JP5985791B2 - Manufacturing method of polarizer - Google Patents

Description

  The present invention relates to a method for manufacturing a polarizer.

  A liquid crystal display device includes a polarizing plate as an essential component due to its display mechanism. The polarizing plate typically has a protective layer bonded to a polarizer that is uniaxially stretched by adsorbing a dichroic substance to a polyvinyl alcohol (PVA) resin film. By the way, as the use of the liquid crystal display device expands, there is an increasing demand for an increase in size and cost of the liquid crystal display device, and there is also a demand for an increase in size and cost of the polarizing plate.

  In order to meet such a demand, for example, a method of manufacturing a wide polarizer by controlling the shrinkage in the drying process by drying with a hot roll has been proposed (Patent Document 1). However, according to such a method, unevenness (for example, elliptical unevenness that can be seen on the surface of the polarizer) is likely to occur in the drying process, which causes a problem of poor appearance of the obtained polarizer. In addition, there is a problem that the yield is remarkably reduced due to the occurrence of such unevenness.

JP 2009-48179 A

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a method for producing a polarizer having excellent productivity and excellent appearance.

In the method for producing a polarizer of the present invention, a polarizer preparation film is subjected to a wet treatment and a drying treatment in this order while the polarizer preparation film is conveyed by a conveyance roll. Apply nip pressure to.
In preferable embodiment, the tensile elasticity modulus of the film for polarizer preparations before the said drying process is 500 Mpa or more.
In a preferred embodiment, the nip pressure is 0.1 MPa to 1 MPa.
In a preferred embodiment, the nip pressure is applied with a silicone rubber roll.
In a preferred embodiment, the drying treatment is performed using a hot roll.
According to another aspect of the present invention, a polarizer is provided. This polarizer is manufactured by the above manufacturing method.

  According to the present invention, a polarizer having an excellent appearance can be produced with high yield by applying a nip pressure to the film for producing a polarizer after wet processing. Specifically, by applying a nip pressure to the film for producing a polarizer after wet processing, it is possible to prevent bubbles, water droplets and the like from being bitten into the film for producing a polarizer. By performing the drying process in this state, the occurrence of unevenness is suppressed, and a polarizer having an excellent appearance can be manufactured with a high yield.

It is the schematic explaining an example of the manufacturing method of the polarizer of this invention. It is an observation photograph of the nonuniformity which generate | occur | produced in the comparative example.

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

A. Manufacturing method The manufacturing method of the polarizer of this invention performs a wet process and a drying process in this order to the film for polarizer preparations, conveying the film for polarizer preparation with a conveyance roll. The film for producing a polarizer is typically long.

  A typical example of a material for forming a film for producing a polarizer is a polyvinyl alcohol (PVA) resin. The PVA resin can be obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer. The saponification degree of the PVA resin is preferably 80.0 mol% to 99.9 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using a PVA resin having a saponification degree in the above range, a polarizer having excellent durability can be obtained.

  As the average degree of polymerization of the PVA-based resin, an appropriate value can be selected according to the purpose. The average degree of polymerization is preferably 1000 to 10,000. The average degree of polymerization can be determined according to JIS K 6726-1994.

  Examples of the wet treatment include swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment, adjustment treatment, and washing treatment. These processes can be selected according to the purpose. In addition, the processing order, the processing timing, the number of processings, and the like can be appropriately set. Each process will be described below.

  In the dyeing treatment, iodine or a dichroic dye is preferably adsorbed on the film for producing a polarizer. Dyeing is usually performed by immersing the film for preparing a polarizer in a dyeing solution (dyeing bath). As the staining solution, an iodine solution is generally used. The iodine concentration in the iodine solution is preferably 0.01% by weight to 1% by weight, more preferably 0.02% by weight to 0.5% by weight. The temperature of the dyeing solution is usually about 20 ° C to 50 ° C, preferably 25 ° C to 40 ° C. The immersion time in the dyeing solution is usually 10 seconds to 300 seconds, preferably 20 seconds to 240 seconds.

