KR20090107649A - Method for manufacturing polyvinyl alcohol film and polyvinyl alcohol polarizer using thereof - Google Patents

Abstract

PURPOSE: A method for manufacturing a polyvinyl alcohol film is provided to improve dyeing efficiency in a dye process by evenly diffusing iodide(I-) inside a polyvinyl alcohol film. CONSTITUTION: A method for manufacturing a polyvinyl alcohol film comprises the steps of: preparing a base solution by mixing an iodine compound consisting of iodine or iodine compound to molten polyvinyl alcohol; and forming a polyvinyl alcohol film by casting the base solution and drying it. A polarizer has the form in which a polarizer protection film(300) is laminated at both sides of a polarized light device(100) in a medium of adhesive(200).

Description

Method for manufacturing polyvinyl alcohol film and polyvinyl alcohol polarizer manufactured therefrom {METHOD FOR MANUFACTURING POLYVINYL ALCOHOL FILM AND POLYVINYL ALCOHOL POLARIZER USING THEREOF}

The present invention relates to a method for producing a polyvinyl alcohol film used in a thin film transistor liquid crystal display (TFT-LCD) for mobile, notebook, computer monitor and TV, and a polyvinyl alcohol polarizer prepared therefrom, and more particularly, to a polarizer. The iodine compound was added to the polyvinyl alcohol solution as a raw material of the polyvinyl alcohol solution, and a polyvinyl alcohol film was prepared by the solution casting method, so that the iodine ions (I ⁻ ) were evenly dispersed in the polyvinyl alcohol film, thereby being a dyeing step. The present invention relates to a polyvinyl alcohol polarizer manufacturing method and a polyvinyl alcohol polarizer produced therefrom to improve the dyeing efficiency in order to obtain a polarizing plate excellent in light efficiency.

Polarizing plates are used inside and outside the liquid crystal cell for the purpose of controlling the vibration direction of light in order to visualize the display pattern of the liquid crystal display device. Generally used polarizing plate is a polyvinyl alcohol (PVA) resin film is dyed and uniaxially stretched by adsorption of a dichroic dye, the transparent resin film through one or both sides of the polarizer oriented the dichroic dye through an adhesive layer In particular, a cellulose acetate-based polarizer protective film represented by triacetyl cellulose (TAC) is laminated. This is bonded to the liquid crystal cell with an adhesive through another optical film as necessary to form a liquid crystal display device. Dichroic pigments include anthraquinones and azo dyes, as well as iodine.

In general, a method of manufacturing a polarizer is prepared through a process of dyeing a polyvinyl alcohol (PVA) film substrate, dyeing in an aqueous solution of iodine, drying through a color correction process using potassium iodine, or washing with water.

The polarizer prepared above uses a PVA-based adhesive to produce a polarizing plate through a process of laminating a protective film such as a triacetate cellulose (TAC) film, which is a polarizer protective film, and an appropriate optical compensation film.

In order to manufacture a polarizing plate having excellent light efficiency, when the upper and lower polarizing plates are attached to the upper substrate and the lower substrate of the liquid crystal display, and the polarization axes are orthogonal to each other, the light leakage phenomenon should be reduced over the entire visible light region (380 to 780 nm).

The dyeing process is an important process for determining the light efficiency of the polarizing plate. In order to manufacture a polarizing plate having excellent light efficiency, iodine is adsorbed on the surface of a polyvinyl alcohol (PVA) film, and diffusion into the polyvinyl alcohol film is efficiently performed, so it is important to improve iodine orientation in the stretching process. .

Here, as a method of manufacturing the PVA film which becomes a raw material of a polarizer, arbitrary methods, such as the casting method, the solution casting method, and the extrusion method, which cast-film-form the raw liquid melt | dissolved in water or an organic solvent, are used suitably, double casting Law is the most used.

The solution casting method generally takes a method in which a raw material solution (dope) is cast on a support such as a belt that rotates through a casting die, and then the cast dope is peeled off from the support, dried, and wound in the form of a PVA film. .

