value according to the forming material of the resin substrate, the stretching method, and the like. When the aerial stretching method is employed, the stretching temperature is preferably not less than the glass transition temperature (Tg) of the resin substrate, more preferably not less than the glass transition temperature (Tg) of the resin substrate +10°C, particularly preferably Tg + 15°C or higher. On the other hand, the extending|stretching temperature of a laminated body becomes like this. Preferably it is 170 degrees C or less. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin, thereby suppressing troubles due to the crystallization (eg, interfering with the orientation of the PVA-based resin layer due to stretching).

When an underwater stretching method is employed as the stretching method, the liquid temperature of the stretching bath is preferably 40°C to 85°C, more preferably 50°C to 85°C. If it is such a temperature, it can extend|stretch at a high magnification, suppressing melt|dissolution of a PVA-type 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, when the stretching temperature is lower than 40°C, there is a possibility that the stretching cannot be performed satisfactorily even in consideration of plasticization of the resin substrate by water. 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 fear that excellent optical properties cannot be obtained.

When the underwater stretching method is employed, the laminate is preferably immersed in an aqueous solution of boric acid and stretched (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, the rigidity which withstands the tension|tensile_strength required at the time of extending|stretching, and the water resistance which does not melt|dissolve in water can be provided to a PVA-type resin layer. Specifically, it can be crosslinked by hydrogen bonding with a PVA-based resin by generating a tetrahydroxyboric acid anion in an aqueous solution of silver boric acid. As a result, the PVA-based resin layer can be stretched favorably by imparting rigidity and water resistance, and a polarizing film having excellent optical properties can be produced.

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

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

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

The elongation (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 employ|adopting the underwater extending|stretching system (boric acid underwater extending|stretching). In addition, in the present specification, "maximum draw ratio" means a draw ratio just before the laminate is broken, check the draw ratio at which a separate laminate breaks, and refers to a value 0.2 smaller than the value.

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, when an underwater stretching method is employed, 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 with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 50°C. Preferably, the insolubilization treatment is performed after the laminate production, before the dyeing treatment or the underwater stretching treatment.

(crosslinking treatment)

The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing a crosslinking process, water resistance can be provided to a PVA-type resin layer. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. Moreover, when crosslinking treatment is performed after the said dyeing|staining treatment, it is more preferable to mix|blend an iodide. By mix|blending an iodide, the elution of the iodine made to adsorb|suck to the PVA-type resin layer can be suppressed. The blending amount of the iodide is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C. Preferably, the crosslinking treatment is performed before the underwater stretching treatment. In a preferred embodiment, the dyeing treatment, the crosslinking treatment and the water stretching treatment are performed in this order.

(cleaning treatment)

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

(dry treatment)

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

The obtained polarizing film is substantially a PVA-type resin film in which the dichroic substance was adsorbed-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, particularly preferably 5 µm or less. Such a polarizing film can suppress the occurrence of cracks or the like in an environmental test (eg, an 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 have very good transportability during manufacture, etc.

The polarizing film preferably exhibits absorption dichroism at a wavelength in the range of 380 nm to 780 nm. The polarizing film preferably 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 separate 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, olefin resins such as cycloolefin resin and polypropylene, and ester resins such as polyethylene terephthalate resin. Resin, polyamide-type resin, polycarbonate-type resin, these copolymer resin, etc. are mentioned. 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 peeling from the polarizing film. In another embodiment, the resin substrate is peeled off from the polarizing film and another film is laminated. A protective film may be laminated|stacked on a polarizing film through an adhesive layer, or may be laminated|stacked by making it adhere|attach (not via an adhesive layer). The adhesive layer is typically formed of an adhesive or a pressure-sensitive adhesive. ADVANTAGE OF THE INVENTION According to this invention, since the polarizing film excellent in the uniformity of thickness can be obtained, lamination|stacking of the protective film to a polarizing film can be performed favorably.

[Example]

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

[Example 1-1]

(Production of laminate)

It is composed of amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) with a water absorption rate of 0.75% and a glass transition temperature (Tg) of 75°C, and has a long shape that is TD stretched 2.0 times at 115°C in advance, and a resin substrate with a thickness of 100 μm is applied with a tension of 100N. It was stored as a resin base roll wound in a roll shape at /m, and stored for 30 days at 25° C. and a relative humidity of 60% RH in the wound state.

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, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl denaturation degree 4.6%, sensitization degree 99.0 mol% or more, Japan Synthetic Chemical Industry Co., Ltd. product, product name "Kose After applying an aqueous solution containing “Fimer Z200 (GOHSEFIMER Z200)” in a ratio of 9:1 at 25° C. by die coating, drying at 60° C. for 200 seconds to form a PVA-based resin layer with a thickness of 10 μm to form a laminate made

(Production of polarizing film)

The free-end uniaxial stretching of the obtained laminated body at 2.0 times in the longitudinal direction between the rolls from which the circumferential speed differs in oven at 115 degreeC (air-stretching) was carried out.

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

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

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

After that, while immersing the laminate in an aqueous solution of boric acid at a liquid temperature of 70° C. (an aqueous solution obtained by blending 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water), 2.7 in the longitudinal direction between rolls having different circumferential speeds. It was uniaxially stretched by a ship (underwater stretching).

