TWI693156B - Manufacturing method of laminate - Google Patents

Abstract

The invention provides a layered body capable of forming a polarizing film with uniform performance. The method for manufacturing a laminate of the present invention includes sequentially a step of heating a resin substrate to a glass transition temperature (Tg) of the resin substrate of -15°C or higher, and a step of forming a polyvinyl alcohol-based resin layer on the resin substrate .

Description

Manufacturing method of laminate Field of invention

The invention relates to a method for manufacturing a laminate. Specifically, the present invention 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.

Background of the invention

There has been proposed a method for producing a polarizing film by coating and forming a PVA-based resin layer on a resin substrate and stretching and dyeing the laminate (such as Patent Document 1 and Patent Document 2). According to the above method, a thin polarizing film can be produced, and therefore it is attracting attention because it contributes to the thinning of an image display device, for example. However, in this case, the performance of the obtained polarizing film (specifically, the film thickness, optical characteristics, and appearance) is prone to inconsistency.

Prior technical literature Patent Literature

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

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

Summary of the invention

The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a laminate that can produce a polarizing film with uniform performance.

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

In one embodiment, the resin substrate is wound out of a resin substrate roll formed by winding a long resin substrate into a roll shape, and the above heating step is performed.

In one embodiment, after storing in the above-mentioned bundle state, the above heating step is performed.

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

In one embodiment, the above-mentioned heating step is performed with the glass transition temperature (Tg) of the above-mentioned resin substrate + 15°C or less.

In one embodiment, the above-mentioned heating step is performed while conveying the resin base material with a conveying roller provided in a heating furnace.

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

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

In one embodiment, the above-mentioned resin base material is conveyed by a tenter, and the above-mentioned heating step is simultaneously performed.

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

In one embodiment, the resin base material is formed of polyethylene terephthalate 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 onto the resin substrate by a die coating method and then drying it.

According to another aspect of the present invention, a method for manufacturing a polarizing film can be provided. The manufacturing method of this polarizing film uses the laminated body manufactured by the manufacturing method mentioned above.

In one embodiment, it includes a step of stretching the laminate.

According to still another aspect of the present invention, a method for manufacturing a polarizing plate can be provided. The manufacturing method of the polarizing plate includes a step of laminating a protective film on the polarizing film, and the polarizing film is manufactured according to the above manufacturing method.

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

According to still another aspect of the present invention, a manufacturing apparatus for a laminate can be provided.

In one embodiment, the manufacturing apparatus includes a roll-out mechanism, a heating furnace, and a coating mechanism; the roll-out mechanism rolls out the resin substrate roll formed by winding a long resin substrate into a roll shape Resin substrate; the heating furnace is provided with a conveying roller for conveying the elongated resin substrate, and the heating furnace heats the resin substrate to a glass transition temperature (Tg) of the resin substrate -15°C Above; the coating mechanism is to apply a coating solution containing a polyvinyl alcohol-based resin on a heated resin substrate.

In one embodiment, the resin base material is conveyed by a conveying roller provided in the heating furnace while being heated.

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

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

In one embodiment, the manufacturing apparatus includes a roll-out mechanism, a heating mechanism, and a coating mechanism; the roll-out mechanism rolls out the resin substrate roll formed by winding a long resin substrate into a roll shape Resin base material; the heating mechanism is provided with a tenter for holding both ends of the elongated resin base material for transportation, and the heating mechanism is for holding both ends by the clip of the tenter The aforementioned resin base material is heated to a glass transition temperature (Tg) of the resin base material of -15°C or higher; the coating mechanism applies a coating liquid containing a polyvinyl alcohol-based resin to the heated resin base material.

In one embodiment, the resin base material is conveyed and heated by the tenter at the same time.

According to the present invention, by subjecting the resin substrate to heat treatment at a predetermined temperature or higher, it is possible to alleviate (uniform) the surface unevenness of the resin substrate (for example, a gauge band that occurs when the resin substrate is wound up). As a result, a PVA-based resin layer with good thickness uniformity can be formed on the resin substrate. By performing various treatments on such a PVA-based resin layer with good thickness uniformity, a polarizing film that does not cause inconsistency in performance (specifically, film thickness, optical characteristics, and appearance) and has extremely good uniformity can be manufactured (for example, it fully satisfies the requirements of LCD TVs). Required quality).

