JPS6151323A - Preparation of uniaxially stretched polyester film for liquid crystal display - Google Patents

Abstract

PURPOSE:To enable a clear image to be obtained when a film is incorporated in a liquid crystal display device by a method wherein uniaxially stretched film having a restricted longitudinal orientation conditions and undergoing suitable molecular orientation is heat-set in two zones respectively under specified conditions. CONSTITUTION:The magnification to stretch amorphous film is given by 3.0-3.8 times in a longitudinal direction. Heat setting is carred out in the device having two zones capable of setting temperature and width shrinkage to respectively independent conditions. The heat setting temperature of the 1st zone is given by 180-240 deg.C, the width shrinkage of the film at that time is in the range 0-5%. The heat setting temperature in the 2nd zone is 120 deg.C or higher or within the heat setting temperature in the 1st zone and the shrinkage in the width direction of the film at that time is within 1-10%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a uniaxially stretched polyester film for liquid crystal displays. More specifically, the present invention is a method for producing a uniaxially stretched polyester film that provides clear images in liquid crystal display applications in which a transparent conductive film and/or polarizing film is attached to one or both sides of the film.

[Conventional technology]

Conventionally, a method for producing uniaxially stretched polyethylene terephthalate in which the film is stretched in the longitudinal direction and heat-set is known (for example, Japanese Patent Publication No. 49-20385).

[Problem that the invention seeks to solve]

However, such conventional methods have drawbacks such as a high thermal shrinkage rate of the film and a misalignment between the two longitudinal directions of the film and the direction of molecular orientation caused by stretching. I didn't like it though.

The present invention aims to eliminate such drawbacks and provide a method for producing a uniaxially stretched polyester film for liquid crystal display, which can provide a clear display image when incorporated into a liquid crystal display element.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention adopts the following nine configurations.That is, an amorphous polyester film is stretched 5.0 to 68 times in the longitudinal direction. When the film is heat-set in the first zone and the second zone, the film is heat-set at a temperature of 180 to 240°C in the first zone with a contraction rate of 0 to 5 in the width direction, and then in the second zone. In this method, a uniaxially stretched polyester film for a liquid crystal display is heat-set at a temperature of 120° C. or higher in the zone and lower than the heat-setting temperature of the film in the first zone, with a contraction rate of 1 to 1° in the width direction of the film.

The polyester applied to the present invention may be any known polyester, and is preferably polyethylene tere 7-thale obtained by polycondensing terephthalic acid or its alkyl ester with ethylene glycol.
) de begging. Of course, dicarboxylic acids other than terephthalic acid 2, such as isophthalic acid, acyhinic acid, sepathic acid, naphthalene dicarboxylic acid, metal salts of sulfonic acids, etc., are added at a mole ratio of 20 or less, preferably 1
Copolymerization may be carried out at a molar ratio of 0 or less. In addition, diol components 9 other than ethylene glycol, such as jetin diol, polyethylene glycol, cyclohexane dimetatool, etc., may be added at 20 molar or less based on the total diol components.
Preferably, copolymerization may be carried out at a molar ratio of 10 or less. All of these copolymers are included in the expression PE'[' in the present invention. Furthermore, the polyester of the present invention may contain known lubricants 2, such as inorganic particles such as titanium dioxide, kaolin, silicon oxide, and calcium carbonate, 9 polyethylene glycol-modified compounds of silicone, and organic lubricants such as carnauba wax. -05 parts by weight may be added.

In addition, an amorphous film is a film in which polyester is melt-extruded using an extruder, guided through a T-die, formed into a sheet, wrapped around a cooled drum, and cooled to below the glass transition temperature (Tg). A substantially unoriented film.

The method for stretching the amorphous film is a known method.

For example, one method is to stretch the film in the longitudinal direction using a group of rolls consisting of a low-speed heating roll and a high-speed cooling roll, or the other is to grip the edge of the film with a tenter equipped with a pantograph clip that can stretch the film in the longitudinal direction. Although any method of stretching may be used, preferred is a method of stretching using a group of rolls.

The stretching ratio of the amorphous film is 5.0 to 5.0 in the longitudinal direction.
It is 3.8 times, preferably 3.2 to 5.6 times. If the stretching ratio is smaller than this range, the flatness of the film after heat setting will be impaired, and if the stretching ratio is larger than this range, the heat shrinkage rate in the longitudinal direction of the film will increase, which is undesirable. .

The stretching temperature is not particularly limited, but uniaxial stretching is preferably carried out within a range of 80 to 110°C.

