JPH07120618A - Manufacture of polarizing film - Google Patents

Abstract

PURPOSE:To provide a polyvinylalcohol-based polarizing film excellent in polarizing performance and dimensional stability at the time of a high temperature. CONSTITUTION:At the time of manufacturing the polarizing film with final drawn magnification (ab) by manufacturing a polyvinylalcohol-based resin film and processing it with a boron compound after dyeing it with iodine dye or bicolor dye 1, uniaxial drawing by (a) times is performed in a dyeing or preceding process, and uniaxial drawing by (b) times is further performed in a boron compound treatment process so as to satisfy an expression: 0.1<(a-1) /(ab-1), where a>1, b>1.

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 polyvinyl alcohol-based resin polarizing film, and more specifically, a method for producing a polyvinyl alcohol-based resin polarizing film having excellent optical durability and heat resistance dimensional stability. Regarding

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used in desk-top electronic computers, electronic timepieces, word processors, measuring instruments such as automobiles and machines, and the demand for polarizing plates has increased accordingly. In particular,
Highly polarized films are required for accurate instruments.

At present, one of the known typical polarizing films is a polyvinyl alcohol type polarizing film,
The polarizing film includes a polyvinyl alcohol-based film dyed with iodine and a dichroic dye, which is prepared by forming an aqueous solution of polyvinyl alcohol into a film.
This is produced by uniaxially stretching and dyeing it, or after dying after dying after dying, preferably, it is subjected to a durability treatment with a boron compound. Therefore, in the stretching step as described above, the applicant of the present invention for producing a film having a higher polarization performance, was uniaxially stretched at 4.5 times or less during the boron compound treatment step, and then at 2 times or less. A two-stage stretching method for uniaxial stretching was proposed. (Japanese Patent Application No. 2-4176
No. 81)

[0004]

However, in the case of the polyvinyl alcohol type polarizing film obtained by the above method, although the polarizing performance is sufficiently good, the dimensional stability at high temperature is still improved. There was room.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors formed a polyvinyl alcohol resin film, dyed it with an iodine dye or a dichroic dye, and then added a boron compound. Final stretch ratio ab
In producing a double-fold polarizing film, when it is a-time uniaxially stretched in a process of dyeing or before so as to satisfy the following formula (I) and further b-fold uniaxially stretched in a boron compound treatment process, excellent polarization performance is obtained. Further, they have found that a polarizing film having excellent dimensional stability at high temperature can be obtained, and completed the present invention. 0.1 <(a-1) / (ab-1) ... (I) (however, a> 1, b> 1)

As described above, the effect of the present invention is obtained by uniaxially stretching before the treatment step with the boron compound and then uniaxially stretching so as to reach the final stretching ratio in the treatment step with the boron compound. It is obtained by adopting. The present invention will be specifically described below.

The polarizing film of the present invention is a uniaxially stretched film of polyvinyl alcohol resin film. Polyvinyl alcohol is generally produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not necessarily limited to this, and a small amount of unsaturated carboxylic acid (salt, ester, amide, nitrile, etc. , Etc.), olefins, vinyl ethers, unsaturated sulfonates and the like, and may contain a component copolymerizable with vinyl acetate. The average degree of saponification in polyvinyl alcohol is 85
Is practically 100 to 100 mol%, preferably 98 to 100 mol%.

In order to obtain the effects of the present invention, the average degree of polymerization may be any of 500 to 5,000, but usually 500 to 4,000 is advantageous. The polyvinyl alcohol is formed into a film by a known method. A general method is to dissolve polyvinyl alcohol in water, an organic solvent, a water / organic solvent mixed solvent, or the like and cast the solution. The concentration of the solution is 5-20
Practical use is about weight%. In addition, a so-called gel film forming method in which a solution of polyvinyl alcohol is introduced into a coagulation bath to form a film can be carried out. A suitable thickness of the original film is 40 to 120 μm.

