JPS6345083B2 - - 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 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, polarizing films made of highly durable thermoplastic resin/dye systems have been considered in place of conventional polarizing films made of polyvinyl alcohol/iodine systems, but they are comparable to the former in terms of optical properties, especially polarization performance. I'm not getting anything.

In addition, as a method for manufacturing a polarizing film, a method is generally adopted in which a base polymer is oriented in one direction using a longitudinal uniaxial stretching method using tension stretching between rolls, and a polarizing element (iodine, dye, etc.) is 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. (Tokukai Akira
54−40874).

However, when a crystalline thermoplastic resin film is stretched by this long stretch stretching method, stretching points occur near the low speed rolls, so-called "necking stretching", and the effect thereof is not achieved. Furthermore, even if long-distance stretching is possible by devising heating conditions, equipment, etc., if you are trying to stretch a particularly wide film at a high magnification, the distance between the rolls will need to be quite long, and the equipment will also be large. This increases manufacturing costs and tends to result in unstable quality.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for stably producing a polarizing film with good polarizing performance 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 it is possible to prevent netting by sliding the film being stretched on rotating heating rolls and moving the frictional force, regardless of the distance between the rolls. They found that a good polarizing film could be obtained as a result, conducted further studies, and 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 in that the film in contact with the surface of the roll is slid while being maintained 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, polyether, polysulfone, polyvinyl, etc. homo or copolymers of. Among these, hydrophobic and crystalline polyester resins and polyamide resins are preferred.

The photodichroic substance used in the present invention is a substance that has 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 0.001~
10% by weight, preferably 0.01-3% by weight is suitable.

In the present invention, first, a film is formed by adding or not adding a dichroic organic dye to the thermoplastic resin using a normal melt extrusion method or solution casting method, suppressing crystallization as much as possible, and forming an unstretched film. Manufactured. 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 a low speed roll and a 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 will not slide 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 forcibly driven roll is selected depending on the base resin used, but in order to ensure uniform sliding of the film, adhesion to the film, and prevention of scratches, it should be 0.1 to 5 μm.
It is desired that the thickness is preferably about 0.5 to 2 μm.
What is the surface roughness (Hmax) mentioned here? JIS B-0601
is the maximum height of the surface roughness measured by .

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

It is desirable that the surface temperature of the roll is at least 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, making it impossible to obtain a good polarizing film.

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, preheating with a normal hot roll or hot air, auxiliary 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 above the temperature at which stretching is possible, but in order to prevent the film from sticking or to improve the orientation of the base polymer, it is preferably close to the lower limit temperature for stretching.
When using more than one sliding roll that is forcibly driven, it is desirable to increase the temperature sequentially from the supply side.

As an example of the manufacturing process of the present invention, an unstretched film is supplied from a low-speed film supply roll consisting of a pair of pinch rolls, and after being preheated, the film is brought into contact with the forcibly driven rolls for as long as possible, and then stretched at high speed. The film is stretched to a predetermined magnification using rolls, and heat-set if necessary to obtain 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 it is usually about 3 to 10, and it is best to stretch to a high ratio at the lowest possible temperature. . The stretching ratio is the surface speed of the high speed roll (Vs)/the surface speed of the low speed roll on the co-feeding side (Vp)
It is determined by the ratio of

At this time, the surface speed (Vr) of the roll provided between the low-speed roll and the high-speed roll is not particularly limited, but it is recommended that it be rotated at a speed that satisfies Vp≦Vr<Vs to ensure uniform sliding. This is preferable for making it happen.

The contact of the film with this roll is as follows:
It is preferable that the length be as long as possible because 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 at a distance close to almost the entire circumference, or by providing two or more sliding rolls and sliding them in multiple stages,
The overall sliding length can be increased.

〔Effect of the invention〕

According to the method of the present invention, a moderate amount of frictional resistance is applied as the film slides on the heating roll,
Since the film can be stretched without causing netting, a polarizing film with excellent polarizing performance can be produced using a relatively small roll stretching machine, which has a large 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 useful in the field of liquid crystal displays that require durability. Preferably used.

〔Example〕

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

In addition, the light transmittance mentioned 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 a value calculated by the following formula from the light transmittance (T‖ or T⊥) measured by superimposing two polarizing films so that their absorption axes are parallel or perpendicular to each other.

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

Example 1 Anthraquinone dichroic dye added to 10 kg of polyethylene terephthalate resin pellets (IV0.71)
Miketon Polyester Blue TGSF” (manufactured by Mitsui Toatsu Chemical Co., Ltd.) 20g was added and mixed uniformly, then melt extruded (290°C) through a T-die (400mm width) using an extruder (40mmφ) and rapidly cooled. Then, an unstretched film (300 mm width) with a thickness of 150 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, it was then chrome-plated to a surface roughness (Hmax) of 0.5 μm and heated to 70°C. The film was stretched 4 times in the longitudinal direction using high-speed rolls (surface speed 12 m/min) consisting of a pair of pinch rolls.

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 was heat-treated using an annealing roll (180°C) to obtain a polarizing film (70 μm thick).

The light transmittance (To) of this polarizing film is 40%,
The degree of polarization (V) was 85%.

Comparative Example 1 In Example 1, the thickness of the unstretched film was
A polarizing film (approximately 70 μm thick ) was prepared and its optical properties were measured, and the light transmittance was almost the same as in Example 1, with To=39% and V=64%, but the degree of polarization was inferior.

Example 2 Azo dichroic dye “Miketon Polyester Orange” was added to 10 kg of nylon-6 resin pellets (IV0.6).
3GSF" (manufactured by Mitsui Toatsu Chemical Co., Ltd.) was added, and a film was formed to a thickness of approximately 100 μm using an extruder. After passing this through a supply side pinch roll (surface speed of 5 m/min),
Two sliding rolls with surface roughness (Hmax): 1μm and outer diameter: 300mmφ arranged in parallel (surface temperature: 95
°C and 105 °C, surface speed; 7 m/min and 11
m/min) and high-speed roll (surface speed
15 m/min) to obtain a polarizing film (about 60 μm thick).

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

Comparative Example 2 In Example 2, the thickness of the unstretched film was approximately
A polarizing film (approximately 60 μm thick) was prepared in the same manner as in Example 2, except that a rubber roll was placed on top of two rolls placed in the middle and the film was stretched in close contact with each other. When the optical properties were evaluated, To=36% and V=50%, and the degree of polarization was inferior to Example 2.

Claims (1)

[Claims] 1. When producing a polarizing film made of a thermoplastic resin and a dichroic substance 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 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 0.1 to 5 μm. 3. The method for producing 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 greater than or equal to the surface speed of the low speed roll and less than the surface speed of the high speed roll. 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.