The birefringence of the film is in the range of 0.05 to 0.12.

and the refractive index in the thickness direction of the film is 1.51 to 1,57.
It is preferable to set it as the range of.

The heat setting of the present invention is carried out using an apparatus having two zones in which the heat setting temperature and the shrinkage rate in the width direction can be individually set to different conditions. 9. For example, the first zone is a two-zone heat fixing method.

A method of heat-setting using a tenter method, in which the ends of the film are held with clips and hot air is blown from above and below the film, and then heat-setting in the second zone is as follows:
Either the tenter method, the heated roll method in which the film is heat-set via a group of heated rolls, or the hot-air open method in which the film is heat-set by passing it through a hot-air oven with guide rolls appropriately arranged can be used. ,
Among these methods, the tenter method is preferred.

In the present invention, when heat fixing is performed in two zones,
First, the heat setting temperature of the first zone is 180 to 240°C, preferably 200 to 230°C.

If the heat setting temperature is lower than this range, the effect of reducing the heat shrinkage rate of the film will be reduced, and conversely, if the heat setting temperature is higher than this range, the film will tend to crack in the stretching direction, so it is preferable. do not have. In addition, the shrinkage rate of the film in the width direction when heat-setting in the first zone is 0 to 5 qb,
Preferably it is in the range of 0 to 3 inches. If the shrinkage rate in the width direction is smaller than this range (meaning stretching in the width direction), the stretching direction and the optical axis direction of the film may be misaligned, which is not preferable. On the other hand, if the shrinkage rate in the width direction is larger than this range, the deviation between the stretching direction and the optical axis direction of the film tends to become large, which is not preferable.

Here, the optical axis direction of the film refers to the direction of the polarization axis that is perpendicular to the
Place a film between two polarizing plates, rotate the film, and when the darkest field is obtained, the direction of the polarization axis of the polarizing plate is close to the stretching direction of the film.

This is called the optical axis direction of the film. This optical axis direction is generally considered to be the same direction as the stretching direction, but in the process of heat setting the uniaxially stretched film.

The optical axis direction of the film may be deviated by an angle at which the entire width of the film or a portion thereof is rotated from the stretching direction. Hereinafter, in the present invention, the deviation between the stretching direction and the optical axis direction of the film will be simply referred to as optical axis deviation.

The optical axis deviation is expressed as the deviation angle between the stretching direction and the optical axis direction of the film. When a roll of this film with a large optical axis deviation is used and incorporated into a liquid crystal display element, the contrast of the image displayed on the liquid crystal is poor and a clear image is not displayed. In reality, this optical axis deviation is 2
If it is within °, it can be said to be at a practical level.

Also, here, the method of determining the shrinkage rate in the width direction of the film is to stamp a 10 square square on the film before heat setting, and then measure the length in the width direction of the square after heat setting the film. The amount of shrinkage is divided by the original length in the width direction of the square, which is calculated as a percentage (%).

Next, when the film heat-set in the first zone is further heat-set in the second zone, the heat-setting temperature in the second zone is preferably 120°C or higher and lower than the heat-setting temperature of the film in the first zone. , 150° C. or higher, but lower than the heat setting temperature of the film in the first zone. This is not preferable because the effect of making the thermal contraction rate in the thermal transverse direction of the second zone almost the same and lowering the contraction rate is not sufficient. Conversely, if the heat fixation temperature is lower than this range,
It is not preferable that the effect of reducing the thermal shrinkage rate is insufficient.

In addition, the shrinkage rate of the film in the second zone in the width direction is 1 to 1.
10%, preferably in the range of 2-7%. If the shrinkage rate in the width direction in the second zone is smaller than this range, the effect of reducing the heat shrinkage rate of the film will not be sufficient, which is not preferable. On the other hand, if it is larger than this range, the film tends to become corrugated, which is not preferable.

The heat fixing of the present invention involves a method of continuously heat fixing the film between the first zone and the second zone without cooling it to room temperature, or a method of continuously heat fixing the film between the first zone and the second zone without cooling the film to room temperature. - After cooling, any method of heat setting in the second zone may be used, but a method of continuous heat setting is preferred.

The heat fixing time in each heat fixing zone ranges from 1 to 100
The time is preferably 3 to 30 seconds, more preferably 3 to 30 seconds.

Furthermore, the heat shrinkage rate of the uniaxially stretched polyester film produced by the method of the present invention is 0.9 at a treatment temperature of 100''C.
The content is preferably 3% or less.

