JPH01193803A - Production of polarizing film - Google Patents

Abstract

PURPOSE:To have good polarization performance and to improve surface characteristics by subjecting a film to longitudinal stretching and heat fixing while bringing the film into tight contact with rolls provided with electrostatic tight contact devices. CONSTITUTION:The sheet is first heated by a preheating roll group and thereafter, wire electrodes 4 are installed in respective positions A, B, C and the film is brought into tight contact with the rolls. The film is stretched by the stretching rolls 2, 3. The stretched film is guided to the preheating roll group for heat fixing and after the film is heated, the film is guided to a heater 5 using hot air and far IR heaters in combination between the rolls and is thereby heat-set. The electrostatic tight contact device disposed with the wire electrodes 4 in the positions A, B, C is installed between these rolls as well. The polarizing film having good surface characteristics and excellent polarization performance is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a polarizing film. Specifically, the present invention relates to a method for producing a polarizing film that has good polarizing performance and excellent surface properties.

<Prior Art and Problems to be Solved by the Invention> In recent years, the demand for polarizing films has increased rapidly with the development of liquid crystal displays. As a result, the required properties of polarizing films are becoming more diverse.
In addition to -I2-based polarizing films, the characteristics of polyester-dichroic dye-based polarizing films, which are excellent in heat-and-moisture resistance and heat-resistant dimensional stability, are also attracting attention. By the way, in order to produce a polyester paste polarizing film, a method is generally used in which an amorphous sheet is uniaxially stretched at a high magnification and then heat-set. Regarding stretching methods, two commonly used methods are longitudinal stretching, in which the film is stretched in the longitudinal direction between two rolls with different circumferential speeds, and horizontal stretching, in which both ends of the film are held between tenter clips and stretched in the width direction. Although it is known,
In stretching a polarizing film, which requires the film to be highly oriented, the longitudinal stretching method is more advantageous in that the strain rate can be very high, and the film can be highly oriented. However, the reality is that polyester polarizing films produced by the longitudinal stretching method have not been put into practical use to date, and the biggest obstacle to this is the problem of roll scratches that occur during stretching. When creating a polarizing film by stretching a non-oriented sheet in the uniaxial direction, the stretching should be done at as low a temperature as possible without causing whitening, and at a high magnification to improve film orientation and obtain good polarizing performance. . However, since the stretching stress generated at this time is very large, slippage is likely to occur at the contact point between the film and the roll, and as a result, many roll scratches occur on the film.

- In boat fishing, in order to prevent slippage between the roll and the film, a method is used in which an opposing roll is installed at an appropriate position around the opening involved in stretching, and pressure is applied to bring the film into close contact with the roll. However, in this method, the limit of the stretching stress that can be withstood is low, and new problems such as the introduction of deposits by bringing the facing roll into contact with the film arise.

This phenomenon in which the stretching stress becomes extremely large is particularly noticeable in the stretching of polarizing films, which requires a low temperature and high stretching ratio, unlike the case of obtaining ordinary biaxially stretched films where the stretching ratio is low in roll stretching. This is a problem.

Next, regarding the method of heat-setting a film that has been highly oriented in the longitudinal direction by longitudinal stretching, it is similar to heat-setting a biaxially stretched film. For convenience, methods such as heating a plurality of roll groups to a heat-setting temperature and passing an axially stretched film therethrough have been used for convenience.

These methods have fatal drawbacks; the former method allows free shrinkage in the longitudinal direction, resulting in an extremely poor orientation obtained by stretching; There are also problems with the heat-setting method itself, such as severe adhesion that causes the film to wrap around the roll, or even if the film flows smoothly, there are significant adhesion marks on the film surface, resulting in a film with poor surface properties. There is. In addition, in order to heat-set a film that is highly oriented in the longitudinal direction without deteriorating its orientation, it is necessary to keep the film length constant against the enormous shrinkage stress in the longitudinal direction. If a roll is used, slipping occurs between the roll and the film, resulting in scratches on the film.

