KR20120124903A - Method for preparing polarizer - Google Patents

Abstract

PURPOSE: A polarizer manufacturing method is provided to have an excellent optical property and prevent degradation even under a mud crack. CONSTITUTION: A polyvinylalcoholic film is soaked in cross linked water soluble liquid. The cross linked water soluble liquid contains a boron compound, an iodide compound, and alkali metal chloride. The alkali metal chloride is selected from a group composed of lithium chloride, sodium chloride, and potassium chloride.

Description

Manufacturing Method of Polarizer {METHOD FOR PREPARING POLARIZER}

The present invention relates to a method for producing a polarizer having excellent optical characteristics and preventing deterioration even after being left under dry heat and excellent in color durability.

The polarizing plate usually has a structure in which a transparent protective film is laminated on both surfaces or one side of a polarizer made of a polyvinyl alcohol-based resin in which a dichroic dye is adsorbed and oriented.

The polarizer using iodine as a dichroic dye is an iodine type polarizer, and the polarizer using a dichroic dye is called a dye type polarizer. Dual iodine polarizers have high transmittance and high polarization (high contrast) compared to dye polarizers and are widely used.

However, iodine polarizers have superior optical characteristics than dye-based polarizers, but have low optical durability. For example, when the iodine polarizer or the polarizing plate including the polarizer is left under dry heat, there is a problem that the transmittance is reduced or discolored.

Moreover, in recent years, as the field of use of the liquid crystal display device is expanded and the peripheral technology is advanced, the demand for the performance of the polarizing plate is becoming more stringent. Specifically, a polarizing plate having high contrast (high transmittance and high polarization) and excellent optical durability such as heat resistance is required.

On the other hand, Japanese Patent Laid-Open No. 2006-17747 attempts to improve problems such as a decrease in transmittance and discoloration under dry heat by using a metal sulfate during the crosslinking process of an iodine polarizer.

However, the method has a disadvantage that the color value is too bluish by leaking iodine using metal sulfate in the crosslinking tank.

On the other hand, Japanese Patent Application Laid-Open No. 2005-283758 adds an electrolyte (potassium halide) in the swelling process of an iodine polarizer, but it is not related to color durability in order to solve the imbalance of positional transmittance.

The present invention is to provide a method of manufacturing a polarizer which is prevented from deterioration and excellent in color durability after being left under dry heat.

In addition, the present invention is to provide a method of manufacturing a polarizer having excellent optical properties such as transmittance and polarization degree by preventing the leakage of the iodine complex.

In another aspect, the present invention is to provide a polarizing plate and a liquid crystal display including the polarizer.

When the present inventors use a crosslinked aqueous solution containing a boron compound, an iodide, and an alkali metal chloride during the manufacturing process of the polarizer, the optical properties such as transmittance and polarization degree are maintained, and deterioration is prevented after being left under dry heat and color is maintained. It was found that the polarizer with excellent durability can be manufactured to complete the present invention.

Accordingly, the present invention provides a method for producing a polarizer comprising immersing a polyvinyl alcohol-based film in a crosslinked aqueous solution containing a boron compound, an iodide and an alkali metal chloride.

The alkali metal chloride may be at least one selected from the group consisting of lithium chloride, sodium chloride and potassium chloride.

The alkali metal chloride may be included in a 0.22 to 4.5 molar ratio with respect to 1 mole of iodide.

The boron compound may be included in an amount of 1 to 10% by weight based on 100% by weight of the crosslinking aqueous solution.

The iodide may be included in an amount of 0.05 to 15 wt% based on 100 wt% of the crosslinked aqueous solution.

Furthermore, this invention provides the polarizer which is manufactured by the said manufacturing method, and whose following A700 change amount is 0.001-1.3 after leaving for 30 minutes in 105 degreeC and a dry atmosphere.

(Wherein T _{MD, 700} is the parallel transmittance at a wavelength of 700 nm obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T _{TD, 700} is the state where the absorption axis is orthogonal to the pair of polarizers). Orthogonal transmittance at a wavelength of 700 nm obtained when disposed)

In addition, the present invention provides a polarizing plate in which a protective film is laminated on at least one surface of the polarizer manufactured by the manufacturing method.