10‧‧‧Layered body

11‧‧‧Resin base material

12‧‧‧Polyvinyl alcohol (PVA) resin layer

100‧‧‧Layer manufacturing device

21‧‧‧Clamp

30‧‧‧Resin base roll

40‧‧‧roll out roller

50‧‧‧Heating device

60‧‧‧Coating device

70‧‧‧Drying device

80‧‧‧roll beam roller

90‧‧‧Convey roller

A‧‧‧Oven

R1, R2, R3, R4, R5, R6‧‧‧‧Free roller

W0, W1‧‧‧Width

θ‧‧‧ holding angle

FIG. 1 is a schematic cross-sectional view of a laminate in an embodiment of the present invention.

2(a) and 2(b) are schematic diagrams illustrating a method of heating a resin substrate in an embodiment.

Fig. 3 is a schematic diagram illustrating a method of heating a resin substrate in another embodiment.

4 is a schematic diagram showing an example of the present invention.

5(a) and 5(b) are schematic diagrams illustrating the appearance evaluation method of the PVA-based resin layer.

Forms for carrying out the invention

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

A. Laminate

FIG. 1 is a schematic cross-sectional view of a laminate in an embodiment of the present invention. The laminate 10 is produced by forming a polyvinyl alcohol (PVA) resin layer 12 on a resin substrate 11.

A-1. Resin base material

The resin base material 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 base material include ester resins such as polyethylene terephthalate resins, olefin resins such as cycloolefin resins and polypropylene, (meth)acrylic resins, and polyamide resins. Polycarbonate resins and their copolymer resins. It is preferable to use polyethylene terephthalate resin. Among them, it is preferable to use amorphous polyethylene terephthalate resin. Specific examples of the amorphous polyethylene terephthalate-based resin include copolymers that further contain isophthalic acid as a dicarboxylic acid or copolymers that further contain cyclohexanedimethanol as a glycol.

The glass transition temperature (Tg) of the resin substrate is preferably 170°C or lower. By using the above resin base material, the laminate can be stretched at a temperature at which the crystallization of the PVA-based resin does not rapidly accelerate, and problems caused by the crystallization can be suppressed (for example, hindering PVA caused by stretching Department of resin layer orientation). In addition, the glass transition temperature of the resin substrate is preferably 60°C or higher. The glass transition temperature (Tg) is a value determined based on JIS K 7121.

The resin substrate can be formed by any suitable method. Examples of the molding method include a melt extrusion method, a solution casting method (solution casting method), a calender molding method, and a compression molding method. Among them, the melt extrusion method is preferred.

Surface modification treatment (such as corona treatment, etc.) may be performed on the surface of the resin substrate, and an easy adhesion layer may also be formed. Through the above treatment, the adhesion between the resin base material and the PVA-based resin layer can be improved. The surface modification treatment and/or the formation of an easy-adhesion layer may be performed before the heat treatment described later, or may be performed after the heat treatment. In addition, to perform the stretching described later, it may be performed before the stretching, or may be performed after the stretching.

In one embodiment, the resin substrate is stretched before heat treatment described later. Any suitable method can be adopted for the stretching method of the resin substrate. Specifically, fixed-end stretching or free-end stretching may be used. Moreover, simultaneous biaxial stretching or successive biaxial stretching can also be used. The stretching of the resin substrate can be performed in one stage or in multiple stages. When performed in multiple stages, the stretching ratio of the resin base material described later is the product of the stretching ratios of the respective stages. Moreover, the stretching method is not particularly limited, and may be an aerial stretching method or an underwater stretching method.

The stretching direction of the resin substrate can be appropriately set. For example, a long resin substrate is stretched in the width direction. Specifically, the resin base material is transported in the longitudinal direction and stretched in a direction (TD) orthogonal to the transport direction (MD). In this specification, the term "orthogonal" also includes substantially orthogonal forms. Here, the term "substantially orthogonal" includes 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°. By stretching the resin substrate in the width direction (TD), the resin substrate can be effectively used. Moreover, the thickness of the resin base material in TD can be made uniform, and the inconsistency of the partial film thickness described later can be suppressed.

The stretching temperature of the resin substrate can be set to any appropriate value according to the forming material of the resin substrate, the stretching method, and the like. The typical stretching temperature is preferably Tg-10°C to Tg+80°C relative to the glass transition temperature (Tg) of the resin substrate. When polyethylene terephthalate resin is used as the material for forming the resin substrate, the stretching temperature is preferably 70°C to 150°C, and 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 as the above-mentioned range, it is possible to satisfactorily suppress the partial film thickness inconsistency described later. In addition, the stretching ratio of the resin base material is preferably 3.0 times or less with respect to the original length of the resin base material. By setting it as the said range, the wrinkle generation in the heating process mentioned later can be suppressed well.

