JP3268556B2 - Manufacturing method of polarizing film - Google Patents

Description

The present invention relates to a method for producing a polarizing film.

More specifically, the present invention relates to a method for producing a polarizing film having excellent optical properties.

B. Prior Art Conventionally, a liquid crystal display device has been used as a display device having a relatively small screen such as a clock, a calculator, a word processor, and instrument of a machine, and a demand for display quality has not been particularly severe. However, in recent years, liquid crystal display devices have been widely used as displays for televisions and laptop personal computers, and as instrument panel displays for automobiles and aircraft, and demands for larger sizes, higher display quality, improved durability, and the like. Have been. Therefore, with respect to the polarizing film as a component of the liquid crystal display device, improvement of optical characteristics such as enlargement of area, high degree of polarization and high transmittance is required in order to achieve the above object.

Conventionally, as a polarizing film, a uniaxially stretched film of polyvinyl alcohol to which iodine or a dichroic dye is adsorbed is often used, but this polarizing film does not sufficiently satisfy the above-mentioned degree of polarization. On the contrary,
Proposals using a uniaxially stretched film of polyvinyl alcohol having a high degree of polymerization as a base material (for example, JP-A-1-105204) and proposals using a uniaxially stretched film of polyester as a base material (see, for example, No. 68008). However, when the present inventors examined these methods, in the former, when both the degree of polymerization and the degree of saponification of polyvinyl alcohol were high, it was difficult to uniformly dissolve the polyvinyl alcohol in a solvent, and severe conditions were required. It was found that the dissolution in the above resulted in a decrease in the degree of polymerization of polyvinyl alcohol, and that a polarizing film having satisfactory performance could not be obtained. In the latter, the disadvantage of the polyvinyl alcohol-based polarizing film has been improved to some extent, but the degree of polarization is insufficient,
It cannot meet the above requirements.

C. Problems to be Solved by the Invention Under such circumstances, the present invention aims to provide a method for producing a polarizing film having excellent optical characteristics such as the degree of polarization and transmittance.

D. Means for Solving the Problems The present inventors have conducted intensive studies for solving the above problems, and as a result, in a method for producing a polarizing film obtained by orienting a dichroic substance in a polyvinyl alcohol-based polymer, A membrane was formed using an aqueous solution of a polyvinyl alcohol (hereinafter, polyvinyl alcohol may be abbreviated as PVA) -based polymer having a syndiotacticity of 45 to 52.5 mol% or a mixed solution of water and an organic solvent. The inventors have found that the above object is achieved by using a film obtained by uniaxially stretching a film as a base material, and completed the present invention.

PVA conventionally used as a base material for polarizing films
Has a syndiotacticity of 53.0 mol%. In contrast, the polarizing film obtained by the production method of the present invention,
It is composed of a PVA polymer with a syndiotacticity of 45 to 52.5 mol%, so it has good uniaxial stretchability and improves the orientation of dichroic substances such as iodine and dyes in order to stretch the molecular chain more linearly. As a result, the optical characteristics are excellent.

 Hereinafter, the present invention will be described in detail.

The method for producing a polarizing film of the present invention is a method for producing a polarizing film obtained by orienting a dichroic substance in a polyvinyl alcohol-based polymer, in which the syndiotacticity of PVA has been used for a conventional polarizing film. It is characterized in that a film is formed using a low, so-called atactic PVA-based polymer aqueous solution or a mixed solution of water and an organic solvent, and the obtained film is uniaxially stretched.

In the present invention, the syndiotacticity of the PVA-based polymer needs to be 45 to 52.5 mol%, preferably 48 to 52.0 mol%.

Syndiotacticity used in the present invention, the hydroxyl proton of PVA d ₆ - dimethyl sulfoxide solution, ¹ H
Calculated from the absorption intensity of each 3-unit chain structure measured by -NMR. The absorption of three hydroxyl protons appears in the chemical shift around 4.0 to 4.5 ppm, and is assigned to isotactic (I), heterotactic (H), and syndiotactic (S) from the low magnetic field side, respectively. .

Isotactic (I): Heterotactic (H): Syndiotactic (S): The amount of syndiotacticity is expressed as a percentage based on the absorption intensities of syndiotactic (S), heterotactic (H) and isotactic (I) measured by ¹ H-NMR, and then expressed as the following ( 1) The amount of syndiotacticity of the two-chain structure is determined from the equation.

