JPS60248332A - 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 providing a forcible driving roll between a low speed roll and a high speed roll and causing a film consisting of a thermoplastic resin and an optical two-tone substance to slide on the roll surface at the stretching temperature or more. 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 passed on at least one forcible driving roll positioned between a high speed roll and a low speed roll comprising a pair of pinch rolls, thereby causing the film in contact with the roll surface to slide thereon at the stretching temperature 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 important elements in liquid crystal displays, but as the fields of their use have expanded, there has been a strong demand for polarizing films to have durability such as moisture resistance and heat resistance.

In recent years, in place of the conventional polarizing film made of polyvinyl alcohol/iodine, highly durable thermoplastic resin/
Polarizing films made of dye-based films have been studied, but none comparable to the former in terms of optical properties, particularly polarization performance, have yet to be obtained.

In addition, as a manufacturing method for polarizing film, a method is generally adopted in which the base polymer is oriented in one direction using a longitudinal-axial stretching method using tension stretching between rolls, and the polarizing elements (iodine, dye, etc.) are simultaneously arranged. . Among them, it is known that the so-called long stretch stretching method, in which tension stretching is performed with a long distance between rolls, is good for this stretching because it improves the orientation of the base polymer. A polarizing film based on dehydrochlorinated polyvinyl resin (polyene) can be produced. (Unexamined Japanese Patent Publication No. 54-4087
4).

However, when a crystalline thermoplastic resin film is stretched by this long-distance stretching method, a stretching point occurs near the low-speed roll, which is so-called "necking stretching", and the effect thereof is not manifested. Even if it were possible to stretch over a long period of time by improving the heating conditions, equipment, etc., especially when trying to stretch a wide film at a high magnification, the distance between the rolls would need to be quite long, and the equipment would also need to be stretched. The larger the size, the higher the manufacturing cost, and the quality tends to be unstable.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for producing a polarizing film with good polarization performance with good stability using a relatively small roll stretching device.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the present inventors have found that cinesoking can be prevented by causing the film being stretched to slide on rotating heating rolls to exert a frictional force, regardless of the distance between the rolls. They found that it was possible and that a good polarizing film could be obtained as a result, and after further study, they completed the present invention.

That is, the present invention provides at least one forcibly driven roll between a low speed roll and a high speed roll when manufacturing a polarizing film made of a thermoplastic resin and a dichroic substance by a roll stretching method. This method of producing a polarizing film is characterized by sliding the film in contact with the roll surface while keeping the film at a temperature higher than the stretching temperature.

The thermoplastic resin used in the present invention is a thermoplastic resin that can be formed into a transparent film and can be stretched. Examples include polyester, polyamide, polyolefin, polyester, polysulfone, polyvinyl, etc. Mention may be made of homo- or copolymers.

Among these, hydrophobic and crystalline polyester resins and polyamide resins are preferred.

The photo dichroic substance used in the present invention is a substance having anisotropy in light absorption, and can be preferably selected from commercially available dyes and pigments. Among them, those that can be dispersed and dissolved in the resin or dyed are particularly preferred.

The content is determined by the degree of coloring of the final polarizing film, but is usually 0001 to 10 by weight,
Preferably, the amount is 0.001 to 3% by weight.

In the present invention, first, a photodichroic organic dye is added to the thermoplastic resin, and a -C film is formed by suppressing crystallization as much as possible by a normal coating melt extrusion method or a solvent casting method without adding dust. An unstretched film is produced. If no dye is added at this time, the film is colored by dyeing or the like before or after stretching.

In the present invention, at least one forcibly driven roll is provided between the low speed roll and the high speed roll on the film supply side. If the roll installed between the low-speed roll and the high-speed roll is not forced to drive and rotates freely, the film will not slide uniformly, while if the roll stops rotating, changes may occur due to friction and wear on the roll surface. , which is not preferable because the film does not slip stably. Although the direction of rotation by forced drive is not particularly limited, it is preferable to match the direction of film movement.

The surface roughness (Hmax) of this forcedly driven roll is
Although it is selected depending on the base resin used, it is desired that the thickness be about 01 to 5 μm, preferably about 05 to 2 μm, in order to ensure uniform sliding of the film, adhesion to the film, and prevention of scratches. Surface roughness (Hmax)
is the maximum height of surface irregularities measured according to JIS B-0601.

The surface material of the roll is not particularly limited, but it is usually preferably metal plated or repeatedly coated with resin, rubber, ceramic, or the like.

It is desirable that the surface temperature of the roll is higher than or equal to the temperature at which the base resin film can be stretched; if it is lower than that, the film will not be stretched on the roll and a good polarizing film will not be obtained.

As a heating means, it is usually possible to pass a heat medium such as water or oil through the roll, and as a heating method for the film, it is possible to use a normal heating roll, preheating with hot air, heating with infrared rays, etc. It can also be used in combination.

The surface temperature of the roll is not particularly limited as long as it is at least the temperature at which it can be stretched, but in order to prevent the film from sticking or to improve the orientation of the profiteering polymer, it is preferable that the surface temperature be close to the lower limit temperature for stretching. When using forcedly driven rolls for sliding, it is desirable to increase the temperature sequentially from the supply side.

