JPH0220962B2 - - Google Patents

Description

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

[Conventional technology]

Polarizing films have been widely used as important elements in liquid crystal displays. In recent years, as the field of use has expanded, there has been a strong demand for improved moisture resistance and heat resistance for polarizing films. Polarizing films based on hydrophobic resins are also being developed.

Traditionally, as a general manufacturing method for polarizing films, the base resin is uniaxially stretched by a roll tension method, a roll rolling method, or a tenter tension method, etc., so that the polymer chains are highly oriented in one direction, and the polarizing element is A method has been adopted in which dyes and iodine are arranged in one direction. Among these stretching methods, the transverse stretching method using a tenter stretching machine is particularly preferable because it can produce a polarizing film with excellent film surface condition and thickness uniformity and good optical uniformity. When horizontally stretched continuously in a tenter, a tensile force acts in the horizontal direction and a tensile force acts in the longitudinal direction at the same time, and a slight stretching is applied in the longitudinal direction as well, and the orientation in the transverse direction decreases accordingly. do. As a result, there is a problem that sufficient polarization performance cannot be imparted.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for continuously producing a polarizing film with excellent polarization performance and good optical uniformity by a transverse stretching method.

[Means for Solving the Problem] As a result of intensive studies to achieve the above object, the present inventors have found that if an unstretched film that has been previously shrunk in the vertical direction is stretched, the vertical direction that accompanies horizontal stretching can be reduced. It was discovered that the tensile strength could be reduced and a good polarizing film could be obtained as a result, and the present invention was completed after further investigation.

That is, in the production of a polarizing film made of a thermoplastic resin and a dichroic substance, the present invention provides that when an unstretched film is stretched in the transverse direction at a stretching ratio of 2.5 to 10, the apparent length in the vertical direction is adjusted in advance to the actual length. This method of producing a polarizing film is characterized in that it uses an unstretched film that has been shortened to have a length of 80% or more and 30% or more.

The thermoplastic resin used in the present invention can be formed into a transparent film and can be stretched, and is, for example, a homo- or copolymer of polyester, polyamide, polyolefin, polyether, polysulfone, polyvinyl, etc. . In particular, polyester resins and polyamide resins are preferred for applications requiring moisture resistance and heat resistance.

On the other hand, the photodichroic substance is a substance that is anisotropic in light absorption, and is preferably an organic dye, which can be suitably selected from commercially available organic dyes and pigments. Among these, those that can be dispersed, dissolved, or dyed in the thermoplastic resin are preferred.

Its content is determined by the color density of the final polarizing film, but is usually 0.001 to 10% by weight, preferably 0.01 to 3% by weight.

The unstretched film as used in the present invention refers to a film in which a photodichroic substance is added or not added to the thermoplastic resin, and
The film is formed by a conventional melt extrusion method or solution casting method with crystallization suppressed as much as possible. If a dichroic substance is not added in advance, it can be colored by dyeing or the like in the film before or after stretching.

In the present invention, an unstretched film is shortened in advance so that the apparent length in the vertical (longitudinal) direction is 80% or more and 30% or more of the actual length. If the apparent length is 80% or more of the actual length, a polarizing film with sufficient polarizing properties cannot be obtained. Moreover, if it is less than 30%, the flatness will be impaired and cracks and tears will occur in the stretching direction. The apparent length l here means the length when a wrinkled unstretched film that has been shortened from a flat film with an actual length L is projected onto a flat surface, and is fixed in advance in the longitudinal direction of the flat film. If a length L mark is engraved, the length of the mark on the processed deformed film can be determined by measuring with a flat scale. The apparent length is appropriately selected depending on the stretching ratio (R) at that time, but preferably the ratio of l to L is 1/
It is close to √×100 (%).

As a method for shortening the apparent length in the longitudinal direction of an unstretched film, for example, at a temperature higher than the heat deformation temperature of the unstretched film, the unstretched film is shortened into a corrugated shape by passing the film between gear mesh rolls; Alternatively, when stretching the film using a tenter transverse stretching machine, there is a method in which a clip with a corrugated film gripping surface is used to grip the film and at the same time wrinkle the film.

The shape in this case is not particularly limited, but a wave shape with a smooth curve is desirable from the viewpoint of the flatness of the film after stretching and the uniformity of quality.

The pitch and depth in the case of a corrugated shape can be appropriately selected depending on the required apparent length ratio, subsequent stretching conditions, and the like.

The lateral stretching ratio in the present invention is 2.5 or more.
It is 10 or less, preferably 3.5 to 10, and if it is less than 2.5, a polarizing film with sufficient polarization cannot be obtained. Moreover, if it is 10 or more, the orientation is not improved as much as the stretching ratio is increased, and the film may break during stretching, which is not preferable. As long as the apparent longitudinal length of the unstretched film is sufficiently short compared to its actual length, the magnification should be as high as possible. In other words, it is preferable to perform greater shortening processing when the magnification is high.

