HK1092877B - Dye-containing polarizer - Google Patents

Description

Dye-based polarizing plate

Technical Field

The present invention relates to a dye-based polarizing plate characterized by containing a high-purity azo compound-based water-soluble dye or a salt thereof.

Background

A polarizing plate having a light transmitting/shielding function is a liquid crystal having a light conversion function and is also a basic component of a Liquid Crystal Display (LCD). The application fields of such LCDs have been expanding from small devices such as desktop computers and watches in the first days to a wide range of notebook computers, information processors, liquid crystal projectors, liquid crystal televisions, car navigation guides, and indoor and outdoor instruments.

The polarizing plate for ultraviolet region (400nm or less) can be used in a spectrophotometer such as a fluorescence spectrophotometer, an exposure device for ultraviolet irradiation, and the like. As described in non-patent document 1, non-patent document 2, non-patent document 3, and the like, the polarizing plate can be used for display applications as a polarizing plate for a liquid crystal display device having a fluorescent layer that emits light by the action of near ultraviolet rays (hereinafter referred to as a photoluminescent liquid crystal display device).

As a polarizing plate having absorption in such an ultraviolet region, a polarizing device in which a polarizing film base material such as a film of a stretch-oriented polyvinyl alcohol or a derivative thereof contains iodine or a dichroic dye, a polyolefin-based film in which a polyvinyl chloride film is dehydrochlorinated or a polyvinyl alcohol-based film is dehydrated to form a polyolefin-oriented, and the like are known.

Among these polarizing films, iodine-based polarizing films using iodine as a polarizing device have a problem in durability when used for a long period of time under high temperature and high humidity conditions, because they have a relatively poor polarizing performance in the near ultraviolet region and are poor in water resistance and heat resistance, although they have a good initial polarizing performance in the visible light range. In order to improve the durability, a method of treating with formalin or an aqueous solution containing boric acid, or a method of using a polymer film having low moisture permeability as a protective film, etc. have been considered, but the method is not sufficient. On the other hand, a dye-based polarizing film using a dichroic dye is superior to an iodine-based polarizing film in moisture resistance and heat resistance, but is not sufficient as a polarizing element in the ultraviolet region.

Although the dyes used for producing the dye-based polarizing films described above include the water-soluble compounds described in patent documents 1 and 2, the compounds do not have good polarizing performance or durability under high-temperature or high-humidity conditions, and improvement is desired.

In addition, in the case of producing the compound represented by the formula (1), a method of treating the amino compound represented by the formula (2) in an aqueous solvent with sodium hypochlorite is generally used, but in this case, a large amount of the by-produced azine compound represented by the formula (3) is contained. Therefore, when the azine compound is used as a polarizing film, the azine compound of formula (3) is also contained in a base material, and therefore, a problem arises that desired polarizing properties cannot be obtained.

Therefore, it is difficult to obtain a polarizing plate having excellent polarizing performance in the visible light range and the ultraviolet region, and having moisture resistance and heat resistance.

Patent document 1: japanese unexamined patent publication No. 2002-357719

Patent document 2: japanese laid-open patent publication No. 2003-35819

Patent document 3: japanese patent laid-open publication No. Sho 54-153648

Patent document 4: japanese patent application laid-open No. 1854685

Patent document 5: japanese patent application laid-open No. 2622748

Patent document 6: japanese unexamined patent publication Hei 1-252904

Patent document 7: japanese unexamined patent application publication No. 2001-27708

Patent document 8: japanese laid-open patent publication No. 2001-33627

Non-patent document 1: crossland et al, journal of the SID 6/2, 1998pp 117-

Non-patent document 2: crossland et al, SID 97 Digest pp 837-

Non-patent document 3: four names of S.L.Njo, SID 00 Digest pp 343-345

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a high-performance polarizing plate which has little influence of by-products contained in a dye and has excellent polarizing performance in the visible light range and ultraviolet region, and moisture resistance and heat resistance.

Means for solving the problems

The present inventors have made extensive studies to achieve the above object and found that a polarizing film and a polarizing plate containing a high-purity dye are excellent in polarizing performance, moisture resistance and heat resistance, and thus completed the present invention.