Syndiotacticity amount (mol%) = (S) (mol%) + (H) / 2 (mol%) ... (1) When the syndiotacticity of the PVA polymer exceeds 52.5 mol%, Sufficient polarization characteristics cannot be obtained because the stretchability decreases. Furthermore, in the case of a PVA-based polymer having a high degree of polymerization and a high degree of saponification, it is difficult to uniformly dissolve the PVA-based polymer in a solvent, and thus it is difficult to obtain a uniform polarizing film. If the syndiotacticity is less than 45 mol%, a satisfactory polarizing film cannot be obtained due to insufficient film strength.

The degree of polymerization and the degree of saponification of the PVA-based polymer also affect the performance of the polarizing film obtained by the production method of the present invention.

The degree of polymerization is required to be 1000 or more from the viewpoint of film strength and processing characteristics, preferably 1500 or more, more preferably 1700 or more, and 30 from the viewpoint of processing characteristics such as film formation and stretching.
000 or less. Here, the polymerization degree of the PVA-based polymer is 30 ° C. in acetone of polyvinyl acetate obtained by re-acetylating the PVA-based polymer.
It is represented by a viscosity average degree of polymerization determined from the intrinsic viscosity measured in the following formula.

= ([Η] × 1000 / 7.94) ^{(1 / 0.62) The} degree of saponification of the PVA-based polymer is at least 85 mol% or more, preferably 95 mol% or more, and more preferably 98 mol% or more.
Mol% or more.

Syndiotacticity in the present invention is 45-52.5
Mole% of PVA-based polymer cannot be obtained from the conventional method for producing PVA by bulk polymerization of vinyl acetate monomer and boiling point polymerization of methanol solution system. The atactic PVA-based polymer as used in the present invention is a polyvinyl ester-based polymer polymerized in a dipole aprotic solvent and a polyvinyl ester-based polymer obtained by polymerizing a vinyl ester in which an aromatic ring and a carbonyl group can have the same planar structure. It is obtained using a polymer as a raw material.

Examples of such a dipole aprotic solvent include dimethyl sulfoxide, sulfolane, carbonate and the like, and dimethyl sulfoxide is particularly preferably used. Examples of the vinyl ester in which the aromatic ring and the carbonyl group can have the same planar structure include vinyl benzoate, vinyl p-fluorobenzoate, vinyl p-chlorobenzoate, and p-vinyl benzoate.
Vinyl bromobenzoate, vinyl p-methylbenzoate, p
P-substituted vinyl benzoate such as -methoxy vinyl benzoate and the like, and m-substituted vinyl benzoate such as m-chloro benzoate and m-fluoro benzoate;
In particular, a polymer of vinyl benzoate is preferred.

Further, the copolymer may be a copolymer obtained by copolymerizing a monomer copolymerizable with the above-mentioned vinyl ester monomer, and is used within a range not to impair the purpose of the present invention. Examples of such copolymerized units include olefins such as ethylene, propylene, 1-butene, and isobutene, acrylic acid and its salts, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, N-butyl acrylate, i-butyl acrylate,
Acrylates such as t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid and salts thereof, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-methacrylate Methacrylates such as propyl, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylamide, n-methylacrylamide, N-ethyl Acrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, N-methylol alcohol Acrylamide derivatives such as rilamide and derivatives thereof, methacrylamide, N-methylacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and salts thereof, methacrylamidopropyldimethylamine and salts thereof or quaternary salts thereof, N-methylolacrylamide And methacrylamide derivatives such as derivatives thereof, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, vinyl ethers such as stearyl vinyl ether, Acrylonitrile,
Nitriles such as methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride, vinyl halides such as vinylidene fluoride, allyl acetate, allyl compounds such as allyl chloride, maleic acid and salts or esters thereof, itaconic acid and Examples thereof include salts or esters thereof, vinylsilyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate.

The PVA-based polymer in the present invention has a syndiotacticity of 45 to 52.5 mol% obtained by the above method or the like.
Obtained by saponifying the polyvinyl ester-based polymer described above by a known method.

As the dichroic substance used in the production of the polarizing film in the present invention, a so-called dichroic dye is used alone or in combination with iodine. For example,
black17,19,154; brown44,106,195,210,223; red2,23,28,
31,37,39,79,81,240,242,247; blue1,15,22,78,90,98,15
1,168,202,236,249,270; violet9,12,51,98; green1,85; y
ellow8, 12, 44, 86, 87; orange26, 39, 106, 107 and the like. If the amount of the dichroic substance in the film is too small, the optical properties of the polarizing film cannot be exhibited, and if the amount is too large, the optical properties, water resistance, and heat resistance are reduced. It is adjusted in the range of 0.01% by weight to 1% by weight based on the weight of the polymer.

