JPS59133509A - Polarizing film and its manufacture - Google Patents

Abstract

PURPOSE:To improve the polarizing characteristics, dimensional stability and tear resistance of a polarizing film by specifying the difference between the coefft. of orientation of polymer segments in all the amorphous regions of the film and the coefft. of orientation of dye molecules. CONSTITUTION:The difference (DELTAF) between the coefft. of orientation of polymer segments in all the amorphous regions of a polarizing film and the coefft. (>=0.75) of orientation of dye molecules is adjusted to >=0.15. In the film, highly oriented polymer segments forming amorphous regions having adsorbed dye molecules coexist with slightly oriented polymer segments forming amorphous regions in a well-balanced state. The film has >=100% elongation in the stretching direction, superior polarizing characteristics, dimensional stability and tear resistance. The film is obtd. by allowing a dichroic dye to be adsorbed on a hydrophilic polymer film at <=30 deg.C and by orienting the film by stretching in a water bath at <=20 deg.C, especially 0-15 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel polarizing film with excellent polarizing properties, dimensional stability and tear resistance, and a method for producing the film.

In recent years, liquid crystal display systems that use a polarizing plate with a surface protection LA formed on at least one surface of a polarizing film have been widely used in applications ranging from small items such as watches and calculators to large items such as automobile meters, measuring instruments, and terminal display devices. The scope of its use is being expanded to include articles.

In line with this trend, polarizing films constituting a part of polarizing plates are required to have increasingly high polarizing properties and durability.

So far, polyene-based polarizing films and iodine and/or dichroic dye-based polarizing films have been known.

Polyene-based polyenes are formed by partially dehydrochlorinating a polyvinyl chloride film or partially dehydrating a polyvinyl alcohol film, and then stretching the film in one direction to form a polyethylene. However, the drawback is that the durability of polyene is insufficient.

In addition, iodine-based products are made by adsorbing and aligning iodine onto a hydrophilic polymer film, but this combined with the fact that iodine is sublimable has the disadvantage of fading when stored under humid heat. Furthermore, since the degree of polymerization of the iodine complex cannot be adjusted, there is a disadvantage that a polarizing film having an arbitrary hue cannot be obtained.

On the other hand, dichroic dyes can be produced using the same methods as iodine dyes, have the advantage of having a desired hue depending on the dye selection, and are more durable than iodine dyes. It has the disadvantage that its properties are inferior to those of iodine-based materials.

In general, iodine and/or dichroic dye-based polarizing films are
A polarizing element made of iodine and/or dichroic dye is adsorbed to the amorphous region of a hydrophilic polymer film, but in order to achieve the same polarizing properties as above, the polymer segments in the amorphous region must be highly concentrated. It is necessary to orient yourself. but,
The more highly oriented the polymer segments in the amorphous region are, the lower the dimensional stability of the film under heating or humidification will be, and the easier it will be to tear in parallel to the stretching direction of the film. Cracks occur during the process of bonding plastic films and the like, resulting in a significant decrease in product yield.

In view of the state of the prior art, the present inventors have determined that the polarization characteristics,
As a result of extensive research into polarizing films that satisfy both dimensional stability and tear resistance, and the manufacturing method for these films, we have determined the orientation coefficient of polymer segment i in the entire amorphous region and the orientation coefficient of dye molecules. The inventors have discovered that a polarizing film that satisfies the above requirements can be obtained by providing a predetermined difference (hereinafter referred to as orientation coefficient difference, ΔF) between

That is, the present invention provides a polarizing film in which a dichroic dye is adsorbed and oriented on a hydrophilic polymer film, the polarizing film having an orientation coefficient (0.75 or more) between molecular segments of the entire amorphous region of the polarizing film and dye molecules. ) is at least 0.15.

According to the polarizing film of the present invention, the mu F is at least 0.
15. Preferably, it is in the range of 0.2 to 0.04, so that the highly oriented polymer segment consisting of the amorphous region adsorbing P outside the dye and the low oriented polymer segment consisting of the amorphous region coexist in a well-balanced manner, and the stretching direction (TD) elongation of at least 100%, which combines good polarizing properties, dimensional stability and tear resistance.

