JPH10170721A - Production of polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for polarizing film capable of improving durability of the polarizing film by subjecting a polarizing film base body to fixing treatment in a boric acid potassium iodide soln. having a specified liquid compsn. ratio of boric acid concn./potassium iodide concn. SOLUTION: A transparent polyvinylalcohol(PVA) resin film F having 20 to 100μm thickness as a polarizing film substrate is released from a releasing coil 22 to successively travel through a swelling tank 10, dyeing tank 12, stretching tank 14, fixing tank 16, washing tank 18 and drying furnace 20 and wound on a winding coil 24. In the fixing tank 16, polyiodine in the dyed and stretched PVA resin film F is first fixed. The liquid compsn. of the fixing tank 16 is controlled to 10 to 30 ratio of the boric acid concn./potassium iodide (KI) concn. In this case, the KI concn. is controlled to 0.1 to 0.4wt.% to 3wt.% of the boric acid concn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polarizing film applied to a liquid crystal display or the like.

[0002]

2. Description of the Related Art Conventionally, a polarizing film is provided on a liquid crystal panel surface of a liquid crystal display or the like so that the panel surface is easy to see. As shown in FIG. 4, the polarizing film has a transparent polyvinyl alcohol (PV).
A) A protective film layer (hereinafter, referred to as a “TAC layer”) made of a transparent triacetyl cellulose (TAC) resin material on both sides of a polarizing function film (hereinafter, referred to as a “polarizer”) 30 made of a resin material. A) 32a,
An acryl-based or silicon-based hard coat layer 3 is further provided on the TAC layer 32a on the front side.
4 are provided.

[0003] A transparent antireflection film 36 of a metal oxide or a fluorine compound is formed on the hard coat layer 34 as necessary, and furthermore, protection for protecting the outermost surface during transportation and handling (protection). The film 38 is stuck. Also, a release film 42 made of a polyethylene terephthalate (PET) resin material or the like as a base material is adhered to the TAC layer 32b on the back side via an adhesive 40 made of an acrylic material.

[0006] In using this polarizing film F _a on the liquid crystal display or the like, as also shown in FIG. 4, peeled release film 442 and the protective film 38, liquid crystal 44 of the pair of glass substrates 46a, 46b of the It is stuck on the surface of the liquid crystal panel 48 interposed therebetween. Although this polarizing film F _b on the back surface side of the liquid crystal panel 48 is stuck, the anti-reflection in the polarizing film F _b of the back-side film 36 and the hard coat layer 34 is not provided.

As _a method of manufacturing the polarizing films F _a and F _b , a swelling method of impregnating and swelling the PVA resin film with water is performed as a base treatment of the polyvinyl alcohol (PVA) resin film as a base material of the polarizer 30. Process,
Each of a step of dyeing the swollen resin film with an iodine solution, a step of stretching the dyed resin film, a step of immobilizing the iodine dye on the surface of the resin film, a step of washing the resin film with water, and a drying step What is processed by a process is generally performed.

In each of these steps, the immobilization step of immobilizing an iodine dye on the surface of the polarizing film substrate after the swelling step, the dyeing step, and the stretching step is performed by dyeing the PVA resin film with the iodine dyeing step. The durability of the polarizing film is improved by immobilizing the iodine dye attached thereto, and the immobilizing step ensures that optical characteristics such as polarization performance are permanently maintained on the polarizing film substrate. This is an indispensable step as above.

[0007] The liquid composition in the immobilization step usually includes boric acid (H ₃ BO ₃ ) and potassium iodide (K
A liquid mixture with I) is used, and the composition of the liquid is generally a condition of a boric acid concentration of 3% by weight and a KI concentration of 0.5% by weight. The liquid temperature is about 35 ° C and PVA
The immersion time of the resin film is about 40 seconds.

In this liquid composition, boric acid is drawn P
The VA resin film functions to crosslink and suppress swelling, and potassium iodide (KI) functions to retain a polyiodine complex of an iodine dye dyed on the PVA resin film. Therefore, in this immobilization step, the polyiodine complex as an iodine dye is fixed to the film while suppressing swelling by crosslinking the PVA resin film.

