JPH05119216A - Production of polarizing plate - Google Patents

Abstract

PURPOSE:To obtain the polarizing plate which has excellent optical performance, heat resistance and moisture resistance and substantially obviates the generation of cracks in a polarizable thin layer even in high-temp. environment. CONSTITUTION:The polarizing plate formed by sticking polycarbonate films as protective layers to both surfaces of the polarizable thin layer obtd. by adsorbing a dichromatic material to a polyvinyl alcohol film and orienting this film is subjected to a high temp. humidifying treatment for >=12 hours in an atmosphere of 60 to 98 deg.C temp., moreover 80 to 98% RH humidity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polarizing plate having excellent optical performance, heat resistance and moisture resistance. The polarizing plate obtained by the production method of the present invention has excellent optical performance and durability, and since cracks are unlikely to occur in the polarizing thin layer even in a high temperature environment, high durability is required for automobile instruments and outdoor displays. It can be used very advantageously for the purpose of anti-glare purposes such as liquid crystal display devices in the field, sunglasses, goggles, windshields for helmets and motorcycles, sun visors for automobiles and mirrors.

[0002]

2. Description of the Related Art Conventionally, a polarizing plate has a polarizing thin layer formed by containing or adsorbing orienting iodine or a dichroic dye in a film of polyvinyl alcohol or a derivative thereof, and triacetyl cellulose as a surface protective layer. It is generally manufactured by a method of laminating a cellulose-based film or sheet (hereinafter, the film or sheet may be simply referred to as a sheet) or an acrylic sheet.

[0003]

However, a conventional polarizing plate having a cellulose-based sheet or an acrylic-based sheet as a surface protective layer is inferior in the moisture resistance and heat resistance of the protective layer, so that the polarizing plate has poor moisture resistance and heat resistance. The required use is not sufficient.
Further, in order to improve durability, for example, JP-A-57-3
As in 0808, a polarizing plate using a polycarbonate sheet or the like as a surface protective layer has been proposed. However, the polarizing thin layer used for the polarizing plate is stretched for the purpose of orienting the dichroic substance, and is very weak against a force perpendicular to the stretching direction and is in a state of being easily torn. It is well known that the polarizing thin layer is treated with boric acid or an aqueous metal ion solution in order to further improve durability or to improve polarizing performance, but in this case, the tendency becomes more remarkable. When this polyvinyl alcohol-based film is stretched and a polarizing thin layer treated with boric acid or metal ions is laminated with a polycarbonate sheet or the like as a protective layer, even if the polarizing thin layer tries to shrink in a high temperature environment, the protective layer is protected. However, since it does not follow it, cracks often occur in the thin polarizing layer and the original function cannot be fulfilled in many cases.

[0004]

Means for Solving the Problems As a result of intensive studies on the method for solving the above-mentioned drawbacks of the conventional method, the present inventors have found that
The present invention has been reached. That is, a polarizing plate in which a transparent resin sheet as a protective layer is laminated (hereinafter referred to as a laminate) on a polarizing thin layer in which a dichroic substance is adsorbed and oriented on a polymer film,
It is intended to solve the above problems by performing the treatment under high temperature and high humidity. That is, according to the present invention, a polarizing plate in which a transparent resin film or sheet is laminated as a protective layer on a polarizing thin layer obtained by adsorbing and orienting a dichroic substance on a polymer film is used at a temperature of 60 ° C to 98 ° C and a humidity of 80 ° C. % RH ~ 98
It is a method for producing a polarizing plate having excellent optical performance, heat resistance and humidity resistance, which is characterized by performing high temperature humidification treatment in an atmosphere of% RH.

