KR102580445B1 - Method for producing laminate - Google Patents

Abstract

A laminate capable of forming a polarizing film with uniform performance is provided. The manufacturing method of the laminate of the present invention includes the process of heating the resin substrate 11 to the glass transition temperature (Tg) of the resin substrate 11 -15°C or higher, and forming a polyvinyl alcohol-based resin layer on the resin substrate 11 ( 12) includes the forming processes 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 of 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 has been proposed by applying and forming a PVA-based resin layer on a resin substrate, and then stretching and dyeing this laminate (see, for example, Patent Document 1 and Patent Document 2). Since a thin polarizing film can be obtained from this method, it is attracting attention because, for example, it can contribute to thinning of image display devices. However, in this case, there is a problem that irregularities easily occur in the performance (specifically, film thickness, optical characteristics, and appearance) of the obtained 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 was conceived to solve the above existing problems, and its main purpose is to provide a laminate capable of manufacturing a polarizing film with uniform performance.

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

In one embodiment, the heating process is performed by unwinding the elongated resin substrate from a resin substrate roll wound into a roll shape.

In one embodiment, the heating process is performed after being stored in the rolled state.

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

In one embodiment, the heating process is performed below the glass transition temperature (Tg) of the resin substrate +15°C.

*In one embodiment, the heating process is performed while conveying the resin substrate with a conveyance roll installed in the heating furnace.

In one embodiment, the folding angle of the conveyance 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 process is performed while transporting the resin substrate using a tenter.

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

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

In one embodiment, the resin substrate is pre-stretched.

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

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 laminate obtained by the above manufacturing method.

In one embodiment, a process of stretching the laminate 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 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 the polyvinyl alcohol-based resin layer has an irregularity of 200 mm (MD) × 200 mm ( The variation of the slow axis within the size of TD) is less than 0.50°.

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

In one embodiment, the manufacturing apparatus is provided with an unwinding means for unwinding the resin substrate from a resin substrate roll in which the elongated resin substrate is wound into a roll shape, and a conveyance roll for conveying the elongated resin substrate. It is provided with a heating furnace that heats the resin substrate to the glass transition temperature (Tg) of the resin substrate -15°C or higher and an application means that applies a coating liquid containing a polyvinyl alcohol-based resin onto the heated resin substrate.

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

In one embodiment, the folding angle of the conveyance 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 device includes an unwinding means for unwinding the resin substrate from a resin substrate roll in which the elongated resin substrate is wound into a roll, and a tenter for grasping and transporting both ends of the elongated resin substrate. It is provided with a heating means for heating the resin substrate held at both ends by clips of the tenter to a glass transition temperature (Tg) of -15° C. or higher, and a polyvinyl alcohol-based resin on the heated resin substrate. It is provided with an application means for applying the coating liquid.

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

According to the present invention, surface irregularities of the resin substrate (for example, gauge bands that occur when the resin substrate is wound) can be alleviated (evenized) by subjecting the resin substrate to a heat treatment at a predetermined temperature or higher. As a result, a PVA-based resin layer with excellent thickness uniformity can be formed on the resin substrate. By subjecting the PVA-based resin layer, which has excellent thickness uniformity, to various treatments, there is no change in performance (specifically, film thickness, optical properties, and appearance), and a polarizing film with excellent uniformity (e.g., used in liquid crystal televisions) (that sufficiently satisfies the required quality) can be manufactured.

1 is a schematic cross-sectional view of a laminate according to an embodiment of the present invention.
In Figure 2 (a) and (b) are schematic diagrams explaining a method of heating a resin substrate according to an embodiment.
Figure 3 is a schematic diagram explaining a method of heating a resin substrate according to another embodiment.
Figure 4 is a schematic diagram showing an example of the present invention.
Figure 5 is a schematic diagram explaining 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 embodiments.

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 material

The resin substrate typically has a long shape. The thickness of the resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm.

Materials for forming the resin base include, for example, ester resins such as polyethylene terephthalate resins, cycloolefin resins, olefin resins such as polypropylene, (meth)acrylic resins, polyamide resins, and polycarbonate resins. copolymer resins, etc. can be mentioned. Preferably, polyethylene terephthalate resin can be used. Among them, amorphous polyethylene terephthalate 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 lower. By using such a resin substrate, it is possible to stretch the laminate at a temperature where crystallization of the PVA-based resin does not proceed rapidly, and troubles caused by the crystallization (for example, interference with the orientation of the PVA-based resin layer due to stretching) are eliminated. It can be suppressed. Meanwhile, the glass transition temperature of the resin substrate is preferably 60°C or higher. In addition, the glass transition temperature (Tg) is a value that can be determined according to JIS K 7121.