[0009]

However, for a polarizing film which has been subjected to a fixing treatment under such conditions, it is required that the optical characteristics such as the polarizing performance be maintained well over a long period of time. Therefore, various durability tests are performed on the polarizing film.

As a durability test, for example, the above-mentioned triacetyl cellulose (TA) is placed on the upper and lower surfaces of a polarizing film.
C) Attach the film and apply it at 80 ° C x 90% RH.
For 24 hours. Then, optical properties such as the degree of polarization and single transmittance are measured for the sample taken out, and it is assumed that these optical property values must be above a certain quality level.

When the durability (wet heat) test was performed,
Deterioration in optical characteristics such as polarization performance was observed in the polarizing film fixed under the conventional fixing treatment conditions as described above. This is because the polarizing film is originally susceptible to moisture, so that the moisture
This is probably because the polyiodine complex in the A resin film collapsed or fell off.

The problem to be solved by the present invention is to improve the durability as a polarizing film by controlling the liquid composition ratio between the concentration of boric acid and the concentration of potassium iodide (KI) in the fixing treatment of the polarizing film substrate. An object of the present invention is to provide a method for manufacturing a polarizing film that can be improved. This aims at achieving permanent stability of optical characteristics such as polarization performance as a polarizing film.

[0013]

Means for Solving the Problems In order to solve this problem, a method for producing a polarizing film according to the present invention comprises a swelling step of swelling a polarizing film base, and a step of dyeing the polarizing film base after the swelling step. Stretching the polarizing film substrate after the dyeing step; fixing the dyeing agent to the polarizing film substrate after the stretching step; and washing the polarizing film substrate after the fixing step with water. The process of
Drying the polarizing film substrate after the water washing step, wherein the liquid composition ratio of boric acid concentration / potassium iodide concentration is 10 to 10 in the fixing step.
The gist is that the immobilization treatment is performed using an aqueous solution of boric acid and potassium iodide in the range of 30.

In the fixing step, the polarizing film substrate having undergone the swelling step, the dyeing step, and the stretching step is fixed with an aqueous boric acid-potassium iodide solution having a controlled concentration of boric acid / potassium iodide. The swelling of the polarizing film substrate is suppressed by this, and the polyiodine complex as the iodine dye is held and fixed by the polarizing film substrate. Therefore, the orientation of the polarizing film substrate is maintained,
The durability as a polarizing film is improved, and optical characteristics such as polarizing performance are maintained.

In this case, the concentration of boric acid in the boric acid / potassium iodide aqueous solution in the fixing step is 3%.
-5% by weight, and the concentration of potassium iodide is preferably 0.1-0.4% by weight. When the boric acid concentration is 3% by weight or less, the effect of suppressing the swelling of the polarizing film substrate is weakened, the orientation of the film substrate is lost, and the durability is impaired. As a result, the optical characteristics of the polarizing film deteriorate. Further, the boric acid concentration is hardly soluble at a concentration of 5% by weight or more. Therefore, the boric acid concentration is set to 3 to 5% by weight.

On the other hand, the concentration of potassium iodide (KI) is 0.1 to 0.4% by weight, and the KI concentration is 0.1% by weight.
When the content is less than 1% by weight, as a result, the concentration of boric acid becomes too high and the polyiodine complex cannot be sufficiently held.
Optical properties after the durability test are impaired. If the concentration of potassium iodide (KI) exceeds 0.4% by weight, the concentration of boric acid becomes too low, and the polarizing film substrate becomes hygroscopic. The optical characteristics of are deteriorated.

In the present invention, an aqueous solution of potassium iodide (KI) may be used as a washing solution in the washing step following the fixing step. In the immobilization step, the concentration of potassium iodide is suppressed by controlling the concentration of boric acid / potassium iodide. Therefore, the holding power of polyiodine (staining agent) to be dyed on the polarizing film substrate is weak, and there is a concern that the iodine is washed away by water. Holds a complex of polyiodine (dyeing agent) and maintains optical characteristics such as polarization performance. Finally, a polyvinyl alcohol (PVA) resin film is generally used as a polarizing film substrate, and the thickness of the film is about 20 to 35 μm after a drying step.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail. First, a manufacturing line and a process chart for realizing the present invention will be described with reference to FIG. As shown, the production line includes a swelling tank 10, a dyeing tank 12, a stretching tank 14, a fixing tank 16, a washing tank 18, and a drying furnace 20.