As a specific example of the manufacturing process of the present invention, for example, the resin and the dichroic dye are uniformly mixed, then melt-extruded using an extruder and rapidly cooled to form a flat unstretched film. This is then corrugated in the longitudinal direction by gear-type meshing rolls to form a wave-shaped unstretched film with a predetermined apparent length. The unstretched film is stretched to a predetermined magnification at a temperature, and if necessary, a heat setting treatment is performed to obtain a polarizing film.

〔Effect of the invention〕

According to the method of the present invention, compared to the case where a conventional flat film is continuously stretched horizontally as it is, it is possible to reduce the tension in the vertical direction accompanying the horizontal stretching, and as a result, the uniaxial orientation in the horizontal direction is improved, and the polarization It is possible to continuously and efficiently produce a hydrophobic polarizing film with excellent performance.

The method of the present invention can be applied to the production of conventional polyvinyl alcohol-based polarizing films, and this case also falls within the scope of the present invention.

The polarizing film obtained by the present invention has excellent optical uniformity as well as polarizing performance.
Those using hydrophobic resin as a base material are suitably used in fields where durability is required.

〔Example〕

The present invention will be further explained below with reference to Examples.

The optical properties measured in the Examples were determined by the following method.

The light transmittance (T ₀ ) of one polarizing film is measured using a self-recording spectrophotometer, and then two polarizing films are stacked so that their absorption axes are parallel or perpendicular to each other. The light transmittance (T ₁₁ and T ₁ , respectively) was measured at the maximum absorbance wavelength (λmax), and the degree of polarization was determined using the following formula.

Example 1 20 g of anthraquinone dichroic dye "Miketon Polyester Blue TGST" (manufactured by Mitsui Toatsu Chemical Co., Ltd.) was added to 10 kg of polyethylene terephthalate resin pellets (IV0.71), mixed uniformly, and then transferred to an extruder ( Melt extrusion (290℃) using a T-die (40φ),
It was rapidly cooled to form an unstretched film (about 150 μm thick).

A 100 mm long mark was engraved with ink in the vertical direction on this flat film, passed through a meshing gear to form a continuous wave film with a pitch of about 8 mm and a depth of about 8 mm, and the above mark was measured using a flat scale.
It was 55mm. This corrugated film was supplied to a tenter transverse stretching machine, and was transversely stretched at a stretching ratio of 4.5 times in a preheating section of 80°C, a stretching section of 75°C, and a heat treatment section of 180°C, and heat set.

This polyester polarizing film (thickness 70μm)
When we measured the optical properties of the flat part excluding the ear ends, T ₀ = 40% and V = 88%, and the quality variations in vertical and horizontal thickness, light transmittance, degree of polarization, etc. were small. No external holes such as die lines were observed.

Comparative Example 1 The unstretched film formed in Example 1 was laterally stretched in the same manner without being shortened.
Heat set and make polyester polarizing film (thickness approx.
50μm) was created.

When I measured the optical product of this, T ₀ = 45%,
V=54%, which was considerably inferior to that of Example 1.

Example 2 Azo dichroic dye “Miketon Polyester” was added to 10 kg of nylon-6 resin pellets (IV0.6).
Orange3GSF” (manufactured by Mitsui Toatsu Chemical Co., Ltd.) 10kg was uniformly added and mixed, and then a T-die extruder (40φ) was used to
An unstretched film with a thickness of 100 μm was formed. After stamping a 100 mm length mark in the longitudinal direction of this film, the film was fed to a tenter horizontal stretching machine equipped with a clip whose gripping part was corrugated with a pitch of 20 mm and a depth of 20 mm. Laterally stretched at a stretching ratio of 3.5 at 110°C in the stretching part and 180°C in the heat treatment part, and heat-set to produce a nylon polarizing film (approximately 50 μm thick).
I got it.

Before the unstretched film enters the stretching zone, the length of the above mark was measured using a flat scale, and it was 75mm.
The optical properties of this polarizing film are T ₀ = 36
%, V=78%, and the surface condition of the film was also good.

Comparative Example 2 The unstretched film prepared in Example 2 was laterally stretched and heat-set under the same conditions using a tenter having clips as ordinary flat gripping parts.

The optical properties of the obtained polarizing film (about 40 μm thick) were T ₀ =39% and V=51%, which were inferior to those of Example 2.

Claims (1)

[Claims] 1. In the production of a polarizing film made of a thermoplastic resin and a dichroic substance, when an unstretched film is stretched in the transverse direction at a stretching ratio of 2.5 to 10, the apparent length in the vertical direction is determined in advance to the actual length. Less than 80% of 30
A method for producing a polarizing film, characterized by using an unstretched film that has been shortened to a length of % or more. 2. The method for producing a polarizing film according to claim 1, wherein the unstretched film has a wavy cross-sectional shape in the longitudinal direction. 3. The method for producing a polarizing film according to claim 1, wherein the thermoplastic resin is a polyester resin or a polyamide resin, and the dichroic substance is an organic dye.