Next, the above-mentioned raw film is dyed and treated with a boron compound. Before the treatment with the boron compound, there is a relationship between the stretching ratio a of the raw film and the stretching ratio b during the treatment with the boron compound. It is necessary to uniaxially stretch so as to satisfy the relationship of the above formula (I). In other words, based on the desired final draw ratio ab, the draw ratio a is set so as to satisfy the relationship of the above formula (I). The stretching may be performed before or after dyeing or during dyeing. The iodine dyeing of the film, that is, the adsorption of the polarizing element is performed by bringing the liquid containing the polarizing element into contact with the film. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 2 g / l, the concentration of potassium iodide is 10 to 50 g / l, and the weight ratio of iodine / potassium iodide is 20 to 100. Appropriate. Staining time is 30 ~ 500
Seconds is practical. A small amount of an organic solvent compatible with water may be contained in addition to the water solvent.

As the contact means, immersion is preferable, but any means such as coating and spraying can be applied.

The original film before treatment with the boron compound in the present invention is uniaxially stretched as described above, but the ratio a is usually 1.1 to 6 times, preferably 1.2 to 4 times. It is preferably selected. The present invention is characterized in that the final draw ratio ab and the draw ratio a are drawn so as to satisfy the above formula (I).
It is an essential condition that the value of the formula (I) is larger than 0.1, preferably 0.15 to 0.95. If it is smaller than this range, the heat-resistant dimensional stability becomes inferior, and conversely, if it is larger, the optical durability due to changes in the degree of polarization and changes in the transmittance becomes poor.
The stretching temperature in the stretching treatment is about 30 to 70 ° C,
The treatment time is preferably about 60 to 600 seconds, and if necessary, some stretching operation may be performed before and after the treatment.

[0012] In order to draw in such a range, any method such as roll drawing and tenter drawing is carried out, but the former is usually carried out. Roll stretching can be performed in either a single-stage type or a multi-stage type.

The film thus stretched and dyed is then treated with a boron compound. Boric acid and borax are practical as the boron compound. The boron compound has a concentration of 0.1% in the form of an aqueous solution or a water-organic solvent mixture.
It is used at about 5 to 2 mol / l, and it is practically desirable to allow a small amount of potassium iodide to coexist in the liquid. The treatment method is preferably a dipping method, but of course, a coating method and a spraying method can also be carried out. During the treatment with the boron compound, the film has a final draw ratio ab.
The film is stretched again until it becomes a polarizing film. Also during the stretching, the stretching method before the treatment with the boron compound can be similarly adopted. The polarizing film thus obtained is appropriately washed, dried, and heat-treated according to a conventional method, and then a protective film having excellent optical transparency and mechanical strength is attached to both sides or one side thereof and dried to be used as a polarizing plate. Examples of the protective film include conventionally known cellulose acetate film, acrylic film, polyester resin film, polyolefin resin film, polycarbonate film, polyetherketone film, and polysulfone film.

[0014]

Since the polarizing film of the present invention is manufactured by a special stretching method, it has excellent polarization performance and dimensional stability at high temperatures. Utilizing such characteristics, it can be used for liquid crystal displays. It is particularly useful for vehicle applications, various industrial instruments, and display of household electric appliances.

[0015]

EXAMPLES Next, the polarizing film of the present invention will be described in more detail by way of examples. The degree of polarization referred to in the present invention is expressed by the following equation.

[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2
× 100 (%)

Here, H ₁₁ is the transmittance (%) measured by using a spectrophotometer in a state where the two polarizing film samples are superposed on each other so that the orientation directions of the polarizing films are the same. , H ₁ is the transmittance (%) measured in a state where the two samples are superposed so that the orientation directions of the polarizing films are orthogonal to each other.

