KR101938410B1 - Method of preparing polarizer - Google Patents

Abstract

More particularly, the present invention relates to a polarizer-forming film which is subjected to a swelling step, a dyeing step, a stretching step and a crosslinking step, and then irradiated with infrared rays having an energy of 2.9 to 50 J / cm ² per unit area To thereby produce a polarizer having a small amount of deformation and a large iodine complex amount.

Description

[0001] METHOD OF PREPARING POLARIZER [0002]

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

Polarizing plates used in various image display devices such as a liquid crystal display (LCD), an electroluminescence (EL) display, a plasma display (PDP), a field emission display (FED) and an OLED are generally made of polyvinyl alcohol alcohol, PVA) film comprises a polarizer in which an iodine compound or a dichroic polarizing material is adsorbed and oriented, a polarizer protective film is laminated on one side of the polarizer, and a polarizer protective film, a liquid crystal cell Layer structure in which a pressure-sensitive adhesive layer and a release film are laminated in this order.

Polarizers constituting the polarizing plate having such a structure are produced through a complicated process of swelling, dyeing, stretching, crosslinking, washing, and drying a PVA film. Stress occurs in such a complicated process or handling process, A crack easily occurs in a direction parallel to the stretching direction (MD direction). In addition, the polarizer is repeatedly subjected to repeated shrinkage and expansion under repeated high temperature and low temperature environments, so that stress is generated, thereby causing cracks easily.

Particularly, in recent years, various types of image display devices have become larger and larger, and polarizers and polarizing plates to be used are also becoming larger. Therefore, the handling becomes more disadvantageous in the handling process in the process, and the amount of deformation generated under repeated high temperature and low temperature environments during use is further increased, and a polarizer excellent in durability is required.

Korean Patent Laid-Open Publication No. 2009-70085 discloses a method of manufacturing a polarizer, but fails to provide an alternative to the above problem.

Korea Patent Publication No. 2009-70085

An object of the present invention is to provide a production method capable of producing a polarizer having excellent durability and having a small amount of deformation (low shrinkage) and a large amount of iodine complex.

1. A process for producing a polarizer, which comprises subjecting a polarizer-forming film to a swelling step, a dyeing step, a stretching step and a crosslinking step, and then heat-treating the film by irradiating infrared rays with an energy of 2.9 to 50 J / cm ² per unit area.

2. The method of producing a polarizer according to 1 above, wherein the infrared ray has a wavelength of 1 to 5 mu m.

3. The method of producing a polarizer according to item 1 above, wherein the infrared irradiation time is from 1 minute to 10 minutes.

4. The method for producing a polarizer according to item 1 above, wherein the surface temperature of the polarizer-forming film upon irradiation with infrared rays is 50 to 90 占 폚.

5. The method of producing a polarizer according to item 1 above, further comprising a cleaning step after the crosslinking step.

The polarizer manufacturing method of the present invention can produce a polarizer having a small amount of deformation of a polarizer (low shrinkage) by removing infrared rays and heat treatment under specific conditions and simultaneously removing moisture of the polarizer and internal stress.

Further, the polarizer producing method of the present invention can accelerate the boric acid crosslinking inside the polyvinyl alcohol polarizer to increase the complex amount of polyvinyl alcohol with I ₅ , and accordingly, Lt; / RTI >

The present invention relates to a polarizer-forming film which is subjected to a swelling step, a dyeing step, a stretching step and a crosslinking step and then subjected to heat treatment by irradiating infrared rays having an energy of 2.9 to 50 J / cm ² per unit area, The present invention relates to a method for producing a polarizer having a large amount.

Hereinafter, the present invention will be described in more detail.

The method for producing a polarizer according to the present invention includes a swelling step, a dyeing step, a crosslinking step, a stretching step and a heat treatment step of a film for forming a polarizer. The number of repetitions of each step, the process conditions, and the like are not particularly limited as long as they do not deviate from the object of the present invention, and the stretching step may be performed in an independent step or may be performed simultaneously with at least one of swelling, dyeing and crosslinking steps.