The polarizer according to the present invention is prevented from deterioration after being left under dry heat and excellent in color durability, which is useful for a liquid crystal display device which is likely to be exposed to high temperatures such as for cellular phones or in-vehicle vehicles.

In addition, the polarizer according to the present invention is excellent in optical properties such as transmittance and polarization degree by preventing the leakage of the iodine complex.

The present invention relates to a method for producing a polarizer having excellent optical characteristics and preventing deterioration even after being left under dry heat and excellent in color durability.

Hereinafter, the present invention will be described in detail.

The method of manufacturing a polarizer according to the present invention includes immersing a polyvinyl alcohol-based film in a crosslinked aqueous solution containing a boron compound, an iodide and an alkali metal chloride.

In the present invention, the polarizer means a conventional iodine-based polarizer in which iodine is adsorbed and oriented on the polymer film.

The polymer film for preparing the polarizer is not particularly limited as long as it is a dichroic material, that is, a film that can be dyed by iodine, and specifically, a polyvinyl alcohol film, a partially gumified polyvinyl alcohol film; Hydrophilic polymer films such as polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, partially gumified film thereof and the like; Or a polyene alignment film such as a dehydrated polyvinyl alcohol-based film, a dehydrochloric acid-treated polyvinyl alcohol-based film, or the like. Among them, polyvinyl alcohol-based films are preferred in that they are excellent in effect of enhancing uniformity in polarization degree and excellent in dyeing affinity for iodine.

Usually, the method of manufacturing a polarizer includes a swelling step, a dyeing step, a crosslinking step, an stretching step, a washing step and a drying step, and are mainly classified by the stretching method. For example, a dry drawing method, a wet drawing method, or the hybrid drawing method which mixed the said two types of drawing methods, etc. are mentioned. Hereinafter, the manufacturing method of the polarizer of the present invention will be described using the wet stretching method as an example, but is not limited thereto.

The remaining steps except the drying step are performed in a state in which a polyvinyl alcohol-based film is immersed in a constant temperature bath filled with at least one solution selected from several kinds of solutions.

In addition, the order of the steps and the number of repetitions are not particularly limited, and the steps may be performed simultaneously or sequentially, and some steps may be omitted. For example, the stretching step may be performed before the dyeing step or after the dyeing step, or may be performed simultaneously with the swelling step or the dyeing step.

The swelling step is immersed in a swelling tank filled with an swelling aqueous solution before dyeing the unstretched polyvinyl alcohol-based film, to remove impurities such as dust and antiblocking agent deposited on the surface of the polyvinyl alcohol-based film and to remove polyvinyl alcohol It is a step for improving the physical properties of the polarizer by swelling the system film to improve the stretching efficiency and to prevent dyeing unevenness.

As the aqueous solution for swelling, water (pure water, deionized water) can be usually used alone, and when a small amount of glycerin or potassium iodide is added thereto, the processability can be improved together with the swelling of the polymer film. It is preferable that content of glycerin is 5 weight% or less with respect to 100 weight% of aqueous solutions for swelling, and content of potassium iodide is 10 weight% or less.

The swelling bath temperature is preferably 20 to 45 캜, more preferably 25 to 40 캜.

The execution time (swelling tank immersion time) of the swelling step is preferably 180 seconds or less, more preferably 90 seconds or less. When the immersion time is within the above range, it is possible to prevent the swelling from becoming excessive and saturation, to prevent breakage due to softening of the polyvinyl alcohol film and to improve the polarization degree by uniformly adsorbing iodine in the dyeing step have.

The stretching step may be performed together with the swelling step, wherein the stretching ratio is preferably about 1.1 to 3.5 times.

The swelling step can be omitted, and swelling can be performed simultaneously in the dyeing step.

The dyeing step is a step of adsorbing iodine to the polyvinyl alcohol-based film by immersing the polyvinyl alcohol-based film in a dye bath filled with a dichroic material, for example, an aqueous solution for dyeing containing iodine.