Polarizing film obtained by the production method of the present invention is a conventional PV
A very useful polarizing film with improved optical characteristics of the A-based polarizing film. The ideal value of the optical characteristics of the polarizing film is that the degree of polarization at a transmittance of 50% is 100%. However, since the dichroic ratio of dichroic molecules has a finite value and the molecules are not completely oriented in the base polymer, the degree of polarization of the conventional polarizing film is 99.9%. Had a transmittance of about 40%. In contrast, the polarizing film obtained by the production method of the present invention,
Sufficient polarization characteristics can be obtained with a dichroic substance having a lower concentration than that of a conventional polarizing film, and a high degree of polarization and high transmittance can be achieved. For example, when the transmittance is 42 to 44%, the polarization degree is 98 to 100.
%, More preferably 44-48%, the degree of polarization
A 99-100% polarizing film is obtained.

The following method can be exemplified as a method for producing the polarizing film of the present invention.

One way is to have a syndiotacticity of 45-52.5
In this method, after preparing a mol% PVA-based polymer film, adsorption of a dichroic substance such as iodine or a dye and uniaxial stretching are performed, and the order of the adsorption of the dichroic substance and the stretching operation is arbitrary. As another method, there is a method of adding a dichroic substance at the time of producing a film and stretching the film uniaxially.

First, if syndiotacticity is 45-52.5 mol%
In the preparation of the PVA-based polymer solution, the solvent used at this time is water alone or dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, glycerin, ethylenediamine, diethylenetriamine and the like. A mixed solution of an organic solvent and water is used. Aqueous solutions of inorganic salts such as lithium chloride and calcium chloride can also be used alone or in combination with the organic solvents. Among them, a mixed solution of dimethyl sulfoxide or dimethylformamide and water is preferably used. The concentration of the PVA polymer at the time of film formation varies depending on the film formation method, but is usually 1 to 50% by weight, preferably 2 to 30% by weight.

In the method for producing a polarizing film of the present invention, as one method of incorporating a polarizing element into a PVA-based polymer film, a method of preparing a solution in which iodine or a dichroic dye is dissolved in a PVA-based polymer solution is given. The concentration of the polarizing element used at this time varies depending on the type of the polarizing element, but is usually adjusted in the range of 0.01 to 1% by weight based on the PVA-based polymer. The PVA-based polymer solution in which such a polarizing element is dissolved is usually prepared at a temperature from room temperature to 120 ° C.
In this case, depending on the solvent used, it is preferable to adopt a lower preparation temperature within the above-mentioned temperature range in order to suppress a decrease in the degree of polymerization due to decomposition of the PVA-based polymer.

 Next, a film is formed from the PVA-based polymer solution.

Examples of the film forming method include a cast film forming method from the PVA-based polymer solution and a dry film forming method by extruding the film into an inert gas such as air or nitrogen. In addition, wet film formation can be performed by extruding the PVA-based polymer solution into a poor solvent. Further, a dry-wet film forming method in which the PVA-based polymer solution is once extruded into air or an inert gas such as nitrogen to form a liquid film and then introduced into a coagulating liquid to form a film is also possible. To explain the dry-wet film formation in more detail, a liquid film of the PVA-based polymer solution is formed in an atmosphere, and then the liquid film is solidified by cooling with a cooling medium such as decalin, paraffin, trichloroethylene, and carbon tetrachloride. After gelation, the mixture may be introduced into a solvent-removing solution to remove the solvent, thereby forming a film. Further, it is of course possible to introduce the liquid film into a cooling space such as a freezing room, cool and coagulate and gel, and then remove the solvent to form a film.
As the coagulant, it has compatibility with the solvent of the PVA-based polymer solution, and a poor solvent for the PVA-based polymer, for example, alcohols such as methanol, ethanol, and propanol, acetone, benzene, Toluene, a mixed solution thereof with a solvent of the PVA-based polymer solution, and an aqueous solution of an inorganic salt are used. The liquid film of the PVA-based polymer solution is
Depending on the solvent of the PVA polymer solution, usually -3
Prepared at 0-120 ° C.