The polarizing thin layer used for producing the polarizing plate of the present invention is a dichroic substance adsorbed on a polymer film and oriented, and its production method is known per se. As the polymer film as the base material of the polarizing thin layer, a polyvinyl alcohol film is suitable,
As a specific example, a polyvinyl alcohol film,
A polyvinyl formal film, a polyvinyl acetal film, a saponified film of a poly (ethylene-vinyl acetate) copolymer, and the like can be mentioned. Among them, a polyvinyl alcohol film is particularly preferable. Examples of the dichroic substance for imparting polarizability to the polymer film described above include chlorantine fast red (C.I.
8160), chrysophenin (C.I. 24895),
Sirius Yellow (C.I. 29000), Benzopurpurin (C.I. 23500), Direct Fast Red (C.I. 23630), Brilliant Blue 6B
(C.I. 24410), Chlorazole Black BH
(C.I. 22590), Direct Blue 2B (C.I.
I. 22610), Direct Sky Blue (C.I.
24400), diamine green (C.I. 3029)
5), Solophenyl Blue 4GL (C.I. 3420)
0), Direct Copper Blue 2B (C.I.241
85), Nippon Brilliant Violet BKco
nc. (C.I. 27885), Congo Red (C.I.
I. 22120), acid black (C.I. 2047)
0), iodine and the like. Usually, among these dichroic substances, iodine, chloranthine fast red, congo red, brilliant blue 6B, direct copper blue 2B, chrysophenin and the like are preferably used.

The adsorption and orientation of these dichroic substances on the polymer film can be carried out, for example, by the following method. That is, a polymer film (particularly a polyvinyl alcohol film) is immersed in an aqueous solution in which a dichroic substance is dissolved at room temperature to 60 ° C. to allow the dichroic substance to be adsorbed on the film, and then a metal ion, boric acid or the like is added. It can be manufactured by stretching in an unidirectional direction 2.5 to 8 times at room temperature to 80 ° C. in water in which additives are dissolved.

The thickness of the polarizing thin layer used in the present invention is not particularly limited, and from the viewpoint of raw material film used and operability, a thickness of 10 to 120 μm is usually used, but a thickness of 20 to 80 μm is particularly preferable. ..

The transparent resin sheet used as the protective layer has a heat distortion temperature of 90 ° C. or higher and is not particularly limited as long as it is a resin sheet excellent in transparency and durability, but it is a polycarbonate sheet or a polyester sheet. Suitable are polyimide sheet, polyamide sheet, and the like. Among them, a polycarbonate sheet having excellent transparency, durability and mechanical strength is particularly preferable. The term "polycarbonate sheet" as used herein refers to a sheet made from a normal polycarbonate having bisphenol A as a skeleton, a transparent polycarbonate resin-based copolymer, or a composition of a polycarbonate and another resin. Can also be used, and the surface of the sheet is subjected to surface hardening treatment, anti-fog treatment, infrared reflection or absorption to improve abrasion resistance,
Those that have been subjected to ultraviolet ray reflection or absorption treatment or other functionalization treatment can also be appropriately used.

The thickness of the transparent resin sheet is not particularly limited, but from the viewpoint of operability, it is about 20 μm to about 4 m.
m is preferably about 50 μm to about 3 mm.

The method of laminating the polarizing thin layer and the protective layer according to the present invention is not particularly limited, but it is preferable to interpose an adhesive layer in terms of adhesiveness and operability. The adhesive forming the adhesive layer is transparent and is a polymer polymerized with at least one bonding group selected from an amide bond, an ester bond, a urethane bond and an ether bond, and has a number average molecular weight. Is 600-20
Those up to 0000 are suitable, and preferably 5000.
Those having a number average molecular weight of up to 100,000 are preferable.
If the number average molecular weight is less than 500, the curing speed of the adhesive will be remarkably reduced, and if it exceeds 200,000, the adhesion to the transparent resin sheet will be unfavorably reduced. These adhesives are prepared by appropriately diluting with a solvent to adjust the viscosity, and further containing a catalyst for promoting the reaction, a defoaming agent, a leveling agent, and the like. In addition, an adhesive obtained by adding a functionalizing agent such as an infrared absorbing agent, an ultraviolet absorbing agent, or a dye to the adhesive can be appropriately used.