An example of using a uniaxially stretched polyester film for liquid crystal display produced by the method of the present invention in a liquid crystal display element is9. It is used in liquid crystal display elements in a state where a transparent electrode film such as tin oxide or indium oxide is pasted or attached.

The thickness of the film in the present invention is not particularly limited, but is 3.
0 to 200 μm is preferable.

[Effect]

In the present invention, a uniaxially stretched film with appropriate molecular orientation is heat-set in two zones by limiting longitudinal stretching conditions, and in the first zone, the movement of uniaxially oriented molecules is fixed while , which promotes thermal crystallization, then in the second zone,
It is presumed that the object of the present invention is achieved by alleviating the residual strain inside the film. Furthermore, it is unclear whether the residual strain is greater in the orthogonal direction than in the orientation direction of the uniaxially stretched film.

〔Effect of the invention〕

The present invention is a method for producing a uniaxially stretched polyester film in which an amorphous film is stretched and the stretched film is heat-set in two zones, thereby achieving the following excellent effects. It is something.

(b) The heat shrinkage rate of the film is not necessarily small, and the difference between the heat shrinkage rates in the vertical and horizontal directions is small.

(b) In the width direction of the film, the deviation between the stretching direction and the optical axis direction of the film can be reduced.

(c) Because fibrillation of the film was suppressed.

This eliminates problems such as film cracking during the film manufacturing process.

) The film has good flatness.

[Measurement method and evaluation criteria for physical properties]

(1) Heat shrinkage rate: Attach marked lines with a distance of 7.5 Mn in the width direction and longitudinal direction of the film, and accurately measure the length between the marked lines (lゎ). After processing in a hot air oven at ℃ for 2 hours and cooling to room temperature, the length between the marked lines 2) was measured again and the thermal shrinkage rate was calculated from the 9th equation.

l.

A positive value of the heat shrinkage rate means that the film has shrunk, and a negative value means that the film has expanded.

In addition, the length between the marked lines was measured in a room at 25°C and 65% RH using a glass scale with a 10 μm graduation.
It was read using a microscope with a magnification of 40 times.

(2) Refractive index and birefringence According to ASTM-D542-50, with an Atsube refractometer,
The measurement was performed using methylene iodide (refractive index: 1.7425) as a contact liquid and a sodium lamp (wavelength: 589 nm) as a light source. Measurements were taken at 25°C.

It was conducted at 651RH. Note that the birefringence was determined by subtracting the refractive index in the direction perpendicular to the stretching direction from the refractive index in the stretching direction.

(3) Film fibrils (film cracks)
Fold the film with one hand so that the stretching direction of the film is in the direction of the crease until it fits tightly! It was determined as follows.

The film will not break...
・・ ○Film breaks ・・・・・・・・・・・
・・・・・・×(4) Flatness of the film A film measuring 30 cII in length and 30 cIn in width was placed on a flat glass plate and observed from the horizontal direction. When the film was in close contact with the film, it was considered that the film had good flatness.

(5) Optical axis misalignment A film is inserted between two polarizing plates that are orthogonally crossed so that their polarizing axes are oriented perpendicular to the horizontal direction, and a halogen lamp is inserted from one side. Apply a parallel beam of light (luminous flux diameter is 10 mm) as a light source, and
The amount of light leaking through the two polarizing plates is measured using a phototube. In addition, a uniaxially stretched polyester film of the same thickness whose optical axis direction is known in advance is inserted so that the optical axis direction is perpendicular, and the film is rotated to determine the rotation angle (which is the optical axis deviation angle of the film). Find the relationship between the amount of light passing through the polarizing plate and the amount of light leaking out. From this calibration curve,
Find the angle of deviation between the stretching direction and the optical axis direction of the film to be measured. Optical axis misalignment.

Excluding unnecessary edges of the film, measurements were taken continuously over the entire width of the film as a product, and the largest deviation angle was indicated as the optical axis deviation angle of the film.

〔Example〕

Next, two embodiments of the present invention will be described based on Examples.

Examples 1-5. Comparative Examples 1 and 2 PET having an intrinsic viscosity (I, V) of 0.62 (containing 0.01% of hydrated silica fine particles with an average particle diameter of 0°82 μm) was melt-extruded using an extruder and introduced into a T-die with a width of 650 mm.