The syndiotacticity city obtained in this way is
A film made of a PVA-based polymer of 45 to 52.5 mol% (hereinafter abbreviated as a raw film) is subjected to adsorption of a dichroic substance and uniaxial stretching. There is no problem if the adsorption operation and the stretching operation are performed simultaneously or separately, and the order is arbitrary.
In addition, a boron compound such as boric acid or borax may be added for the purpose of strengthening the adsorption of the dichroic substance to the raw film, but this may be performed simultaneously with the adsorption or stretching.
It is optional to carry out at any time before and after these operations.

Adsorption of the dichroic substance to the raw film is usually performed by immersing the raw film in a liquid containing the dichroic substance, but there is no particular limitation on the operating conditions and method, and for example, In the case of using iodine, an aqueous solution of iodine-potassium iodide is used, and in the case of a dye, an aqueous solution of a dye is used.

Stretching is performed by wet stretching, dry stretching, or a combination of both, and it is preferable that the stretching is performed three times or more, and preferably four times or more, in the uniaxial direction. The stretching speed is preferably 10 to 300% / min based on the original length of the raw film. The temperature during stretching depends on the stretching conditions,
Usually between 10 ° C and 260 ° C. It is preferable to carry out the operation in an inert gas during the dry heat stretching. In the case where adsorption is performed after the stretching operation, it is preferable to subject the uniaxially stretched film to heat treatment at 160 to 260 ° C. in air or an inert gas before the adsorption. The thickness of the stretched film is not particularly limited, but is preferably 5 to 100 μm, and 10 to 40 μm.
μm is particularly preferred.

The adsorbed and stretched raw film is dried and heat-treated in air or in a nitrogen stream under a fixed length.

The polarizing film thus obtained by the production method of the present invention can be used alone, or a protective film that is optically transparent and has mechanical strength is bonded to both sides or one side thereof. Can also be used.
As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

E. Examples Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In the examples, "%" and "part" represent "% by weight" and "part by weight", respectively, unless otherwise specified.

The transmittance and the degree of polarization were measured using a spectrophotometer. The transmittance was measured according to JIS-Z-8701, and the degree of polarization was calculated by the following equation.

Degree of polarization (%) = {(T ₁ −T ₂ ) / (T ₁ + T ₂ )} ^1/2 × 100 Here, T ₁ and T ₂ each extend two polarizing films with their stretching axes parallel and orthogonal to each other. This is the transmittance measured by superimposing. The polarizing film is usually used in a state where a protective film is laminated, but in the following Examples and Comparative Examples, the measurement was performed on the polarizing film alone without the protective film.

Example 1 A vinyl acetate monomer 200 was placed in a reaction vessel equipped with a stirrer.
And 290 parts of dimethyl sulfoxide, and the system was sufficiently purged with nitrogen by bubbling with nitrogen gas. Separately, a solution in which 0.028 part of 2,2'-azobisisobutyronitrile was dissolved as an initiator in 10 parts of dimethyl sulfoxide was prepared, and the atmosphere was replaced with nitrogen by bubbling with nitrogen gas. 60 reaction solution
When the temperature reached ° C, a dimethyl sulfoxide solution in which an initiator was dissolved was injected to start polymerization. After 190 minutes, when the polymerization rate reached 60%, methanol in which a polymerization inhibitor was dissolved was added, and the mixture was further cooled to stop the polymerization. Thereafter, unreacted vinyl acetate monomer was removed while adding methanol under reduced pressure to obtain a dimethyl sulfoxide-methanol mixed solution of polyvinyl acetate. Take a part of this solution, concentration 10%, [NaOH] / [VAc] (molar ratio) = 0.1,
Saponify at a temperature of 40 ° C., and add 0.1 part of the obtained PVA to acetic anhydride 8
Of pyridine and 2 parts of pyridine at 120 ° C for 20 hours with occasional stirring, re-acetylation, and re-precipitation purification with acetone-ether and acetone-water systems was repeated to obtain purified re-acetylated polyvinyl acetate. Was. The obtained PVA was dissolved in d ₆ -DMSO, and ¹ H-NMR was measured to determine the tacticity of each three-unit chain structure of the hydroxyl proton.
The syndiotacticity of the chain structure was 51.3 mol%, and the viscosity average polymerization degree of the polyvinyl acetate obtained by re-acetylation, determined from [η] measured in acetone at 30 ° C., was 2200.