The polarizing film substrate of the present invention, 20 to 1
A transparent polyvinyl alcohol (PVA) resin film F having a thickness of 00 μm is unwound from an unwinding coil 22 and sequentially passes through a swelling tank 10, a dyeing tank 12, a stretching tank 14, a fixing tank 16, a washing tank 18, and a drying furnace 20. After passing through the winding coil 24.

In the swelling tank 10, the PVA resin film F is immersed in water and swelled. Film F usually has a liquid temperature of 3
It is wet and swells by being slightly immersed in hot water at 5 ° C. for about 5 minutes. Thereby, the iodine dye is easily dyed on the PVA resin film F in the next iodine dyeing step.

In the next dyeing tank 12, the swollen PVA resin film F is dyed with an iodine solution. Usually, the dyeing tank 12 has a concentration of 3% by weight of potassium iodide (K
I) 1% by weight of boric acid and 0.023% by weight of iodine (I ₂ ) are blended. This dyeing tank 12
Is 35 ° C. and the dipping time of the film is about 80 ° C.
Seconds.

In the next stretching tank 14, iodine-stained P
The VA resin film F is stretched in the production line direction. The tension is applied to the film by the speed difference between the nip rollers 15a and 15b on the input side of the stretching tank 14 and the nip rollers 15c and 15d on the output side. The liquid composition of the stretching tank 14 is usually set to a boric acid concentration of 3% by weight and a potassium iodide (KI) concentration of 3% by weight. And the liquid temperature is 50 ℃
The dipping time of the film is about 50 seconds, and the stretching ratio in the stretching step is 1.3 times.

In the next fixing tank 16, the dyed and stretched PV
The polyiodine in the A resin film F is fixed. In the present invention, the liquid composition of the fixed tank 16 is controlled so that the ratio of the concentration of boric acid / the concentration of potassium iodide (KI) falls within the range of 10 to 30. In practice, the KI concentration is set to 0.1 to 0.4% by weight while the boric acid concentration is approximately 3% by weight. The liquid temperature is 35 ° C. and the dipping time of the film is about 40 seconds.

In the next washing tank 18, actually about 20
C. shower water is sprayed on the film surface, and chemicals such as boric acid attached to the film surface are washed away. Usually, ordinary water is used in the water washing tank 18. In this embodiment, an aqueous potassium iodide (KI) solution having a potassium iodide (KI) concentration of 3% by weight is particularly used in this embodiment.

In the drying oven 20 in the final step, hot air (about 90 μm) is applied to the film surface from which chemicals such as boric acid have been washed away.
° C) and the film is dried. The blowing time of the hot air is about 70 seconds. After the drying step, the PVA resin film has a thickness of about 20 to 3
5 μm.

Next, various tests were performed, and the test results will be described. First, FIGS. 2 and 3 show graphs obtained by measuring the light transmittance of a polarizing film by measuring a spectral spectrum by a polarizing prism method. FIG. 2 shows a case of a polarizing film element alone, and FIG. 3 shows a result after a TAC film is attached to the polarizing film element and subjected to a wet heat treatment as a durability test.

As the liquid composition of the fixing tank 16, the concentration of boric acid is fixed at 3% by weight, and the concentration of potassium iodide (KI) is (1) 0% (no addition), (2) 0.1% by weight. ,
(3) 0.5% by weight and (4) 1.5% by weight of an aqueous solution changed in four stages are used. 3 for the measurement wavelength range
In the visible light range of 80 to 780 nm, the horizontal axis represents the wavelength, and the vertical axis represents the orthogonal transmittance (%) of the polarizing film.

The measuring instrument was "MCPD-100" manufactured by Otsuka Electronics Co., Ltd.
The orthogonal transmittance (%) of the polarizing film element alone is calculated by the following equation 1. Further, a TAC film is bonded to the polarizing film element and the polarizing film element is subjected to a wet heat treatment. The single transmittance is calculated by Equation 2.

