JPH06118231A - Optical film - Google Patents

Abstract

PURPOSE:To provide an optical film, a phase difference film, and a polarization film excellent in optical uniformity. CONSTITUTION:An optical film is made of PVA having the viscosity average polarization degree of 1,000 or above, the ratio between the weight average polarization degree (Pw) and number average polarization degree (Pn) Pw/Pn of 5 or above, and the polarization degree of 3,500 or above at the peak position of the maximum molecular weight in the molecular weight distribution by GPC(gel permeation chromatography) measurement. A phase difference film is obtained by applying the orientation-treatment to the optical film. A polarization film is obtained by applying the adsorption treatment and orientation treatment of a dichroic material to the optical film.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a novel optical film,
The present invention relates to a phase film and a polarizing film. More specifically, the present invention relates to an optical film having excellent optical uniformity, a retardation film having excellent retardation uniformity, and a polarizing film having excellent transmittance and polarization degree uniformity.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device has been used as a display device having a relatively small screen such as a timepiece, a calculator, a word processor, and instrumentation for machinery, and the demand for display quality has not been particularly strict. However, in recent years, liquid crystal display devices have been widely used as displays for laptop word processors, laptop computers, notebook computers; displays for instrument panels of automobiles and aircraft; liquid crystal projectors, etc., and have become large in size and high in display quality. And improved durability are required. Therefore, in order to achieve the above-mentioned problems, the polarizing film, which is a component of the liquid crystal display device, the retardation film, and the optical film, which is the base film that is the basis of these films, have optical characteristics such as high polarization degree and high transmittance. In order to cope with the increase in screen size and the high quality of display quality, it is required to improve the uniformity of optical characteristics.

Hitherto, as a method for producing an optical film, there has been a method of cast film formation from various solvent solutions and a method of pressure drawing with a roll. The optical film obtained by these methods is an optical film. The uniformity was not sufficient. On the other hand, regarding the polyvinyl alcohol-based polymer (hereinafter, abbreviated as PVA) as a raw material, the degree of polymerization or the degree of syndiotacticity has been increased for the purpose of improving durability and optical characteristics. PVA has a high solution viscosity (or melt viscosity), and the concentration of the solution that can be formed into a film is low due to restrictions on the film forming apparatus. There have been problems such as non-uniformity.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical film, a retardation film and a polarizing film which are excellent in the uniformity of optical properties which are important for the performance of the optical film.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the viscosity average degree of polymerization is 1000 or more, the weight average degree of polymerization (Pw) and the number average degree of polymerization ( Pn) having a ratio Pw / Pn of 5 or more and having a maximum molecular weight peak position of 3500 or more in the molecular weight distribution measured by gel permeation chromatography (hereinafter abbreviated as GPC). The present invention has been completed and the present invention has been completed.

The present invention will be described in detail below. The viscosity average degree of polymerization of PVA used in the optical film of the present invention is 1
It is necessary to be 000 or more, preferably 1300 or more, more preferably 1700 or more. When the viscosity average degree of polymerization is less than 1000, durability such as heat resistance (change in optical properties at high temperature) and resistance to moist heat (change in optical properties at high temperature and high humidity), strength, and toughness decrease. In addition, the processing characteristics (particularly the stretching characteristics) in the manufacturing process of the polarizing film or the retardation film are deteriorated, and a polarizing film having high transmittance and high polarization cannot be obtained. The upper limit of the viscosity average degree of polymerization is not particularly limited, but is preferably 30,000 or less, more preferably 20,000 or less. If the viscosity average degree of polymerization is more than 30,000, some problems will occur in workability in the production process for forming a film. Therefore, the viscosity average degree of polymerization is preferably 1,000 to 30,000, more preferably 1,300 to 20,000. Here, the viscosity average degree of polymerization means a value measured according to JIS-K6726.

In the PVA of the present invention, the ratio Pw / Pn of the weight average polymerization degree (Pw) and the number average polymerization degree (Pn), which is an index of the molecular weight distribution, needs to be 5 or more. Pw / P
When n is less than 5, the contribution on the high molecular weight side contained in the film of the present invention becomes small, the durability (heat resistance, moist heat resistance), strength and toughness of the film are lowered, and further, the production of a polarizing film. An optical film with excellent optical uniformity, in which the processing characteristics (particularly the stretching characteristics) in the process are deteriorated, a polarizing film with high transmittance and high polarization cannot be obtained, and the contribution on the low molecular weight side is small. Can't get Pw / Pn in the present invention can be determined by GPC measurement.