The resin substrate is molded by any suitable method. Molding methods include, for example, melt extrusion method, solution casting method (solution casting method), calendering method, compression molding method, etc. Among these, the melt extrusion method is preferable.

The surface of the resin substrate may be subjected to surface modification treatment (e.g., corona treatment, etc.) or may be formed with a reverse adhesive layer. According to this treatment, the adhesion between the resin substrate and the PVA-based resin layer can be improved. The surface modification treatment and/or the formation of the easy adhesive layer may be performed before or after the heat treatment described later. In addition, when performing stretching described later, it may be performed before or after stretching.

In one embodiment, the resin substrate is stretched before the heat treatment described later. Any appropriate method can be employed as a method for stretching the resin substrate. Specifically, it may be fixed-end stretching or free-end stretching. Additionally, simultaneous biaxial stretching may be used or sequential biaxial stretching may be used. Stretching of the resin substrate may be performed in one step or may be performed in multiple steps. When carried out in multiple steps, the draw ratio of the resin substrate described later is the product of the draw ratios of each step. Additionally, the stretching method is not particularly limited and may be an air stretching method or an underwater stretching method.

The direction of stretching of the resin substrate can be set appropriately. For example, a long resin substrate is stretched in the width direction. Specifically, the resin substrate is transported in the longitudinal direction and stretched in a direction (TD) perpendicular to the transport direction (MD). In this specification, “orthogonal” also includes cases of substantially orthogonal. Here, “substantially orthogonal” includes the case of 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°. The resin substrate can be effectively used by stretching it in the width direction (TD). In addition, the thickness in TD of the resin substrate 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 forming material of the resin substrate, the stretching method, etc. The stretching temperature is typically preferably Tg-10°C to Tg+80°C relative to the glass transition temperature (Tg) of the resin substrate. When using a polyethylene terephthalate-based resin as a forming material for the resin base, the stretching temperature is preferably 70°C to 150°C, more preferably 90°C to 130°C.

The stretching ratio of the resin substrate is preferably 1.5 times or more relative to the original length of the resin substrate. By setting it within this range, partial film thickness fluctuations, which will be described later, can be well suppressed. Meanwhile, the stretch ratio of the resin substrate is preferably 3.0 times or less relative to the original length of the resin substrate. By setting it within this range, the generation of wrinkles can be well suppressed in the heating process described later.

A-2. Winding and storage

In one embodiment, the elongated resin substrate is wound into a roll shape. When molding the resin substrate, partial film thickness changes occur, so if it is wound in this state, irregularities may appear on the resin substrate. The winding tension is typically 60 N/m to 150 N/m (unit: N/m is tension per unit width length). The wound resin substrate (resin substrate roll) can be stored (left) in the wound state for any appropriate period of time until used in the next process. For example, after molding the resin substrate, if the PVA-based resin layer is not continuously formed (cannot be formed), the resin substrate is stored in a rolled state. If this storage period is prolonged (e.g., 3 days or more), the occurrence of irregularities (degree of irregularities, number of occurrences of irregularities) becomes noticeable, and film thickness fluctuations tend to occur in the resulting PVA-based resin layer (laminated body). . Therefore, the longer the storage period of the resin base roll, the more significantly the effect of the heat treatment described later can be obtained. Additionally, the resin base roll may 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 using hot air, an infrared heater, a roll heater, etc. The heating temperature is above the glass transition temperature (Tg) of the resin substrate -15°C or higher, preferably above Tg-10°C, and more preferably above Tg-5°C. When polyethylene terephthalate resin is used as the forming material for the resin substrate, the heating temperature is preferably 68°C or higher. By heating the resin substrate to this temperature, surface irregularities of the resin substrate can be alleviated (evenized). As a result, the PVA-based resin layer described later can be formed satisfactorily, and a PVA-based resin layer with excellent thickness uniformity can be formed. Meanwhile, the heating temperature is preferably (Tg)+15°C or lower, more preferably Tg+10°C or lower. When using polyethylene terephthalate-based resin as a forming material for the resin substrate, the heating temperature is preferably 80°C or lower. By heating the resin substrate to this temperature, the occurrence of wrinkles (thermal wrinkles) can be well suppressed.