A-2. Rolling and storage

In one embodiment, the long resin base material is wound into a roll shape. When the resin base material is molded, some of the film thicknesses may not be uniform, and winding in this state may cause unevenness in the resin base material. The typical coil tension is 60N/m to 150N/m (unit: N/m is the tension per unit width and length). The bundled resin base material can be stored (placed) while being kept in a bundle state for any appropriate period before being supplied to the next step. For example, when the PVA-based resin layer is not (unable) to be continuously formed after the molding of the resin base material, the resin base material is kept in a bundle state and stored. Once the storage period becomes longer (for example, more than 3 days), the occurrence of unevenness (the degree of unevenness, the number of unevenness) becomes significant, and the produced PVA-based resin layer (laminate) has a film thickness inconsistency tendency. Therefore, the longer the storage period of the resin substrate roll body, the more remarkable the effect of the heat treatment described below can be obtained. In addition, the resin substrate roll can be stored under any suitable gas environment. 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 above resin substrate is heated. Specifically, the resin substrate is heated by hot air, an infrared heater, a roller heater, or the like. The heating temperature is the glass transition temperature (Tg) of the resin base material at -15°C or higher, preferably Tg-10°C or higher, and more preferably Tg-5°C or higher. When using polyethylene terephthalate-based resin as the material for forming the resin substrate, the heating temperature is preferably 68°C or higher. By heating the resin substrate at the above temperature, the unevenness of the surface of the resin substrate can be alleviated (uniform). As a result, a PVA-based resin layer described later can be formed well, and a PVA-based resin layer with good thickness uniformity can be formed. In addition, the heating temperature is preferably (Tg) + 15°C or lower, and (Tg) + 10°C or lower is more preferable. When polyethylene terephthalate resin is used as the material for forming the resin substrate, the heating temperature is preferably 80°C or lower. By heating the resin base material at the above temperature, the occurrence of wrinkles (hot wrinkles) can be suppressed well.

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

The resin substrate can shrink due to heating. For example, when the resin substrate has been stretched in the width direction before heating, the resin substrate may shrink in the width direction (TD shrink) 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. When the shrinkage ratio is within the above range, the occurrence of wrinkles is suppressed and a good appearance can be obtained. In addition, TD shrinkage is calculated according to the following formula.

TD shrinkage (%)={1-(resin base width after heating (W1)/resin base width before heating (W0))}×100

In one embodiment, the resin substrate is heated while being transported. When the resin base material is wound into a roll shape as described above, it is preferable to apply heat treatment to the resin base material rolled out from the resin base material roll. The heating method may be, for example, a method of transporting the resin base material by a transport roller provided in a heating furnace, or a method of simultaneously heating the resin base material by a tenter. Using the former can suppress the enlargement of the equipment. With the latter, the occurrence of wrinkles can be suppressed extremely well.

2(a) and 2(b) show specific examples when the conveying roller is used. In the example of the figure, the resin base material 11 is conveyed in the longitudinal direction by the free rollers R2 to R5 provided in the oven A, thereby heating the resin base material 11. From the viewpoint of production speed, it is advisable to install more than 4 free rollers in the oven as shown in the example.

The angle of the free roller in the oven should be above 90℃. In the example shown in FIG. 2(a), the wrap angle θ of the free rolls R2 and R5 is set to 90°, and the wrap angle θ of the free rolls R3 and R4 is set to 180°. In the example shown in FIG. 2(b), the wrap angle θ of the free rollers R2 to R5 is set to 90°. By setting it as the said wrap angle, the shrinkage of the resin base material is suppressed and the occurrence of wrinkles can be suppressed. In addition, the so-called angle is the straight line connecting the center point of the free roller and the starting point of contact between the resin base material and the free roller when viewed from the cross section perpendicular to the axial direction, and the center point of the free roller and the The angle formed by the straight line between the contact end point of the resin substrate and the free roller. The distance between the free rollers in the oven (the distance between the centers of the rollers) should be 2m or less. In addition, the distance between the two free rollers installed across the entrance and exit of the oven (between R1-R2 and R5-R6 in the illustrated example) should also be 2m or less. By setting the interval, the shrinkage of the resin base material is suppressed and the occurrence of wrinkles can be suppressed. In addition, in the present embodiment, the shrinkage of the resin base material is also related to the stretching ratio of the resin base material, the heating temperature, and the like.

Figure 3 shows a specific example when a tenter is used. In the example shown in the figure, both ends of the resin base material 11 (located on a line perpendicular to the conveying direction) are held by clips 21 and 21 on the left and right of the tenter, respectively, and conveyed in the heating area at a predetermined speed in the longitudinal direction ， Thereby heating the resin substrate 11. The distance between the clips in the conveying direction (the distance between the ends of adjacent clips) is preferably 20 mm or less, and more preferably 10 mm or less. The width of the clip should be more than 20mm, more preferably 30mm. 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 moving without changing the distance between the left and right clips, the TD shrinkage rate is substantially 0%. Conversely, by widening the distance between the left and right clips, the resin substrate can be stretched by TD. The TD change rate of the resin substrate is preferably 1.00 times or more, and 1.00 times to 1.10 times is even better. In addition, the TD change rate is calculated according to the following formula.