In the PVA of the present invention, the peak position of the maximum molecular weight in the molecular weight distribution measured by GPC is the degree of polymerization of 35.
It must be 00 or more. As a method for measuring the molecular weight distribution of PVA used in the present invention by GPC,
Method for measuring an aqueous solution of PVA using an aqueous column and polyvinyl acetate obtained by reoxidizing PVA used in the present invention in pyridine with acetic anhydride is used as an organic solvent solution in an organic solvent such as tetrahydrofuran. A method of measuring using a system column can be mentioned. As a preferable measurement condition for the GPC measurement in the present invention, an organic solvent system column having a theoretical plate number of 6000 is used, and the column temperature is 4
500 microliters of a tetrahydrofuran solution containing 0.25% by weight of polyvinyl acetate at 0 ° C. is injected, and the measurement conditions include a tetrahydrofuran flow rate of 1 milliliter / minute. In the molecular weight distribution obtained under these measurement conditions, the peak position of the maximum molecular weight needs to be 3500 or more, preferably 4000 or more. The peak of the maximum molecular weight in the molecular weight distribution simply refers to the position of the peak of the maximum molecular weight when independent peaks of several peaks are obtained. Due to the spread of the peaks and the like, it is often obtained in the form of several single peak waveforms superimposed. In such a case, it is necessary to separate each peak and extract accurate values such as the peak position, height, and area. As a method for separating the peak, Gauss-N is used.
ewton method (GN method), Davidon-Flech
er-Powell method (DFP method), Simplex
Method, Damped-Least-Squares method (D
Many methods using a computer, such as the LS method), are known, and many improved methods have been proposed, and any method can be used. In the present invention, G
The degree of polymerization at the maximum peak position in the molecular weight distribution measured by PC means the value in terms of standard polystyrene. further,
The content of PVA corresponding to the maximum molecular weight calculated from the area of the peak of the maximum molecular weight obtained by this separation treatment is not particularly limited, but it is preferably 5% by weight or more based on the total PVA. That is, P used in the film of the present invention
VA needs to include a high molecular weight PVA portion having a degree of polymerization of 3500 or more, and this PVA portion contributes to the strength, toughness, durability of the film, and the high transmittance and high polarization degree of the polarizing film. It is considered that PVA having a low degree of polymerization contributes to obtaining an optically uniform optical film, retardation film and polarizing film.

The degree of saponification of the PVA used in the present invention is not particularly limited, but from the viewpoint of the durability of the retardation film and the polarizing film and the adsorption of the dichroic substance, it is 80-100.
Mol% is preferred, 95-100 mol% is more preferred, and 98-100 mol% is even more preferred. The PVA used in the present invention is obtained by hydrolysis or alcoholysis of polyvinyl ester. The polyvinyl ester includes a homopolymer of vinyl ester, a copolymer of two or more kinds of vinyl ester, and a copolymer of vinyl ester and another ethylenically unsaturated monomer. here,
As the vinyl ester, vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, vinyl pivalate and the like can be used, and among them, industrially inexpensive vinyl acetate is generally used. P used in the present invention
VA may be copolymerized with another monomer, and a polymer having a polymer terminal modified with a chain transfer agent may also be used. The ethylenically unsaturated monomer copolymerizable with vinyl ester is not particularly limited as long as it is copolymerizable with vinyl ester, and α-olefin, a halogen-containing monomer, a carboxylic acid-containing monomer, (Meth) acrylic ester, vinyl ether, sulfonic acid group-containing monomer, amide group-containing monomer, amino group-containing monomer, quaternary ammonium base-containing monomer, silyl group-containing monomer, hydroxyl group-containing Examples thereof include monomers and acetyl group-containing monomers.

