JPH08201627A - Production of polarizing film - Google Patents

Abstract

PURPOSE: To obtain a high-polarization-degree polarizing film and to obtain a polarizing film improved in dyeability with dichroic substance by using a PVA polymer of specified polymerization degree for an original sheet, swelling the film in a specified swelling soln. and dyeing the film with a dichroic dye. CONSTITUTION: A PVA polymer film having >=2400 polymerization degree or a PVA polymer having >=55% syndiotacticity is used for an original sheet. The film is swollen in a swelling soln. fulfilling (hydrothermal cutting temp.)-(swelling temp. before dyeing) <=20 deg.C and then dyed with a dichroic dye. Namely, a PVA having a higher polymerization degree than the PVA used in the conventional polarizing film or a PVA having a higher syndiotacticity is used, swollen and dyed or drawn in a specified temp. range. An org. dye called a dichroic dye or its salt alone or the mixture of both is used as the dichroic substance used in a polarizing film.

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 dye-based polarizing film having a high degree of polarization and a high degree of transmission.

[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, has a large screen, improved optical characteristics such as high polarization degree and high transmittance, and water resistance, heat resistance, moist heat resistance, and durability. In addition to the improvement of the productivity, it is required to improve the processing characteristics of the original film of the polarizing film from the viewpoints of improving productivity and ensuring quality.

Conventionally, a uniaxially stretched film of polyvinyl alcohol on which an iodine compound or a dichroic dye is adsorbed is often used as a polarizing film, and it is required to improve polarization performance and durability. On the other hand, PV with a high degree of polymerization
Proposals using A or high syndiotactic PVA as a raw material have been made (for example, JP-A-1-105204 and JP-A-3-206402), but the effect of high polymerization degree and high syndiotacticity is Although it is recognized in terms of polarization characteristics and durability, when an iodine compound is used as a dichroic substance, the polarization performance is high but the durability is low,
In the case of the dye type, although the durability is high, there are problems that the polarization performance is insufficient, the dyeability is poor, and the production efficiency and quality are deteriorated.

[0004]

An object of the present invention is to obtain a polarizing film having a high degree of polarization as compared with a conventional polarizing plate,
Further, the present invention provides a method for producing a polarizing film using a dichroic dye, which gives a polarizing film having good dyeability.

[0005]

Means for Solving the Problems As a result of intensive studies aimed at solving the above problems, the present inventors have found that a polyvinyl alcohol polymer (hereinafter abbreviated as PVA polymer) film or syndiotactic polymer having a degree of polymerization of 2400 or more. Ticity is 5
Using 5% or more of PVA-based polymer film as a raw material, swelling the film in a swelling liquid satisfying the condition of the following formula 1, and then dyeing the film with a dichroic dye. A method for producing a polarizing film (first invention), wherein a PVA-based polymer film having a degree of polymerization of 2400 or more or a PVA-based polymer film having a syndiotacticity of 55% or more is used as a raw material, and the condition of the following formula 2 is satisfied. A method for producing a polarizing film, characterized in that the film is dyed with a dichroic dye in a dyeing solution that satisfies
Invention); PVA-based polymer film having a degree of polymerization of 2400 or more or PVA having a syndiotacticity of 55% or more
In a method for producing a polarizing film using a polymer film as a raw material and a dichroic dye as a dye, the film is adjusted to a water content of 40% or more, and then the film is heated to 50 ° C.
To 98 ° C. Stretching at a temperature of 98 ° C. (3rd invention); PV having a degree of polymerization of 2400 or more
In a method for producing a polarizing film using an A-based polymer film or a PVA-based polymer film having a syndiotacticity of 55% or more as a raw material and a dichroic dye as a dye, the water content of the film is less than 40%. After adjusting to
A method for producing a polarizing film (fourth invention), which comprises stretching the film at a temperature of 80 ° C. or higher,
The present invention has been completed. (Hot water cutting temperature)-(Swelling temperature before dyeing) ≤ 20 ° C (Equation 1) (Hot water cutting temperature)-(Dyeing temperature) ≤ 20 ° C (Equation 2)

Hereinafter, the present invention will be described in detail. The polarizing film of the present invention is a PVA having a higher degree of polymerization or a P having a higher syndiotacticity than PVA used in conventional polarizing films.
It is characterized in that VA is used and swelling, dyeing or stretching is performed within a specific temperature range.

The present invention will be described in detail below. In the present invention, the viscosity average degree of polymerization (hereinafter, abbreviated as the degree of polymerization) 240
When 0 or more PVA-based polymer film is used for the raw fabric, the degree of polymerization of the PVA-based polymer needs to be 2400 or more, preferably 3500 or more. Although the upper limit of the degree of polymerization is not limited, it is preferably 30,000 or less from the viewpoint of film-forming property of the film and processability such as stretching. A suitable range of the degree of polymerization depends on the content of the hydrophilic functional group,
4000-20000 is the most preferable. Degree of polymerization is 240
When it is less than 0, the polarization performance and the durability deteriorate.