That is, the present invention relates to

(1) A dye-based polarizing film comprising a polyvinyl alcohol resin film and an aqueous dye having a purity of 90% or more represented by the following formula (1) or a salt thereof in the form of a free acid,

(wherein R1 and R2 each represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a carboxyl group, and R₃、R₄Represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a hydroxyl group, and X represents O, S, NH or NCH₃. And 1, m represent 0, 1 or 2, 1+ m > 0)

The polarizing film has polarizing properties in the near ultraviolet region.

(2) A polarizing plate comprising the near-ultraviolet polarizing film of (1) and, bonded to at least one surface thereof, a film having a transmittance of 70% or more at 380 nm.

(3) The polarizing plate according to the above (1) or (2), wherein the one or more polarizing film substrates contain an organic dye other than the water-soluble dye of the formula (1) having polarizing properties in the visible light range, or a salt thereof.

Effects of the invention

It was confirmed that the polarizing film of the present invention has significantly improved polarization characteristics compared to the polarizing film containing an azo compound produced by a conventional production method, and the polarizing plate of the present invention has high polarizing performance even in the near ultraviolet region and also has excellent durability, and thus is suitable for display applications in industrial instruments used in various environments, such as a photoluminescent liquid crystal display device.

Best mode for carrying out the invention

The polarizing film of the present invention contains a high-purity product of 90% or more of the azo compound represented by formula (1) or a salt thereof. R in the formula (1)₁、R₂Represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a carboxyl group, R₃、R₄Represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a hydroxyl group, and X represents O, S, NH or NCH₃. And 1 and m represent 0, 1 or 2, and 1+ m > 0.

The azo compound represented by the formula (1) or a salt thereof can be obtained in high purity by treating the amino compound represented by the formula (2) with manganese dioxide as an oxidizing agent and subjecting the resulting product to oxidative coupling.

The following are representative examples of the azo compound represented by formula (1) and salts thereof used in the present invention.

When the azo compound of formula (1) is present in the form of a salt, examples of the salt include lithium salts, alkali metal salts such as sodium salts and potassium salts, ammonium salts, and organic amine salts, but when the polarizing film is dyed, sodium salts and potassium salts are preferred.

The base material (polymer film) used for the polarizing film of the present invention may be a polyvinyl alcohol base material, and examples of the polyvinyl alcohol base material include polyvinyl alcohol or a derivative thereof, and a base material modified with any of these materials using an olefin such as ethylene or propylene, or an unsaturated carboxylic acid such as crotonic acid, acrylic acid, methacrylic acid, or maleic acid. Among them, a film made of polyvinyl alcohol or a derivative thereof is preferably used from the viewpoint of the adsorption property and orientation property of the dye.

The compound represented by the formula (1) or a salt thereof of the present invention can be used alone or can be mixed with another organic dye having polarization properties in the visible light range as needed to produce a polarizing film having high polarization properties. The other organic dye to be blended may be any dye having absorption characteristics in a wavelength region different from the absorption wavelength region of the compound of the formula (1) of the present invention, and examples thereof include c.i. direct yellow 12, c.i. direct yellow 44, c.i. direct orange 26, c.i. direct orange 39, c.i. direct orange 107, c.i. direct red 2, c.i. direct red 31, c.i. direct red 79, c.i. direct red 81, c.i. direct red 247, c.i. direct green 80, C or I direct green 59, and dyes described in patent document 4, patent document 5, patent document 6, or patent document 7, and these dyes may be used as salts such as free acids, alkali metal salts, ammonium salts, and amine salts.

When the compound represented by formula (1) of the present invention or a salt thereof is contained in a polymer film, a method of dyeing the polymer film is generally employed. The dyeing is performed, for example, in the following manner. First, a water-soluble dye is dissolved in water to adjust a dye bath. The dye concentration in the dye bath is not particularly limited, but is usually selected from the range of about 0.001 to 10% by weight. Further, a dyeing assistant may be used as needed, and for example, mirabilite is preferably used at a concentration of about 0.1 to 10 wt%. The polymer film was immersed in the dye bath thus adjusted to be dyed. The dyeing temperature is preferably about 40-80 ℃, and more preferably 70-80 ℃.