  In the crosslinking treatment, a boron compound is usually used as a crosslinking agent. Examples of the boron compound include boric acid and borax. Boron compounds are usually used in the form of an aqueous boric acid solution. The boric acid concentration of the boric acid aqueous solution is about 2 to 15% by weight, preferably 3 to 13% by weight. When the boric acid concentration is in such a range, heat resistance and the like can be efficiently imparted to the obtained polarizer by the crosslinking treatment. The boric acid aqueous solution may contain an iodide compound such as potassium iodide. The crosslinking treatment is usually performed by immersing the film for preparing a polarizer in an aqueous boric acid solution (crosslinking bath). Or you may apply a boron compound to the film for polarizer preparation by the apply | coating method, the spraying method, etc. The treatment temperature is usually 25 ° C or higher, preferably 30 ° C to 85 ° C, more preferably 30 ° C to 60 ° C. The treatment time (immersion time) is usually 5 seconds to 800 seconds, preferably 8 seconds to 500 seconds.

  In the above stretching treatment, the film for producing a polarizer is usually subjected to uniaxial stretching. The stretching process can be performed together with, for example, a dyeing process, a crosslinking process, and a swelling process. Further, an iodide compound can be contained in the treatment liquid (stretching bath) used for stretching. In this case, the iodide compound concentration is preferably 0.1 wt% to 10 wt%, more preferably 0.2 wt% to 5 wt%. The treatment temperature is usually 25 ° C or higher, preferably 30 ° C to 85 ° C, more preferably 30 ° C to 60 ° C. The immersion time in the stretching bath is usually 10 seconds to 800 seconds, preferably 30 seconds to 500 seconds. As the stretching method, not only wet but also dry methods can be adopted.

  The draw ratio by stretching is preferably 3 to 17 times, more preferably 4 to 10 times, and particularly preferably 4 to 8 times the original length of the film for producing a polarizer. In addition, the said draw ratio is a product (total draw ratio) of the draw ratio of each step, when extending | stretching in multiple steps. When the draw ratio is too low, the orientation is insufficient and a polarizer having high optical properties (typically, the degree of polarization) cannot often be obtained. If the stretch ratio is too high, the film is likely to break during stretching, and the resulting polarizer becomes too thin, and the processability in subsequent processing may be reduced.

  The swelling treatment is typically performed before the dyeing treatment. The swelling treatment is usually performed by immersing the polarizer production film in a treatment liquid (swelling bath). By performing the swelling treatment, it is possible not only to clean the surface of the polarizer-producing film surface and the anti-blocking agent, but also to prevent unevenness such as uneven dyeing. As the treatment liquid, water, distilled water, or pure water is usually used. If the main component of the treatment liquid is water, an additive such as an iodide compound or a surfactant, alcohol or the like may be contained. The treatment temperature is usually 20 ° C to 45 ° C, preferably 25 ° C to 40 ° C. The immersion time in the swelling bath is usually 10 seconds to 300 seconds, preferably 20 seconds to 240 seconds. Here, it is preferable to uniformly swell the film for preparing a polarizer. By uniformly swelling, for example, uneven dyeing can be prevented.

  The adjustment process is typically performed by immersing the film for preparing a polarizer in an iodide compound solution (for example, a potassium iodide solution). The iodide compound concentration in the iodide compound solution is usually 0.5% to 10% by weight, preferably 0.5% to 8% by weight, and more preferably 1% to 6% by weight. The treatment temperature is usually 15 ° C to 60 ° C, preferably 25 ° C to 40 ° C. The treatment time (immersion time) is usually 1 second to 120 seconds, preferably 3 seconds to 90 seconds.

  In the washing treatment, washing is preferably performed by immersing the film for producing a polarizer in water (typically pure water such as ion-exchanged water or distilled water). The washing treatment temperature with water is usually 5 ° C to 50 ° C, preferably 10 ° C to 45 ° C, and more preferably 15 ° C to 40 ° C. The treatment time (immersion time) is usually 10 seconds to 300 seconds, preferably 20 seconds to 240 seconds. The washing process with water may be combined with the adjustment process. Further, a liquid alcohol such as methanol, ethanol, isopropyl alcohol, butanol, propanol or the like may be appropriately added to water to form a cleaning liquid. Typically, the adjustment process and the cleaning process are performed in this order at the end of the wet process.