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

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

TD shrinkage rate (%) = {1-(Resin base material width after heating (W ₁ )/Resin base material width before heating (W ₀ ))}×100

In one embodiment, the resin substrate is heated while being transported. As described above, when the resin substrate is wound into a roll shape, it is preferable to heat-treat the resin substrate unwound from the resin substrate roll. Examples of heating methods include a method of conveying the resin substrate with a conveyance 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 when using a conveyance roll is shown in Figures 2(a) and 2(b). In the illustrated example, the resin substrate 11 is heated by conveying the resin substrate 11 in its longitudinal direction using prerolls R2 to R5 installed in the oven A. From the viewpoint of production speed, it is desirable to install four or more pre-rolls in the oven as shown in the example.

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

A specific example when using a tenter is shown in Figure 3. In the illustrated example, both ends of the resin base material 11 (on a line perpendicular to the transport direction) are held by the clips 21 and 21 on the left and right sides of the tenter, respectively, and the heating zone is transported at a predetermined speed in the longitudinal direction, thereby forming the resin. The base material 11 is being heated. The distance between clips in the conveyance direction (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, TD shrinkage of the resin substrate can be controlled, for example, by adjusting the distance between the left and right clips. Specifically, when the clips on the left and right are moved without changing the distance between them, the TD shrinkage rate becomes substantially 0%. Conversely, by widening the distance between the left and right clips, the resin substrate can be stretched in TD. The TD change rate of the resin substrate is preferably 1.00 times or more, more preferably 1.00 to 1.10 times. Additionally, 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

As the PVA-based resin forming the PVA-based resin layer, any appropriate resin can be employed. Examples include polyvinyl alcohol and ethylene vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene vinyl alcohol copolymer can be obtained by saponifying ethylene vinyl acetate copolymer. The degree of saturation of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of sensitization can be obtained according to JIS K 6726-1994. By using a PVA-based resin with such a sensitivity, a polarizing film with excellent durability can be obtained. If the degree of saturation 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 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. Additionally, 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 PVA-based resin onto a resin substrate and drying it. The coating liquid is typically a solution obtained by dissolving the PVA-based resin in a solvent. Solvents include, for example, water, dimethyl sulfoxide, 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 alone or in combination of more than one type. Among these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. With this resin concentration, a uniform coating film that adheres to the resin substrate can be formed.

The coating liquid may contain additives. Additives include, for example, plasticizers and surfactants. Plasticizers include, for example, polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. These are used for the purpose of further improving the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer. Additionally, additives include, for example, an easy-adhesion component. By using an easy 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 underwater stretching, which will be described later, can be performed satisfactorily. As an easy adhesive component, for example, modified PVA such as acetoacetyl modified PVA can be used.

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

In one embodiment, a die coating method is employed. The die coating method applies the coating solution while maintaining a constant gap between the resin substrate and the die (e.g., fountain die, slot die), so a coating film with excellent uniformity in thickness can be obtained. On the other hand, when irregularities occur 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 adopted, the effect of the heat treatment can be significantly achieved.

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

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

Additionally, 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 is formed on the resin substrate. The material constituting the primer layer is not particularly limited as long as it is a material that exhibits a certain degree of strong adhesion to both the resin substrate and the PVA-based resin layer. For example, a thermoplastic resin with excellent transparency, thermal stability, stretchability, etc. can be used. Examples of thermoplastic resins include acrylic resins, polyolefin-based resins, polyester-based resins, polyvinyl alcohol-based resins, and mixtures thereof.

A-5. etc

In one embodiment, unwinding the resin substrate from the resin substrate roll (unwinding process), heating the resin substrate (heating process), and forming a PVA-based resin layer (PVA-based resin layer forming process) are performed continuously. According to this embodiment, the effect of the heat treatment can be favorably obtained. As a specific example of this embodiment, as shown in FIG. 4, a long-shaped resin substrate is unwound through a series of conveying lines, and heating and PVA-based resin layer forming steps are performed sequentially. The laminate manufacturing apparatus 100 shown in FIG. 4 includes an 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 An application 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 equipped with a plurality of conveyance 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 by an air stretching method at a stretch ratio of 1.5 to 3.0 times. Details of the method for stretching the laminate will be described later. In a stretched laminate, the film thickness variation of the PVA-based resin layer within a size of 200 mm (MD) x 200 mm (TD) is preferably 0.25 μm or less, more preferably 0.20 μm or less. In the stretched laminate, the slow axis variation 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, and particularly preferably 0.25° or less. am.

