KR101008230B1 - Polarizing film and Manufacturing method for the same - Google Patents

Abstract

The present invention relates to a polarizing film and a method of manufacturing the same, wherein the water absorption rate defined as the weight ratio of water measured by vacuum drying at 50 ° C. for a polarizing film left at 25 ° C. and 65% RH for 24 hours is 0.5 to 5.7%. It discloses a phosphor polarizing film, which can improve durability while maintaining a constant polarization efficiency and transmittance.

Description

Polarizing film and manufacturing method {Polarizing film and Manufacturing method for the same}

1 is a graph showing the durability test results for polarizing films crosslinked with different concentrations of butanetetracarboxylic acid according to Examples 1 to 4,

Figure 2 is a graph of the durability test results for polarizing film crosslinked with different concentrations of citric acid according to Examples 5 to 8.

The present invention relates to a polarizing film and a method for manufacturing the same, and more particularly, to a dichroic dye-based polarizing film and a method of manufacturing the same, which has a low water absorption and ultimately improves durability against moisture. .

1928 E.H. The polarizer film first studied by Land was extremely limited in its industrial use. However, as the modern industrial society develops into a high information age, the demand is increasing in earnest. This is a result of the increasing importance of the electronic display.

Currently commercially available polarizing film can be classified into various types according to its type and performance. Firstly, it is an iodine-based polarizing film, which is a polarizing film for high-definition LCD which has high transmittance and high polarization characteristics. Refers to a film using iodine having high dichroism to impart an absorption ability. Most of the polarizing films used in LCDs to date are iodine polarizing films. Secondly, a dye-based polarizing film, which has been studied to solve the problem of durability due to the sublimability of iodine, may be mentioned. This is a highly durable polarizing film with a small change in optical properties even under high temperature and high humidity conditions, and has been used for LCDs requiring high durability due to its high durability. In addition, in the case of the dye-based polarizing film is relatively easy to control the color can be produced a polarizing film of various colors, which is also used in the field of sunglasses and the like. Thirdly, it is a polarizing film mainly used for a high speed response liquid crystal display (STN-LCD: Super Twisted Nematic LCD) called a retardation polarizing film. This makes a wide variety of products depending on the angle applied to the retardation film having a characteristic in the polarizing film. The retardation film is a film that compensates for the phase difference generated in the liquid crystal and currently, a polycarbonate-based retardation film is mainly used. Fourth, a semi-transmissive reflective polarizing film having both transmissive and reflective characteristics may be mentioned. Semi-transparent polarizing film is involved in power consumption efficiency, which is one of the most important factors in the display of mobile devices, which has a problem of shortening the use time of the product when the power consumption is high. It is a functional film that is used as a material for the bottom plate used in semi-transmissive LCD by adding a reflective function that utilizes external light instead of a transmissive product. There are various kinds of such semipermeable films depending on the materials and property values used. And a product in which a pigment is added to an adhesive to control transmittance (ST type) and a product (TDF, 3M company) that stacks hundreds of layers of polymer thin films having different refractive indices. Fifthly, the highly reflective semi-transmissive polarizing film has been used to increase the reflectance and diffuse adhesive by using metal deposition film instead of the translucent polarizing film using the conventional pigment to reduce power consumption and make the appearance of the display more clear in recent STN-LCDs. It is a polarizing film that improved the appearance using. Sixth, the polarizing film (AG / AR) which prevented surface reflection is mentioned. There are two types of surface anti-reflection: AG (Anti-glare) processing and AR (Anti-reflection) processing. The AG process forms an irregular surface on the surface of the film, which diffusely reflects external light from the surface, and exhibits antireflection effect. The AR process uses a deposition method or a coating method to deposit thin films of different layers on the surface of the film by vapor deposition or coating. By forming, it exhibits an antireflection effect. In general, the reflectivity of the polarizing film not subjected to the anti-reflection process is about 4%, the AG film has a reflectance of about 2%, AR film has a value of less than 1% reflectance. Finally, there is a reflective polarizing film, which is a product made by laminating a metal deposition reflector film on a general iodine polarizing film, which is used in a reflective LCD.

