JPS60248333A - Manufacture of polarizing film - Google Patents

Abstract

PURPOSE:To obtain a polarizing film that is excellent in durability and will be used for a liquid crystal display and so on, by stretching laterally an unstretched film consisting of a thermoplastic resin and an optical two-tone material and at the same time contracting the length of the film forcibly by a specified amount. CONSTITUTION:An optical two-tone material (e.g. anthraquinone type two-tone dyes, etc.) is added to a thermoplastic resin (e.g. polyethylene terephthalate resins, etc.), and after the mixture is stirred uniformly, the mixture is melt-extruded from a T-die of an extruder, and is quenched to produce an unstretched film. This unstretched polarizing film is stretched laterally at a draw ratio of 2.5 or over and at the same time is contracting longitudinally forcibly by an amount of 20% or more to produce the desired polarizing film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a polarizing film having good polarizing performance.

[Conventional technology]

Polarizing films are widely used as an important element of liquid crystal displays, and in recent years, as the field of use has expanded, there has been a strong demand for improved temperature resistance and heat resistance for polarizing films (C). Polarizing films based on hydrophobic resins are being developed instead of polarizing films based on polyvinyl alcohol resins.

By the way, conventionally, as a manufacturing method of polarizing film, a base resin polymer is oriented in one direction by longitudinal-axial stretching such as a roll tension method or roll rolling method, or horizontal uniaxial stretching such as a tenter tension method, and a polarizing element is produced. A method has been adopted in which dyes, iodine, etc. are arranged in the same direction.

Among these stretching methods, the tenter full stretching method is particularly preferable because it improves the surface condition and thickness uniformity of the film, and provides a polarizing film with good optical uniformity. However, when continuous production is performed using the same stretching method, When a stretching tensile force is applied in the transverse direction, a tensile force is applied in the longitudinal direction, and a slight stretching effect also appears substantially in the longitudinal direction 1, and the degree of orientation of the polymer in the transverse direction is reduced accordingly. As a result, there is a problem that sufficient polarization performance cannot be imparted.

[The problem that the invention is trying to solve]

An object of the present invention is to provide a method by which a good polarizing film can be continuously produced by horizontal uniaxial stretching.

[One-shot measure to solve the shoulder point] In order to achieve the above object, the inventors of the present invention found that ((as a result of intensive study), it was possible to forcibly shorten the length in the vertical direction at the same time as stretching in the horizontal direction. It was discovered that the tensile strength in the longitudinal direction can be reduced, and that the polarizing film thus obtained has good polarizing properties, and further studies have led to the present invention.

That is, in the remanufacturing of a polarizing film made of a thermoplastic resin and a dichroic substance, the present invention provides a method of forcing the length of the film in the longitudinal direction at the same time as stretching the unstretched film in the transverse direction at a stretching ratio of 25 or more. This is a method for producing a polarizing film characterized by shrinking the polarizing film by 20% or more.

The thermoplastic resin used as the base material of the polarizing film in the present invention is one that can be formed into a transparent film and can be stretched. For example, it is a homo or copolymer of polyester, polyamide, polyolefin, polyether, polysulfone, polyvinyl, etc., and has moisture resistance,
When heat resistance is required, polyester resins, polyamide thread resins, etc. are preferred.

On the other hand, the dichroic substance used as a polarizing element is a substance that exhibits anisotropy in light absorption, and organic dyes are usually preferably used, and can be suitably selected from commercially available organic dyes and pigments. can. Among these, those that can be dispersed and dissolved in a thermoplastic resin or dyed are preferred.

The content thereof is determined by the coloring density of the final polarizing film, but is usually from o, ooi to 10% by weight, preferably from 001 to 3% by weight.

The unstretched film as used in the present invention is a film formed by adding or not adding a dichroic substance to the base resin and suppressing crystallization as much as possible by a normal melt extrusion method or solvent casting method. be. If a film is formed without adding a dichroic substance in advance, the film can be impregnated by dyeing or the like before or after stretching.

In i6 of the present invention, the unstretched film is stretched in the transverse direction ((
It is stretched to a stretching ratio of 25 or more, preferably 35 to 10.

If it is less than 25, a polarizing film l having sufficient polarizing properties cannot be obtained. For example, when horizontally stretching with a tenter stretching machine, the stretching ratio is determined by the width of the film gripping clip on the supply inlet side (
Ll) and the exit side width (I, 2) ratio (r, , /■,
□).

The stretching temperature is usually a temperature equal to or higher than the glass transition temperature of the base resin and equal to or lower than its melting point, and is heated by heated air, infrared radiation, or the like.

In Invention 1C, it is necessary to forcibly shrink the film by 20% or more in the machine direction at the same time as stretching it in the transverse direction. The shrinkage ratio here means the rate of change in the length of the film in the longitudinal direction before and after stretching.
Measure the length l of the same mark after stretching (L-1/LX
It can be determined by i 00%.

If the shrinkage ratio is less than 20 degrees, a polarizing film with good polarizing properties cannot be obtained even if it is stretched at a stretching ratio of 25 or more. The preferred shrinkage ratio is (1) for the stretching ratio R.
-1/, /T)

A method for reducing the film in the longitudinal direction at the same time as horizontal stretching is, for example, in the case of a continuous tenter stretching machine, a method in which the interval between the film gripping clips is gradually narrowed by 6τ in the stretching section, or a method known in the art. It is possible to modify the pantograph method used in simultaneous biaxial stretching, and conversely reduce the moving speed of the clip in the machine direction ((more possible).・If it is a machine, attach the film gripping clip to the symmetrical scree shaft centered at the center,
The shaft can be rotated at the same time as stretching to shrink the film in the stretching direction (vertical direction (longitudinal direction). This is preferable in order to prevent appearance defects (wrinkles, sagging, etc.) of the stretched film and not to impair optical uniformity.