However, in manufacturing the PVA film by such a solution casting method, if the properties in the direction of the generated PVA thickness is formed non-uniformly, when the above-described dyeing process is performed, iodine cannot be adsorbed deeply inside the PVA film, resulting in As a result, a problem occurs in that a polarizing plate in which light efficiency is lowered is manufactured.

The present invention is to solve the above problems, an object of the present invention is a method for producing a polyvinyl alcohol film, after mixing the iodine compound in a polyvinyl alcohol solution, by producing a polyvinyl alcohol film by a solution casting method, It is to provide a method for producing a polyvinyl alcohol film that can obtain a polarizing plate excellent in light efficiency by maximizing the dyeing efficiency.

Polyvinyl alcohol film production method according to the present invention for solving the above problems, raw material solution production step of preparing a raw material solution by mixing an iodine compound composed of at least one of iodine or potassium iodide to the polyvinyl alcohol in the molten state; Solution casting the raw material solution, followed by drying to form a polyvinyl alcohol film.

Here, the iodine compound is composed of a mixture of iodine and potassium iodide, the weight ratio of the iodine and potassium iodide is 1: 1 to 1: 3, the iodine compound is 3 to 70 with respect to 100 parts by weight of the polyvinyl alcohol A weight part is preferable in order to maximize dyeing efficiency.

In addition, the thickness of the polyvinyl alcohol film produced after the film forming step is preferably 40 to 100㎛ for performing the stretching step and lamination in the process of laminating with the polarizer protective film.

In addition, the polyvinyl alcohol polarizer according to the present invention is produced by dyeing and stretching the polyvinyl alcohol film produced by the above production method.

According to the polyvinyl alcohol film production method and the polyvinyl alcohol polarizer manufactured therefrom, by adding iodine compound to the polyvinyl alcohol solution, iodine ions are present in the polyvinyl alcohol film to improve the dyeing efficiency In addition, the orientation of iodine ions is increased in the stretching process so that a polarizing plate having excellent light efficiency can be manufactured.

Hereinafter, the present invention will be described in detail.

1 is a front sectional view of a polarizing plate according to an embodiment of the present invention.

As shown in Figure 1, the polarizing plate 10 according to an embodiment of the present invention forms a polarizer protective film 300 is laminated on both sides of the polarizer 100 via the adhesive 200.

Here, the polarizer 100 is made of a polyvinyl alcohol (PVA) film to be described later, unlike in the embodiment, the polarizer protective film 300 is formed on only one side of the upper or lower side of the polarizer 100 Can have

The polyvinyl alcohol film produced by the present invention is not particularly limited as long as it is a PVA film, and examples thereof include a modified PVA film such as a partially formalized PVA film and an acetoacetyl group-modified PVA film.

The polarizer 100 is manufactured by the manufacturing method mentioned later, Although the thickness is not specifically limited, Preferably it is 10-30 micrometers, More preferably, it is 10-20 micrometers.

The adhesive 200 is a material for adhering the polarizer 100 and the polarizer protective film 300, and an adhesive made of a vinyl alcohol-based polymer, or a vinyl alcohol-based adhesive such as boric acid or borax, glutaraldehyde, melamine, oxalic acid, or the like. A water-soluble crosslinking agent or the like of the polymer can be made alone or mixed. Such an adhesive is formed by the application drying layer of an aqueous solution, etc., and can add another additive, a catalyst, such as an acid, as needed. In particular, it is preferable to use an adhesive made of polyvinyl alcohol in that the adhesiveness with the PVA substrate for polarizer is the best.

The polarizer protective film 300 is a film attached to both upper and lower sides of the polarizer 100 to support and protect the polarizer, and a polymer having excellent transparency, mechanical strength, thermal stability, moisture shielding, or the like is preferably used. For example, an acetate resin such as triacetyl cellulose (TAC), a polyester resin, a polyether sulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, an acrylic resin, a polynor Borneen resin etc. are mentioned. In consideration of polarization characteristics, durability, and the like, most preferably, a triacetyl cellulose (TAC) film having a thickness of 80 µm or more obtained by saponifying the surface with alkali or the like is used.

The present invention relates to a production method for producing a polyvinyl alcohol film that is a raw film for producing a polarizer in the above configuration.