Scratches and adhesive marks that occur on the polarizing film can cause blanking or blurring of the display when, for example, a liquid crystal display pattern is created using the polarizing film, so the polarizing film must have no scratches or adhesive marks. However, it has been difficult with conventional techniques to create a polyester-based polarizing film by longitudinal stretching that satisfies this requirement.

Means for Solving the Problems> The gist of the present invention is to melt-extrude a polyester resin containing a photodichroic substance to form an amorphous sheet, then longitudinally stretch the amorphous sheet, and then heat set it. In the method for producing a polarizing film, the longitudinal stretching and heat setting are performed while the film is brought into close contact with a roll using a roll equipped with an electrostatic adhesion device.

The present invention will be explained in detail below.

The photodichroic substance in the present invention is a substance that has anisotropy in light absorption, and specifically includes dyes, pigments, rod-shaped fine powders such as apatite, etc., but in terms of polarization performance, Dichroic dyes that are soluble in the polyester in the melt are most preferred. Specifically, common dyes such as anthraquinone dyes, quinophthalone dyes, and styrene dyes can be used. The content is determined by the light loss rate of the final polarizing film, but is usually 0.0θ/~10% by weight, preferably 0.07~10% by weight.
3% by weight is suitable.

The polyester resin used in the present invention is suitably one with good transparency, and specifically, aromatic polyesters such as polyethylene terephthalate and polyethylene naphthalate are preferred. These polyesters may be homopolymers, but as acid components, 4t'-biphenyldicarboxylic acid, p-hydroxybenzoic acid, terephthalic acid, isophthalic acid, phthalic acid, co-, ≦- or λ
, 7-naphthalenedicarboxylic acid, O-hydroxynaphthalene-2-carboxylic acid, etc., as a glycol component, g,
Use a polyester copolymerized with x'-dihydroxybiphenyl, y,<t'-dihydroxydiphenyl ether, 2,2-bis(4t-hydroxyphenyl)propane, trimethylene glycol, etc. within a range that does not impair transparency. You can also do it.

The above-mentioned dichroic material may be incorporated into the polyester by direct tri-blending, or by preparing a high-concentration masterbatch in advance and diluting it before use. When obtaining an amorphous sheet by melt extrusion, it is preferable to bring the molten sheet into close contact with a cooling drum by electrostatic application according to a conventional method.

Next, the method of the present invention will be explained with reference to the drawings.

Longitudinal stretching as used in the present invention refers to a known method in which a peripheral speed difference is applied between rolls, and an amorphous sheet is stretched in the longitudinal direction between a pair of rolls at a magnification according to the peripheral speed ratio. For example, Figure 1,
There are stretching methods shown in FIG. 2, but the method is not limited thereto. Heat-setting the film after longitudinal stretching means, for example, that the film passes through a heating device (5) installed between two rolls, as shown in Figure 2, to increase the crystallinity of the film. It refers to increasing.

In the case of longitudinal stretching as referred to in the present invention, the low-speed roll (for example, (2) in Figures 1, 2, and 3) is heated as necessary, but the temperature is such that the stretched film does not whiten. It is preferable to adjust the temperature to as low as possible within the range from the viewpoint of highly oriented the film.

The electrostatic adhesion device in the present invention is: /) An electrode is installed in a non-contact manner to the film and parallel to the roll surface, and the atmosphere near the electrode is ionized by applying a voltage.
2) A device that electrostatically brings the film into close contact with the roll by applying the ions to the film, and 2) a counter electrode roll that comes into contact with the film, which sandwiches the film and creates a high potential difference between it and the roll. This includes anything that holds the film in close contact with the roll electrostatically.