Typical examples of the stretching method include dry stretching, wet stretching, or hybrid stretching in which the two types of stretching methods are mixed. Hereinafter, a method for producing the polarizer of the present invention will be described by taking wet stretching as an example. It is not. Among the above steps, the remaining steps except for the heat treatment step are performed in a state in which the film for forming a polarizer is immersed in a constant temperature bath.

Polarizer  Forming film

The polarizer-forming film is not particularly limited as long as it is a film which can be dyed with a dichroic substance, that is, iodine or the like, for example, a polyvinyl alcohol film, a partially saponified polyvinyl alcohol film; A hydrophilic polymer film such as a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ethylene-vinyl alcohol copolymer film, a cellulose film, a partially saponified film thereof and the like; Or a dehydrated polyvinyl alcohol film, a dehydrochloric acid-treated polyvinyl alcohol film, and the like. Of these, a polyvinyl alcohol-based film is preferable because it has an excellent effect of enhancing the uniformity of the degree of polarization in the plane and is excellent in dye affinity for iodine.

<Swelling step>

The swelling step is carried out by immersing the unstretched polarizer forming film in a swelling tank filled with a swelling aqueous solution before dyeing to remove impurities such as dust and anti-blocking agent deposited on the surface of the polarizing film, Is a step for improving physical properties of the polarizer by swelling to improve the drawing efficiency and to prevent uneven dyeing.

Water (pure water, deionized water) can usually be used as a swelling aqueous solution, and when a small amount of glycerin or potassium iodide is added thereto, the swelling of the polymer film and the processability can be improved.

The content of glycerin and potassium iodide is not particularly limited and may be, for example, 5 wt% or less and 10 wt% or less, respectively, in the total weight of the aqueous swelling solution.

The temperature of the swelling bath is not particularly limited, and may be, for example, from 0 to 60 캜, and preferably from 10 to 50 캜. When the temperature of the swelling bath is within the above range, the stretching and dyeing efficiency is excellent thereafter, and expansion of the film due to excessive swelling can be prevented.

<Stage of dyeing>

The dyeing step is a step of dipping the polarizing film in a dyeing bath filled with a dyeing aqueous solution containing a dichroic substance, for example, iodine, to adsorb iodine to the polarizing film.

The dyeing aqueous solution may comprise water, a water-soluble organic solvent or a mixed solvent thereof and iodine. The content of iodine in the dyeing aqueous solution may be 0.4 to 400 mmol / L, preferably 0.8 to 275 mmol / L, more preferably 1 to 200 mmol / L.

The dyeing aqueous solution may further contain iodide as a solubility aid for improving the dyeing efficiency.

The kind of iodide is not particularly limited and includes, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like , And potassium iodide is preferred in view of high solubility in water. These may be used alone or in combination of two or more.

The content of iodide is not particularly limited and may be, for example, 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the dyeing aqueous solution.

The temperature of the dye bath is not particularly limited and may be, for example, 5 to 42 캜, and preferably 10 to 38 캜.

The time for immersing the film for forming a polarizer in the dye bath is not particularly limited, and may be, for example, 0.5 to 20 minutes, and preferably 2 to 10 minutes.

<Bridging stage>

The cross-linking step is a step of immersing the dyed polarizer-forming film in a crosslinking aqueous solution so as to fix the adsorbed iodine molecules so that the dyeability due to physically adsorbed iodine molecules is not lowered by the external environment. Although dichroic dyes are not often eluted in a humidity environment, iodine molecules often dissolve or sublimate depending on the environment when the crosslinking reaction is unstable, and sufficient crosslinking reaction is required.

The aqueous solution for crosslinking may further comprise water as a solvent and a boron compound such as boric acid or sodium borate, and may further comprise an organic solvent mutually soluble with water.

The content of the boron compound is not particularly limited and may be, for example, 1 to 10% by weight, and preferably 2 to 6% by weight based on the total weight of the aqueous crosslinking solution. When the content of the boron compound is less than 1% by weight, the crosslinking effect of the boron compound may be decreased and it may be difficult to impart rigidity. When the content of the boron compound exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessively activated, It can be difficult.

The aqueous crosslinking solution may further contain a small amount of iodide to obtain the uniformity of the degree of polarization in the plane of the polarizer.

The iodide may be the same as that used in the dyeing step.