Polyvinyl alcohol film production method according to the present invention comprises a raw material solution manufacturing step of preparing a raw material solution by mixing an iodine compound composed of at least one of iodine and potassium iodide to the polyvinyl alcohol solution; After solution casting the raw material solution, and drying and heat treatment is made to include a film forming step of forming a polyvinyl alcohol film.

Hereinafter, the manufacturing method of the polyvinyl alcohol film will be described for each step.

1. Manufacturing process of raw material solution

Specifically, the raw material solution production step according to a preferred embodiment of the present invention, (1) is carried out by preparing a raw material solution by adding and mixing the iodine compound consisting of iodine (I ₂ )-potassium iodide (KI) to the polyvinyl alcohol solution do.

Since the polyvinyl alcohol component and the iodine compound component are mixed with each other in the raw material solution formed by directly adding and mixing the iodine compound to the polyvinyl alcohol solution through the raw material solution manufacturing step, the inside of the polyvinyl alcohol film manufactured through a post process In iodine ions are evenly dispersed, thereby allowing the dyeing process, which is a post process, to be carried out more efficiently, and a polarizing plate with maximized light efficiency can be obtained.

As the iodine compound, iodine and potassium iodide are mixed and used, and in order to generate iodine ions most effectively, the weight ratio of iodine (I ₂ ) and potassium iodide (KI) is preferably 1: 1 to 1: 5, more preferably. Is 1: 1 to 1: 3, and more preferably 1: 1.5 to 1: 2.5. Here, iodine (I ₂ ) plays a role of effectively generating iodine ions from potassium iodide (KI).

Examples of the iodide compounds used in addition to the potassium iodide include lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like.

The iodine compound is preferably added to 3 to 70 parts by weight, more preferably 5 to 50 parts by weight based on 100 parts by weight of the polyvinyl alcohol. If the iodine compound is less than 3 parts by weight, the dyeing effect by the iodine is not sufficiently exhibited, and if it exceeds 70 parts by weight there is a disadvantage that is not economical compared to the amount added.

Stirring the raw material solution is carried out for 5 seconds to 900 seconds, more preferably 10 to 600 seconds.

In addition, known additives may be further added to the present invention, and examples of such additives include plasticizers, UV-absorbers, optically anisotropic compounds, and matting agents.

2. Film Forming Step

The film forming step is a step of solution casting the raw solution produced in the raw material solution manufacturing step, and then dried to form a polyvinyl alcohol film.

The solution casting method and the drying method may be performed by conventional methods, and are not limited to special conditions. For example, after the raw material solution is cast on a support such as a rotating belt or drum having a surface temperature of about 25 ° C. through a casting die at 80 ° C. to 100 ° C., the cast dope is peeled off from the support to be 60 to 90 ° C. It can be dried by a drying roll, it may be by a method of winding in the form of polyvinyl alcohol (PVA) film.

The polyvinyl alcohol film formed by the above production method is usually 40 to 100 μm thick, preferably 45 to 75 μm thick, more preferably 50 to 60 μm thick film. When the thickness of the base film exceeds 100㎛, not only the dyeing efficiency is lowered, but also when the manufactured polarizer is mounted on the liquid crystal display, there is a fear that the color change of the display panel may increase, and the thickness thereof is less than 40㎛. In this case, there is a problem that it is not easy to perform the stretching step. However, in the case of using the base film having a thin thickness of 40 to 75㎛ high swelling degree of the base film in the swelling step, the possibility of wrinkles is high, the moisture evaporation during the drying step is large, brittleness becomes large Therefore, since there is a high possibility of cracking in the process of laminating with the polarizer protective film after manufacturing the polarizer, it is preferable to manufacture a suitable base film according to the process conditions.

The method of manufacturing the polarizer 100 using the polyvinyl alcohol film manufactured by the above method is not limited by a specific method, but is preferably performed as follows.

The polyvinyl alcohol polarizer manufacturing method includes a swelling step, a dyeing step, a crosslinking step, a drying step, and a stretching step.