Example 1 Polyvinyl alcohol having an average degree of polymerization of 1700 and an average degree of saponification of 99.5 mol% was dissolved in water to obtain an aqueous solution having a concentration of 5.0% by weight. The solution was cast on a polyethylene terephthalate film and dried to obtain a film having a film thickness of 60 μm. This film was cut to a width of 10 cm and mounted on a chuck. Iodine 0.2 g / l, potassium iodide 50
Uniaxially stretched 1.5 times in an aqueous solution of g / l at 30 ° C., then boric acid 60 g / l, potassium iodide 30 g / l
While being dipped in an aqueous solution having the composition of, the composition was uniaxially stretched at a temperature of 40 to 60 ° C. to a draw ratio of 2.7 times (final draw ratio of 4.05 times). Finally, it was dried at room temperature for 24 hours to obtain the polarizing film of the present invention. In order to measure the polarization performance of the polarizing film, a triacetyl cellulose film having a thickness of 80 μ was attached to both sides of the film via an acrylic adhesive.
A polarizing plate was obtained by drying at 0 ° C.

The polarization degree of this polarizing plate was 99.8%, and the single transmittance was 41.5%. Furthermore, the polarizing plate was set to 70 ° C. 9
When the same measurement was carried out after leaving it for 20 days under the condition of 0% RH, the polarization degree was 99.5%, and the single transmittance was 4
At 1.8%, the change in polarization degree was -0.3%, and the change in single-element transmittance was 0.3%. In addition, the polarizing film (MD × T
D = 180mm × 25mm) at 105 ℃ (dry) 2
When the dimensional change rate in the MD direction was measured by leaving it for a period of time-
It was 1.1%.

Examples 2 to 5 and Comparative Examples 1 to 3 A polarizing film was produced according to Example 1 by changing the stretching conditions before the boron compound treatment and the stretching conditions during the boron compound treatment as shown in Table 1. It evaluated similarly. However,
In Example 3, an a-fold stretching treatment was performed before the dyeing treatment step, and in Example 4, an a-fold stretching treatment was performed after the dyeing treatment step. In Examples 4 and 5, polyvinyl alcohol having an average degree of polymerization of 3800 was used. The evaluation results are shown in Table 2.

[0021]

[Table 1] Stretch ratio a Stretch ratio b Final draw ratio ab (a-1) / (ab-1) value Example 1 1.5 2.7 4.05 0.16 〃 2 2.0 2.0 4.00 0.33 〃 3 3.8 1.05 3.99 0.94 〃 4 2.5 1.6 1.6 4.00 0.50 〃 5 2.2 1.6 3.52 0.47 Comparative Example 1 1.2 3.3 3.96 0.07 〃 2 1.4 4.3 4.3 02 0.08 〃 3 1.1 1.1 3.0 3.30 0.04

[0022]

[Table 2] Polarization performance * Dimensional change rate Polarization degree change (%) Transmittance change (%) (%) Example 1 -0.3 0.3 -1.1 〃 2 -0.2 0.3 -0.7 〃 3 -0.2 0.3 -0.6 〃 4 -0.1 0.2 -0.8 〃 5 -0.1 0.2 -0.6 Comparative Example 1 -2.0 4.0-2.1 〃 2 -2.0 4.0 -2.4 〃 3 -1.7 3.9 1.9 * Measured value after wet heat treatment (%)-Measured value before treatment ( %) Represents the difference (%).

[0023]

Since the polarizing film of the present invention is manufactured by a special stretching method, it has excellent polarization performance and dimensional stability at high temperatures. It is particularly useful for vehicle applications, various industrial instruments, and display of household electric appliances.

Claims (1)

[Claims] 1. A polyvinyl alcohol resin film is formed into a film, which is dyed with an iodine dye or a dichroic dye and then treated with a boron compound to produce a polarizing film with a final draw ratio ab of the following formula (I). A process for producing a polarizing film, which comprises uniaxially stretching a-times in a dyeing process or a process before that, and further uniaxially-bending in a boron compound treatment process so as to be satisfied. 0.1 <(a-1) / (ab-1) ... (I) (however, a> 1, b> 1)