The orientation of the water-soluble dye is carried out by stretching the dyed polymer film. As a method of stretching, any known method such as a wet method or a dry method can be used. The polymer film may be stretched before dyeing. In this case, the water-soluble dye is oriented at the time of dyeing, and the polymer film containing the water-soluble dye and oriented is subjected to post-treatment such as boric acid treatment by a known method as required. Such post-treatment is performed in order to improve the light transmittance and the polarization degree of the polarizing film. The boric acid treatment conditions vary depending on the type of the polymer film to be used and the type of the dye to be used, and the treatment is generally carried out at a boric acid concentration of 0.1 to 15 wt%, preferably 1 to 10 wt%, in an aqueous boric acid solution, at a temperature of 30 to 80 ℃, preferably 40 to 75 ℃. If necessary, the fixing treatment may be carried out in combination with an aqueous solution containing a cationic polymer compound.

The polarizing film obtained by the present invention can be used as a polarizing plate with a protective film, a spectroscopic analyzer such as a fluorescence spectrophotometer, or a polarizing plate for a photoluminescent liquid crystal display device. Thus, the polymer film contains another organic dye having a polarization characteristic in the visible light range, which is advantageous for inspecting defects such as alignment disorder of the LCD.

The dye-based polarizing film thus obtained can be produced into a polarizing plate by laminating a protective film having excellent optical transparency and mechanical strength on one or both surfaces of the polarizing film using a polyvinyl alcohol-based or isocyanate-based adhesive. The material for forming the protective film may be any one conventionally used, for example, a fluorine-based film such as a tetrafluoroethylene/hexafluoropropylene copolymer, a polyester resin, a polyolefin resin, or a polyamide resin may be used in addition to the cellulose acetate-based film or the acrylic film. The protective film used here should have a transmittance of 70% or more at 380nm, preferably 80% or more.

The polarizing plate of the present invention may further have a layer subjected to antireflection treatment, corona prevention treatment, antistatic treatment, corona treatment, or hard coat treatment on the surface thereof.

The dye-based polarizing plate thus configured has excellent polarizing performance, does not cause discoloration or deterioration in polarizing performance even under high-temperature and high-humidity conditions, and is characterized by no light leakage at a position orthogonal to the visible light or near ultraviolet region.

Examples

The present invention will be described in more detail with reference to the following examples, which are only illustrative and not intended to limit the scope of the present invention. In the examples, "%" and "part(s)" are based on weight unless otherwise specified.

Synthesis example 1

To 260 parts of an aqueous solution in which 25.5 parts of 2- (4-aminophenyl) -6-methylbenzothiazole-7-sulfonic acid (purity: 78.3%) was dissolved, 350 parts of manganese dioxide (powder: pure chemical, special grade reagent) was added, and then 200 parts of a 10% aqueous solution of potassium permanganate was added to complete oxidative coupling. Sodium thiosulfate was added to remove excess potassium permanganate and manganese dioxide was filtered. The obtained filtrate was salted out with sodium chloride and filtered to obtain 13.7 parts of a salt of the azo compound represented by the above formula (4).

Example 1

As a result of measuring the purity of the azo compound (4) obtained in Synthesis example 1 by high performance liquid chromatography using a high performance liquid chromatograph having a maximum absorption wavelength of 389nm in water, the purity of the azo compound of formula (4) was 97%, and the azine compound represented by formula (6) was not detected.

Comparative example 1

The maximum absorption wavelength of an aqueous solution of Solophenyl yellow FFL (manufactured by Ciba-Geigy) generally commercially available as C.I. direct yellow 28 was 395 nm. Further, as a result of measuring the high performance chromatographic purity using a high performance liquid chromatograph, the purity of the azo compound of formula (4) was 64%, and the azine compound by-produced was present in an amount of 27%.