C. Polarizer

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

Treatments for forming the polarizing film include, for example, dyeing treatment, stretching treatment, insolubilization treatment, cross-linking treatment, washing treatment, and drying treatment. These treatments can be selected appropriately depending on the purpose. In addition, the processing order, processing time, processing number, etc. can be appropriately set. Below, each process is explained.

(dyeing treatment)

The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance. Preferably, this is carried out by adsorbing the dichroic substance to the PVA-based resin layer. The adsorption method includes, for example, a method of immersing the PVA-based resin layer (laminated body) in a dyeing solution containing a dichroic substance, a method of coating the dyeing solution on the PVA-based resin layer, and spraying the dyeing solution on the PVA-based resin layer. How to do it, etc. Preferably, the method is to immerse the laminate in a dyeing solution. This is because dichroic substances can be adsorbed well.

Examples of the dichroic material include iodine and organic dyes. These can be used alone or in combination of two or more types. The dichroic substance is preferably iodine. When using iodine as a dichroic material, the dyeing solution is preferably an aqueous iodine solution. The amount of iodine to be added is preferably 0.05 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 desirable to add iodide to the iodine aqueous solution. Iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferable. The amount of iodide to be added is preferably 0.3 to 15 parts by weight based on 100 parts by weight of water.

The temperature of the dyeing liquid during dyeing is preferably 20°C to 40°C. When immersing the PVA-based resin layer in the dyeing solution, the immersion time is preferably 10 to 300 seconds. Under these conditions, the dichroic material can be sufficiently adsorbed to the PVA-based resin layer. In addition, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or single transmittance of the finally obtained polarizing film is within a predetermined range. In one embodiment, the immersion time is set so that the polarization degree of the obtained polarizing film is 99.98% or more. In another example, the immersion time is set so that the single transmittance of the obtained polarizing film is about 40%.

(Stretching treatment)

Any suitable method can be adopted as the method for stretching the laminate. Specifically, it may be fixed-end stretching (for example, a method using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls with different peripheral speeds). Moreover, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) may be used or sequential biaxial stretching may be used. Stretching of the laminate may be performed in one step or may be performed in multiple steps. When carried out in multiple stages, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of each step.

The stretching treatment may be an underwater stretching method performed while immersing the laminate in a stretching bath, or an air stretching method. Preferably, the underwater stretching treatment is performed at least once, and more preferably, the underwater stretching treatment and the air stretching treatment are combined. By underwater stretching, the resin substrate or 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 with excellent optical properties (eg, degree of polarization) can be manufactured.

Any appropriate direction can be selected as the direction for stretching the laminate. In one embodiment, the elongated laminate is stretched in the longitudinal direction. Specifically, the laminated body is transported in the longitudinal direction and the transport direction (MD) is. In another example, the elongated laminate is stretched in the width direction. Specifically, the laminated body is transported in the longitudinal direction and the direction (TD) is perpendicular to the transport direction (MD).

The stretching temperature of the laminate can be set to any appropriate value depending on the forming material of the resin base, the stretching method, etc. When adopting the air stretching method, the stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the resin substrate +10°C, and particularly preferably equal to or higher than Tg+. It is above 15℃. Meanwhile, the stretching temperature of the laminate is preferably 170°C or lower. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, thereby suppressing problems caused by the crystallization (for example, disrupting the orientation of the PVA-based resin layer due to stretching).

When adopting the underwater stretching method 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. At this temperature, it is possible to stretch 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 lower than 40°C, there is a risk that satisfactory stretching may not be possible even considering plasticization of the resin substrate by water. On the other hand, as the temperature of the stretching bath becomes higher, the solubility of the PVA-based resin layer increases, and there is a risk that excellent optical properties cannot be obtained.