The solvent used for adjusting the viscosity of the adhesive is ethyl acetate, propyl acetate, isopropyl acetate,
Ester solvents such as methyl propionate; ketone solvents such as methyl ethyl ketone, methyl propyl ketone and methyl isobutyl ketone; ether solvents such as dioxane; aromatic hydrocarbon solvents such as xylene and toluene; N, N-dimethylacetamide, Any of the above-mentioned polymeric adhesives such as amide solvents such as N, N-dimethylformamide, which can dissolve, can be used, and the amount thereof can be appropriately selected depending on the coating conditions and the like.

The adhesive layering is carried out by applying the adhesive of the present invention to a polarizing thin layer so that the thickness after drying is 1 to 50 μm, preferably 3 to 20 μm.
It is preferable that the coating layer is coated with a bar coater, a roll coater, dipping or the like so as to have a thickness of m, dried, and laminated with the protective layer in a state where the solvent is removed. The thickness of the adhesive is 1
If it is less than μm, sufficient adhesive force is not exhibited, and if it exceeds 50 μm, optical blur occurs, which is not preferable.

The high temperature humidification treatment of the present invention means a temperature of 60 ° C. to 9 ° C.
In an atmosphere of 8 ° C. and a humidity of 80% RH to 98% RH,
Preferably, the temperature is 60 ° C. to 95 ° C. and the humidity is 90% RH
The treatment is performed in an atmosphere of 95% RH.
It is a treatment of not less than minutes, preferably not less than 30 minutes and more preferably not less than 12 hours. If the temperature is lower than 60 ° C, there is a problem that cracking of the polarizing thin layer cannot be suppressed in a high temperature environment, and if the temperature is higher than 98 ° C, the film is discolored, which is not preferable. If the humidity is lower than 80% RH, cracking of the polarizing thin layer cannot be suppressed in a high temperature environment, and if the humidity is higher than 98% RH, discoloration of the film similarly occurs, which is not preferable. By performing such a treatment, cracks in the polarizing thin layer are less likely to occur, and
The optical performance of the polarizing plate is further improved. As a method of high temperature humidification treatment, it is preferable that the entire polarizing plate is uniformly treated in the above atmosphere, but even if the treatment is performed in a state where the polarizing plates are stacked, the treatment time,
If the humidity and the like are adjusted appropriately, the same effect as the uniform treatment is exhibited, and the effect of the invention is not hindered.

[0014]

The polarizing plate manufactured by the manufacturing method of the present invention is a polarizing plate excellent in optical performance, excellent in moisture resistance and heat resistance, and resistant to cracking in the polarizing thin layer even in a high temperature environment. , For the purpose of anti-glare purposes such as liquid crystal display devices in fields requiring high durability such as automobile instruments and outdoor displays, or sunglasses, goggles, windshields for helmets and motorcycles, and sun visors and mirrors for automobiles. It can be used to advantage.

[0015]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but these are merely illustrative and the present invention is not limited thereto. In Examples and Comparative Examples, (1) Transmittance was measured using a spectrophotometer (manufactured by JASCO Corporation: trade name, Ubest-35). (2) Single plate transmittance, parallel transmittance (represented by H ₀ , light when two polycarbonate polarizing plates are superposed so that the molecular orientation axes of their polarizing thin layers are parallel to each other. Transmittance) and orthogonal transmittance (represented by H ₉₀ , which is the light transmittance when two polycarbonate polarizing plates are stacked so that the molecular orientation axes of their polarizing thin layers are perpendicular to each other. ) Is an average value in which visibility is corrected in the visible region of 400 to 700 nm. The polarization degree was calculated by the following formula.

[0016]

[Equation 1]

(3) For the cracks and other evaluations of the polarizing thin layer, a polarizing plate was used as a sample piece having a size of 4 cm × 4 cm,
A set of four pieces under the same conditions was dried in an oven at 90 ° C for a certain period of time, and the total number of cracks (total number of cracks generated in all sample pieces) in the polarizing thin layer at that time and all samples It was evaluated by whether or not a crack was generated on one piece.