The content of iodide is not particularly limited and may be, for example, 0.05 to 15% by weight, preferably 0.5 to 11% by weight, based on the total weight of the aqueous crosslinking solution.

The weight ratio of the boron compound to the iodide is not particularly limited and may be, for example, 1: 0.1-3.5, preferably 1: 0.5-2.5.

The aqueous crosslinking solution may further contain an alkali metal chloride to improve the color durability of the polarizer to be produced.

The alkali metal chloride is not particularly limited, and examples thereof include lithium chloride, sodium chloride, potassium chloride and the like.

The content of the alkali metal chloride is not particularly limited and may be in the range of 0.22 to 4.5 molar equivalents, preferably 0.3 to 3.0 molar equivalents relative to 1 mol of iodide. When the content of the alkali metal chloride is within the above range, the improvement in color durability can be maximized.

The temperature of the crosslinking bath is not particularly limited, but may be, for example, 20 to 70 캜, preferably 40 to 60 캜.

The time for immersing the polarizer-forming film in the crosslinking bath is not particularly limited, and may be, for example, 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

< Stretching  Step>

The order of the stretching step is not particularly limited, and may be performed before, after, or after the dyeing step, and may be performed simultaneously with at least one step selected from the group consisting of a swelling step, a dyeing step and a crosslinking step .

When the stretching is carried out together with the swelling step, the stretching ratio may be made to be 1.02 to 3.5 times.

When the stretching is carried out together with the dyeing step, the cumulative stretching ratio may be made to be 1.1 to 5.0 times.

When the stretching is carried out together with the crosslinking step, the total cumulative stretching ratio may be 3.0 to 10.0 times.

<Cleaning step>

If necessary, the production method of the polarizer of the present invention may further comprise a cleaning step after the crosslinking step.

The cleaning step is a step of immersing the polarizing film, which has been crosslinked and stretched, in a cleaning bath filled with a cleaning aqueous solution to remove unnecessary residues such as boric acid attached to the polarizing film in the previous steps.

The cleaning aqueous solution may be water (deionized water), and iodide may be further added thereto. As the iodide, those same as those used in the dyeing step can be used, and among them, sodium iodide or potassium iodide is preferably used. The content of iodide is not particularly limited and may be, for example, 0.1 to 10 parts by weight, preferably 3 to 8 parts by weight, based on the total weight of the cleaning aqueous solution.

The temperature of the cleaning bath is not particularly limited and may be, for example, 5 to 60 캜, preferably 8 to 40 캜.

The cleaning step may be omitted and may be performed each time previous steps such as a dyeing step, a crosslinking step, or a stretching step are completed. It may also be repeated one or more times, and the number of repetition is not particularly limited.

<Heat treatment step>

The heat treatment step according to the present invention is a process for drying a cross-linked (and cleaned) polarizer-forming film and at the same time improving the orientation of molecules of iodine so that the optical characteristics are improved and durability is imparted.

Specifically, the heat treatment step according to the present invention is carried out by irradiating the cross-linked (and cleaned) film for forming a polarizer with infrared rays having an energy of 2.9 to 50 J / cm ² per unit area.

The conventional hot air drying or infrared drying method is designed to concentrate on the drying of the film. However, the present invention is not limited to the drying of the film by irradiating infrared rays under specific conditions, but also the internal stress of the film generated by stretching The deformation of the polarizer can be suppressed and the durability can be increased.

Further, the heat treatment step of the present invention can further accelerate the crosslinking of the additional boric acid, thereby increasing the formation of the iodine complex space in the film for forming a polarizer, so that the polymer (for example, polyvinyl alcohol) -I ₅ complex amount can be increased.

In the present invention, if the if the energy exerted by the infrared less than 2.9 J / cm ² is eliminated the effects of the internal stress mimihayeo the strain of the polarizer increased growth and reduced the iodine complex spatial form, in excess of 50 J / cm ² polarizer Resulting in deterioration of the film for forming. In this respect, the irradiation energy per unit area is more preferably 5 to 40 J / cm ² .

As a preferred embodiment of the present invention, the wavelength of the infrared rays may be 1 to 5 mu m. The effect of inducing vibration of the polymer forming the polarizer-forming film in the wavelength range, for example, the polyvinyl alcohol-based polymer, is maximized, and the effect of resolving the internal stress can be exhibited most effectively.