For example, when using the former non-contact electrode, the electrode (4) is A-A', B-8' as shown in FIG.
It is preferable to provide three locations between , C and C', as this can most effectively prevent slippage between the roll and the film. Further, the electrode (4) is appropriately selected from known wires, bands, knives, needles, etc., the distance between the electrode (4) and the roll surface is preferably from t to θ, and the applied voltage is from 3 to - 〇4 is preferred. These conditions are such that spark discharge does not occur and are appropriately adjusted depending on the speed, stretching ratio, film thickness, etc.

On the other hand, when using the counter electrode roll (6) as an electrostatic adhesion device, for example, as shown in FIG. It is preferable to arrange the electrode roll (6) so that The material of the counter electrode roll (6) is not particularly limited, but it is preferably made of an elastic material, and the contact pressure between the rolls is preferably 9/crn or less per width. The applied voltage is preferably 0.7 to /θ, but as in the case of non-contact electrodes, it may be adjusted as appropriate depending on the speed, stretching ratio, film thickness, etc.
be adjusted.

Using a group of rolls equipped with the electrostatic adhesion device described above, for example, if the peripheral speed ratio between the rolls is set high, the film will be longitudinally stretched, and the film will be stretched longitudinally, and the film will be stretched between the rolls with the peripheral speed ratio close to /. If the film is passed through the heated heating device (5), the film will be heat-set. Especially when heat fixing,
A heat fixing zone using a far infrared heater, a hot air heater, or a combination of both is provided between the two rolls equipped with an electrostatic adhesion device, and the surface temperature of the roll group is kept below the stretching temperature in longitudinal stretching. The preferred method is to do so. In this case, the shrinkage stress associated with the increase in crystallinity due to heat setting is enormous, so as with longitudinal stretching, conventional opposed rolls (e.g. rubber-lined nip rolls) cannot prevent the occurrence of slippage. Furthermore, by making the heat supply source for heat fixing non-contact with the film and by setting the surface temperature of the roll that contacts the film to be below the stretching temperature, it is possible to prevent the film from sticking to the heat fixing roll and being rolled up by the adhesive.

In the present invention, during stretching, an electrostatic adhesion device is installed on the stretching rolls, and during heat setting, a heating device is installed between two rolls equipped with an electrostatic adhesion device, and the roll group is The effect is maximized by keeping the surface temperature below the stretching temperature.

During the above heat fixing, the circumferential speed ratio between the rolls equipped with the electrostatic adhesion device is not limited to 80, but can be set to 7.0 or less, for example, to loosen the stretched film and improve longitudinal dimensional stability. 7. By making the film larger than θ, it is possible to further enhance the orientation of the stretched film by further stretching it in the longitudinal direction during heat setting. However, in these cases, if the peripheral speed ratio deviates significantly from 7.0, the orientation will decrease and the film strength will decrease, so the peripheral speed ratio during heat setting is 0. ? It is preferable to adjust the temperature within the range of evening to /, /evening.

According to the method of the present invention, it is possible to suppress the film from sliding on the roll as much as possible under the pressure of producing a polarizing film, which is subject to stronger stress than usual, and to prevent the occurrence of scratches.

Furthermore, since the film on the roll can be firmly adhered to the roll, the stretching section can be strictly fixed, and as a result, a polarizing film with less thickness fluctuation and orientation unevenness can be obtained.

<Examples> Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Incidentally, the measured values described in the examples were obtained by the measuring method shown below.

(1) Birefringence; Δn The retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and the birefringence Δn in the film plane was determined by the following formula.
I asked for

Δn=R/d However, in the above formula, R represents retardation and d represents film thickness.

(2) Dye orientation coefficient; FD The absorbance is determined from the intensity of light at the maximum absorption wavelength that has passed through the sample film, of polarized light vibrating parallel and perpendicular to the stretching axis of the film, and the dye orientation coefficient FD is determined using the following formula. Ta.

Fo = (D-/) / (D+, 2) However, in the above formula, D (dichroic ratio) = A, /A, where A and / represent the absorbance of polarized light parallel to the stretching axis, and A The upper part represents the absorbance of light perpendicular to the stretching axis.