A polarizing film having such a difference in orientation coefficient can be obtained by adsorbing a dichroic dye onto a hydrophilic polymer film and stretching and aligning it in a low-temperature water bath. A low temperature, preferably 0 to 15° C., is preferred because the orientation coefficient of the dye can be as high as 0.75 or more and ΔF can be increased at a low draw ratio of 2.5 to 4 times.

According to this production method, when a hydrophilic polymer film is stretched in low-temperature water, the crystalline regions that behave as crosslinking points remain unbroken, so the swelling period of the film is small, and the polymer segments Such stress becomes large, and as a result, the polymer segments in the crystalline and amorphous regions are effectively oriented, and the polymer segments in the amorphous region with highly anisotropic dichroic dye molecules are adsorbed. Apparently, due to the lengthening of the motion unit of the middle segment, the orientation coefficient of the polymer segment to which dye molecules are adsorbed is It exhibits a unique phenomenon in which the orientation coefficient is nearly twice as large as the total orientation coefficient of the amorphous region, and as a result, the highly oriented polymer segment consisting of the amorphous region that has adsorbed dye molecules in the polarizing film and the amorphous A polarizing film having good polarizing properties, dimensional stability, and tear resistance can be obtained by coexisting with low-oriented polymer segments consisting of regions.

In addition to the above-mentioned stretching method in a water bath, methods for producing the polarizing film of the present invention include stretching in an aqueous solution of inorganic salts such as sodium chloride and sodium sulfate, methanol,
There are methods of stretching in an aqueous solution of an alcohol such as ethanol and/or a non-aqueous solvent such as acetone. In particular, in these systems, unlike in water, it is possible to stretch at a temperature of 0° C. or lower, and a polarizing film that achieves the object of the present invention can be obtained from a low stretching ratio of about 1.8 times.

The orientation coefficient used in the claims and main text of the present invention is a value measured as follows. The orientation coefficient (FD) of dye molecules is the characteristic absorption peak wavelength of the dye at the same stretching rate: 0 for undyed film, 11 for dyed film when the polarization plane of the incident light and the stretching axis are perpendicular and parallel, and FD. Measure and calculate from the following formula.

D = ROg IO/1. / ll0g Io/eng.

-1 FD-- D+2 The orientation coefficient a (FA) of the polymer segment in the entire amorphous region is
X-ray diffraction intensity of (101/10〒) plane: Birefringence and crystallinity were measured and calculated from the following formula.

A rz−Δn'OF□ M(3+Δn0h FA(1
-Xa) (where 4n is the birefringence of the sample film, Δno
c and munoA are the 1 ml birefringence of the crystalline and amorphous regions, Fo and FA are the orientation coefficients of the crystalline and amorphous regions, and Xc
is the crystallinity. ) Hydrophilic polymer films used in the practice of the present invention include (c) polyvinyl alcohol films, partially formalized polyvinyl alcohol films, ethylene-
Vinyl acetate copolymer-based saponified film, cellulose-based film fx and Iff are obtained.

Therefore, a polyvinyl alcohol film having an average degree of polymerization of 1100 to 2600, preferably 300 to 2200, is desirable because it has excellent orientation of polymer segments and film formation is a threat to WR. The residual vinyl acetate content t of the saponified ethylene-vinyl acetate copolymer film is 10 mol φ or less, preferably 5
It is preferable to use a material having a molar value of φ or larger, such as a physical part V during water cooling.

-Also, the dichroic dye is not particularly limited as long as it has high dichroism and adsorbs parallel to the molecular chain of the polymer segment of the hydrophilic polymer film, but for example, Co1
or Index (hereinafter referred to as C8■) Direct
Black 17.19.22.32.38.51.
56.62.71.74.75, 77 or 94, a,
I, Ac1d Orange 12, O, X, Ac1
dBlue 120, C0■, Ba5ic Blue
i or 9,0. ■.