The dyeing aqueous solution may include water, a water-soluble organic solvent or a mixed solvent and iodine thereof. The content of iodine is preferably 0.4 to 400 mmol / L, more preferably 0.8 to 275 mmol / L, and most preferably 1 to 200 mmol / L with respect to 100 wt% of the aqueous solution for dyeing. In order to further improve dyeing efficiency, iodide may be further included as a dissolution aid. As the iodide, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide may be used alone or in combination of two or more. Of these, potassium iodide is preferable in view of high solubility in water. The content of iodide is preferably 0.010 to 10% by weight, more preferably 0.100 to 5% by weight based on 100% by weight of the aqueous solution for dyeing.

The temperature of the dye bath is preferably 5 to 42 ° C, more preferably 10 to 35 ° C. The immersion time of the polyvinyl alcohol film in the dyeing bath is not particularly limited, and is preferably 1 to 20 minutes, and more preferably 2 to 10 minutes.

The drawing step may be performed together with the dyeing step, in which case the cumulative drawing ratio is preferably 1.1 to 4.0 times. In this specification, "cumulative draw ratio" represents the value of the product of draw ratios in each step.

The crosslinking step is a step of fixing the adsorbed iodine molecules by immersing the dyed polyvinyl alcohol-based film in an aqueous solution for crosslinking so that the dyeability by physically adsorbed iodine molecules is not lowered by the external environment. Dichroic dyes are not often eluted in a humid environment, but iodine is often dissolved or sublimed depending on the environment when the crosslinking reaction is unstable, and sufficient crosslinking reaction is required. In addition, in order to orient all polyvinyl alcohol molecules and iodine molecules located between the molecules to improve optical properties, the crosslinking step is important because it generally has to be drawn at the largest draw ratio in the crosslinking step.

The present invention uses a crosslinked aqueous solution containing alkali metal chlorides. The alkali metal chloride is prevented from deterioration (reddening phenomenon) even after being left under dry heat by removing iodine ions contained in the polyvinyl alcohol-based film and preventing leakage of iodine complex (combination of polyvinyl alcohol and polyvalent iodine ion). It is excellent in optical characteristics such as transmittance and polarization degree.

The crosslinked aqueous solution may include water as a solvent, a boron compound such as boric acid, sodium borate, iodide and an alkali metal chloride, and may further include an organic solvent that is mutually soluble with water.

The boron compound provides short crosslinking and stiffness to suppress wrinkles during the process, thereby improving handleability and forming iodine orientation.

It is preferable that content of a boron compound is 1 to 10 weight% with respect to 100 weight% of crosslinking aqueous solution, More preferably, it is 2 to 6 weight%. If the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and thus it is difficult to impart rigidity. If the content is more than 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessively activated, so that the crosslinking reaction of the organic crosslinking agent is difficult to proceed effectively.

Iodide is used to prevent the uniformity of the degree of polarization in the plane of polarizers and the desorption of dyed iodine. The iodide may be the same as that used in the dyeing step, the content may be 0.05 to 15% by weight relative to 100% by weight of the crosslinking aqueous solution, preferably 0.5 to 11% by weight. If the content is less than 0.05% by weight, the iodine ions in the film is released and the transmittance is increased, if the content exceeds 15% by weight iodine ions in the aqueous solution is penetrated into the film there is a problem that the transmittance is reduced.

The alkali metal chloride may be used at least one selected from the group consisting of lithium chloride, sodium chloride and potassium chloride, the content of which is 0.22 to 4.5 molar ratio, preferably 0.3 to 3.0 molar ratio with respect to 1 mole of iodide. If the content is less than 0.22 molar ratio, there is no redness improvement effect, and if the content exceeds 4.5 molar ratio, there is a problem of becoming blue.

The temperature of the crosslinking bath is 20 to 70 캜, and the immersion time of the polyvinyl alcohol film in the crosslinking bath may be 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

The stretching step may be performed together with the crosslinking step, in which case it is preferable that the stretching is performed such that the total cumulative stretching ratio is 3.0 to 8.0 times.