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

In this way, a polarizing film with a thickness of 5 µm 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 heat treatment temperature 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 heat treatment temperature 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]

(Production of laminate)

It carried out similarly to Example 1-1, and produced the laminated body.

(Formation of polarizing film)

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

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

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

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

After that, the laminate was immersed in a washing bath at 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) for 10 seconds, and then dried with warm air at 60°C for 60 seconds (washing and drying). process).

In this way, a polarizing film having a thickness of 2.5 µm 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 heat treatment temperature 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 no heat treatment was 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.

[Relatively 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 the comparative example.

1. Film thickness fluctuation

The film thickness of the PVA-based resin layer after (I) polyvinyl alcohol aqueous solution was applied and dried (before stretching) and (II) after aerial stretching was measured using “MCPD3000” manufactured by Otsuka Electronics. Cut out the part including the flaw (the part where the gauge band was originally) to a size of 200 mm (MD) x 200 mm (TD) and use it as a measurement sample. The difference between the thickness and the minimum film thickness was evaluated.

2. Slow axis fluctuation and absorption axis fluctuation

(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 part including the fault part was cut out to the size of 200 mm (MD) x 200 mm (TD), it was set as the measurement sample, and the largest axial direction difference of the fault part in a plane was measured. In addition, about (I) and (II), after sticking a PVA-type resin layer to a glass plate through an adhesive layer, the resin base material was peeled and the slow axis of the PVA-type resin layer was measured.

3. Appearance

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

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

Regarding (I) and (II), as shown in Fig. 5(a), a commercially available polarizing plate was superposed on each of the upper and lower sides of the laminate (sample), irradiated with light from the bottom, and visually observed from above. In that case, the two polarizing plates were arrange|positioned so that the absorption axis|shaft of each other might be orthogonal, and it arrange|positioned so that the laminated body extending|stretching direction and the absorption axis of the lower polarizing plate may be orthogonal.

Regarding (III), as shown in Fig. 5(b), a commercially available polarizing plate was superposed under the laminate (sample), light was irradiated from the bottom, and visually observed from above. In that case, it has arrange|positioned so that the absorption axis of the polarizing film of a laminated body and the absorption axis of the lower polarizing plate may be orthogonal.

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

○: The change of the defect part cannot be visually recognized.

x: the change of the defect part can be visually recognized

4. Polarization

The single transmittance (Ts), parallel transmittance (Tp) and orthogonal transmittance (Tc) of the polarizing film were measured using a spectrophotometer (Murakami Color Co., Ltd. product name “Dot-41”), and the degree of polarization (P) was obtained by the following formula. . In addition, these transmittance|permeability are the Y values which measured by the 2 degree field of view (C light source) of JIS Z 8701, and performed visibility correction.

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

In the Example, the film thickness fluctuation|variation and slow axis fluctuation|variation and absorption axis fluctuation|variation of the PVA-type resin layer were suppressed in all the time points. The appearance was also excellent. Moreover, in Example 1-5 and Example 2-3, the generation|occurrence|production of wrinkles was confirmed visually. This is considered to be due to thermal wrinkles generated in the resin substrate by heat treatment.

[Industrial Applicability]

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

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

Claims (14)

An unwinding step of unwinding the resin substrate from the resin substrate roll in which the elongated resin substrate is wound in a roll shape;
A step of heating the unwound resin substrate to a glass transition temperature (Tg) of -15°C or higher of the resin substrate;
A process of corona-treating the surface of the resin substrate;
A coating solution containing a polyvinyl alcohol-based resin is applied on the resin substrate subjected to the corona treatment 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, including in this order. According to claim 1,
The manufacturing method which performs a heating process after storing in the said wound up state. According to claim 1,
The manufacturing method which continuously performs the said unwound process, a heating process, a corona treatment, and a polyvinyl alcohol-type resin layer forming process. 4. The method according to any one of claims 1 to 3,
The manufacturing method which performs the said heating process at the glass transition temperature (Tg) of a resin substrate +15 degreeC or less. 4. The method according to any one of claims 1 to 3,
The manufacturing method which performs the said heating process, conveying the resin base material with the conveyance roll provided in the heating furnace. 6. The method of claim 5,
A manufacturing method, wherein the envelope angle of the conveying roll in the heating furnace is 90° or more. 6. The method of claim 5,
The distance between the centers of the conveyance rolls in the said heating furnace is 2 m or less, the manufacturing method. 4. The method according to any one of claims 1 to 3,
The manufacturing method which performs the said heating process, conveying a resin base material by a tenter. 4. The method according to any one of claims 1 to 3,
The manufacturing method in which the said resin base material is formed from polyethylene terephthalate-type resin. 4. The method according to any one of claims 1 to 3,
The manufacturing method in which the said resin base material is stretched beforehand. 4. The method according to any one of claims 1 to 3,
The polyvinyl alcohol-based resin layer is formed by applying a coating solution containing a polyvinyl alcohol-based resin on a resin substrate by a die coating method and drying. The manufacturing method of a polarizing film using the laminated body obtained by the manufacturing method in any one of Claims 1-3. 13. The method of claim 12,
The manufacturing method including the process of extending|stretching the said laminated body. The manufacturing method of a polarizing plate including the process of laminating|stacking a protective film on the polarizing film obtained by the manufacturing method of Claim 12.

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