The swelling step makes the molecular chain of PVA in the PVA base film more flexible before performing this process including the dyeing step, and it is easy to dye dyes such as iodine compounds into the PVA film in the dyeing process by relaxing the molecular chain. In the swelling step of the present invention, the polyvinyl alcohol (PVA) film, which is the base film of the polarizer, is swelled in a swelling tank containing a swelling liquid as a pretreatment step before the dyeing step.

The dyeing step is a process of adsorbing the dye inside the base film by immersing the base film in iodine or dichroic dye. Here, when using an aqueous solution of iodine as a dye, a mixed aqueous solution containing iodine ions can be used by using an aqueous solution of potassium iodide in iodine as a dissolution aid.

In addition, it is preferable that the temperature range of the iodine aqueous solution used as the said dyeing solution is 20-40 degreeC, More preferably, it is 25-35 degreeC. If the temperature of the dyeing solution exceeds 40 ℃ there is a problem that wrinkles occur in the base film, if the temperature is less than 20 ℃ it does not easily relax the PVA molecular chain is not easy to dye inside the PVA There is a problem.

The crosslinking step is a step performed to crosslink the PVA molecular chain of the base film by depositing the base film on a crosslinking agent, and the crosslinking agent used preferably uses boric acid or borax aqueous solution. The boric acid aqueous solution may include potassium iodide.

The drying step is a step of drying the base film at a temperature of 45 to 70 ° C, preferably 60 to 65 ° C, and a temperature of 40 to 60 ° C, preferably 55 to 60 ° C when using a base film of less than 75 μm. .

The stretching step may be performed together with at least one of the swelling step and the drying step, or may be performed before or after the start of at least one of the above steps, or between each step.

The stretching method used in the stretching step is not particularly limited, but both a wet stretching method and a dry stretching method can be used. The stretching method by the dry stretching method includes, for example, an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. Can be performed.

The method of bonding the polarizer 100 and the polarizer protective film 300 generated through the above process is not particularly limited, but a top-down method, a down-top method, and It is divided into horizontal lamination method. In the present invention, all three methods can be used.

When the polarizer protective film 300 is adhered to the polarizer 100, the adhesive may be applied by applying an adhesive in advance, or the adhesive may be adhered by dropping the adhesive when the polarizer 100 and the polarizer protective film 300 are laminated. have. In the present invention, it is possible to select one of the methods of applying the adhesive by applying an adhesive, or dropping the adhesive, or both may be used together.

An optical member such as another optical layer may be applied to the polarizing plate manufactured by the manufacturing method. The optical member is not particularly limited, but for example, a reflecting plate, a semi-transmissive reflecting plate, a retardation plate (including λ plates such as a 1/2 wave plate and a quarter wave plate), a visual compensation film, and a brightness enhancement film Etc. One or two or more layers of suitable optical layers that can be used for forming a liquid crystal display device or the like can be used.

Hereinafter, the present invention will be described in more detail with reference to examples of the present invention and comparative examples compared with the present invention.

Example  One

Iodine compound having a weight ratio of 1: 2 of iodine (I ₂ , manufactured by Wako) and potassium iodide (KI, manufactured by SQM) with respect to 100 parts by weight of an aqueous solution in which 6% by weight of polyvinyl alcohol resin (manufactured by Nippon Synthetic Co., Ltd.) was melted. After adding 5 parts by weight of the mixture to prepare a raw material solution, a polyvinyl alcohol film having a thickness of 73 μm was prepared by solution casting and drying.

The polyvinyl alcohol film is sequentially swelled in a swelling bath containing a solution of boric acid at 25 ° C., a dye bath containing a mixed solution of iodine and potassium iodide having a boric acid concentration of 2.5% by weight and a temperature of 30 ° C., and a crosslinking bath containing a solution of 50 ° C. boric acid. After stretching uniaxially and stretching at a draw ratio of 2.70 times, the base film was uniaxially stretched while immersing in a drawing bath containing an aqueous solution of boric acid, stretched at a stretching ratio of 2.33 times, stretched at a total draw ratio of 6.3 times, and dried under a 55 ° C. environment to polarizer. Prepared. After preparing the polarizer, a polarizing plate was manufactured by laminating a tetraacetate cellulose (TAC) film, which is a polarizer protective film, with a polarizer.