When using the underwater stretching method, it is preferable to stretch the laminate by immersing it in an aqueous boric acid solution (boric acid underwater stretching). By using an aqueous boric acid solution as a stretching bath, the PVA-based resin layer can be given rigidity to withstand the tension required during stretching and water resistance that does not dissolve in water. Specifically, boric acid can generate tetrahydroxyboric acid anions in an aqueous solution and crosslink with PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance are given to the PVA-based resin layer and it can be stretched well, making it possible to produce a polarizing film with excellent optical properties.

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

Preferably, iodide is added to the stretching bath (boric acid aqueous solution). By mixing iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, 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 laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio (maximum stretching 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 this specification, “maximum stretch ratio” refers to the stretch ratio just before the laminated body breaks. The stretch ratio at which the laminated body breaks is confirmed separately and is 0.2 smaller than that 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 adopted, water resistance can be imparted to the PVA-based resin layer by performing insolubilization treatment. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight based on 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C. Preferably, the insolubilization treatment is performed after manufacturing the laminate and before dyeing treatment or underwater stretching treatment.

(Cross-linking treatment)

The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing crosslinking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight based on 100 parts by weight of water. Moreover, when crosslinking treatment is performed after the above dyeing treatment, it is more preferable to mix iodide. By mixing iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide to be added is preferably 1 part by weight to 5 parts by weight based on 100 parts by weight of water. Specific examples of 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, cross-linking treatment and underwater stretching treatment are carried out 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 essentially 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, further preferably 7 μm or less, and particularly preferably 5 μm or less. This polarizing film can suppress the occurrence of cracks, etc. in environmental tests (eg, 80°C environmental tests). Meanwhile, the thickness of the polarizing film is preferably 0.5 μm or more, and more preferably 1.0 μm or more. Such a polarizing film can have very excellent transport properties, such as during manufacturing.

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

D. Polarizer

The polarizing plate of the present invention has the above 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 resin substrate may be used as is, or a film separate from the resin substrate may be used. Materials for forming the protective film include, for example, (meth)acrylic resin, cellulose-based resin such as diacetylcellulose and triacetylcellulose, cycloolefin-based resin, olefin-based resin such as polypropylene, and ester-based resin such as polyethylene terephthalate-based resin. Resins, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof can be mentioned. The thickness of the protective film is preferably 10 μm to 100 μm.

As described above, in one embodiment, the resin substrate is not peeled off from the polarizing film and can be used as a protective film. In another embodiment, the resin substrate is peeled from the polarizing film and another film is laminated. The protective film may be laminated on the polarizing film through an adhesive layer, or may be laminated in close contact (without an adhesive layer). The adhesive layer is typically formed of an adhesive or adhesive. According to the present invention, a polarizing film with extremely excellent thickness uniformity can be obtained, and thus the lamination of the protective film onto the polarizing film can be performed satisfactorily.

[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 made of amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) with an absorption rate of 0.75% and a glass transition temperature (Tg) of 75°C, and is pre-stretched by 2.0 times TD at 115°C. The long-shaped, 100㎛ thick resin substrate is tensioned at 100N. It was made into a resin base roll wound into a roll shape at a rate of /m and stored in a wound state at 25° C. and a relative humidity of 60% RH for 30 days.

After that, 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. To this corona-treated surface, polyvinyl alcohol (degree of polymerization 4200, degree of saturation 99.2 mol%) and acetoacetyl-modified PVA (degree of polymerization 1200, degree of acetoacetyl modification 4.6%, degree of saturation 99.0 mol% or more, manufactured by Japan Synthetic Chemical Industry Co., Ltd., product name “Kose”) An aqueous solution containing “GOHSEFIMER Z200” at a ratio of 9:1 was applied by die coating at 25°C and then dried at 60°C for 200 seconds to form a PVA-based resin layer with a thickness of 10㎛ to form a laminate. produced.

(Production of polarizing film)

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

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

Next, adjust the iodine concentration and immersion time so that the single transmittance (Ts) of the polarizing film obtained in a dye 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. It was immersed (dyed).

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

Thereafter, the laminate was immersed in an aqueous solution of boric acid (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) at a liquid temperature of 70°C, while rolling the laminate in the longitudinal direction between rolls with different circumferential speeds. Uniaxial stretching was performed with a boat (underwater stretching).

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

[Example 2-1]

(Production of laminate)

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

(Formation of polarizing film)

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

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

Next, in a dye 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, the iodine concentration is adjusted so that the single transmittance (Ts) of the resulting polarizing film is 40% or less. , immersed while adjusting the immersion time (dyeing treatment).