In general, a polarizing film uses a film having polarization characteristics treated with iodine or dichroic dye in PVA as a polarizer, and forms a protective layer to prevent deformation of the film due to high sublimation and low durability of iodine.

In the case of a polarizing film treated with a dichroic dye, it is slightly improved in terms of durability compared to iodine, but there is no satisfactory durability improvement. In particular, in recent years, the environment in which display devices using the polarizing film are placed has high humidity such as in a car interior. Since it can be placed under the environment, there is a need for further improvement in durability.

As an effort to improve durability, conventionally, after dyeing is completed, the step of fixing the dye in an aqueous PVA crosslinking agent such as boric acid has been further performed.

However, when crosslinked in an aqueous PVA crosslinking agent solution such as boric acid, the crosslinking force is weak, and when exposed to moisture, the fixation state of the dye becomes worse, and as a result, durability of the polarizing film is deteriorated.

Thus, the present invention while seeking to improve the durability while maintaining the polarization efficiency and transmittance at a certain level, by lowering the water absorption of the polarizing film, it is found that the durability is improved while satisfying a certain polarization efficiency and transmittance The present invention has been completed.

Therefore, an object of the present invention is to provide a polarizing film with improved durability.

It is also an object of the present invention to provide a polarizing film having a polarization efficiency and transmittance equivalent to those of the conventional polarizing film.

The polarizing film of the present invention for achieving the above object is a polarizing film obtained by dyeing the dichroic dye before, during or after uniaxial stretching of the polyvinyl alcohol-based film, and then fixing the dye in an aqueous solution of the crosslinking agent, 25 The water absorption rate, which is defined as the weight ratio of water measured by the vacuum drying method at 50 ° C. with respect to the polarizing film left at 24 ° C. and 65% RH for 24 hours, is characterized in that the water absorption is 0.5 to 5.7%.

The polarizing film of the present invention is selected from polycarboxylic acids such as butanetetracarboxylic acid (BTCA) or citric acid, cyclic urea compounds such as dimethylol dihydroxyethylene urea (DMDHEU), and aldehyde compounds such as formaldehyde as a crosslinking agent. It is characterized by the thing obtained using one or more types.

The density | concentration of preferable crosslinking agent aqueous solution has the characteristic also that it is 1-20 weight%.

The fixing of the preferred dyes is characterized in that it is carried out at 100 ° C to 200 ° C.

Hereinafter, the present invention will be described in detail.

The present invention relates to a polarizing film, specifically, the water absorption is 0.5 to 5.7%, wherein if the water absorption is less than 0.5% high crosslinking density, the mechanical properties of the polarizing film is excessively lowered and the water absorption is higher than 5.7% The durability improvement of the polarizing film is reduced.

At this time, the water absorption is defined as the weight ratio of water measured by vacuum drying at 50 ℃ for a polarizing film left at 25 ℃, 65% RH for 24 hours.

When the water absorption rate is satisfied, the polarizing film maintains the polarization efficiency of 98.8 or more and the transmittance of 24.2 or more, and the durability is usually improved by 10.3% or more based on the polarization efficiency.

As a method of satisfying the water absorption rate as described above, various methods may be possible. In the present invention, a method of fixing a dye by introducing a crosslinking agent other than boric acid or borax, commonly known as a PVA crosslinking agent, is introduced. That is, complete crosslinking was induced.

In general, the polarizing film is dyed before diaxial stretching of the polyvinyl alcohol-based film, during or after the dyeing, and then fixed in a crosslinking agent aqueous solution, the crosslinking agent serves to fix the dye do. However, boric acid, borax, etc., which are usually added as a PVA crosslinking agent, have a weak crosslinking problem. Thus, in the present invention, a more thorough crosslinking can be used as a crosslinking agent, butanetetracarboxylic acid, polycarboxylic acid such as citric acid, cyclic urea compounds such as dimethylol dihydroxyethylene urea, aldehyde compounds such as formaldehyde and the like.