Examples of the manufacturing process in the present invention include an in-line method in which an unstretched film immediately after film formation is fed to the tenter stretching machine and horizontally stretched, or an unstretched film formed on a separate line is fed to the tenter stretching machine. A polarizing film can be continuously manufactured by an offline method of supplying and transversely stretching.

Furthermore, after stretching, heat treatment can be performed as necessary to improve thermal dimensional stability. Alternatively, as long as continuity is not a concern, it can be produced using the above-mentioned batch type stretching machine.

[Efficacy of invention]

According to the present invention, it is possible to reduce the tensile force in the longitudinal direction that occurs at the same time as the transverse stretching, and as a result, it is possible to produce a polarizing film that has excellent polarizing performance and satisfies optical uniformity. In particular, those using base material 1 resin which has excellent moisture resistance and moisture resistance are suitable for use as liquid crystal display elements that require durability.

〔Example〕

Hereinafter, Example 1 (therefore, the present invention will be further explained).

In addition, the pass rate as an optical characteristic in the examples is as follows:
It is the light transmittance ('ro) of one sheet of polarizing film measured by a spectrophotometer, and the degree of polarization is the degree of polarization when two sheets of polarizing film are used and their i% axes are superimposed in parallel or perpendicular position. Light transmittance (To or -tozu- respectively)
) is measured, and the value at which itching occurs is determined by the following formula.

However, all values are measured at the maximum absorbance wavelength (λmnZ).

Example 1 Polyethylene terephthalate resin pellets (IVo, 7
1) Anthraquinone dichroic dye “M^J-” in 10 and 9
Addition of 20 g of AnPer% Mun B Mushi TGSF'' (manufactured by Mitsui Toatsu Chemical Co., Ltd.) 1-1 After mixing uniformly,
The extruder (40-φ) melt-extrudes the film through a T-die (600-φ) (290°C), rapidly cools it, and produces an unstretched film (290°C).
A film with a thickness of approximately 150 μm was formed.

Almost in the center of this film, 'ro' is applied by ink.
0mm length mark in the longitudinal direction (C), simultaneous biaxial stretching with a pantograph type clip, two-cross l111 rough processing, and in the stretching section, the film is stretched in the direction of film flow I.
Contrary to C, the running speed is smooth at a constant rate (C is supplied to a tenter stretching machine that becomes a groove that decreases, and the lip width at the entrance part is 2 oomm and the stretching outlet clinobu d) is 900 mm.
The film was stretched in the transverse direction (at a stretching ratio of 45) and heat-set to obtain a polyester polarizing film (about 6011 m thick).

At this time, the temperature of the tenter preheating section, stretching section, and heat treatment section is 1.
The vessels were at 90°C, 80''C and 180°C, respectively, and the film speed at the exit was 5 m/min.

The mark length on the obtained film was 55 mm (
When the optical properties were measured, the transparency rate ('ro) was 42%, the degree of polarization (V) was -87'%, and no defects were observed for external use.

Comparative Example 1 In Example 1, the thickness of the unstretched film was changed to about 250 μm.
m, and the film was stretched 45 times in the transverse direction in the same manner as in Example 1, except that a conventional tenter stretching machine was used, and heat setting was performed to obtain a 4-light film (about 60 μm thick).

The mark length on this film was 94 mm (shrinkage rate 6%), and when the optical properties were measured, To = 4
The degree of polarization was inferior to that of Example 1, with a coefficient of 1% and ■=61.

Example 2 Azo dichroic dye MLLiyn PJLyc, z, je, a O
-xr-zghro GSFll (Mitsui Toatsu Chemical Co., Ltd.-;
! 7) Cool down 10.9, mix 1, and after T1, conduct 1g 11
An unstretched film (270 mm width) with a thickness of approximately 100 μπ was formed by extrusion film production, Ql L 7j.

This film is cut to a length of 5QCm, and a 10mm length mark is engraved in the longitudinal direction at the center of the dowel. During the stretching period, the screw shaft is used to stretch the film from the left and right to the center C (toward the center C). Using a hatch-type stretching machine capable of Transfer it to the open state of about +aot and heat it for about 1 minute to form a polyamide polarizing film (about 40
(μm thickness) was obtained.

The mark length on this film is 72 mm (shrinkage rate 2
8), and its optical properties are T. -69 section, V near was 6%.

Comparative Example 2 A polarizing film was produced by stretching 35 times in the transverse direction under the same stretching conditions as in Example 2, except that the rotational speed of the screw shaft was lowered and the clip reduction distance during the stretching period was shortened, and a polarizing film was heat-treated in the same manner. (Thickness about 35μ?y+,
)It was created.

The mark length in this film is B6fnfn (m
14%), and its optical properties are T. -41 section, ■=5
9th section is l1ii better than that of Example 2! Inferior patent applicant for luminosity Mitsui Too Chemical System Company

Claims (1)

[Claims] 1. In the production of a polarizing film made of a thermoplastic resin and a dichroic substance, an unstretched film is stretched in the direction of the horizontal mark at a stretching ratio of 2.
A method for producing a polarizing film, characterized in that the length of the film in the vertical (longitudinal) direction is forcibly reduced by 20% or more at the same time as stretching when stretching 5 or more. or a polyamide-based resin, and the method for producing a polarizing film according to claim 11, wherein the dichroic material is an organic dye.