TD change rate (times) = width of resin substrate after heating (W1) / width of resin substrate before heating (W0)

A-4. Formation of PVA resin layer

Any appropriate resin can be used for the PVA-based resin forming the PVA-based resin layer. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be prepared by saponification of polyvinyl ethyl ester. Ethylene-vinyl alcohol copolymer is prepared by saponification of ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, 95.0 mol% to 99.95 mol% is preferable, and 99.0 mol% to 99.93 mol% is more preferable. The degree of saponification can be determined based on JIS K 6726-1994. By using the above-mentioned PVA-based resin with a degree of saponification, a polarizing film with good durability can be produced. When the degree of saponification is too high, there is a fear of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1200 to 4500, and more preferably 1500 to 4300. In addition, the average degree of polymerization can be determined based on JIS K 6726-1994.

The PVA-based resin layer is preferably formed by applying a coating solution containing a PVA-based resin on a resin substrate and drying. Typically, the coating liquid is a solution obtained by dissolving the PVA-based resin in a solvent. As the solvent, polyhydric alcohols such as water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane, etc. Amines such as amines and diethylenetriamine. These can be used alone or in combination of two or more. Among them, water is better. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. If the above resin concentration is used, a uniform coating film adhered to the resin substrate can be formed.

The coating liquid may contain additives. Examples of additives include plasticizers and surfactants. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. The surfactant can be exemplified by a nonionic surfactant. The above-mentioned ones can be used for the purpose of further improving the uniformity, dyeability, or stretchability of the produced PVA-based resin layer. In addition, the additive can be exemplified by easily accessible ingredients. By using the easy-access component, the adhesion between the resin substrate and the PVA-based resin layer can be improved. As a result, problems such as peeling of the PVA-based resin layer from the resin substrate can be suppressed, and dyeing and water stretching described below can be performed satisfactorily. As the easily accessible component, modified PVA such as acetyl acetyl modified PVA can be used.

Any appropriate method can be used for the coating method of the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a doctor blade coating method (comma blade coating method, etc.), etc. are mentioned.

In one embodiment, the die coating method is used. The die coating method fixes the gap between the resin base material and the mold (such as a fountain mold and a slit mold) to apply the coating liquid, so that a coating film with extremely uniform thickness 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, and it may be difficult to form a uniform coating film. Therefore, when the die coating method is used, the above-mentioned heat treatment effect can be remarkably obtained.

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

It is preferable to form the PVA-based resin layer after the above heating. For example, after heating, the resin substrate is not wound, and the PVA-based resin layer is formed on the resin substrate. This is because the above heating effect can be obtained well.

In addition, before forming the PVA-based resin layer, a primer layer (primer layer) may be formed in advance on the side of the resin substrate on which the PVA-based resin layer is formed. The material constituting the primer layer is not particularly limited as long as it exerts a certain degree of strong adhesion to both the resin base material and the PVA-based resin layer. For example, thermoplastic resins with good transparency, thermal stability, and stretchability can be used. Examples of the thermoplastic resin include acrylic resins, polyolefin resins, polyester resins, polyvinyl alcohol resins, and mixtures thereof.

A-5. Other

In one embodiment, rolling out the resin base material from the resin base material roll body (roll-out step), heating the resin base material (heating step), and forming the PVA-based resin layer (PVA-based resin layer forming step) are continuously performed. According to the above embodiment, the effect of the above heat treatment can be obtained well. As a specific example of this embodiment, the embodiment shown in FIG. 4 can be taken as an example: the steps of rolling out, heating, and forming a PVA-based resin layer are sequentially performed on a series of production lines for conveying elongated resin substrates. The laminated body manufacturing apparatus 100 shown in FIG. 4 is provided with a take-out roller 40, a heating device 50, a coating device 60, a drying device 70, and a take-up roller 80; Unrolled from the resin substrate roll 30, the heating device 50 is used to heat the resin substrate 11, the coating device 60 is used to apply the coating solution containing the PVA-based resin on the surface of the resin substrate 11, the drying The apparatus 70 is for drying the applied coating liquid, and the winding roller 80 is for winding the laminated body 10. In addition to this, the laminated body manufacturing apparatus 100 further includes a plurality of conveying rollers 90.