Example 1 (a) Production of Polarizing Thin Layer (1) Polyvinyl alcohol (Kuraray Co., Ltd .: trade name, Kuraray Vinylon # 7500) was mixed with chlorantine fast red.
0.4 g / l, Brilliant Blue 6B 0.3 g / l
l, chrysophenin 4 in an aqueous solution containing 0.3 g / l
Stained for 5 minutes at 0 ° C. The dyed film was immersed in an aqueous solution containing 0.3 g / l of nickel acetate tetrahydrate and 35 g / l of boric acid at 40 ° C. for 10 minutes, and then stretched 4 times in the uniaxial direction in the same solution. The product was taken out of the solution, washed with water and dried while maintaining a tension state to obtain a polarizing thin layer. (B) Polycarbonate film (2) A polycarbonate film having a thickness of 75 μm (manufactured by Mitsubishi Gas Chemical Co., Inc.) was used. (C) Adhesive (3) An adhesive composition was prepared by using 25 parts by weight of diphenylmethane-4,4′-diisocyanate and 600 parts by weight of ethyl acetate as a solvent per 100 parts by weight of polypropylene glycol (M = 900). .. (D) Production of Polarizing Plate (4) The adhesive (3) was applied to one surface of the polarizing thin layer (1) obtained in (a) using a bar coater (# 24) and dried at room temperature for 5 minutes. After that, the polycarbonate film (2) is laminated with a laminator (manufactured by Mitsuba Shoji, nip pressure 4.0 Kg / cm ² G).
It was laminated with. The adhesive thickness was 10.4 μm. Then, after forming an adhesive layer on the opposite surface of the polarizing film, a polycarbonate film was laminated to obtain a polarizing plate. (E) High Temperature Humidification Treatment of Polarizing Plate The polarizing plate (4) was placed in a thermo-hygrostat at a temperature of 80 ° C. and a humidity of 90.
The high temperature humidification treatment was performed for 15 hours under the condition of% RH. As a result, the single plate transmittance is 40.3% and the polarization degree is 95.
A polarizing plate of 1% was obtained. In the obtained polarizing plate, neither peeling from the protective layer nor cracking of the polarizing thin layer was observed. The polarizing plate was left in a dryer at 90 ° C. for 1000 hours, but cracks in the polarizing thin layer were not found in all the sample pieces. Further, in the humidity resistance test at 80 ° C. and 90% RH and the heat resistance test at 90 ° C., changes in transmittance and polarization degree after 1000 hours were within 0.5%, respectively, and no noticeable deterioration was observed.

Comparative Example 1 The same operations as in (a) to (d) of Example 1 were carried out to obtain a polarizing plate having a transmittance of 40.0% and a polarization degree of 93.0%. When this polarizing plate was placed in a drier at 90 ° C. and cracks in the polarizing thin layer were observed, after 5 minutes, a sample piece having a crack in the polarizing thin layer was observed. After 30 minutes, all the sample pieces were cracked, a total of 18 cracks were observed, after 2 hours, all the sample pieces were cracked with 5 or more cracks, and a total of 33 cracks were observed. It is no longer usable.

Example 2 The same operations as in (a) to (d) of Example 1 were carried out to obtain a polarizing laminate. This is 3 at 60 ℃, 90% RH atmosphere
A high temperature humidification treatment was performed for 0 minutes to obtain a polarizing plate having a transmittance of 40.2% and a polarization degree of 95.3%. No crack was observed in the polarizing thin layer of this polarizing plate in a dryer at 90 ° C. for up to 5 hours. After 24 hours, only one of the four sample pieces cracked, but the number of cracks did not increase until 1000 hours thereafter. 80 ℃, 90% RH humidity resistance test and 90 ℃
In the heat resistance test, the changes in transmittance and polarization degree after 1000 hours were within 0.5% respectively as in Example 1, and no noticeable deterioration was observed.