It is preferable that the concentration of the crosslinking agent solution is 1 to 20% by weight. If the concentration of the crosslinking agent solution is less than 1% by weight, the crosslinking effect is not observed. Can be.

The dye fixation by the crosslinking agent is preferably carried out at a temperature of 100 to 200 ℃, if the dye fixing temperature by the crosslinking agent is lower than 100 ℃ can not see the cross-linking effect, if higher than 200 ℃ to damage the PVA film under unreasonable crosslinking temperature conditions There may be a problem.

The immersion time in the crosslinking agent aqueous solution is not particularly limited, but is usually 1 second to 15 minutes, preferably 5 seconds to 10 minutes. In addition to the aqueous solvent, a small amount of an organic solvent compatible with water may be contained.

After the dye is fixed under the crosslinking agent aqueous solution, washing and drying may be performed according to a conventional method to obtain a polarizing film.

On the other hand, in the present invention, the type of PVA film, the stretching method, the dyeing method, and the like are not particularly limited, but as one example, the polyvinyl alcohol-based polymer in the polyvinyl alcohol-based film used in dry uniaxial stretching is an acetic acid. The thing which saponified after superposing | polymerizing vinyl, or copolymerizing the copolymerizable monomers, such as a small amount of unsaturated carboxylic acid, unsaturated sulfonic acid, cationic monomer, with vinyl acetate, etc. are mentioned. Although the polymerization degree of a polyvinyl alcohol polymer is not specifically limited, Any thing can be used, but considering the solubility to water of a film, only the average degree of polymerization of 500-1 is preferable, More preferably, it is 1000-6000. The degree of saponification is preferably 75 mol% or more, and more preferably 95 to 100 mol%. The thickness of a film is 5-150 micrometers, Preferably it is 10-100 micrometers.

The dry uniaxial stretching method is not particularly limited, but for example, a method of rolling with a pressure roll by applying a rear tension, a method of contacting and stretching a heating roll while applying a rear tension to a film, between rolls installed in or outside a heating oven And stretching using a heating roll such as passing through a heating roll and compressing stretching, and stretching using a tenter stretching machine. The draw ratio is preferably 2 times or more, more preferably 2 to 6 times, particularly preferably 2 to 5 times.

As for the heating roll or oven temperature at the time of extending | stretching, 50-200 degreeC is preferable, Especially preferably, it is 60-150 degreeC.

The composition of the dye-containing aqueous solution for dyeing is usually 0.001 to 1 part by weight of the dichroic dye with respect to 100 parts by weight of water. The temperature of aqueous solution is the range of 10-80 degreeC normally. The immersion time is not particularly limited, but is usually 1 second to 10 minutes, preferably 5 seconds to 5 minutes. In addition to the aqueous solvent, a small amount of an organic solvent compatible with water may be contained.

Uniaxial stretching is preferably performed prior to dyeing the dye, but may be thereafter.

Although the thickness of the polarizing film of this invention is not specifically limited, 1-80 micrometers is common and 2-40 micrometers is especially preferable.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the present invention is not limited to the Examples.

Experimental Example 1

Butanetetracarboxylic acid (BTCA) aqueous solution (BTCA aqueous solution concentration) containing 0.3 mol ratio of sodium hypophosphite (NaH ₂ PO ₂ ) catalyst with respect to butanetetracarboxylic acid at 20 ° C by varying the concentration of the uncolored PVA film in the butanetetracarboxylic acid solution. 1 to 7% by weight) immersed for 1 minute and then pre-dried for 5 minutes at 90 ℃ and fixed to the crosslinking agent at 160 ℃ for 3 minutes was measured water absorption, swelling ratio and maximum draw ratio as shown in Table 1 below. At this time, the water absorption rate is the weight ratio of water measured by vacuum drying method at 50 ^° C. for the polarizing film left at 25 ° C., 65% RH for 24 hours.

