JP2005241689A - Iodine polarizing film, method for producing the same, and polarizing plate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iodine polarizing film and a polarizing plate having improved durability based on a polyvinyl alcohol resin, and a manufacturing method thereof.
An iodine-based polarizing film comprising a polyvinyl alcohol-based resin film in which iodine is adsorbed and oriented and further containing a triterpenoid glycoside such as glycyrrhizic acid is provided. The process of uniaxially stretching a polyvinyl alcohol resin film, the process of dyeing a polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide, and immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid And a method of dissolving a triterpenoid glycoside in an aqueous solution used in the stage after iodine staining when producing an iodine-based polarizing film through a step of washing with water after an immersion treatment in an aqueous solution containing boric acid. This polarizing film can be manufactured.

[Selection figure] None

Description

  The present invention relates to an iodine polarizing film, a production method thereof, and an iodine polarizing plate using the iodine polarizing film.

  The polarizing film is generally produced by adsorbing and orienting a dichroic dye, iodine or a dichroic dye, onto a polyvinyl alcohol-based resin film. A protective film made of triacetyl cellulose or the like is bonded to at least one surface of the polarizing film via an adhesive layer to form a polarizing plate, which is used for a liquid crystal display device or the like. A polarizing film using iodine as a dichroic dye is referred to as an iodine polarizing film, while a polarizing film using a dichroic dye as a dichroic dye is referred to as a dye polarizing film. Among these, iodine-based polarizing films are widely used because they exhibit a high transmittance and a high degree of polarization, that is, high contrast, compared to dye-based polarizing films. Although the iodine-based polarizing film is superior to the dye-based polarizing film in terms of optical properties as described above, the iodine-based polarizing film is inferior to the dye-based polarizing film in terms of optical durability. If left untreated, problems such as a decrease in transmittance and discoloration of the polarizing plate occurred.

  On the other hand, in recent years, the demand for the performance of polarizing plates has become more severe due to the expansion of the application field of liquid crystal display devices and the advancement of peripheral technologies. Specifically, there is a demand for a polarizing plate having high transmittance and degree of polarization, that is, high contrast, and excellent heat resistance and moist heat resistance. On the other hand, for example, JP-A-58-68008 (Patent Document 1) proposes a polarizing film in which a polyester resin is uniaxially stretched and used as a base material. However, it is insufficient to obtain a polarizing film excellent in both polarization performance and durability, and further improvement has been demanded.

  JP-A-2000-35512 (Patent Document 2) discloses that a polyvinyl alcohol-based resin film dyed with iodine is immersed in a boric acid aqueous solution containing zinc ions and potassium iodide. It has been proposed that a predetermined amount of zinc is contained in the polarizing film to increase the durability of the polarizing film at high temperatures.

JP 58-68008 A JP 2000-35512 A

  The present inventors conducted research to increase the durability of an iodine-based polarizing film made of a polyvinyl alcohol-based resin and a polarizing plate having a protective film bonded thereto by means different from those in Patent Documents 1 and 2. The invention has been reached. Accordingly, an object of the present invention is to provide an iodine-based polarizing film having improved durability based on a polyvinyl alcohol-based resin, a method for producing the same, and a polarizing plate having excellent durability using the polarizing film. Is to provide.

  As a result of conducting research under such a purpose, the inventors of the present invention have produced an iodine-based polarizing film by stretching a polyvinyl alcohol-based resin film, iodine staining, boric acid treatment after dyeing, and washing with water. At least one of an aqueous solution containing iodine used for the treatment, an aqueous solution containing boric acid used for boric acid treatment, and water used for the water washing treatment is dissolved and contained in a triterpenoid glycoside such as glycyrrhizic acid. By treating the polyvinyl alcohol-based resin film, it can be found that a triterpenoid glycoside can be contained in the polarizing film, thereby exhibiting an effect of suppressing problems such as discoloration of the polarizing film under dry heat, The present invention has been reached.

  That is, according to the present invention, there is provided an iodine-based polarizing film comprising a polyvinyl alcohol-based resin film in which iodine is adsorbed and oriented, and the polyvinyl alcohol-based resin film further contains a triterpenoid glycoside.