In the present invention, when a PVA polymer film having a syndiotacticity of 55% or more is used as an original fabric, the degree of polymerization of the PVA polymer is not particularly limited, but the strength of the film is not limited. To 500 or more are preferable, and from the viewpoint of the polarization performance of the obtained polarizing film, it is 10
00 or more is preferable and 1500 or more is more preferable. P
The upper limit of the degree of polymerization of the VA polymer is not particularly limited, but it is preferably 20,000 or less from the viewpoint of film-forming property of the film and processability into a polarizing film. The preferred range of the degree of polymerization is 1
It is 500 to 10,000.

The syndiotacticity of the PVA polymer needs to be 55% or more, preferably 58% or more. The upper limit of syndiotacticity is not limited, but it is preferably 75% or less from the viewpoint of film-forming property of the film and processability such as stretching. The most preferable range of syndiotacticity is 60 to 68%. When the syndiotacticity is lower than 55%, the polarization characteristics and durability are deteriorated. Incidentally, the PV referred to in the present invention
The "syndiotacticity" of the A-based polymer is NMR
It is a value based on the diad display measured by the method, and specifically, it is measured by the method described in JP-A-3-121102.

The method for producing the PVA-based polymer of the present invention is not limited and is generally produced by the following method. That is, it is obtained by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester such as vinyl acetate.

Examples of the method for polymerizing the polyvinyl ester polymer of the present invention include a solution polymerization method, a bulk polymerization method, a suspension polymerization method and an emulsion polymerization method. In order to obtain PVA having a high degree of polymerization, a low temperature polymerization method can be used in combination with these polymerization methods. The high syndiotacticity PVA-based polymer is generally obtained by saponifying a polyvinyl ester-based polymer obtained by polymerizing a vinyl ester such as vinyl pivalate, vinyl trifluoroacetate, or vinyl trichloroacetate. To be

A PVA-based polymer is obtained by saponifying the polyvinyl ester-based polymer thus obtained. Generally, transesterification called alcoholysis is carried out using an alcohol solution of polyvinyl ester and an alkali catalyst such as caustic soda. Done by There is no particular limitation on the degree of saponification, which is the conversion rate at which the vinyl ester unit is converted to a vinyl alcohol unit, but if the degree of saponification is low, the durability as a polarizing film may be adversely affected, and thus 90 mol% or more. Is preferable, and 95 mol% or more is more preferable.

The amount of 1,2-glycol bond of the PVA polymer of the present invention is not particularly limited, and is generally 1.6 to
Although 1.8 mol% of PVA is used, it is preferably 1.6 mol% or less from the viewpoint of high polarization degree and high durability. The PVA-based polymer of the present invention may be copolymerized with other vinyl monomers within a range that does not hinder the purpose of the present invention.

In the present invention, the method for producing the original film of the polarizing film is not limited, and a method of forming a liquid film from a PVA aqueous solution and drying it to obtain a film is generally adopted. P
Film formation from a VA copolymer solution is cast film formation, dry film formation (extrusion into air or an inert gas such as nitrogen), wet film formation (extrusion of PVA polymer into a poor solvent), Dry-wet film formation and gel film formation (a method of once gelating a PVA-based polymer solution to obtain a film) are carried out, and the solvent used at this time is dimethyl sulfoxide,
Dimethylformamide, dimethylacetamide, ethylene glycol, glycerin, water and the like 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 as a mixture with the organic solvent. Of these, water, dimethyl sulfoxide, and a mixed solvent of dimethyl sulfoxide and water are preferably used.
Alternatively, a dichroic substance may be mixed with this solution to form a film,
In order to impart flexibility to the film, polyhydric alcohol such as glycerin, diglycerin, ethylene glycol and its derivatives may be contained.

The film made of the PVA polymer obtained by the above film-forming method is subjected to adsorption (dyeing) of a dichroic substance and orientation treatment by uniaxial stretching, or a dichroic substance is added at the time of film formation. Only uniaxial stretching is performed on the film. There is no problem whether the adsorption treatment and the orientation treatment are performed simultaneously or separately, and the order thereof is arbitrary. You may let me.

As the dichroic substance used in the polarizing film of the present invention, organic dyes called so-called dichroic dyes and salts thereof are used alone or in combination. Typical examples are Direct black 17, 19, 154 and Direct brown.
44, 106, 195, 210, 223, Direct red 2, 23, 2
8, 31, 37, 39, 79, 81, 240, 242, 247, Direct bl
ue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236
, 249, 270, Direct violet 9, 12, 51, 98, Direc
t green 1,85, Direct yellow 8, 12,44,86,87, D
irect orange 26, 39, 106, 107 etc. are mentioned. Moreover, you may add a boron type compound, such as boric acid and borax, to these dichroic dye aqueous solutions.