This was made into a molten sheet, which was then wound around a drum cooled to 0° C. and rapidly cooled to obtain an amorphous PET film. This was stretched in the longitudinal direction using a group of heated rolls to the respective stretching ratios shown in Table 1. Film stretching temperature is 96℃
And so. Next, the stretched film was introduced into a tenter and heat-set. The heat fixation in the first zone at this time is 220°C2
15 seconds.

The shrinkage rate of the film in the width direction was set to 0%. The film was then cooled and immediately followed by a second zone of heat setting. Heat setting was performed at 20 D'o for 15 seconds, and the shrinkage rate in the width direction of the film was set to 4 factors. The thickness of the uniaxially stretched film was adjusted to 85 μm. The properties of the film obtained by this method were as shown in Table 1.

The optical axis shift of the film was measured at a portion with a film width of 400 mm after cutting off the edge of the film.

The films obtained by the method of the present invention were able to have low heat shrinkage rates in both the longitudinal and transverse directions (Examples 1 to 3). However, films obtained with stretching ratios outside the range of the present invention.

Because the flatness of the film was impaired and the heat shrinkage rate in the stretching direction was large, the film could not be the object of the present invention (Comparative Examples 1 and 2).

Moreover, the optical axis deviation of the films of Examples 1 to 3 was within 2 degrees. Comparative Examples 6 to 5 An unheated fixed film of a uniaxially stretched PET film was obtained in the same manner as in Example 2. The film was then introduced into a tenter and heat-set. At that time, the first zone is set under conditions where the heat fixation effect does not substantially occur, that is, the heat fixation temperature is set at 100.
'a, the width of the film was fixed, the film was passed through, and heat set only in the second zone. Heat fixation in the second zone was carried out at a temperature of 220°C for 15 seconds. At that time, the shrinkage percentage of the film in the width direction was determined as shown in Table 2. The properties of the film obtained by this method were as shown in Table 2.

When compared with the heat setting method of the present invention, heat setting was performed in one zone, resulting in a large lateral heat shrinkage rate of the film (Comparative Example 6). Therefore.

When the film was heat-set while increasing the shrinkage rate in the width direction in order to lower the heat shrinkage rate of the film, the deviation of the optical axis of the film increased (Comparative Examples 4 and 5).

The present invention uses a method in which a film that has been uniaxially stretched in the range of 3.0 to 5.8 times in the longitudinal direction is heat-set in two zones, thereby reducing optical axis deviation of the film and The heat shrinkage rate could be significantly reduced.

Example 4 An unheated fixed film of a uniaxially stretched PET film was obtained in the same manner as in Example 2. Next, the film was introduced into a tenter and heat-set. At that time, the heat fixation in the first zone is 220'O
, the shrinkage rate in the film width direction was set to 6 factors. Next, heat setting in the second zone was performed at 180° C. and the shrinkage rate in the width direction of the film was 5 yen.

Next, the film was cooled by blowing air at 30°C at the exit of the tenter. The heat shrinkage rate of the obtained film when processed at 100°C was 0.10% in the machine direction.

The horizontal direction was 0.008%. Furthermore, the optical axis shift of the film (film width: 400 nnn) was 0.7 degrees. A polarizing film was sandwiched between the obtained films and bonded together with an adhesive to make a polarizing plate. Two sheets of 100 square meters were cut out from this laminated body, and on one side of each of the two sheets, by sputtering method,
Vapor-deposited indium and tin oxide.

A transparent conductive film was created. This transparent conductive film was coated with a polyamide-based polymer, and its surface was wrapped with cotton cloth to form an alignment film. Layer the two sheets with the alignment films facing each other and insert a spacer between them to make the gap between the two sheets approximately 10 μm.After filling this gap with TN type liquid crystal, The four sides were sealed with an epoxy adhesive to make 20 liquid crystal cells each having two display areas of 10 mm x -60 mm. A voltage was applied to each to display six numbers on the liquid crystal display screen. As a result, clear images could be obtained with no blurring of the displayed number 9 or poor contrast for all 20 images.

Claims (1)

[Claims] (1) 5. Cut the polyester amorphous film in the longitudinal direction.
When stretching the film by 0 to 3.8 times and heat setting the film in the first zone and the second zone, the film is stretched to 180 to 2 times in the first zone.
The film is heat-set at a temperature of 40°C with a contraction rate of 0 to 5% in the width direction, and then the film is shrunk in the width direction at a temperature of 120°C or higher in the second zone and lower than the heat-setting temperature of the film in the first zone. A method for producing a uniaxially stretched polyester film for liquid crystal displays, which is heat-set at a ratio of 1 to 10%.