  After the wet treatment, a nip pressure is applied to the polarizer production film. Preferably, the nip pressure is applied immediately after the wet process (before the dry process). When performing a drying process using a heat roll, Preferably, a nip pressure is applied to the contact boundary part of the film for polarizer production, and a heat roll. By applying the nip pressure, it is possible to prevent bubbles, water droplets, and the like from being bitten into the film for producing a polarizer. By performing the drying process in this state, the occurrence of unevenness is suppressed, and a polarizer having an excellent appearance can be manufactured with a high yield. The nip pressure is preferably 0.1 MPa to 1 MPa.

  In one embodiment, the nip pressure is applied with a nip roll. Specifically, as shown in FIG. 1, nip pressure is applied while passing the polarizer production film 10 through the gap between the transport roll 21 and the nip roll 22. The nip roll is preferably formed of an elastic body. As the elastic body, silicon rubber is preferably used. Another specific example of the nip roll is a metal elastic roll. The metal elastic roll is configured by injecting a gas like a balloon into a hollow roll formed of a metal thin film. By adjusting the gas injection amount (internal pressure), nip pressure, roll elasticity, hardness, and the like can be controlled. The amount of gas injection is preferably 0.1 MPa to 0.3 MPa. The nip roll surface may be subjected to any appropriate surface treatment for the purpose of preventing the generation of foreign matters. Examples of the surface treatment method include a method of winding a metal film such as hard chrome and a method of plating hard chrome.

  The hardness of the nip roll is preferably Hs30 to Hs90. The hardness can be obtained by adopting a spring A type as a measurement method according to JIS K 6301.

  In another embodiment, a nip pressure is applied by blowing a gas (for example, air) onto the polarizer-making film (air nip). In this case, the nip pressure is preferably 0.5 MPa or less, and more preferably about 0.4 MPa. If the spraying is too strong, there is a risk of winding up foreign matter.

After the wet treatment, the polarizer production film is dried. The weight moisture content of the film for producing a polarizer before the drying treatment is preferably 55% or less, more preferably 25% to 55%, still more preferably 27% to 52%, and particularly preferably 30% to 50%. If the weight moisture content before a drying process is such a range, the polarizer which has the desired weight moisture content mentioned later can be obtained efficiently by selecting drying conditions appropriately. Here, the weight moisture content is measured as follows: A film to be measured is cut into a size of 100 mm × 100 mm to form a sample film, and the initial weight of the sample film is measured. Subsequently, the sample film is dried at 120 ° C. for 2 hours, the dry weight is measured, and the moisture content is determined by the following formula. In the following formula, the initial weight and the dry weight are average values obtained by measuring three times, respectively.
Moisture content (% by weight) = [(initial weight−dry weight) / initial weight] × 100
In addition, the weight moisture content before a drying process can be controlled by adjusting the said wet processing conditions (for example, immersion time etc. in a processing bath).

  The tensile elastic modulus of the film for producing a polarizer before the drying treatment is preferably 500 MPa or more, more preferably 500 MPa to 2500 MPa. Occurrence of unevenness can be effectively suppressed with respect to a film for producing a polarizer having such a tensile elastic modulus. Usually, a film for producing a polarizer having a high moisture content has a low tensile elastic modulus, and is likely to be wrinkled by a shrinkage stress in the width direction during a drying process (for example, in contact with a hot roll). The occurrence of unevenness can be effectively suppressed by applying a nip pressure in advance to the film for producing a polarizer in such a state. The tensile elastic modulus is calculated by, for example, measuring a change in tension and a change in elongation when the film for polarizer production is pulled in the MD direction (conveyance direction) using a precision stretching machine, and the inclination is calculated. It can ask for. Moreover, a tensile elasticity modulus can be controlled by adjusting the said weight moisture content, for example.