  According to the present invention, there is also provided a method for producing this iodine-based polarizing film. This method comprises a step of uniaxially stretching a polyvinyl alcohol-based resin film, and the polyvinyl alcohol-based resin film is an aqueous solution containing iodine and potassium iodide. The iodine polarizing film is manufactured through the step of dyeing in, the step of immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid, and the step of rinsing after the immersion treatment in an aqueous solution containing boric acid. In this case, the triterpenoid glycoside is dissolved and contained in at least one of the aqueous solution containing iodine and potassium iodide, the aqueous solution containing boric acid, and the water for washing.

  Furthermore, according to this invention, the iodine type polarizing plate by which the protective film was bonded by the single side | surface or both surfaces of the iodine type polarizing film containing said triterpenoid glycoside is also provided.

  The iodine-based polarizing film according to the present invention is prevented from deterioration after being subjected to dry heat, and has excellent durability.

  Hereinafter, the present invention will be described in detail. The iodine-based polarizing film is obtained by adsorbing and orienting iodine on a polyvinyl alcohol-based resin film. And in this invention, a triterpenoid glycoside is included in this polarizing film.

  The polyvinyl alcohol resin constituting the polarizing film can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, unsaturated amines, and the like. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, preferably about 98 to 100 mol%. This polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  A film obtained by forming such a polyvinyl alcohol-based resin is used as a raw film for manufacturing a polarizing film. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. Although the film thickness of the raw film which consists of polyvinyl alcohol-type resin is not specifically limited, For example, it is about 5 micrometers-150 micrometers, Preferably it is about 10 micrometers-150 micrometers.

  The iodine polarizing film includes a step of uniaxially stretching such a polyvinyl alcohol resin film, a step of dyeing the polyvinyl alcohol resin film with iodine to adsorb the iodine, and a polyvinyl alcohol resin film on which iodine is adsorbed. It is manufactured through a step of treating with a boric acid aqueous solution and a step of washing with water after the treatment with the boric acid aqueous solution.

  Uniaxial stretching may be performed before iodine staining, may be performed simultaneously with iodine staining, or may be performed after iodine staining. When uniaxial stretching is performed after iodine staining, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural stages. For uniaxial stretching, rolls with different peripheral speeds may be uniaxially stretched or may be stretched uniaxially using a heating roll. Moreover, the dry-type extending | stretching which extends | stretches in air | atmosphere may be sufficient, and the wet extending | stretching which extends | stretches in the state swollen with the solvent may be sufficient. The draw ratio is usually about 4 to 8 times.

  Adsorption of iodine to the polyvinyl alcohol-based resin film is performed by immersing and staining the polyvinyl alcohol-based resin film in an aqueous solution containing iodine, usually an aqueous solution containing iodine and potassium iodide. In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to water before this dyeing | staining process. The content of iodine in the aqueous solution containing iodine and potassium iodide is about 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is 0.5 to 20 parts by weight per 100 parts by weight of water. About a part. The temperature of this aqueous solution is about 20 to 40 ° C., and the immersion time in this aqueous solution is about 20 to 1,800 seconds.

  The boric acid treatment after iodine staining is performed by immersing a polyvinyl alcohol resin film dyed with iodine in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. The boric acid aqueous solution preferably contains potassium iodide. When the boric acid aqueous solution contains potassium iodide, the amount of potassium iodide is usually 40 parts by weight or less, preferably 30 parts by weight or less per 100 parts by weight of water. The immersion time in the boric acid aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed by immersing a boric acid-treated polyvinyl alcohol resin film in water. After washing with water, drying treatment is performed to obtain a polyvinyl alcohol resin film in which iodine is adsorbed and oriented, that is, an iodine polarizing film.

  In the present invention, a triterpenoid glycoside is included in the iodine-based polarizing film. In this case, the triterpenoid glycoside is usually introduced at a stage after dyeing with an aqueous solution containing iodine. Specifically, during the process of producing an iodine-based polarizing film as described above, an aqueous solution containing iodine and potassium iodide, an aqueous solution containing boric acid used for boric acid treatment, and water used for washing after boric acid treatment Among them, a method of dissolving a triterpenoid glycoside or a triterpenoid glycoside-containing substance in any one or a plurality of them can be employed. Among these, a method of dissolving and containing a triterpenoid glycoside or a triterpenoid glycoside-containing substance in an aqueous solution containing boric acid is preferable.