The adsorption (dyeing) of the dichroic dye is generally performed by the following method. First, prior to dyeing, the film is immersed in water to swell the film. Then, it is immersed in an aqueous dichroic dye solution to perform dye adsorption treatment, that is, dyeing.
The temperature of the swelling step and the dyeing step is a feature of the present invention,
Very important. That is, it is preferable to swell the film in a swelling liquid satisfying the condition of the following formula 1 before dyeing the film (first invention). Further, it is preferable to dye the film in a dyeing liquid that satisfies the following expression 2 (second invention). Further, it is more preferable that the swelling condition before dyeing of the first invention and the dyeing condition of the second invention are simultaneously satisfied. When the swelling treatment is performed at a temperature lower than that of Equation 1 or the dyeing treatment is performed at a temperature lower than Equation 2,
There is a tendency that the dyeability deteriorates, it takes a long time to adsorb the dye, color spots occur, and the productivity and quality are adversely affected. In addition, when swelling is performed at a temperature higher than the hot water cutting temperature or when dyeing is performed at a temperature higher than the hot water cutting temperature, color spots, film fusing, etc. occur, and quality and process passability deteriorate. Cause (Hot water cutting temperature)-(Swelling temperature before dyeing) ≤ 20 ° C (Equation 1) (Hot water cutting temperature)-(Dyeing temperature) ≤ 20 ° C (Equation 2) More preferable ranges of Equation 1 and Equation 2 are as follows. Equations 3 and 4 of 5 ≦ (hot water cutting temperature) − (swelling temperature before dyeing) ≦ 15 ° C. (equation 3) 5 ≦ (hot water cutting temperature) − (dyeing temperature) ≦ 15 ° C. (equation 4) In the above equation, “hot water "Cutting temperature" means a width of 0.5c
A load of 10 kg / cm ² is applied to the cross-sectional area of the PVA polymer film having a length of m × 15 cm, and the film is placed in water at 40 ° C. in an amount 100 times or more the weight of the film, and then the water temperature is 3 ° C. / It is the temperature (° C.) of hot water when the film is melted by being raised at a rate of minutes.

The orientation treatment by stretching is carried out by wet stretching carried out in a state where the film is hydrated or swollen, or dry heat type stretching carried out in a low hydrated state or in a dried state, preferably uniaxially at least 3 times and preferably at least 4 times. It is more preferable to perform the stretching. The temperature condition during stretching is a feature of the present invention, and it is preferable to carry out the following conditions.

The water content of the PVA polymer film is 40%
When adjusted to the above, the PVA polymer film is
Stretching is performed at a temperature of 0 ° C to 98 ° C. In this case, the stretching may be carried out in water, or the film which has been subjected to humidity conditioning or water treatment in advance may be carried out under an air atmosphere or under steam. The preferred range of the stretching temperature is 55 ° C. to 90 ° C., more preferably 60 ° C. to 80 ° C., although it depends on the water content condition of the film. If the stretching temperature is less than 50 ° C., sufficient stretching cannot be performed and a high stretching ratio cannot be obtained, and as a result, a polarizing film having a high degree of polarization cannot be obtained. If the stretching temperature is higher than 98 ° C., the film may melt and the stretching may not be possible.

The water content of the PVA polymer film is 40%.
If adjusted to less than 8, PVA-based polymer film
Stretch at 0 ° C or higher. In this case, the stretching is preferably performed in a gas (air, inert gas) atmosphere or in a water vapor atmosphere. At this time, the water content of the film is preferably adjusted in water or in a constant humidity atmosphere. The upper limit of the stretching temperature is not limited, but the higher the stretching temperature, the more the dichroic dye and the PVA polymer are thermally decomposed. The preferred range of stretching temperature is 90
C. to 230.degree. C., and 110.degree. C. to 200.degree. C. is a more preferable range. If the stretching temperature is less than 80 ° C., a high stretch ratio cannot be obtained, and as a result, a polarizing film having a high degree of polarization cannot be obtained. The water content (%) in the present invention is a value represented by the following formula. Moisture content = (1- (dry film weight) / (hydrated film weight)) × 100 However, the dry film weight is 105 ° C. for the hydrated film.
It is the film weight after being dried for 24 hours.

The film subjected to the dyeing treatment and the stretching treatment is dried in air or an inert gas under a fixed length. The dried film may be subjected to heat treatment at a temperature of 80 ° C. to 230 ° C. in order to impart water resistance and moisture heat resistance. 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 base film and imparting water resistance and moist heat resistance. It may be carried out at the same time as the stretching, or at any point before, after or during these treatments.