  The drying process can be performed under any appropriate conditions. The drying temperature is typically 30 ° C to 110 ° C. The drying time is typically 5 seconds to 300 seconds. The heating may be performed by conveying the film in a heating atmosphere using a heating furnace (hot air drying method) or by heating the conveying roll (using a so-called hot roll) (hot roll drying). System), and these may be used in combination. Preferably, it uses a heat roll. By drying using a hot roll, shrinkage in the width direction of the film for producing a polarizer can be suppressed to obtain a wide polarizer, which can cope with the recent increase in size of liquid crystal display devices. . Further, it is possible to prevent appearance defects (for example, uneven stripes) that occur when the moisture content is reduced, and this is also excellent in terms of drying efficiency.

  In one embodiment, the drying process is performed in two stages. Preferably, a first drying process that dries at a low temperature and a second drying process that dries at a high temperature are performed. By performing two-stage drying using such specific conditions, a polarizer having excellent dimensional stability and optical durability in a humidified environment can be obtained. Although it is not theoretically obvious, a film having such a low weight moisture content in the second drying process can be achieved by reducing the weight moisture content of the film to the vicinity of a desired weight moisture content described later by the first drying treatment. It is presumed that high crystallization and cross-linking are realized by heating at a high temperature. More preferably, the drying process is performed by combining the two-stage drying and the hot roll drying method. By performing the first drying process by the hot roll drying method, the shrinkage in the width direction of the film is effectively suppressed (constrained drying), and the second drying process is higher by making contact drying by the hot roll drying method. Crystallization can be realized. By these synergistic effects, it is presumed that a polarizer having excellent dimensional stability and optical durability can be obtained in a humidified environment. In addition, there is an advantage that continuous production can be performed without separately installing a heating furnace or the like.

  As described above, the polarizer of the present invention can be manufactured. Of the specific operations and conditions in the method for producing a polarizer of the present invention that are not described in this specification, the operations described in JP2009-48179A and JP2009-163202A are described. Or general conditions or conditions in the industry may be employed.

B. Polarizer The polarizer produced by the above production method has a weight moisture content of preferably 14% or less, more preferably 13% or less, and particularly preferably 12% or less. The thickness of the polarizer is typically about 0.5 μm to 80 μm.

  The polarizer is practically provided with a protective layer on at least one side thereof and used as a polarizing plate. As a protective layer, it forms with the arbitrary appropriate films which can be used as a protective layer of a polarizing plate. Specific examples of the material as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the resin composition.

  The transmittance of the polarizing plate is preferably 38.3% to 44.3%, more preferably 39.2% to 44.2%, and particularly preferably 41.1% to 44.2%. Yes, most preferably from 41.7% to 44.2%.

  The polarization degree of the polarizing plate is preferably 99% or more, more preferably 99.5% or more, particularly preferably 99.7% or more, and most preferably 99.8% or more.

The degree of polarization can be measured using a spectrophotometer [product name “DOT-3” manufactured by Murakami Color Research Laboratory Co., Ltd.]. As a specific method for measuring the polarization degree, measured parallel transmittance of the polarizing plate (H0) and quadrature transmittance _{(H 90),} wherein: the degree of polarization _{(%) = {(H 0} -H 90) / (H ₀ + H ₉₀ )} ^1/2 × 100. The parallel transmittance (H ₀ ) is a transmittance value of a parallel laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are parallel to each other. The orthogonal transmittance (H ₉₀ ) is a value of the transmittance of an orthogonal laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are orthogonal to each other. In addition, these transmittance | permeability is Y value which performed visibility correction | amendment by the 2 degree visual field (C light source) of JlS Z 8701-1982.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. Unless otherwise specified, “parts” and “%” in the examples are based on weight. In addition, the measuring method of a weight moisture content and a tensile elasticity modulus is as follows.
[Weight moisture content]
In each example and comparative example, a film for preparing a polarizer before drying treatment (after wet treatment) was cut into a size of 100 mm × 100 mm to obtain a sample film, and the initial weight of the sample film was measured. Subsequently, the sample film was dried at 120 ° C. for 2 hours, the dry weight was measured, and the moisture content was determined by the following formula. In the following formula, the initial weight and the dry weight were measured three times, and the average value was adopted.
Moisture content (% by weight) = {(initial weight−dry weight) / initial weight} × 100
[Tensile modulus]
The film was pulled in the MD direction (conveyance direction) using a precision stretching machine, and the tension change and elongation change at the time of pulling were measured, and the inclination was calculated.