B. Stretch 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 in an air stretching method at a draw ratio of 1.5 times or more and 3.0 times or less. The details of the method of stretching the laminate will be described later. In the stretch laminate, the thickness difference of the PVA-based resin layer within the size of 200 mm (MD) × 200 mm (TD) is preferably 0.25 μm or less, and more preferably 0.20 μm or less. In the stretched laminate, the inconsistency of the slow axis of the PVA-based resin layer within the size of 200 mm (MD) × 200 mm (TD) is preferably 0.50° or less, more preferably 0.30° or less, and particularly preferably 0.25° or less.

C. Polarizing film

The polarizing film of the present invention is produced by performing a process for making the PVA-based resin layer of the laminate as a polarizing film.

Examples of the treatment for forming the polarizing film include dyeing treatment, stretching treatment, insolubilization treatment, cross-linking treatment, washing treatment, and drying treatment. These treatments can be appropriately selected depending on the purpose. Moreover, the processing order, processing timing, processing times, etc. can be appropriately set. The following describes each process.

(Dyeing treatment)

The above dyeing process is typically performed by dyeing the PVA-based resin layer with a dichroic substance. It is preferable to make the PVA-based resin layer absorb the dichroic substance. Examples of the adsorption method include 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 the PVA-based resin layer, and spraying the dyeing solution on the PVA-based system Resin layer method, etc. It is better to soak the laminate in the dyeing solution. This is because the dichroic substance can be adsorbed well.

Examples of the dichroic substance include iodine and organic dyes. These can be used alone or in combination of two or more. 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 parts by weight to 5.0 parts by weight relative to 100 parts by weight of water. In order to improve the solubility of iodine in water, it is appropriate to mix iodide in the iodine aqueous 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, and titanium iodide. Among others, potassium iodide is preferred. The blending amount of iodide is preferably 0.3 to 15 parts by weight relative to 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 from 10 seconds to 300 seconds. Under the above conditions, the PVA-based resin layer can sufficiently absorb the dichroic substance. Moreover, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or the light transmittance of the polarized film finally produced is within a predetermined range. In one embodiment, the immersion time is set so that the polarization degree of the produced polarizing film is 99.98% or more. In another embodiment, the immersion time is set so that the light transmittance of the prepared polarizing film is about 40%.

(Stretching)

Any suitable method can be used for the stretching method of the laminate. Specifically, fixed-end stretching (for example, the method of using a tenter stretching machine) or free-end stretching (for example, a method of passing the laminate through rollers with different peripheral speeds for uniaxial stretching) ). Moreover, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) or successive biaxial stretching may also be used. The stretching of the laminate can be performed in one stage or in multiple stages. When performed in multiple stages, the stretching magnification (maximum stretching magnification) of the laminate to be described later is the product of the stretching magnification in each stage.

The stretching treatment may adopt a water stretching method in which the laminate is immersed in a stretching bath, or an aerial stretching method. It is preferable to perform at least one underwater stretching treatment, and it is better to combine the underwater stretching treatment and the aerial stretching treatment. If it is stretched in water, it can be stretched at a temperature lower than the glass transition temperature (typically around 80°C) of the above resin base material or PVA-based resin layer, thereby suppressing the crystallization of the PVA-based resin layer Under high-strength stretching. As a result, a polarizing film having excellent optical characteristics (for example, polarization degree) can be manufactured.

The stretching direction of the laminate can be selected in any appropriate direction. In one embodiment, it is stretched in the longitudinal direction of the elongated laminate. Specifically, the laminate is transported in the longitudinal direction, and the stretching direction is the transport direction (MD). In another embodiment, it is stretched in the width direction of the elongated laminate. Specifically, the laminate is transported in the longitudinal direction, and the stretching direction is the direction (TD) orthogonal to the transport direction (MD).

The stretching temperature of the laminate can be set to any appropriate value according to the forming material of the resin base material and the stretching method. When using the air stretching method, the stretching temperature is preferably higher than the glass transition temperature (Tg) of the resin substrate, more preferably the glass transition temperature (Tg) + 10 ℃ or more of the resin substrate, and more preferably Tg + 15 ℃ or more. In addition, the stretching temperature of the laminate is preferably 170°C or lower. By stretching at the above temperature, the rapid crystallization of the PVA-based resin can be suppressed and the problems caused by the crystallization (such as hindering the orientation of the PVA-based resin layer due to stretching) can be suppressed.

When the stretching method adopts the underwater stretching method, the liquid temperature of the stretching bath is preferably 40°C to 85°C, and 50°C to 85°C is even better. If it is the above temperature, the PVA-based resin layer can be stretched at a high rate while suppressing the dissolution. Specifically, as described above, the relationship between the glass transition temperature (Tg) of the resin substrate and the formation of the PVA-based resin layer is preferably 60° C. or higher. At this time, if the stretching temperature is lower than 40°C, even if the plasticization of the resin substrate due to water is considered, it may not be stretched well. In addition, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and it may be impossible to obtain excellent optical characteristics.