  Even if the triterpenoid glycoside or the triterpenoid glycoside-containing substance is dissolved at any stage, the amount of the triterpenoid glycoside is usually about 0.01 to 60 parts by weight per 100 parts by weight of water, preferably 0.5 parts by weight or more, further 1 part by weight or more, preferably 30 parts by weight or less, and further 15 parts by weight or less. If the amount of triterpenoid glycoside is less than 0.01 parts by weight per 100 parts by weight of water, the effect of suppressing problems such as discoloration of the obtained polarizing film under dry heat cannot be sufficiently exhibited.

Triterpenoid glycosides are glycosides of triterpenoids ( _C30 compounds), and are distributed in the plant kingdom, and glycyrrhizic acid and the like are known. Triterpenoid glycosides are usually obtained and marketed as extracts from plants containing them. If the triterpenoid glycoside or the triterpenoid glycoside-containing substance used in the present invention has an effect of suppressing problems such as discoloration under dry heat by containing it in a polarizing film, it is a dry crude powder extraction Or a crude extract as a liquid preparation containing an extraction solvent such as alcohol, and the purity of the triterpenoid glycoside is not particularly limited. Needless to say, it can be a refined product. Moreover, you may contain a small amount of additives, such as a stabilizer and antiseptic | preservative, in the range which does not inhibit the effect of this triterpenoid glycoside.

  In addition to glycyrrhizic acid, triterpenoid glycosides include natural modifications of these compounds distributed in the plant kingdom. The triterpenoid glycoside used in the present invention is not necessarily limited to those specifically exemplified herein, but its molecular weight is preferably 1,400 or less, more preferably 1,000 or less. is there. When the molecular weight exceeds 1,400, it becomes difficult to be introduced into the polyvinyl alcohol-based resin film. These triterpenoid glycosides may be used alone or in combination of two or more.

Among these triterpenoid glycosides, glycyrrhizic acid C ₄₂ H ₆₂ O ₁₆ is a preferred example. Glycyrrhizic acid has the following structure and is an extract from licorice (Glycyrrhiza glabra).

  The content of the triterpenoid glycoside in the polarizing film is about 0.01 to 30% by weight, preferably 0.1% by weight or more, and preferably 25% by weight or less. If the amount is too small, the effect of suppressing problems such as discoloration of the obtained polarizing film under dry heat cannot be sufficiently exhibited. Moreover, if the amount is too large, the physical properties of the polarizing film may be affected.

  The triterpenoid glycoside in the polarizing film made of a polyvinyl alcohol-based resin film can be quantified by, for example, dissolving the polarizing film in a solvent and analyzing the sample using liquid chromatography.

  Thus, the polarizing film obtained by containing the triterpenoid glycoside is formed into a polarizing plate by laminating a protective film on one side or both sides thereof. Examples of the protective film include cellulose acetate resin films such as triacetyl cellulose and diacetyl cellulose, acrylic resin films, polyester resin films, polyarylate resin films, polyether sulfone resin films, and cyclic olefins such as norbornene. And a cyclic polyolefin resin film. The thickness of the protective film is usually about 10 μm to 200 μm.

  The polarizing plate may have various known functional layers such as an antireflection layer, an antiglare layer, a hard coat layer, and an antistatic layer on one surface, that is, the exposed surface of the protective film. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these. In addition, the orthogonal hue shown in the example means the hue of transmitted light when two polarizing films are overlapped so that their transmission axes are orthogonal to each other.