<Example 1>
A PVA-based resin film having a polymerization degree of 2400, a saponification degree of 99.7 mol%, and a thickness of 75 μm was used as a film for producing a polarizer, and wet treatment was performed while the film was conveyed by a conveyance roll. Specifically, the film was stretched 3 times in the film transport direction while being dyed in an aqueous iodine solution at 30 ° C., and then in an aqueous solution of 4 wt% boric acid at 5 ° C., 5 wt% potassium iodide, Drawing was performed so that the total draw ratio was 6 times the original length. Furthermore, the stretched film was washed by immersing it in a 2 wt% potassium iodide aqueous solution at 30 ° C. for several seconds. At this time, the weight moisture content of the film was 26%, and the tensile elastic modulus was 2000 MPa.
Next, as shown in FIG. 1, the film was passed through the gap between the transport roll and the nip roll (silicon rubber roll, hardness: Hs60), and nip pressure (0.2 MPa) was applied. Thereafter, the film was dried at 70 ° C. for 12 seconds while being transported by a hot roll, and then dried at 80 ° C. for 75 seconds. A nip pressure was applied to the contact boundary between the film and the heat roll. In this way, a polarizer was produced.

<Example 2>
A polarizer was produced in the same manner as in Example 1, except that the weight moisture content of the film before the drying treatment was 35% and the tensile modulus was 1500 MPa.

<Example 3>
A polarizer was produced in the same manner as in Example 1, except that the weight moisture content of the film before the drying treatment was 45% and the tensile modulus was 800 MPa.

<Example 4>
A polarizer was produced in the same manner as in Example 1 except that the weight moisture content of the film before the drying treatment was 50% and the tensile modulus was 500 MPa.

<Comparative Example 1>
A polarizer was produced in the same manner as in Example 1 except that no nip pressure was applied.

<Comparative example 2>
A polarizer was produced in the same manner as in Example 2 except that no nip pressure was applied.

<Comparative Example 3>
A polarizer was produced in the same manner as in Example 3 except that no nip pressure was applied.

<Comparative example 4>
A polarizer was produced in the same manner as in Example 4 except that no nip pressure was applied.

<Evaluation>
The appearance of the polarizer obtained in each example and comparative example was visually observed. The polarizers obtained in Examples 1 to 4 did not generate unevenness and had an excellent appearance. On the other hand, in Comparative Examples 1 to 4, during drying with a hot roll, as shown in FIG. 2, elliptical unevenness (groove shape) occurred on the entire surface. This elliptical unevenness is caused by air bubbles, water droplets, etc. biting into the wrinkles generated by the shrinkage stress in the width direction when the film contacts the hot roll, and in this state, the film is conveyed by the hot roll. it is conceivable that.

  The polarizer and the polarizing plate obtained by the production method of the present invention can be suitably used for an image display device such as a liquid crystal display device.

10 Polarizer Production Film 21 Transport Roll 22 Nip Roll

Claims (3)

While carrying the polarizer production film with a carrying roll, the polarizer production film is subjected to wet treatment and drying treatment using a heat roll in this order,
A method for producing a polarizer, wherein a nip pressure of 0.1 MPa to 1 MPa is applied to a contact boundary between the film for producing a polarizer and the hot roll after the wet treatment and before the drying treatment.   The manufacturing method of the polarizer of Claim 1 whose tensile elasticity modulus of the film for polarizer preparations before the said drying process is 500 Mpa or more. Applying said nip pressure in silicone rubber roll, the production method of a polarizer according to claim 1 or 2.