[0029]

(Equation 1)

[0030]

(Equation 2)

As a method of attaching a TAC film to a polarizing film element and performing a durability test by wet heat treatment, triacetyl cellulose (TAC) is used as a protective film on the upper and lower surfaces of a dyed and stretched polyvinyl alcohol (PVA) polarizer. 80 ° C ×
The sample is kept in an atmosphere of 90% RH for 24 hours, and optical measurements such as the degree of polarization and single transmittance are performed on the sample taken out.

As a result, in the case of the polarizing film element alone shown in FIG. 2, the orthogonal transmittance was not applied to any of the test samples up to the potassium iodide (KI) concentration of 0% to 1.5% by weight in the fixing tank 16. (%) Has no significant difference. As shown in FIG. 3, when the TAC film was attached to the polarizing film element and subjected to the wet heat treatment, a clear difference was observed in the measurement of the single transmittance.

That is, for the sample in which the TAC film was bonded to the polarizing film element, the sample in which the potassium iodide (KI) in the fixing tank 16 was not added (0% by weight) and the sample in which the excess amount was 1.5% by weight were used. However, it can be seen that the unitary transmittance increases due to the wet heat treatment, and the polarization characteristics as a polarizing film deteriorate. In contrast, potassium iodide (KI)
Regarding those having a concentration of 0.1% by weight and 0.5% by weight, the increase in the single transmittance was not so much recognized even by the wet heat treatment, and it was confirmed that the polarizing characteristics as the polarizing film were maintained. .

The following Table 1 summarizes the test results for various test samples by selecting test conditions in more detail. As test conditions, the concentration of boric acid in the fixed tank 16 was fixed at 3% by weight, and the concentration of potassium iodide (KI) was (1) no addition (0% by weight), (2) 0.1% by weight,
(3) 0.2% by weight, (4) 0.3% by weight, (5) 0.5%
A total of six test conditions were employed: wt% and (6) 1.5 wt%. Then, measurement and evaluation were performed to determine how the optical properties of the polarizing film after the durability test were affected by the liquid composition ratio between the boric acid concentration and the KI concentration in the fixing tank 16.

[0035]

[Table 1]

In Table 1, "initial characteristics" means the optical characteristics of the polarizing film element alone, and shows the measurement results of the degree of polarization V and the unit transmittance Y of each test sample by the above-described polarizing prism method. I have. The polarization degree V is calculated by the following equation (3). Further, the single transmittance Y is calculated by the equation shown in Equation 2 described above.

[0037]

(Equation 3)

The “characteristics after the durability test” is as follows.
The polyvinyl alcohol (P
VA) Optical characteristics of a sample in which a TAC film is bonded to the upper and lower surfaces of a polarizer and kept in an atmosphere of 80 ° C. × 90% RH for 24 hours. Similarly, the measurement results of the polarization degree V and the single transmittance Y are shown.

From the data shown in Table 1, the sample (1)
With a boric acid concentration of 3% by weight and a KI concentration of 0% by weight (no addition), the optical characteristics after the durability test were greatly impaired in both the polarization degree V and the single transmittance Y, and were judged to be defective (marked by x). .
On the other hand, in sample (2) boric acid concentration of 3% by weight, KI concentration of 0.1% by weight, (3) 0.2% by weight, and (4) 0.3% by weight.
The optical properties after the durability test were not deteriorated in both the polarization degree V and the single transmittance Y, and were good (良好).
Mark).

Sample (5) having a further increased KI concentration (5) A sample having a boric acid concentration of 3% by weight and a KI concentration of 0.5 wt. (△ mark). Further, the sample having the highest KI concentration (6), the boric acid concentration of 3% by weight and the KI concentration of 1.
With 5% by weight, both the degree of polarization V and the single transmittance Y were poor (marked by x) in the durability test.

To summarize the results, as shown in Table 1 above, the overall evaluation of durability was indicated by a circle, a triangle, a cross, etc.
When the KI concentration of the fixed tank 16 was not added (0% by weight) and when the KI concentration was too high (1.5% by weight), the overall durability evaluation was judged to be poor (marked by x).