As described above, the stretching step may be performed together with the swelling step, the dyeing step, and the crosslinking step, or may be performed as an independent stretching step using a separate drawing tank filled with an aqueous solution for drawing after the crosslinking step.

The washing step is a step of removing the unnecessary residue such as boric acid attached to the polyvinyl alcohol-based film in the previous steps by immersing the polyvinyl alcohol-based film cross-linked and stretched in a washing tank filled with aqueous solution for washing.

The aqueous solution for washing may be water, and further iodide may be added thereto.

It is preferable that the temperature of a water washing tank is 10-60 degreeC, More preferably, it is 15-40 degreeC.

The washing step may be omitted and may be performed whenever previous steps such as dyeing step, crosslinking step or stretching step are completed. In addition, it may be repeated one or more times, and the number of repetitions is not particularly limited.

The drying step is a step of obtaining a polarizer having excellent optical properties by drying the washed polyvinyl alcohol-based film and further improving the orientation of the iodine molecules dyed by neck-in by drying.

As the drying method, natural drying, air drying, heating and drying, far infrared ray drying, microwave drying, hot air drying and the like can be used. Recently, microwave drying in which only water in the film is activated and dried is newly used, Drying is mainly used. For example, it may be hot air dried at 20 to 90 DEG C for 1 to 10 minutes. The drying temperature is preferably low in order to prevent deterioration of the polarizer, more preferably 80 ° C or lower, and most preferably 60 ° C or lower.

The present invention provides a polarizer manufactured by the above method. The polarizer is in the range of 0.001 to 1.3 in the following A700 change amount after being left for 30 minutes at 105 ° C in a dry atmosphere.

(Wherein T _{MD, 700} is the parallel transmittance at a wavelength of 700 nm obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T _{TD, 700} is the state where the absorption axis is orthogonal to the pair of polarizers). Orthogonal transmittance at a wavelength of 700 nm obtained when disposed)

In addition, the present invention provides a polarizing plate in which a protective film is laminated on at least one side of the polarizer.

The protective film is not particularly limited as long as the film is excellent in transparency, mechanical strength, thermal stability, moisture shielding, and isotropy. Specifically, polyester-based resin, such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate; Cellulose-based resins such as diacetylcellulose and triacetylcellulose; Polycarbonate resin; Acrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene resins such as polystyrene and acrylonitrile-styrene copolymer; Polyolefin resins such as polyethylene, polypropylene, cyclo-based or norbornene-structured polyolefins, ethylene propylene copolymers; Vinyl chloride resin; Polyamide resins such as nylon and aromatic polyamide; Imide resin; Polyether sulfone type resin; Sulfone resins; Polyether ketone resins: sulfide polyphenylene resins; Vinyl alcohol-based resins; Vinylidene chloride resins; Vinyl butyral resin; Allylate series resin; Polyoxymethylene type resin; Epoxy resin, and the like, and a film composed of the blend of the thermoplastic resin may also be used. Moreover, you may use the film which consists of thermosetting resins or ultraviolet curable resins, such as (meth) acrylic-type, urethane type, epoxy type, and silicone type. Among these, especially the cellulose type film which has the surface saponified by saponification by alkali etc. is preferable in consideration of polarization characteristic or durability. In addition, the protective film may have a function of the following optical layer.

In the present invention, the structure of the polarizing plate is not particularly limited, and various kinds of optical layers capable of satisfying required optical properties may be laminated on the polarizer. For example, a structure in which a protective film for protecting the polarizer is laminated on at least one surface of the polarizer; A structure in which a surface treatment layer such as a hard coating layer, an antireflection layer, an anti-sticking layer, a diffusion preventing layer, an anti-glare layer, or the like is laminated on at least one surface or a protective film of the polarizer; It may have a structure in which an alignment liquid crystal layer or another functional film for compensating a viewing angle is laminated on at least one surface or a protective film of the polarizer. In addition, a phase difference including a wavelength plate (including a λ plate) such as an optical film, a reflector, a semi-transmissive plate, a 1/2 wave plate, or a quarter wave plate, such as a polarization conversion device used to form various image display devices At least one of the plate, the viewing angle compensation film, and the brightness enhancement film may be laminated with an optical layer. In more detail, a polarizing plate having a structure in which a protective film is laminated on one surface of a polarizer, the polarizing plate having a reflector or a transflective reflector laminated on a laminated protective film; An oval or circular polarizing plate in which retardation plates are stacked; A wide viewing angle polarizer on which a viewing angle compensation layer or a viewing angle compensation layer is stacked; Or the polarizing plate in which the brightness improving film was laminated | stacked is preferable.