Ba5ic Red 5, (, ■, Ba5ic
Violet 5, C9 engineering.

Direct Yellow 4.11 or 28, C1
■, DirectRed 20, 28 or 75.
0. Engineering 1 Mordant Red 3, C0■, Br
1lliant Blu3, Oongo Red, etc.

Such dichroic dyes are dissolved in water or the like together with additives such as dyeing aids, if necessary.

The dye concentration in the water bath is preferably adjusted to a range of 0.05 to 5% by weight.The temperature of the water bath is preferably adjusted to 30°C or less, preferably 0 to 25°C. This is preferable because it suppresses the swelling of the hydrophilic polymer film to be immersed and causes the dye molecules to be appropriately adsorbed to a part of the amorphous region. The hydrophilic polymer film is immersed for about 0.1 to 15 minutes, and the dye molecules are adsorbed onto the film.

The film on which dye molecules are adsorbed is kept at a temperature of 20°C or lower, with a good temperature of tL.
< is 0~15'0. Practically, after immersing in a water bath maintained at 0 to 5°C for preferably about 0.2 to 20 minutes to equalize the degree of swelling, the swelling is 1.8 times or more, preferably 2 times more, in the water bath.
．． Stretched 5 to 4 times for orientation These stretching treatments can be carried out in the dyeing water bath if the temperature is 20° C. or lower.

The stretched film thus obtained is air-dried at room temperature and then heat-treated in a dryer maintained at 40 to 150°C. 10 to 300 μm).

On one or both sides of the polarizing film produced in this way, a surface preservation layer (with a thickness of about 30 to 50
00 μm) is formed, used as a polarizing plate, and incorporated into a liquid crystal display device or the like.

The surface protective layer can be formed by applying a coating hardening resin such as polyacrylic resin or polyurethane resin to the surface of the polarizing film, or by applying cellulose acetate resin, polyacrylic resin, or polyester that has been previously formed into a film or sheet. It is formed by laminating resins such as polycarbonate-based resins and polycarbonate-based resins, or glass.

The polarizing plate obtained in this way is used by being incorporated into the liquid crystal display device of the above-mentioned small or large products, and exhibits good polarizing properties and durability. However, the polarizing plate has various functions. In order to increase the brightness, it can be used by bonding it with a reflective plate such as an aluminum plate or a light-diffusing transparent plate such as a plastic film with a matte surface.

The polarizing film of the present invention has excellent polarizing properties, dimensional stability, and tear resistance, as will be demonstrated in the following examples.

Example 1 A polyvinyl alcohol film (thickness: 70 μm) with an average degree of polymerization of 2100 was coated with a congo Red concentration of 0.
Dyeing is carried out by immersing the film in a dyeing water bath (temperature 25°C) at a temperature of 1 weight for 10 minutes.
The film was immersed for 5 minutes and stretched in water at a stretching speed of 50%/min to the magnification shown in the drawing.

This stretched film was air-dried at room temperature and then dried in a dryer maintained at 65°C to obtain a polarizing film. The orientation coefficient of the obtained polarizing film is shown in the drawing. Furthermore, Table 1 shows the properties of the polarizing film when the stretching ratio was 3 times.

Comparative Example 1 Similar to Example 1, a polyvinyl alcohol film with an average degree of polymerization of 2100 (!L)ngORed-47) was used.
Dyeing water bath (temperature 25℃) with concentrated FTio, 1%
) for 10 minutes for staining. After air-drying and heat-drying this dyed film, 10%
A polarizing film was obtained by stretching at a stretching speed of 7 minutes to the magnification shown in the drawing. Furthermore, the properties of the polarizing film when the stretching ratio was 3 times are shown in Table V (M1).