When the underwater stretching method is adopted, it is preferable to immerse the laminate in a boric acid aqueous solution for stretching (boric acid underwater stretching). Using a boric acid aqueous solution as a stretching bath, the PVA-based resin layer can be given rigidity to withstand tension during stretching and water resistance insoluble in water. Specifically, boric acid can generate a tetrahydroxyborate anion in an aqueous solution and hydrogen bond with the PVA-based resin to crosslink. As a result, the PVA-based resin layer can be given rigidity and water resistance, can be stretched well, and can produce a polarizing film having excellent optical characteristics.

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

It is suitable to mix iodide in the above stretching bath (boric acid aqueous solution). By blending iodide, the dissolution of the adsorbed iodine in the PVA-based 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 relative to 100 parts by weight of water, and more preferably 0.5 to 8 parts by weight.

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

Relative to the original length of the laminate, the stretch ratio (maximum stretch ratio) of the laminate is typically 4.0 times or more, preferably 5.0 times or more. Such a higher stretching ratio can be achieved, for example, by using an underwater stretching method (boric acid underwater stretching). In addition, in this specification, the "maximum stretch ratio" refers to the stretch ratio immediately before cracking of the laminate, and also refers to a value that is 0.2 lower than this value after confirming that the stretch ratio of the laminate is cracked.

The water stretching treatment is preferably carried out after the dyeing treatment.

(Insoluble treatment)

The above-mentioned insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. In particular, when the 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 relative 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. The insolubilization treatment is preferably carried out after the laminate is made and before dyeing treatment and water stretching treatment.

(Crosslinking treatment)

The above-mentioned crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing the cross-linking treatment, the PVA-based resin layer can be given water resistance. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight relative to 100 parts by weight of water. In addition, when the cross-linking treatment is performed after the above-mentioned dyeing treatment, it is preferable to further blend iodide. By blending iodide, the dissolution of the adsorbed iodine in the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight relative to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 50°C. The cross-linking treatment is preferably carried out before the water stretching treatment. The preferred embodiment is to perform dyeing treatment, cross-linking treatment and underwater stretching treatment in this order.

(Washing treatment)

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

(Drying)

The drying temperature of the drying process is preferably 30°C to 100°C.

The polarizing film produced is essentially a PVA-based resin film that has adsorbed a dichroic substance and is oriented. The thickness of the polarizing film is preferably 15 μm or less, and preferably 10 μm or less, more preferably 7 μm or less, and particularly preferably 5 μm or less. The above polarizing film can suppress the occurrence of cracks and the like in an environmental test (for example, an environmental test at 80°C). In addition, the thickness of the polarizing film is preferably 0.5 μm or more, and more preferably 1.0 μm or more. The polarizing film has extremely good transportability at the time of manufacturing.

The polarizing film should preferably have absorption dichroism at any wavelength from 380nm to 780nm. When the light transmittance of the monomer is more than 42%, the polarization degree of the polarizing film should be more than 99.9%.

D. Polarizer

The polarizing plate of the present invention has the above polarizing film. The polarizing plate preferably has the polarizing film and a protective film disposed on at least one side of the polarizing film. As the protective film, the above resin base material may be used directly, or a film different from the above resin base material may be used. Examples of materials for forming the protective film include: (meth)acrylic resins; cellulose resins such as cellulose diacetate and cellulose triacetate; cycloolefin resins; olefin resins such as polypropylene; polyethylene terephthalate Ester resins such as diester resins; polyamide resins; polycarbonate resins; and copolymer resins thereof. The thickness of the protective film is preferably 10 μm to 100 μm .

As described above, in one embodiment, the resin substrate is used as a protective film without peeling off the polarizing film. In another embodiment, the resin substrate is peeled off from the polarizing film, and another film is laminated. The protective film may be laminated on the polarizing film through the adhesive layer, or may be laminated on the adhesive film (not through the adhesive layer). The adhesive layer is typically formed with an adhesive or adhesive. According to the present invention, a polarizing film with excellent thickness uniformity can be produced, so that the protective film can be laminated on the polarizing film well.

Examples

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

[Example 1-1]

(Production of laminate)

The resin base material 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 it is previously at 115°C TD stretched to 2.0 times, elongated and 100μm thick; the resin base material was rolled into a roll with a tension of 100N/m to form a roll of resin base material, and it was rolled up at 25°C, Store for 30 days in an environment with a relative humidity of 60%RH.