The method for producing PVA used in the present invention is not particularly limited and may be produced by any method. For example, a method in which PVA having a different degree of polymerization is previously prepared and blended; a method in which polyvinyl esters separately polymerized so as to have different degrees of polymerization are blended and then saponified; A method for feeding back the polyvinyl ester solution in the polymerization tank in which the polymerization has progressed during continuous polymerization of the ester to the previous polymerization tank to saponify the obtained polyvinyl ester; PVA having a low molecular weight portion as an emulsion stabilizer And a method of saponifying vinyl acetate after low-temperature emulsion polymerization. High molecular weight PV with a degree of polymerization of 3500 or more
A is 60 from a conventionally known methanol solution.
It is difficult to manufacture vinyl acetate at around ℃, and it is a high-concentration monomer and is polymerized at a low speed and stopped at a low rate of polymerization; in the case of the production of PVA with a degree of polymerization of 8000 or higher, room temperature is used. It is produced by a method of bulk or emulsion polymerization at a temperature of several tens of degrees below freezing from the area.

The method for producing the optical film of the present invention is not particularly limited, but for example, it is produced by the following method. Examples of the method for producing the optical film of the present invention include a method of forming a film from a PVA solution or a melted state of PVA. Generally, a method of forming a film after preparing a PVA solution is used. Solvents used for preparing the PVA solution include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol,
Glycerin, ethylenediamine, diethylenetriamine and water are used alone or in combination. Further, an aqueous solution of an inorganic salt such as lithium chloride or calcium chloride can be used alone or in combination with the above organic solvent. Among these, water alone; a mixed solvent of dimethyl sulfoxide or dimethylformamide and water; glycerin is preferably used. More preferably, the organic solvent alone or a mixed solvent of water and an organic solvent is preferable from the viewpoint of moist heat resistance, heat resistance and water resistance. The concentration of the PVA solution at the time of film formation is P
It depends on the degree of polymerization of VA and the film forming method, but usually 1
-50% by weight, preferably 1.5-30% by weight.
PVA solutions are usually prepared at temperatures from room temperature to 150 ° C. In this case, depending on the solvent used, PV
In order to suppress the decrease in the degree of polymerization due to the decomposition of A, it is preferable that the adjustment temperature is within the above range and a lower temperature is adopted.

Next, as a film forming method, PV is used.
Cast film formation from solution A; dry film formation method by extrusion into air or an inert gas such as nitrogen; melt molding method. It is also possible to perform wet film formation by extruding the PVA solution into a poor solvent. A dry-wet film forming method is also possible in which the PVA solution is once extruded into the air or an inert gas such as nitrogen to form a liquid film and then introduced into a coagulation bath to form a film. Further, a gel film forming method in which these film forming methods are combined and the resulting liquid film is cooled to gel and then a film is formed is also possible. This gel film forming method will be described in more detail. A liquid film of a PVA solution is formed in a gas atmosphere, and then this liquid film is cooled with a cooling medium such as decalin, paraffin, trichloroethylene, carbon tetrachloride, methanol, etc. It is also possible to form a film by introducing it into the desolvent and then desolvating. Further, it is also possible to introduce the liquid film into a cooling space such as a freezing room, cool and coagulate and gelate it, and then remove the solvent to form a film. Further, the cooling medium is not provided in a gas atmosphere. It is also possible to directly introduce a liquid film into the inside of the solution to form a gel by cooling and then to remove the solvent to form a film. As a coagulant,
A solvent that is compatible with the solvent of the PVA solution and is a poor solvent for PVA, for example, alcohols such as methanol, ethanol, propanol, acetone, benzene, toluene, or a mixed solution of these with a solvent of the PVA solution. In addition, an inorganic salt aqueous solution is used. Although the liquid film of the PVA solution varies depending on the solvent of the PVA solution, it is usually -30.
Adjusted at ~ 120 ° C.

The retardation film of the present invention can be obtained by subjecting the above optical film to orientation treatment. The method for obtaining a retardation film from an optical film (hereinafter sometimes abbreviated as a raw film) is not particularly limited, but the retardation film is produced, for example, by the following method.