TABLE 1

Example 1

A polyvinyl alcohol film (manufactured by Nihon Kosei Co., Ltd.) having an average degree of polymerization of 1700 and a film thickness of about 25 μm was immersed in a dichroic dye bath (Solophenyl Black FR, CiBA specialty chemicals, 0.15 wt%) at 50 ° C. for 2 minutes. Then, an aqueous solution of butanetetracarboxylic acid (BTCA) containing a 0.3 molar ratio of sodium hypophosphite (NaH ₂ PO ₂ ) catalyst with respect to butanetetracarboxylic acid at 20 ° C was washed with water at 40 ° C. in boric acid solution and washed with water. After immersing in 1% by weight) for 5 minutes and pre-dried at 90 ℃ 5 minutes and fixed dye for 3 minutes at 160 ℃ to obtain a polarizing film.

The water absorption rate of the obtained film was measured, and the results are shown in Table 3 below.

Examples 2-4

A polarizing film was prepared in the same manner as in Example 1, except that the concentration of the butanetetracarboxylic acid aqueous solution, which was added as shown in Table 2, was changed.

The water absorption rate of the obtained film was measured, and the results are shown in Table 3 below.

Examples 5-8

Polarizing films were prepared in the same manner as in Examples 1 to 4, except that citric acid was used as the crosslinking agent, and polarizing films were prepared under the same concentration of the crosslinking agent as in Examples 1 to 4, respectively.

Comparative Example 1

A polarizing film was prepared in the same manner as in Example 1, except that the dye fixing process was performed only until the process of stretching and washing with a boric acid solution.

The water absorption rate of the obtained film was measured, and the results are shown in Table 3 below.

TABLE 2

[Table 3]

Experimental Example 2

Transmittance, polarization efficiency and durability of each polarizing film obtained from Examples 1 to 8 and Comparative Example 1 were measured by the following method.

(1) Permeability

The transmittance of one film was measured using a UV-visible spectrophotometer (Agilent 845).

(2) polarization efficiency (PE)

Based on Equation 1, the polarization efficiency was calculated at the maximum absorption wavelength.

[Equation 1]

In the above formula, PE represents the polarization efficiency, T _∥ indicates the transmittance when two sheets of polarizing film in parallel, T _를 indicates the transmittance when two sheets of polarizing film are placed vertically.

(3) durability

The polarizing film prepared in the desiccator maintaining 55 ℃, 95% relative humidity was measured for 120 hours at intervals of 24 hours under high temperature and high humidity conditions, and the optical properties of the polarizing film by the crosslinking agent were compared.

The transmittance and polarization efficiency measurement results are shown in Table 4 below, and the durability test results are shown in FIGS. 1, 2, and 4.

1 is a durability test results according to Examples 1 to 4, Figure 2 is a durability test results according to Examples 5 to 8.

[Table 4]

From the results of Table 4, FIG. 1 and FIG. 2, in the case of the polarizing film satisfying the water absorption of 2.5 to 5.7% as in Examples 1 to 8, the transmittance is about 24.7% or more and the polarization efficiency is about 98.7% or more. As boric acid is used as a crosslinking agent as compared to the case where boric acid is used as a crosslinking agent, the durability is improved because the change in transmittance and polarization efficiency is small compared to the case where boric acid is used as a crosslinking agent.

As described in detail above, the polarizing film that satisfies the water absorption rate in the range of 0.5 to 5.7% according to the present invention is completely cross-linked to satisfy a certain level of polarization efficiency and transmittance while satisfying durability, in particular, durability against moisture and high humidity environment. It is useful as an optical film of a display apparatus which is exposed to.

Claims (4)

In a polarizing film obtained by dyeing a dichroic dye before, during or after uniaxial stretching of a polyvinyl alcohol-based film, and then fixing the dye in an aqueous solution of a crosslinking agent, The water absorption is defined as the weight ratio of water measured by vacuum drying at 50 ℃ for a polarizing film left at 25 ℃, 65% RH for 24 hours, 0.5 to 5.7%, And the crosslinking agent is at least one selected from butanetetracarboxylic acid, citric acid, dimethyl dihydroxyethylene urea, and formaldehyde. delete The polarizing film of claim 1, wherein the aqueous crosslinking agent is in a concentration of 1 to 20% by weight. The polarizing film of claim 1 or 3, wherein the dye is fixed at 100 to 200 ° C.

Images