Such a polarizing plate can be applied to various image display devices such as electroluminescent display devices, plasma display devices, and field emission display devices as well as ordinary liquid crystal display devices.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Example 1

A transparent unstretched polyvinyl alcohol film (VF-PS, KURARAY) having a degree of saponification of 99.9% or more was swelled by immersion in water (deionized water) at 30 ° C. for 2 minutes, and then 3.5 mmol / L of iodine and 2 wt% of potassium iodide It was dyed by immersion for 4 minutes in an aqueous solution for dyeing at 30 ℃ containing. At this time, stretching was performed at a draw ratio of 1.3 times and 1.3 times, respectively, in the swelling and dyeing steps. Subsequently, it was immersed in a 50 degreeC aqueous solution for crosslinking containing 2 weight% of potassium iodide, 3.7 weight% of boric acid, and 4.5 mol of lithium chloride with respect to 1 mol of potassium iodide, and it bridge | crosslinked. At this time, the crosslinking step was such that the total cumulative stretching ratio is 5.8 times. After crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 70 ° C. for 4 minutes to prepare a polarizer.

A triacetylcellulose (TAC) film was laminated on both sides of the prepared polarizer to prepare a polarizing plate.

Example 2

The polarizer was prepared in the same manner as in Example 1, using a crosslinking aqueous solution containing 5.5 wt% of potassium iodide, 3.7 wt% of boric acid, and 1 mol of lithium chloride relative to 1 mol of potassium iodide.

Example 3

The polarizer was prepared in the same manner as in Example 1, using an aqueous solution for crosslinking containing 9.0 wt% of potassium iodide, 3.7 wt% of boric acid, and 0.22 mol of lithium chloride based on 1 mol of potassium iodide.

Example 4

The polarizer was prepared in the same manner as in Example 1, using sodium chloride instead of lithium chloride.

Example 5

The polarizer was prepared in the same manner as in Example 3, using sodium chloride instead of lithium chloride.

Example 6

A polarizer was prepared in the same manner as in Example 1, using potassium chloride instead of lithium chloride.

Example 7

A polarizer was prepared in the same manner as in Example 1, using a swelling solution containing 5 wt% of lithium chloride based on water (deionized water).

Comparative Example 1

The polarizer was prepared in the same manner as in Example 1, using an aqueous crosslinking solution containing 12 wt% of potassium iodide and 3.7 wt% of boric acid.

Comparative Example 2

The same procedure as in Example 1 was carried out using a swelling solution containing 5% by weight of lithium chloride with respect to water (deionized water), and 12% by weight of potassium iodide, and an aqueous solution for crosslinking containing 3.7% by weight of boric acid. To prepare a polarizer.

Comparative Example 3

A polarizer was prepared in the same manner as in Example 6 without adding potassium iodide to the crosslinking bath.

Test Example

Physical properties of the polarizers prepared in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

1. Optical characteristics (polarization, transmittance)

After cutting the prepared polarizer into 4 cm x 4 cm size, the transmittance was measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO). At this time, the polarization degree is defined by the following equation (1).

(Wherein T ₁ is the parallel transmittance obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T ₂ is the orthogonal transmittance obtained when the pair of polarizers are arranged in the state where the absorption axes are orthogonal) .

The transmittance of 450 nm was confirmed by the above method. The large transmittance of 450 nm means that it has a bluish color.