This PVA was re-saponified until the degree of saponification reached 99.9 mol%, and the system was sufficiently purged with nitrogen.
Dissolve in distilled water under heating at 95 ° C so that
A aqueous solution was obtained. The aqueous solution was cast on a polyethylene terephthalate film and air-dried at room temperature to form a film. Next, the film was uniaxially stretched 9 times at 150 ° C., and further heat-set at 190 ° C. for 3 minutes in a nitrogen gas atmosphere under a constant length. The stretched film was immersed in an aqueous solution in which 0.2 g / l of iodine and 50 g / l of potassium iodide were dissolved at 30 ° C. for 2 minutes. Then,
After performing boric acid treatment for 5 minutes at room temperature in an aqueous solution in which boric acid 60 g / l and potassium iodide 30 g / l are dissolved,
The film was dried under hot air at ℃ to obtain a polarizing film having a thickness of 18 μm. The transmittance of the obtained polarizing film is 45.0%, and the degree of polarization is
99.5%.

Comparative Example 1 Example 1 except that PVA having a degree of polymerization of 2400, a degree of saponification of 99.9 mol%, and a syndiotacticity of 53.0 mol% was used.
A polarizing film having a thickness of 18 μm was prepared in exactly the same manner as described above. The stretching ratio of the raw film was 4 times. The transmittance of the polarizing film was 41.9%, and the polarizing degree was 99.1%.

Example 2 Using the same PVA as in Example 1, dimethyl sulfoxide / water was heated at 70 ° C. so that the PVA concentration became 10% by weight.
It was dissolved in a 90/10 (weight ratio) mixed solution to obtain a PVA solution.
After casting the solution on a polyethylene terephthalate film and immersing it in a methanol coagulation bath to form a film,
The mixture was introduced into a methanol extraction bath to remove dimethyl sulfoxide from solution. Then, naturally dry at room temperature, 150 ℃
Stretched 9 times uniaxially in a nitrogen gas atmosphere under constant length.
Heat set at 0 ° C. for 3 minutes. The stretched film is iodine 0.2g /
immersed in an aqueous solution of 50 g / l of potassium iodide at 30 ° C. for 2 minutes. Subsequently, after performing boric acid treatment at room temperature for 5 minutes in an aqueous solution in which boric acid 60 g / l and potassium iodide 30 g / l are dissolved, the resultant is dried under constant-length, 40 ° C hot air,
A polarizing film having a thickness of 18 μm was obtained. The transmittance of the polarizing film was 45.7%, and the polarizing degree was 99.8%.

Comparative Example 2 PVA having a degree of polymerization of 6000, a degree of saponification of 99.9 mol%, and a syndiotacticity of 53.0 mol% was added to dimethyl sulfoxide by adding PVA.
An attempt was made to dissolve it under heating at 70 ° C. so that the VA concentration became 9% by weight, but it took 8 hours to dissolve. A polarizing film having a thickness of 18 μm was prepared from the solution in the same manner as in Example 2, but no uniform film was obtained. The stretching ratio was 6 times. The transmittance of the polarizing film is 40.0%,
The degree of polarization was 99.2%.

F. Effects of the Invention As is clear from the above examples, the production method of the present invention has a higher transmittance and a higher degree of polarization than the polarizing film obtained from the conventional PVA-based polymer, and has excellent optical properties. A film can be obtained. This involves forming a film using an aqueous solution of an atactic PVA-based polymer having a syndiotacticity of 45 to 52.5 mol% or a mixed solution of water and an organic solvent, and uniaxially stretching the obtained film as a base material. This was achieved only by doing so.

Although the reason for this is not clear, the polarizing film obtained by the production method of the present invention is superior in stretchability and synthesizing property because the syndio chain is composed of a PVA-based polymer that is smaller than the conventional polarizing film. It is estimated that

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 5/30

Claims (2)

(57) [Claims] 1. A method for producing a polarizing film comprising a polyvinyl alcohol-based polymer and a dichroic substance oriented therein, the method comprising using an aqueous solution of a polyvinyl alcohol-based polymer having a syndiotacticity of 45 to 52.5 mol%. A method for producing a polarizing film, comprising forming a film and uniaxially stretching the obtained film. 2. A method for producing a polarizing film comprising a polyvinyl alcohol-based polymer and a dichroic substance oriented therein, wherein the syndiotacticity of the polyvinyl alcohol-based polymer is from 45 to 52.5 mol%. A method for producing a polarizing film, comprising forming a film using a mixed solution, and uniaxially stretching the obtained film.