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

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

In this way, a polarizing film with 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 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 heat treatment temperature was 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 heat treatment temperature was 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 heat treatment temperature was 55°C.

[Comparatively 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 heat treatment temperature was set to 55°C.

(evaluation)

The following evaluation was performed for each example and comparative example.

1. Film thickness fluctuations

The film thickness of the PVA-based resin layer (I) after applying and drying the polyvinyl alcohol aqueous solution (before stretching) and (II) after air stretching was measured using “MCPD3000” manufactured by Otsuka Electronics. The part containing the defect (the part where the gauge band was originally located) was cut to a size of 200 mm (MD) The difference between thickness and minimum film thickness was evaluated.

2. Slow axis fluctuation/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 from Axometrics. The part containing the defect was cut to a size of 200 mm (MD) x 200 mm (TD) to serve as a measurement sample, and the maximum axial direction difference of the defect in the plane was measured. Additionally, for (I) and (II), the PVA-based resin layer was bonded to a glass plate through an adhesive layer, then 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 the polyvinyl alcohol aqueous solution (before stretching)

(II) The appearance of the PVA-based resin layer and (III) polarizing film after air stretching were observed with the naked eye.

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

Regarding (III), as shown in Fig. 5(b), a commercially available polarizing plate was polymerized under the laminate (sample), light was irradiated from the bottom, and it was observed with the naked eye from above. At that time, the laminate was arranged so that the absorption axis of the polarizing film and the absorption axis of the lower polarizing plate were perpendicular to each other.

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

○: Changes in defects cannot be recognized

×: Changes in defects can be recognized

4. Polarization degree

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 equation. . Additionally, these transmittances are Y values measured using a 2-degree field of view (C light source) in JIS Z 8701 and subjected to visibility correction.

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

In the Examples, the film thickness fluctuation, slow axis fluctuation, and absorption axis fluctuation of the PVA-based resin layer were suppressed at all times. The appearance was also excellent. Additionally, in Examples 1-5 and 2-3, the occurrence of wrinkles was confirmed with the naked eye. This may be thought to be due to heat wrinkles occurring in the resin substrate due to heat treatment.

The polarizing film of the present invention can be most suitably used in, for example, an image display device. Specifically, it is suitable for use 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., and as anti-reflective plates for organic EL devices. .

10: Laminate
11: Resin base material
12: Polyvinyl alcohol (PVA)-based resin layer

Claims (14)

An unwinding process of unwinding the resin substrate from a resin substrate roll in which a long resin substrate is wound into a roll shape;
A process of heating the unwrapped resin substrate to the glass transition temperature (Tg) of the resin substrate -15°C or higher;
A process of performing corona treatment on the surface of the resin substrate;
A coating liquid containing a 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 of manufacturing a laminate comprising in this order. According to paragraph 1,
A manufacturing method in which a heating process is performed after storage in the coiled state. According to paragraph 1,
A manufacturing method in which the unwinding process, heating process, corona treatment, and polyvinyl alcohol-based resin layer forming process are performed continuously. According to any one of claims 1 to 3,
A manufacturing method in which the heating process is performed at a temperature of +15° C. or lower than the glass transition temperature (Tg) of the resin substrate. According to any one of claims 1 to 3,
A manufacturing method in which the heating step is performed while conveying the resin substrate with a conveyance roll installed in the heating furnace. According to clause 5,
A manufacturing method wherein the folding angle of the conveyance roll in the heating furnace is 90° or more. According to clause 5,
A manufacturing method wherein the distance between the centers of the conveyance rolls in the heating furnace is 2 m or less. According to any one of claims 1 to 3,
A manufacturing method in which the heating step is performed while transporting the resin substrate by a tenter. According to any one of claims 1 to 3,
A manufacturing method wherein the resin substrate is formed of a polyethylene terephthalate-based resin. According to any one of claims 1 to 3,
A manufacturing method wherein the resin substrate is stretched in advance. According to any one of claims 1 to 3,
A manufacturing method in which 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 a laminate obtained by the production method according to any one of claims 1 to 3. According to clause 12,
A manufacturing method including a step of stretching the laminate. A method of manufacturing a polarizing plate, including the step of laminating a protective film on the polarizing film obtained by the manufacturing method according to claim 12.