In the present invention, the irradiation time of infrared rays may be from 1 to 10 minutes, preferably from 2 minutes to 30 seconds to 7 minutes. The film can be efficiently dried while preventing deterioration of the film polymer in the above range, and at the same time, the internal stress reducing effect can be further improved.

The surface temperature of the polarizer-forming film to which infrared rays are irradiated is preferably a temperature at which the internal stress can be solved to the maximum, for example, 50 to 90 ° C. It is possible to prevent deterioration of the film polymer in the above range and to further improve the internal stress reduction effect. If the temperature of the film is less than 50 캜, the effect of resolving the internal stress may be insignificant. If the temperature is more than 90 캜, the film may be deteriorated.

The polarizer of the present invention manufactured as described above can be usefully used in the production of a polarizer having a low strain (low shrinkage) by dissolving internal stress at the same time as drying of the polarizer by performing a heat treatment step with infrared irradiation under specific conditions.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to be illustrative of the invention and are not intended to limit the scope of the claims. It will be apparent to those skilled in the art that such variations and modifications are within the scope of the appended claims.

Example  And Comparative Example

A polyvinyl alcohol film (VF-PS 7500, Kuraray) having an average degree of polymerization of 2,400 and a saponification degree of 99.9% or more was immersed in water (deionized water) at 30 캜 for 2 minutes to swell the polyvinyl alcohol film / L and 2% by weight of potassium iodide was dipped in an aqueous solution for dyeing at 30 DEG C for 4 minutes and then dyed in an aqueous solution for crosslinking at 53 DEG C containing 11% by weight of potassium iodide and 3.7% by weight of boric acid for 2 minutes And crosslinked. The cumulative stretching ratio in each dyeing / crosslinking step was adjusted to 5.8 times, and the crosslinked and stretched polarizer film was immersed in the cleaning bath for about 10 seconds to remove unnecessary residue adhering to the surface of the polarizer in the previous steps.

Then, the resulting mixture was charged into a drying furnace or a hot-air drying furnace for irradiating infrared rays under the conditions described in Table 1 below to prepare a polarizer. The infrared (IR) heater was a Heraeus Twin Tube Transparent Quartz Glass Heavy-Duty Infrared Heater (type BSG800 / 400).

Infrared (IR) drying conditions Hot air drying condition Irradiation energy
(J / cm ² ) Residence time
(min) Film surface temperature ( ^o C) Infrared wavelength (㎛) Drying furnace temperature ( ^o C) Residence time
(min) Film surface temperature ( ^o C) Example 1 5 2 50 1-5㎛ - - - Example 2 10 5 53 1-5㎛ - - - Example 3 15 10 54 1-5㎛ - - - Example 4 20 2 77 1-5㎛ - - - Example 5 30 5 79 1-5㎛ - - - Example 6 40 10 81 1-5㎛ - - - Example 7 3 5 51 1-5㎛ - - - Example 8 45 5 83 1-5㎛ - - - Example 9 48 7 84 1-5㎛ - - - Example 10 30 12 85 1-5㎛ - - - Example 11 15 5 50 0.7-1.0 m - - - Comparative Example 1 - - - - 60 2 56 Comparative Example 2 - - - - 75 5 72 Comparative Example 3 - - - - 85 5 81 Comparative Example 4 - - - - 90 5 86 Comparative Example 5 - - - - 90 10 87 Comparative Example 6 2.5 2 35 1-5㎛ - - - Comparative Example 7 55 2 91 1-5㎛ - - -

Experimental Example : Polarizer  Property measurement

1. Measurement of contraction force

The polarizers prepared in Examples and Comparative Examples were cut into a size of 3.0 cm x 2 mm, and then the shrinkage force was measured with DMA Q800 (dynamic mechanical analyzer, TA corporation). At this time, the pre-load was used to measure the pre-load to maintain the polarizer before the measurement.

2. Polarization measurement

The polarizers prepared in Examples and Comparative Examples were cut into a size of 4 cm x 4 cm, and then the transmittance was measured with an ultraviolet ray spectrophotometer (V-7100, manufactured by JASC Corporation). At this time, the polarization degree is defined by the following equation (1).