The retardation film is obtained by subjecting a raw film to an orientation treatment, and this orientation treatment is mainly carried out by a stretching operation. As the stretching method, there are a wet stretching method, a dry heat stretching method and a wet heat stretching method, and as a stretching operation, a tenter stretching, a roll stretching, a pressure stretching, a uniaxial stretching, a biaxial stretching and a combination of these are possible. The stretching ratio is preferably controlled by the thickness and retardation of the target retardation film, but in the case of uniaxial stretching, it is practically 1.1.
Is preferably 3.0 times or more, and in the case of biaxial stretching, the area stretching ratio is 2.0 times or more, preferably 8.0 times or more, and further 1
5.0 times or more is more preferable, and it is necessary that the ratio of the draw ratios in the longitudinal and transverse stretching axis directions is 1.1 times or more.
1.1-10.0 are preferable and 1.5-8.0 are more preferable. The stretching speed is preferably 10 to 5000% / min, based on the original length of the film. The temperature during stretching varies depending on the physical properties of the raw film, the stretching method and other stretching conditions, but is usually 10 to 250 ° C. Further, it is preferable to carry out the dry heat drawing in an inert gas.

The stretched film is dried and heat-treated in the air or in an inert gas such as nitrogen under constant length or shrinkage. From the viewpoint of water resistance, heat resistance, and moist heat resistance, it is preferable to perform heat treatment on the stretched film in air at 160 to 250 ° C. or in an inert gas. The thickness of the stretched film is not particularly limited, but is preferably 3 to 100 μm, particularly preferably 5 to 50 μm. Also, during or after stretching, the film is PV
Water resistance and durability are imparted by immersing in a cross-linking agent for A, for example, an aqueous solution of boric acid, borax, isocyanates or the like, or by subjecting the stretched film to water treatment such as formalization and acetalization. You can also do it. The retardation film of the present invention thus obtained can be used alone, or an optically transparent protective film on both sides or one side thereof; an optically transparent protective film having mechanical strength Film: A polarizing film can also be attached and used. The protective film is usually a cellulose triacetate film, a polyacrylate film, a polyester film,
A polycarbonate film or the like is used. It is also possible to use a plurality of retardation films by laminating them together.

The polarizing film of the present invention can be obtained by subjecting the above optical film to adsorption treatment and orientation treatment of a dichroic substance. The method for obtaining the polarizing film from the optical film is not particularly limited, but the polarizing film is produced, for example, by the following method. The polarizing film can be obtained by adsorbing a dichroic substance on the original film such as a dyeing operation and performing an orientation treatment by a stretching operation. Any of these operations may be performed first or at the same time. The dyeing operation is usually carried out by immersing the raw film in a liquid containing a dichroic substance, but the operating conditions and operating method are not particularly limited, and for example, an iodine compound is used as the dichroic substance. In this case, an iodine-potassium iodide aqueous solution is used, and when an organic dichroic dye is used, an aqueous dye solution is used. In addition, a cross-linking agent for PVA such as a boron compound such as boric acid or borax or a compound such as phosphoric acid may be contained in these solutions. In addition, a method of dispersing a dichroic substance in a PVA solution to form a film at the time of producing a raw film (so-called undiluted dyeing method)
May be used for dyeing.

The stretching operation is carried out by a wet stretching method, a dry stretching method or a stretching method which is a combination of both methods, and it is preferable to stretch at least 3 times in one direction. The stretching speed is preferably 10 to 1000% / min, based on the length of the base of the raw film. The temperature during stretching varies depending on the physical properties of the original film, the stretching method and other stretching conditions, but is usually 10 ° C to 26 ° C.
It is 0 ° C. Further, it is preferable to operate the dry heat drawing in an inert gas. The thickness of the stretched film is not particularly limited, but is preferably 3 to 100 μm, and 5 to 50 μm.
Is particularly preferable. Further, during or after stretching, the film is immersed in an aqueous solution of a cross-linking agent for PVA, such as boric acid, borax, isocyanates, or the stretched film is subjected to water resistance treatment such as formalization or acetalization. Thus, water resistance and durability can be imparted.

The film that has been subjected to the adsorption treatment and orientation treatment of the dichroic dye is subjected to a crosslinking treatment with a boron compound or a phosphorus compound under a fixed length, or is dried and heat-treated in air or an inert gas. It The polarizing film of the present invention thus obtained can be used alone like the retardation film described above, or an optically transparent protective film on both sides or one side thereof; A protective film having mechanical strength can also be attached and used. As the protective film, a cellulose triacetate film, a polyacrylate film, a polyester film, a polycarbonate film or the like is usually used. It is also possible to use a retardation film, a color film or the like by laminating them.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the following, “parts” and “%” mean “parts by weight” and “% by weight”, respectively, unless otherwise specified. The retardation is a value measured using a polarization microscope and a compensator, an unstretched film was measured using a Senarmont type compensator, and a film after stretching was measured using a Berek type compensator. The transmittance and the polarization degree are measured by the Japan Electronic Machinery Industry Association Standard (EIAJ) LD-201.
It is a value calculated in a C light source and a double field of view using a spectrophotometer according to -1983. The comparison of the uniformity of the optical properties is carried out by measuring the obtained film between the predetermined widths by 1 cm in the width direction.
The phase difference or the transmittance and the degree of polarization were measured for each, and the standard deviations were compared.