Example 1 and Comparative Example IJ) The orientation coefficient (FD) of the dye molecules of the film and the orientation coefficient (FA) of the polymer segment of the entire amorphous region were measured by the method shown in the text and are shown in Figure 1-1. In the drawings, black circles (·) and white circles (○) are the polarizing film of Example 1, 7) FD and FA, and black triangles (mu) and white circles (△) are the FD and FD of the polarizing film of Comparative Example 1. I can get FA. As is clear from the drawings, when stretched in a low-temperature water bath, Fl) is large and ΔF
= Fl) - The value of FA is large. On the other hand, when the film is stretched 1- in heated air, the value of ΔF is small.

Example 2 A polyvinyl alcohol film (thickness 70 am) with an average degree of polymerization of 1700 was processed using C1 process and Direct B1ac.
dyeing water bath with a concentration of k22 of 0.2% by weight (temperature 25%)
℃) for a predetermined time to give a transmittance of 41%, the film was immersed in a 3℃ water bath for 10 minutes, and the film was stretched 3 times in the water bath at a stretching speed of 50/min. Stretched.

This stretched film was air-dried at room temperature and then dried in a dryer maintained at 65°C to obtain a polarizing film.

Example 3 A polarizing film was produced in the same manner as in Example 2, except that the water bath temperature during the dyeing water bath and stretching was 14° C., and the stretching ratio was 4 times.

Example 4 A polarizing film was produced in the same manner as in Example 2, except that the stretching bath was a methanol aqueous solution of s 40 M x % at a temperature of -20° C., and the stretching ratio was 2.8 times.

Comparative Example 2 Similarly to Example 2, a polyvinyl alcohol film (J!Llo μm) with an average degree of polymerization of 1700, C0 engineering, D
Dyeing was carried out by immersing the sample in a dye water bath (temperature: 25° C.) in which the concentration of direct Black 22 was 0.2% by weight for 90 seconds. After air-drying and heat-drying this dyed film, it was stretched at a stretching speed of 10%/min in an atmosphere of 100°C.
A polarizing film was prepared by stretching 5 times.

Table 1 shows the characteristic test results of Examples 1-4 and Comparative Examples 1-2.

Table 1 In Table 1, 1) is the characteristic absorption wavelength of Oongo Rθd of 500 nm for Example 1 and Comparative Example 1.
On the other hand, for Examples 2 to 4 and Comparative Example 2, 1 in the range of 400 nm to 700 nm.
．． Measured using O8Z-8722, and the degree of polarization is calculated using the following formula.0 However, TO and 'J'ao are two polarizers whose orientation directions are parallel and orthogonal. This is the light transmittance when they are stacked like this.

MD and TD in 2) mean the direction perpendicular to the stretching direction and the stretching direction of the film, respectively. The elongation at break in the TD direction is an index of tear resistance, and when this value is large,
This polarizing film has been shown to be tear resistant.

3) is a value measured under the conditions of 80°C x 9t)% RH x 100 hours.

As is clear from Table 1, the polarizing film of the present invention has excellent polarizing properties (light transmittance and degree of polarization), dimensional stability (shrinkage percentage and MD direction elongation at break), and tear resistance (T
It is clear that the material has a well-balanced elongation at break in the D direction.

[Brief explanation of the drawing]

The drawing is a graph showing the orientation coefficients of the polarizing films of Example 1 and Comparative Example 1. Patent applicant Nitto Electric Industry Co., Ltd. Representative Kamigata Sanbe 51

Claims (1)

[Scope of Claims] 1) A polarizing film formed by adsorbing and orienting a dichroic dye on a hydrophilic polymer film, which comprises an orientation coefficient of a polymer segment in the entire amorphous region of the polarizing film and an orientation of dye molecules. Polarizing film 0 characterized in that the difference from the coefficient (0.75 or more) is at least 0.15 2) A dichroic dye is adsorbed onto a hydrophilic polymer film and stretched in a water bath at 20°C or lower. A method for producing a polarizing film, which comprises: 3) Claim 2, wherein the temperature of the water bath when adsorbing the dichroic dye on the hydrophilic polymer film is 30°C or less.
The method for producing a polarizing film described in Section 1. 4) Method 0 for producing a polarizing film according to claim 2, wherein the temperature of the water bath during stretching is 0 to 15°C.