[Equation 1]

The degree of polarization (P) = [(T1 - T2) / (T1 + T2)] ^1/2

(Where T1 is the parallel transmittance obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T2 is the orthogonal transmittance obtained when the pair of polarizers are arranged in a state in which the absorption axes are orthogonal).

Note that it is important to note that the degree of polarization of 0.001 also greatly affects the contrast ratio. Particularly, when the polarization degree is less than 99.990, it is difficult to realize a real black because of a decrease in the contrast ratio.

3. Measurement of change in polarized light transmittance Ty )

The prepared polarizer was cut into a size of 4 cm x 4 cm and the transmittance was measured using an ultraviolet-visible light spectrometer (V-7100, manufactured by JASCO).

4. Measurement of A700 PVA - I ₅ Complex amount  evaluation)

The prepared polarizer was cut into a size of 4 cm x 4 cm, and the value of A 700 was evaluated using an external visible ray spectrometer (V-7100, manufactured by JASCO).

Transmittance (%) Polarization degree (%) A700
(PVA-I complex _5-amount estimate) Shrinkage (N) Example 1 42.5 99.995 4.35 3.1 Example 2 42.4 99.995 4.32 2.5 Example 3 42.5 99.995 4.33 2.0 Example 4 42.5 99.994 4.11 2.1 Example 5 42.5 99.995 4.21 1.9 Example 6 42.3 99.993 4.19 1.7 Example 7 42.7 99.994 4.16 3.6 Example 8 42.9 99.990 4.12 1.6 Example 9 42.8 99.991 4.11 1.4 Example 10 42.8 99.991 4.03 3.0 Example 11 42.5 99.993 4.01 3.7 Comparative Example 1 42.6 99.990 4.25 5.3 Comparative Example 2 42.5 99.989 4.1 4.8 Comparative Example 3 42.6 99.988 3.98 4.7 Comparative Example 4 42.7 99.986 3.64 4.2 Comparative Example 5 42.8 99.985 3.46 4.0 Comparative Example 6 42.7 99.989 4.23 5.2 Comparative Example 7 44.1 97.232 2.15 1.3

Referring to Table 2, it can be seen that the polarizer manufactured according to the present invention exhibits at least the same or almost excellent optical characteristics (transmittance, degree of polarization) as compared with the polarizer produced by the conventional hot air drying.

However, in the case of Example 10 in which the retention time was rather long, it was found that the degree of polarization and A700 decreased somewhat and the retraction force slightly increased as compared with Example 5 in which the same irradiation energy was used. In the case of Example 11, it was found that the A700 was somewhat lower and the retraction force was slightly increased as compared with the other Examples.

However, in all of the comparative examples, the degree of polarization was lower than that in the Examples, and the shrinking force was higher than that in the Examples except Comparative Example 7.

Specifically, in the case of Comparative Examples 1 to 5 in the hot-air drying method, it can be seen that the polarization and shrinkage force did not reach the Examples. Especially, in the case of Comparative Examples 3 to 5, in which the double shrinkage force is rather low, the A700 value is low and the degree of polarization is high and the degree of polarization is lower than that of Comparative Examples 1 and 2. [

Also, in the case of Comparative Examples 6 and 7, which are the same as those of the examples, the shrinkage force of Comparative Example 6 in which irradiation energy is lower than the range of the present invention was excessively high, and the opposite Comparative Example 7 shows that the degree of polarization was excessively low have.

Claims (5)

After the polarizer-forming film is subjected to a swelling step, a dyeing step, a stretching step and a crosslinking step, the polarizer-forming film is dried by infrared irradiation at 2.9 to 50 J / cm ² per unit area, And eliminating the applied stress.
The method of claim 1, wherein the infrared rays have a wavelength of 1 to 5 占 퐉.
The method of producing a polarizer according to claim 1, wherein the infrared irradiation time is from 1 minute to 10 minutes.
The method of producing a polarizer according to claim 1, wherein the surface temperature of the polarizer-forming film during infrared irradiation is 50 to 90 ° C.
The method of claim 1, further comprising a cleaning step after the crosslinking step.