After that, the resin substrate was rolled out from the resin substrate roll, and the resin substrate was transported and subjected to heat treatment at 70° C. for 60 seconds.

Next, one surface of the resin substrate is subjected to corona treatment. Will contain polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetylate modified PVA (polymerization degree 1200, acetoacetylate modification degree 4.6%, saponification degree) at a ratio of 9:1 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd. under the trade name "Gohsefimer Z200"), applied to the corona treated surface by die coating at 25°C, and then dried at 60°C for 200 seconds to form a thickness of 10 μm of PVA-based resin layer to produce a laminate.

(Production of polarizing film)

The prepared laminate was placed in an oven at 115°C and uniaxially stretched in the free direction to 2.0 times in the longitudinal direction between rollers with different peripheral speeds (air stretch).

Next, the laminate was immersed in an insolubilization bath (a boric acid aqueous solution prepared 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).

Next, immerse it in a dyeing bath with a liquid temperature of 30°C (aqueous iodine solution prepared by mixing iodine and potassium iodide in water at a ratio of 1:7 by weight), and adjust the iodine concentration and immersion time to obtain The light transmittance (Ts) of the polarizing film is 40% or less (dyeing treatment).

Next, it was immersed in a crosslinking bath (a boric acid aqueous solution prepared 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 (crosslinking treatment).

After that, the laminate is immersed in a boric acid aqueous solution at a liquid temperature of 70°C (an aqueous solution prepared 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), and passing between rollers with different peripheral speeds Uniaxial stretching was carried out in the longitudinal direction to 2.7 times (in-water stretching).

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

In this way, a polarizing film with a thickness of 5 μm is formed on the resin substrate.

[Example 1-2]

In the production of the laminate, the 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 75°C.

[Example 1-3]

When producing a laminate, the 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 80°C.

[Example 1-4]

In the production of the laminate, the 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 90°C.

[Example 1-5]

In the production of the laminate, the 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 100°C.

[Example 2-1]

(Production of laminate)

It was set to the same as Example 1-1, and the laminated body was produced.

(Formation of polarizing film)

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

Next, the laminate was immersed in an insolubilization bath (a boric acid aqueous solution prepared 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).

Next, immerse it in a dyeing bath with a liquid temperature of 30°C (aqueous iodine solution prepared by mixing iodine and potassium iodide in water at a ratio of 1:7 by weight), and adjust the iodine concentration and immersion time to obtain The light transmittance (Ts) of the polarizing film is 40% or less (dyeing treatment).

Next, it was immersed in a crosslinking bath (a boric acid aqueous solution prepared 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 (crosslinking treatment).

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

In this way, a polarizing film with a thickness of 2.5 μm is formed on the resin substrate.

[Example 2-2]

In the production of the laminate, the 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 75°C.

[Example 2-3]

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

[Comparative Example 1-1]

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

[Comparative Example 1-2]

In the production of the laminate, the 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 50°C.

[Comparative Example 1-3]

When producing a laminate, the 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 55°C.

[Comparative Example 2-1]

In the production of the laminate, the 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 55°C.

(Evaluation)

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

1. Inconsistent film thickness

The film thickness of the PVA-based resin layer after (I) applying a polyvinyl alcohol aqueous solution and drying (before stretching) and (II) after aerial stretching was measured using "MCPD3000" manufactured by Otsuka Electronics. Cut the part containing the defect (the part with the original ribs) into a size of 200mm (MD) x 200mm (TD) as the measurement sample. MD and TD measure the film thickness in the plane of 1mm interval to evaluate the defect The difference between the maximum film thickness and the minimum film thickness of the part.

2. Inconsistent lag phase axis, inconsistent absorption axis

The "Axoscan" manufactured by Axometrics, Inc. was used to measure (I) the slow axis direction of the PVA-based resin layer after coating and drying of the polyvinyl alcohol aqueous solution (before stretching), and (II) the PVA-based resin layer after in-air stretching The direction of the slow axis and (III) the direction of the absorption axis of the polarizing film. The part including the defect part was cut out to a size of 200 mm (MD) x 200 mm (TD) as a measurement sample, and the maximum axial direction difference of the defect part in the plane was measured. In addition, regarding (I) and (II), after the PVA-based resin layer is bonded to the glass plate through the adhesive layer, the resin substrate is peeled off and the slow axis of the PVA-based resin layer is measured.

3. Appearance

The appearances of (I) the PVA-based resin layer after applying the polyvinyl alcohol aqueous solution and drying (before stretching), (II) the PVA-based resin layer after aerial stretching and (III) polarizing film were observed.