Example 1 13% of PVA having a viscosity average degree of polymerization of 2450, Pw / Pn = 14.9, and a peak position of maximum molecular weight of 8100.
The aqueous solution was cast on a drum at 70 ° C. and dried as it was for 1 hour to obtain a raw film having a width of 60 cm. Length 25
cm, width of 25 cm, uniaxially stretched at 30 ° C. in 4% by weight boric acid aqueous solution, and then uniaxially stretched.
It was dried at ℃ and further heat-treated at 120 ℃ for 10 minutes. The width of the obtained retardation film was 17.5 cm. Table 1 shows the uniformity of retardation in the width direction of the original film and the retardation film.

Comparative Example 1 PVA having a viscosity average degree of polymerization of 2450 and Pw / Pn = 2.4.
A raw film having a width of 60 cm was obtained in the same manner as in Example 1. A raw film having a length of 25 cm and a width of 25 cm is uniaxially stretched in a 4% by weight aqueous boric acid solution at 30 ° C., then dried at 50 ° C. under a fixed length, and further heat treated at 120 ° C. for 10 minutes. It was The obtained retardation film had a width of 19 cm. Table 1 shows the uniformity of retardation in the width direction of the original film and the retardation film.

[0022]

[Table 1]

Example 2 Using a raw film obtained in the same manner as in Example 1,
A polarizing film was obtained by the following method. First, length 25c
An original film having a width of 25 m and a width of 25 cm was swollen with distilled water at 30 ° C., immersed in an aqueous solution at 30 ° C. containing 0.025% by weight iodine and 0.1% by weight potassium iodide, and then 4% by weight. The film was stretched 5 times in a 40 ° C. aqueous solution containing boric acid. The stretched film was dried under a constant length in an atmosphere of 50 ° C. for 10 minutes to obtain a polarizing film having a width of 12.4 cm. Table 2 shows the uniformity of the transmittance and the polarization degree in the width direction of the polarizing film.

Comparative Example 2 Using a raw film obtained in the same manner as in Comparative Example 1,
A polarizing film having a width of 13.2 cm was obtained in the same manner as in Example 2. Table 2 shows the uniformity of the transmittance and the polarization degree in the width direction of the polarizing film.

[0025]

[Table 2]

[0026]

As is apparent from the above examples, the optical film, retardation film and polarizing film of the present invention are excellent in uniformity of optical characteristics. This has a viscosity average degree of polymerization of 1000 or more and a weight average degree of polymerization (Pw).
And the number average degree of polymerization (Pn) ratio Pw / Pn is 5 or more, and was achieved for the first time by using PVA in which the peak position of the maximum molecular weight in the molecular weight distribution by GPC measurement is 3500 or more. Is. The optical film, the retardation film and the polarizing film obtained by the present invention make use of the above characteristics, and are high performance liquid crystal displays such as liquid crystal televisions, liquid crystal projectors, word processor displays, personal computer displays, office equipment terminal displays and aircraft. It is also used for displays for automobile instrument panels, other filters, sunglasses, window glass, antiglare for various lights, and various sensors.

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Claims (3)

[Claims] 1. The viscosity average degree of polymerization is 1000 or more, and the ratio Pw / of the weight average degree of polymerization (Pw) and the number average degree of polymerization (Pn).
An optical film made of a polyvinyl alcohol-based polymer having a Pn of 5 or more and having a maximum molecular weight peak position in the molecular weight distribution measured by gel permeation chromatography of 3500 or more. 2. A retardation film obtained by aligning the optical film according to claim 1. 3. A polarizing film obtained by subjecting the optical film according to claim 1 to an adsorption treatment and an orientation treatment of a dichroic substance.