Example 3 The same operations as in (a) to (d) of Example 1 were carried out to obtain a polarizing laminate. This is placed in an atmosphere of 60 ° C and 80% RH for 5
High temperature humidification treatment for 4 minutes, transmittance 40.0%, polarization degree 9
A polarizing plate of 3.5% was obtained. No crack was observed in the polarizing thin layer of this polarizing plate in a dryer at 90 ° C. for up to 30 minutes.
Two cracks were observed in total after 2 hours. 1
After 000 hours, one or more cracks were observed in all the sample pieces, but the total number of cracks was 12 and the effect of the high temperature humidification treatment was revealed. In the moisture resistance test and the heat resistance test, as in Example 1, no noticeable deterioration was observed.

Comparative Example 2 Instead of a polycarbonate film as a protective layer, a triacetyl cellulose film (manufactured by Fuji Photo Film Co.,
Product name: FUJITAC 80 μm) is used, and the same operation is performed from (a) to (d) of Example 1, and the transmittance is 3
A polarizing plate having a polarization ratio of 9.8% and a polarization degree of 94.1% was obtained. When a heat resistance and humidity resistance test was performed on this, cracking of the polarizing thin layer did not occur in the heat resistance test, but shrinkage and deformation of the entire substrate were observed. 10 in a humidity resistance test at 80 ° C and 90% RH
The transmittance dropped to 27% after 00 hours.

Comparative Example 3 A commercially available polarizing plate having a transmittance of 41.5% and a polarization degree of 89.9%, in which the protective layer is a triacetyl cellulose film, was subjected to a heat resistance and humidity resistance test. Although no crack was found, shrinkage and deformation of the substrate were observed. Also, in a humidity resistance test at 80 ° C. and 90% RH, the transmittance decreased to 32.1% and the polarization degree decreased to 86.0%.

Example 4 A transmittance of 37.1% and a degree of polarization of 93 were obtained by the same operations and treatments as in (a) to (e) of Example 1 except that a polyimide film (about 40 μm thick) was used as a protective layer. .2%
To obtain a polarizing plate. Even when this was left in a dryer at 90 ° C. for 1000 hours, cracks in the thin polarizing layer were not observed. Also, in the humidity resistance test at 80 ° C. and 90% RH and the heat resistance test at 90 ° C., changes in transmittance and polarization degree after 1000 hours were both within 1.0%, and no noticeable deterioration was observed.

Comparative Example 4 A polarizing laminate was obtained by the same operation as in (a) to (d) of Example 1. This was subjected to a high temperature humidification treatment for 15 hours in an atmosphere of a temperature of 35 ° C. and a humidity of 90% RH, and a transmittance of 40.2.
%, And the polarization degree was 93.1%. This polarizing plate is 9
When placed in a dryer at 0 ° C. and observed, a cracked sample piece was observed after 5 minutes, and a crack was generated in all sample pieces after 30 minutes.
A book cracked. After 2 hours, a total of 21 cracks had formed, and it became unusable.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Otsu 6-1, 1-1 Shinjuku, Katsushika-ku, Tokyo Mitsubishi Gas Chemical Co., Ltd. Tokyo Research Laboratory

Claims (4)

[Claims] 1. A heat distortion temperature of 90 ° C. as a protective layer on a polarizing thin layer in which a dichroic substance is adsorbed on a polymer film and oriented.
A polarizing plate having the above-mentioned transparent resin film or sheet bonded thereto has a temperature of 60 ° C. to 98 ° C. and a humidity of 80% R.
A method for manufacturing a polarizing plate, which comprises performing a high temperature humidification treatment in an atmosphere of H to 98% RH. 2. The high temperature humidification treatment of the polarizing plate is carried out at a temperature of 60.degree.
The method for producing a polarizing plate according to claim 1, which is carried out at 95 ° C. and a humidity of 90% RH to 95% RH. 3. The method for producing a polarizing plate according to claim 1, wherein the polymer film used for the polarizing thin layer is a polyvinyl alcohol film. 4. The method for producing a polarizing plate according to claim 1, wherein the protective layer of the polarizing plate is a film or sheet of a polycarbonate resin or a polyimide resin.