Regarding (I) and (II), as shown in FIG. 5(a), in a state where a commercially available polarizing plate is laminated on top and bottom of the laminate (sample), light is irradiated from below and visually observed from above. At this time, the arrangement is such that the absorption axes of the two polarizing plates are orthogonal to each other, and the extending direction of the laminate is orthogonal to the absorption axis of the lower polarizing plate.

Regarding (III), as shown in FIG. 5(b), in a state where a commercially available polarizing plate is laminated under the laminate (sample), light is irradiated from below and visually observed from above. At this time, the absorption axis of the polarizing film of the laminate is orthogonal to the absorption axis of the lower polarizing plate.

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

○: The inconsistency of the defective part cannot be seen

×: It can be seen that the defects are inconsistent

4. Polarization

Using a spectrophotometer (manufactured by MURAKAMI COLOR RESEARCH LABORATORY, trade name "Dot-41") to measure the single light transmittance (Ts), parallel light transmittance (Tp) and orthogonal light transmittance of the polarizing film (Tc), and obtain the degree of polarization (P) using the following formula. In addition, these light transmittances are Y values measured and corrected for visual acuity according to JIS Z 8701 2 degree visual field (C light source).

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

[Table 1]

In the examples, the film thickness inconsistency, the slow axis inconsistency, and the absorption axis inconsistency of the PVA-based resin layer are suppressed at all time points. Moreover, its appearance is also good. In addition, in Examples 1-5 and 2-3, wrinkles were visually confirmed. The wrinkles may be caused by thermal wrinkles that occur on the resin substrate due to heat treatment.

Industrial availability

The polarizing film of the present invention is suitable for, for example, an image display device. Specifically, it is suitable for use as a liquid crystal panel for LCD TVs, LCD monitors, mobile phones, digital cameras, cameras, portable game consoles, car navigation, copiers, printers, fax machines, clocks, microwave ovens, etc. And anti-reflection plates for organic EL devices.

1‧‧‧Ground roller

3‧‧‧Optical film

4‧‧‧Processing electrode

5‧‧‧External atmosphere

21、22‧‧‧Guide roller

Claims (15)

A method for manufacturing a laminate, which includes the following steps in sequence: a roll-out step, which is to roll out the resin substrate roll from a resin substrate roll formed by winding a long resin substrate into a roll; a heating step Is to heat the rolled resin substrate to a glass transition temperature (Tg) of -15°C or higher; the corona treatment step is to perform corona treatment on the surface of the resin substrate; and the coating step, A coating film containing a polyvinyl alcohol-based resin is coated on a resin substrate subjected to corona treatment to form a coating film, and the coating film is dried without extending the resin substrate on which the coating film has been formed to form polyethylene Alcohol resin layer. The manufacturing method according to claim 1, which is performed after the above-mentioned heating step after being stored in the aforementioned bundle state. The manufacturing method according to claim 1 or 2, which continuously performs the aforementioned unwinding step, the aforementioned heating step, and the aforementioned polyvinyl alcohol-based resin layer forming step. The manufacturing method according to claim 1 or 2, wherein the heating step is performed at a glass transition temperature (Tg) of the aforementioned resin substrate + 15°C or lower. The manufacturing method according to claim 1 or 2, wherein the resin substrate is transported by a transport roller provided in a heating furnace, and the heating step is performed at the same time. The manufacturing method according to claim 5, wherein the wrap angle of the conveying roller in the heating furnace is 90° or more. The manufacturing method according to claim 5, wherein the distance between the centers of the conveying rollers in the heating furnace is 2 m or less. The manufacturing method according to claim 1 or 2, wherein the resin base material is conveyed by a tenter and the heating step is performed simultaneously. The manufacturing method according to claim 1 or 2, wherein the shrinkage rate of the resin substrate due to the aforementioned heating is 3% or less. The manufacturing method according to claim 1 or 2, wherein the aforementioned resin base material is formed of polyethylene terephthalate-based resin. The manufacturing method according to claim 1 or 2, wherein the aforementioned resin substrate is pre-stretched. The manufacturing method according to claim 1 or 2, wherein the polyvinyl alcohol-based resin layer is formed by applying a coating liquid containing the polyvinyl alcohol-based resin on the resin substrate by a die coating method and then drying it. A method for manufacturing a polarizing film, which uses the layered body produced according to the manufacturing method according to any one of claims 1 to 12. The method for manufacturing a polarizing film according to claim 13 includes a step of stretching the aforementioned laminate. A method for manufacturing a polarizing plate includes a step of laminating a protective film on a polarizing film, and the polarizing film is manufactured according to the method for manufacturing a polarizing film according to claim 13 or 14.

Images