The polarizing film thus obtained is used as a polarizing plate by adhering an optically transparent protective film (support) having mechanical strength on both sides or one side. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used, and among them, a cellulose acetate film such as cellulose triacetate is generally used in view of optical characteristics and the like.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples. Transmittance (T), polarization degree (V), and hue are measured by the Japan Electronic Machinery Manufacturers Association Standard (EIAJ) LD-201-
In accordance with 1983, the spectrophotometer was used to calculate with a C light source and a double visual field. The dichroic ratio (Rd) is a value indicating the polarization performance obtained by the following formula. Rd = log (T (1-V)) / log (T (1 + V))

Examples 1 to 5 and Comparative Examples 1 to 6 (High degree of polymerization PVA) A liquid film cast from a 5% aqueous solution of the PVA polymer shown in Table 1 on a polyethylene terephthalate film was dried at 60 ° C, By heat treatment at 120 ℃ for 3 minutes, PV
An A-type polymer film was obtained. Next, using the obtained PVA-based polymer film as a raw fabric, Direc was used as a dyeing solution.
A polarizing film was obtained by performing swelling, dyeing, stretching and drying treatments using a t Blue 1 aqueous solution (concentration: 2% by weight) under the conditions shown in Table 1.

However, in Examples 1 to 3 and Comparative Examples 1 to 3, stretching was carried out in a bath of an aqueous boric acid solution (boric acid concentration 4% by weight) as a stretching bath, and in Examples 4 to 5 and Comparative Examples 4 to 6. Stretched in air. In addition, in Examples 4 to 5, when stretching was performed at a water content of less than 40%, preliminary drying for adjusting the water content was performed before the stretching step. The above results are shown in Table 1.
Shown in

[0026]

[Table 1]

Examples 6 to 8 and Comparative Examples 7 to 12 (high syndiotacticity PVA)

Using the PVA-based polymers shown in Table 2, Table 2
A polarizing film was manufactured in the same manner as in Examples 1 to 5 except that the polarizing film was manufactured under the conditions shown in.

However, in Examples 6 to 7 and Comparative Examples 7 to 9, drawing was performed in a bath of an aqueous boric acid solution (boric acid concentration 4% by weight) as a drawing bath, and in Examples 8 and Comparative Examples 10 to 12, in the air. Was stretched. In Example 8, the water content was 40
In the case of stretching at less than%, preliminary drying for adjusting the water content was performed before the stretching step. The above results are shown in Table 2.

[0030]

[Table 2]

[0031]

EFFECTS OF THE INVENTION The present invention is superior to conventional dye-based polarizing plates in that
It is intended to provide a method for producing a polarizing film, which can obtain a polarizing film having a high degree of polarization and also has a good dyeability with a dichroic substance. The polarizing film obtained in the present invention is a liquid crystal display having high performance and high durability by taking advantage of the above characteristics, for example, a liquid crystal television, a liquid crystal projector,
Display for word processor, display for PC, O
A device terminal display, instrument panel display for aircraft and automobiles, other filters, sunglasses, window glass, antiglare for various lights, various sensors, etc.

Front page continuation (72) Inventor Toshiaki Sato 1621 Sakata, Kurashiki, Okayama Prefecture Kuraray Co., Ltd.

Claims (4)

[Claims] 1. A swelling solution satisfying the following formula 1 using a polyvinyl alcohol polymer film having a degree of polymerization of 2400 or more or a polyvinyl alcohol polymer film having a syndiotacticity of 55% or more as a raw fabric. In the method for producing a polarizing film, the film is swollen and then the film is dyed with a dichroic dye. (Hot water cutting temperature)-(Swelling temperature before dyeing) ≦ 20 ° C. (Formula 1) 2. A dyeing solution satisfying the following formula 2 using a polyvinyl alcohol-based polymer film having a degree of polymerization of 2400 or more or a polyvinyl alcohol-based polymer film having a syndiotacticity of 55% or more as a raw material. 2. A method for producing a polarizing film, wherein the film is dyed with a dichroic dye. (Hot water cutting temperature)-(Dyeing temperature) ≤ 20 ° C (Equation 2) 3. A polarizing film comprising a polyvinyl alcohol-based polymer film having a degree of polymerization of 2400 or more or a polyvinyl alcohol-based polymer film having a syndiotacticity of 55% or more as a raw material and a dichroic dye as a dye. In the production method, the film is adjusted to have a water content of 40% or more, and then the film is stretched at a temperature of 50 ° C to 98 ° C. 4. A polarizing film comprising a polyvinyl alcohol-based polymer film having a degree of polymerization of 2400 or more or a polyvinyl alcohol-based polymer film having a syndiotacticity of 55% or more as a raw material and a dichroic dye as a dye. In the manufacturing method, the film is adjusted to have a water content of less than 40%, and then the film is stretched at a temperature of 80 ° C. or higher.