Example 1
A polyvinyl alcohol film having an average polymerization degree of about 2,400 and a saponification degree of 99.9 mol% or more and a thickness of 75 μm was brought into contact with a heating roll and uniaxially stretched at a stretch ratio of about 5 times. Further, while maintaining the tension, it was immersed in pure water at 60 ° C. for 1 minute, and then immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.15 / 5/100 at 28 ° C. for 120 seconds. Subsequently, glycyrrhizic acid (obtained from Maruzen Pharmaceutical Co., Ltd., trade name: pure glycymine) / potassium iodide / boric acid / water in an aqueous solution of 3.0 / 25 / 9.5 / 100 by weight at 300 ° C. at 76 ° C. Soaked for 2 seconds. After washing with pure water at 15 ° C. for 3 seconds, it was dried at 50 ° C. to obtain a polarizing film in which iodine was adsorbed and oriented on polyvinyl alcohol and glycyrrhizic acid was adsorbed. About the obtained polarizing film, durability under dry heat was evaluated by the following method.

<< Durability Evaluation Method >>
The spectral transmittance τ (λ) of the polarizing film is measured using a spectrophotometer [“UV-2200” manufactured by Shimadzu Corporation]. Orthogonal hues L ^* , a ^* and b ^* are determined from the obtained spectral transmittance τ (λ). Next, the durability test is performed by leaving the polarizing film in a dry atmosphere at 100 ° C. for 14 hours. With respect to the polarizing film after the durability test, the spectral transmittance τ (λ) is measured again, and the orthogonal hues L ^* , a ^* and b ^* are obtained therefrom. From the orthogonal hues L ^* , a ^* and b ^* before and after the durability test, respective differences ΔL ^* , Δa ^* and Δb ^* are obtained according to the following equations (1) to (3), and further according to the following equation (4). The color difference ΔE ^{* of} is obtained.

ΔL ^* = (L ^* ) _after − (L ^* ) _before (1)
Δa ^* = (a ^* ) _after − (a ^* ) _before (2)
Δb ^* = (b ^* ) _after − (b ^* ) _before (3)
Here, before is a value before the durability test, and after is a value after the durability test.
ΔE ^* = {(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² } ^1/2 (4)

The larger the crossed hue b ^* difference [Delta] b ^* and total color difference Delta] E ^* value of was determined that a large degree of color change under dry heat. The results are shown in Table 1.

Comparative Example 1
A polarizing film was produced in the same manner as in Example 1 except that dyeing with an aqueous solution of iodine and potassium iodide was performed at 28 ° C. for 46 seconds, and glycyrrhizic acid was not added to the boric acid treatment bath thereafter. . About the obtained polarizing film, it evaluated by the method similar to Example 1, and the result was shown in Table 1.

[Table 1]
━━━━━━━━━━━━━━━━━━━
Example No. Boric acid aqueous solution Δb ^* ΔE ^*
Glycyl in
Lithic acid amount ^{* 1}
━━━━━━━━━━━━━━━━━━━
Example 1 3.0 parts by weight 0.4 1.6
───────────────────
Comparative Example 1-3.1 7.5
━━━━━━━━━━━━━━━━━━━
^{* 1} Amount based on 100 parts by weight of water

As can be seen from Table 1, the polarizing film of Example 1 containing glycyrrhizic acid according to the present invention has little change in hue even after being subjected to dry heat and is excellent in durability.

Claims (6)

  An iodine-based polarizing film comprising a polyvinyl alcohol-based resin film in which iodine is adsorbed and oriented, and the polyvinyl alcohol-based resin film further contains a triterpenoid glycoside.   The iodine-type polarizing film according to claim 1, wherein the triterpenoid glycoside is glycyrrhizic acid.   The step of uniaxially stretching a polyvinyl alcohol resin film, the step of dyeing the polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide, and the polyvinyl alcohol resin film after dyeing into an aqueous solution containing boric acid A method for producing an iodine-based polarizing film through a step of immersing and a step of rinsing with an aqueous solution containing boric acid, followed by an aqueous solution containing iodine and potassium iodide, and an aqueous solution containing boric acid And a method for producing an iodine-based polarizing film, comprising dissolving a triterpenoid glycoside in at least one of water for washing.   The method according to claim 3, wherein the aqueous solution containing boric acid contains a triterpenoid glycoside, and the polyvinyl alcohol resin film after iodine staining is immersed in the aqueous solution.   The method according to claim 3 or 4, wherein the triterpenoid glycoside is glycyrrhizic acid. A protective film is bonded to one side or both sides of the iodine type polarizing film of Claim 1 or 2, The iodine type polarizing plate characterized by the above-mentioned.