The test conditions (ie, boric acid concentration of 3
% By weight), the KI concentration in the fixed tank 16 is 0.1%.
It was confirmed that the content was desirably in the range of not less than 0.5% by weight and more preferably in the range of 0.1 to 0.3% by weight. Looking at this as a liquid composition ratio of boric acid concentration and KI concentration, it is most desirable that the boric acid concentration / KI concentration is in the range of 10 to 30 in order to maintain the optical characteristics of the polarizing film after the durability test. It can be said that.

Although the embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, another fixation treatment aid is added to the boric acid-potassium iodide (KI) aqueous solution used in the fixation step, and the liquid composition of another swelling tank, dyeing tank, fixing tank, etc. The present invention can be applied even to different ones. Further, the base material of the polarizing film is also polyvinyl alcohol (PV).
A) Needless to say, the present invention is also applied to improved resin films or other resin film materials.

[0044]

According to the present invention, a swelling step, an iodine dyeing step,
In producing a polarizing film by a stretching step, a fixing step, a washing step, a drying step, and the like, a liquid composition ratio of boric acid concentration and potassium iodide (KI) concentration of the polarizing film substrate in the fixing step is in the range of 10 to 30. And an aqueous solution of boric acid and potassium iodide (KI).

Thus, the polyiodine dye on the dyed and stretched polarizing film substrate is appropriately fixed, and the durability is improved, whereby the optical properties such as the polarizing performance of the polarizing film are permanently maintained. In this case, the concentration of boric acid in the boric acid-potassium iodide (KI) aqueous solution in the immobilization step is 3 to 5% by weight, and the KI concentration is 0.1 to 0.1%.
When the content is controlled to an appropriate range of 4% by weight, the immobilization treatment of polyiodine on the polarizing film substrate is stably performed.

In the present invention, if an aqueous solution of potassium iodide (KI) is used in the washing step after the immobilization treatment, the retention of the polyiodine dye complex on the polarizing film substrate is further improved, and Further good quality of optical characteristics such as performance is maintained. Since the polarizing film produced according to the present invention has good optical properties, it is extremely useful industrially to apply it to a liquid crystal display or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing line and steps for realizing the present invention.

FIG. 2 is a graph showing spectral spectrum measurement results when a polarizing film substrate is fixed under various conditions.

FIG. 3 is a graph showing spectral spectrum measurement results when a durability test was performed on a polarizing film substrate that had been subjected to immobilization treatment under various conditions and then bonded to a TAC film.

FIG. 4 is a sectional view showing an example in which the polarizing film of the present invention is applied to a liquid crystal display.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Swelling tank 12 Dyeing tank 14 Stretching tank 16 Fixed tank 18 Rinse tank 20 Drying furnace F Polarizing film base material (polyvinyl alcohol resin film)

──────────────────────────────────────────────────続 き Continuing on the front page (51) Int.Cl. ⁶ Identification symbol FI // B29K 29:00 (72) Inventor Hideki Shinohara 3600 Gezu, Kita-gaiyama, Komaki-shi, Aichi Tokai Rubber Industries Co., Ltd.

Claims (4)

[Claims] 1. A swelling step of swelling a polarizing film base, a step of dyeing the polarizing film base after the swelling step, a step of stretching the polarizing film base after the dyeing step, and a step of stretching the drawing step. A fixing step of fixing the dye to the polarizing film substrate that has passed, a step of washing the polarizing film substrate that has passed through the fixing step, and a step of drying the polarizing film substrate that has passed through the washing step, In the immobilizing step, the polarizing film substrate is subjected to boric acid having a boric acid concentration / potassium iodide concentration solution composition ratio of 10 to 30.
A method for producing a polarizing film, wherein the polarizing film is fixed by an aqueous solution of potassium iodide. 2. The method according to claim 1, wherein the concentration of boric acid in the aqueous solution of boric acid and potassium iodide is 3 to 5% by weight, and the concentration of potassium iodide is 0.1 to 0.4% by weight. The method for producing a polarizing film according to claim 1, wherein: 3. The method according to claim 1, wherein the washing step includes a potassium iodide concentration of 3%.
The method for producing a polarizing film according to claim 1, wherein a weight% aqueous solution of potassium iodide is used. 4. The method for producing a polarizing film according to claim 1, wherein the polarizing film substrate is a polyvinyl alcohol resin film having a thickness of 20 to 35 μm after a drying step.