As an example of the manufacturing process of the present invention, after the film is fed at low speed by a pair of pinch rolls, the film is brought into contact with the forcibly driven rolls for as long as possible, and then stretched to a predetermined magnification by the high speed tension stretching rolls. If so, heat-set it to make a polarizing film. The stretching ratio in this case varies depending on the resin composition of the unstretched film, the stretching temperature, and the temperature of the forcedly driven rolls, but is usually about 3 to 10, and it is preferable to stretch the film to a high ratio at as low a temperature as possible. The stretching ratio is determined by the ratio of the surface speed of the high speed roll (■θ)/the surface speed of the low speed roll on the supply side (Vp).

The surface speed (vr) of the roll provided between the low speed roll and the high speed roll at this time is not particularly limited, but
Vp! It is preferable to rotate at a speed equal to Vr (Ve) in order to cause uniform slippage.

Note that it is preferable that the contact period of the film with the roll be as long as possible, since this increases the sliding area of the film and increases the effects of the present invention.

For example, by increasing the outer diameter of this roll and making it contact close to the entire circumference of the dowel, or by installing two or more sliding rolls and sliding in multiple stages, the overall sliding length can be increased. can do.

〔Effect of the invention〕

According to the method of the present invention, a suitable amount of frictional resistance is applied as the film slides on the heated roll, and stretching is performed without necking, resulting in a relatively small polarizing film with excellent polarizing performance. It can be manufactured using a roll drawing machine and has a great cost advantage.

Note that 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 not only exhibits high polarization but also has excellent optical uniformity, and those using a moisture-resistant base resin are particularly suitable for the field of liquid crystal displays that require durability. used.

〔Example〕

1-1, the present invention will be further explained by Examples.

In addition, the light transmittance referred to in the examples is the light transmittance (TO) of one polarizing film measured using a self-recording spectrophotometer, and the degree of polarization (V) is the light transmittance (TO) of one polarizing film measured using a self-recording spectrophotometer.
Light transmittance (Th or Tl) measured by stacking two sheets so that their absorption axes are parallel or perpendicular to each other.
This is the value calculated using the following formula.

However, in both cases, the transmittance at the maximum absorbance wavelength (λmax) was used.

Example 1 Polyethylene terephthalate resin pereno l-(IVO,
71) Anthraquinone dichroic dye in I D Kg
Miketon Polyester Blue TG
SF'' (manufactured by Mitsui Toatsu Chemical Co., Ltd.) 20? was added and mixed uniformly, and then a T-die (4
00mm width), melt extruded (290℃), rapidly cooled, and
An unstretched film (300+++++ width) with a thickness of 50 μm was formed.

After this film was fed to a low-speed feed roll (surface speed 3 m/min) consisting of a pair of pinch rolls, the surface roughness (
Hmax) Chrome plated to 0.5μm,
It was brought into contact with about half the circumference of a 400mm diameter metal plating roll (surface speed 8 m, 7 minutes) heated to 70°C, and rolled vertically by a pair of high-speed rolls (surface speed 12 m/min) consisting of a pair of pinch rolls. Stretched twice.

At this time, it was confirmed that the film slipped on the heated roll and was stretched while shrinking in the transverse direction.

Furthermore, this stretched film is annealed (180°C).
A polarizing film (70 μm thick) was obtained by heat treatment.

The light transmittance (TO) of this polarizing film was 40 inches, and the degree of polarization (V) was 85%.

Comparative Example 1 In Example 1, the thickness of the unstretched film was 3C1Oμm.
A rubber pinch roll is installed on the roll between the low-speed roll and the high-speed roll to keep the film in close contact with this roll and prevent slippage! Polarizing film l, (approximately 70
When the optical properties were measured, the light transmittance was almost the same as in Example 1, with T〇2 39% and ■ -64%, but the degree of polarization was inferior.

Example 2 Nylon-6 resin pellets (IVo, 6) 10K
9 is azo dichroic dye “Miketon polyes”
ter orange3GSF” (Mitsui Toatsu Chemical Co., Ltd.
1o2 (manufactured by Kiki Co., Ltd.) was added, and a film was formed to a thickness of about 100 μm using an extruder. After passing this through the supply side pinch rolls (surface speed 5 m/min), the surface roughness (Hmax)
; 1 μm, outer diameter; 2 sliding openings of 500 mmφ ~
(Surface temperature: 95℃ and 105℃, surface speed: 7m
/min and 11m/min) and high speed roll (
The film was longitudinally stretched six times at a surface speed of 15 m/min) to obtain a polarizing film (about 607 zm thick).

The optical properties of this polarizing film are 'TO=35%, 87
It was Chi.

Comparative Example 2 In Example 2, the thickness of the unstretched film was approximately 180 μm.
A polarizing film (approximately 60μ
m thickness) was created and the optical properties were evaluated, and it was To-3.
6%, V=58%, and the degree of polarization was inferior to Example 2.

patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. When producing a polarizing film made of a thermoplastic resin and a dichroic material by a roll stretching method, at least one forcibly driven roll is provided between a low speed roll and a high speed roll, and the roll is A method for producing a polarizing film, which comprises sliding the film in contact with the surface while keeping the film at a temperature higher than the stretching temperature. 2. The method for producing a polarizing film according to claim 1, wherein the roll provided between the low speed roll and the high speed roll has a surface roughness (Hmax) of 01 to 5 μm. 6. Production of a polarizing film according to claim 1 or 2, wherein the surface speed of the roll provided between the low speed roll and the high speed roll is higher than the surface speed of the low speed roll, and the surface speed of the high speed roll is not swirled. Method. 4. 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.