Example  2 to 6

Except that the iodine compound was added to 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight and 30 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol solution to prepare a polyvinyl alcohol film. The polarizer and the polarizing plate were manufactured by the same method as 1.

Comparative example

In the raw material solution, a polarizer and a polarizing plate were manufactured in the same manner as in Example 1 except that the iodine compound was excluded.

For the evaluation of the characteristics of the polarizing plates manufactured by the Examples and Comparative Examples, the following experiment was performed. However, when evaluating the light efficiency of the polarizing plate, in order to exclude the effect of the transmittance (Ts, Tp), the evaluation sample was prepared by adjusting the transmittance for each condition to within ± 0.2.

Transmittance

The transmittance was measured using a spectrophotometer (V-7100, manufactured by Jasco), and obtained using the following formula.

Permeability (%) = (I _out / I _in ) * 100

Where I _in is incident light and I _out is transmitted light,

Single transmittance (Ts) is the total light transmittance (%) of one polarizing plate,

The parallel transmittance (Tp) is the total light transmittance (%) when the polarizing axes of two polarizing plates are parallel to each other,

Orthogonal transmittance Tc is the total light transmittance (%) at the time of orthogonalizing and superimposing the polarization axes of two polarizing plates.

Polarization degree ( PE )

Polarization degree was calculated | required using the following formula.

Degree of polarization (PE) = [(Tp-Tc) / (Tp + Tc)] ^1/2 * 100 (%)

Polarizer CR

Polarizing plate CR was calculated | required using the formula of parallel transmittance (Tp) / orthogonal transmittance (Tc).

The characteristic evaluation data is summarized in Table 1 below.

TABLE 1

Group Transmittance (Ts) (%) Parallel transmittance (T p) (%) Orthogonal Transmittance (Tc) (%) Polarization degree (PE) (%) Polarizer CR (Tp / Tc) Comparative example 43.57 37.43 0.035 99.907 1069.43 Example 1 43.63 37.51 0.025 99.933 1500.40 Example 2 43.48 37.36 0.022 99.941 1698.18 Example 3 43.59 37.32 0.015 99.960 2494.67 Example 4 43.67 37.50 0.013 99.965 2884.62 Example 5 43.63 37.52 0.011 99.971 3410.91 Example 6 43.53 37.41 0.010 99.973 3741.00

As shown in the experimental results of Table 1, as the amount of iodine compound added in the polyvinyl alcohol film increases, the Tc value decreases at the same level of Ts and Tp, and the PE value increases, resulting in improved optical properties. It can be seen that.

As a result of the experiment, it can be seen that by directly adding and mixing the iodine compound in the polyvinyl alcohol film in the raw material solution manufacturing step, it is possible to manufacture a polarizing plate with excellent optical properties.

In the above, this invention was demonstrated in detail with reference to an Example and a comparative example centering on a structure. However, the scope of the present invention is not limited to the above embodiments but may be embodied in various forms of embodiments within the appended claims. Without departing from the gist of the invention as claimed in the claims, any person of ordinary skill in the art is considered to be within the scope of the claims described in the present invention to the extent possible to vary.

1 is a front cross-sectional view of a polarizing plate according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: polarizer 200: adhesive 300: polarizer protective film

Claims (4)

In the molten polyvinyl alcohol, A raw material solution preparation step of preparing a raw material solution by mixing an iodine compound composed of at least one of iodine or potassium iodide; Method of producing a polyvinyl alcohol film, characterized in that it comprises a film forming step of solution casting the raw material solution to form a polyvinyl alcohol film by drying. The method of claim 1, The iodine compound is composed of a mixture of iodine and potassium iodide, the weight ratio of the iodine and potassium iodide is 1: 1 to 1: 3, the content of the iodine compound is 3 to 70 with respect to 100 parts by weight of the polyvinyl alcohol Polyvinyl alcohol film production method, characterized in that parts by weight. The method of claim 1, The polyvinyl alcohol film produced after the film forming step has a thickness of polyvinyl alcohol film, characterized in that 40 to 100㎛. A polyvinyl alcohol polarizer produced by dyeing and stretching a polyvinyl alcohol film produced by the method of any one of claims 1 to 3.

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