2. Durability evaluation (ΔA700, Δ orthogonal b )

The spectrophotometer? The orthogonal spectral transmission spectrum was obtained from the measured spectral transmittance τ (λ), and A700 was calculated using the orthogonal color b and the following equation (2) from the spectral transmission spectrum.

Thereafter, the polarizer was allowed to stand in a dry atmosphere at 105 캜 for 30 minutes (durability test), and the spectral transmittance τ (λ) was measured again. The orthogonal spectral transmittance spectrum was obtained from the measured spectral transmittance τ A700 was obtained from the spectrum using the orthogonal color b and the following equation 2 to determine the difference between the orthogonal color b before and after the durability test as? Orthogonal b, and the difference between before and after the durability test of A700 as? A700. At this time, it is determined that the larger the Δ orthogonal b and ΔA 700 values, the larger the discoloration degree under dry heat.

(Wherein T _{MD, 700} is the parallel transmittance at a wavelength of 700 nm obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T _{TD, 700} is the state where the absorption axis is orthogonal to the pair of polarizers). Orthogonal transmittance at a wavelength of 700 nm obtained when disposed)

When ΔA700 is less than 1.3 and Δorthogonal b is less than 0.3, discoloration is considered small.

After standing for 30 minutes in a dry atmosphere of 105 ℃, it was confirmed by the visual observation whether the occurrence of red light polarizer.

division Transmittance (%) Polarization degree (%) △ A700 450 nm
Transmittance △ Ortho b Redness Example 1 41.6 99.9963 0.9853 0.001 0.15 radish Example 2 41.9 99.996 0.77829 0.0012 0.18 radish Example 3 41.9 99.9951 0.079825 0.0011 0.22 radish Example 4 41.6 99.9947 0.00031 0.0012 0.20 radish Example 5 41.5 99.9945 0.00112 0.0011 0.17 radish Example 6 41.6 99.9947 0.87123 0.0013 0.15 radish Example 7 41.7 99.9960 0.9925 0.0011 0.16 radish Comparative Example 1 41.8 99.9945 1.57581 0.0014 0.49 U Comparative Example 2 41.8 99.9940 1.6041 0.0015 0.52 U Comparative Example 3 42.2 99.92 0.00054 0.7756 3.1 radish

As shown in the table, Examples 1 to 7 comprising immersing the polyvinyl alcohol-based film in a crosslinked aqueous solution containing a boron compound, iodide and alkali metal chloride in accordance with the present invention has optical properties such as transmittance and polarization degree At the same time, it was confirmed that deterioration was prevented and color durability was excellent after being left under dry heat.

On the other hand, Comparative Examples 1 and 2 were excellent in optical properties such as transmittance and polarization degree, but the color durability was low, Comparative Example 3 was confirmed that both the optical properties and color durability is low.

Claims (7)

A method of manufacturing a polarizer comprising immersing a polyvinyl alcohol-based film in a crosslinked aqueous solution containing a boron compound, an iodide, and an alkali metal chloride.
The method of claim 1, wherein the alkali metal chloride is at least one member selected from the group consisting of lithium chloride, sodium chloride and potassium chloride.
The method of claim 2, wherein the alkali metal chloride is included in a ratio of 0.22 to 4.5 moles per 1 mole of iodide.
The method of claim 1, wherein the boron compound is included in an amount of 1 to 10 wt% based on 100 wt% of the crosslinked aqueous solution.
The method of claim 1, wherein the iodide is included in an amount of 0.05 to 15 wt% based on 100 wt% of the crosslinked aqueous solution.
The polarizer manufactured by the manufacturing method of any one of Claims 1-5, and whose following A700 change amount is 0.001-1.3 after leaving for 30 minutes in 105 degreeC and a dry atmosphere:

(Wherein T _{MD, 700} is the parallel transmittance at a wavelength of 700 nm obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T _{TD, 700} is the state where the absorption axis is orthogonal to the pair of polarizers). Orthogonal transmittance at a wavelength of 700 nm obtained when disposed).
A polarizing plate in which a protective film is laminated on at least one side of the polarizer manufactured by the manufacturing method of any one of claims 1 to 5.