Example 2

Polyvinyl alcohol (trade name VF-XS) with a thickness of 75 μm^#7500，クラレ corporation) was immersed in an aqueous solution of the compound (4) obtained in Synthesis example 1 at 45 ℃ for 4 minutes, the dye concentration of the solution being 0.1% and the salt cake concentration of the solution being 0.1%. The film was stretched 5 times in a 3% aqueous boric acid solution at 50 ℃ and washed with water and dried while maintaining the stretched state to obtain a polarizing film. The maximum absorption wavelength of the obtained polarizing film was 406nm, and when the single-plate transmittance was 43.75%, the polarization degree was as high as 98.5%. Further, the film exhibits long-term durability even in a high-temperature and high-humidity state.

Comparative example 2

Polyvinyl alcohol (trade name VF-XS) with a thickness of 75 μm^#7500, クラレ Co.) was immersed in a 45 ℃ aqueous solution of Solophenyl yellow FFL (Ciba-Geigy Co.) having a concentration of 0.1% and a salt cake concentration of 0.1% as described in comparative example 1 for 4 minutes. The film was stretched 5 times in a 3% aqueous boric acid solution at 50 ℃ and washed with water and dried while maintaining the stretched state to obtain a polarizing film. The maximum absorption wavelength of the prepared polarizing film is 417nm, and the polarizing rate is 97.65% when the single plate transmittance is 43.75%.

Example 3 (evaluation of polarizing plate for near ultraviolet ray)

Polyvinyl alcohol (trade name VF-XS) with a thickness of 75 μm^#7500, クラレ Co.) was immersed in an aqueous solution of the compound (4) obtained in Synthesis example 1 at 45 ℃ for 4 minutes, the dye concentration of which was 0.5% and the salt cake concentration of which was 0.1%. The film was stretched 5 times in a 3% aqueous boric acid solution at 50 ℃ and washed with water and dried while maintaining the stretched state to obtain a polarizing film. The polarizing film obtained has a polarizing property of a crossed transmittance of 0.1% or less at 365nm and a degree of polarization as high as 99.9%. TAC films (trade name フジタツク T80SZ, manufactured by fuji film corporation) were attached to both surfaces of the polarizing film using a PVA-based adhesive, and the obtained polarizing plate exhibited long-term durability even under high temperature and high humidity conditions.

Comparative example 3

Polyvinyl alcohol (trade name VF-XS) with a thickness of 75 μm was added^#7500, クラレ Co.) described in example 1 of patent document 2The mixture mainly containing the compound represented by the following formula (7) (mainly in the form of sodium salt) was immersed in an aqueous solution at 45 ℃ for 4 minutes, the mixture having a concentration of 0.5% and a concentration of sodium sulfate of 0.1%. The film was stretched 5 times in a 3% aqueous boric acid solution at 50 ℃ and washed with water and dried while maintaining the stretched state, to obtain a polarizing film. The orthogonal transmittance of the obtained polarizing film at 365nm was 1.2%.

Possibility of industrial utilization

The polarizing film for near-ultraviolet rays of the present invention has high polarizing performance in the near-ultraviolet region and also has good durability, and therefore is suitable for display applications of photoluminescent liquid crystal display devices and industrial instruments used in various environments.

Claims (4)

1. A dye-based polarizing film characterized by containing a water-soluble dye having a purity of 90% or more represented by the following formula (1) or a salt thereof in the form of a free acid in a polyvinyl alcohol-based resin film,

in the formula, R₁、R₂Represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a carboxyl group, R₃、R₄Represents a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a hydroxyl group, and X represents O, S, NH or NCH₃And 1 and m represent 0, 1 or 2, 1+ m > 0, and the polarizing film has polarizing properties in the near ultraviolet region.

2. A polarizing plate comprising the near-ultraviolet polarizing film of claim 1 and, bonded to at least one surface thereof, a film having a transmittance of 70% or more at 380 nm.

3. The polarizing film according to claim 1, wherein the one or more polarizing film substrates contain an organic dye other than the water-soluble dye of the formula (1) having a polarizing property in the visible light range, or a salt thereof.

4. The polarizing plate according to claim 2, wherein the one or more polarizing film substrates contain an organic dye other than the water-soluble dye of formula (1) having polarizing properties in the visible light range, or a salt thereof.