(3) Degree of polarization (%) The degree of polarization P at the highest absorption wavelength was determined by the following formula.

p = (<Shimado T700) - 71) x / 00 (%
) However, in the above formula, T//id is the transmittance measured by stacking two films so that their stretching axes are parallel to each other, and T is the transmittance measured when two films are stacked so that their stretching axes are perpendicular to each other. (4) Heat shrinkage rate of film (%) After leaving a 10 cm long film in a guarded oven at a temperature of θ°C ±/°C for 7 hours without any load. The heat shrinkage rates of the film in the longitudinal and lateral directions were determined according to the following.

However, in the above formula, lo represents the original length of the film, and l represents the length after shrinkage.

(5) Extent of scratches The extent of scratches on the film surface was visually evaluated. The following classification was performed based on the number of scratches of approximately 0.5 or more among the 70 horns.

θ book/ /θ0c shoulder: ○ 7~. 20 pieces 7yooc, : Δ 20 lines or more / 100C shoulder: × Scratches on the entire film: sex pigment (N1honthreueRed FBB d
is, pdr, ) were triblended to a blending amount of 0.10 wt%. This was melted and extruded using an extruder at 2F3°C, and then rapidly solidified on a cooling drum at about 50°C using an electrostatic cooling method to obtain a substantially amorphous sheet with a thickness of 0 μm. This sheet first? After being guided to the first preheating roll group (surface speed 2 m/min) heated to 2°C and heated, it was heated to 3.
．． It was stretched 0 times. This stretching roll has (
A wire electrode (4) (1 tungsten wire with a diameter of 50 μm) was installed at each position of A), (B), and (C), and the distance between each electrode and the roll surface was approximately 10 WIn.
The applied voltage as! , θ■ was applied to bring the film into close contact. Further, this film was guided to a second preheating roll group heated to 7J"C (surface speed 4 rrt 7 minutes), and after heating, it was passed through a stretching roll equipped with an electrostatic adhesion device similar to the second stage to 37 times the temperature. It was stretched (tota1 magnification!, 0 times).

At this time, a voltage of 7.0 KV was applied to each electrode. This stretched film was heated to a group of preheating rolls for heat setting (surface speed, 2 m
/min) and heated, then introduced into a heating device (5) using both hot air and a far-infrared heater between the rolls arranged as shown in FIG. 2, and heat-fixed at / and 0°C. Between these rolls are (A), (B), and C shown in Figure 2.
An electrostatic adhesion device having the wire electrodes (4) described above is installed at the position C'), and each electrode has an applied voltage of ? Electrostatic adhesion was performed with a distance of about 10 rrrm between the surface of the electrode and the surface of the electrode. Further, the circumferential speed ratio between the rolls was set at 80.

The properties of the obtained film are shown in Table 1.

Pigment structural formula: (Production method of polyethylene naphthalate) 2, O-naphthalene dicarboxylic acid dimethyl ester 10 θ parts, ethylene glycol 60 parts and magnesium acetate tetrahydrate θ, 0
Nine parts of the mixture were placed in a reactor and heated to raise the temperature, and a transesterification reaction was carried out while methanol was distilled off. The temperature was raised to 230°C over about 9 hours after the start of the reaction, and the transesterification reaction was substantially completed. Then ethyl acid phosphate 0
．． After adding 0 parts, 0.09 parts of antimony dioxide was added, and the temperature was gradually increased until it finally reached 20°C, and the pressure was gradually reduced from normal pressure to /mmHg. . The reaction was stopped 3 hours after the start of the reaction, and the polyethylene-2. T-naphtha v-1 was discharged. The intrinsic viscosity of the obtained polyethylene naphthalate was 0. It was great.

The polymer was pre-crystallized under nitrogen at 770° C. for 1 hour, further dried at 0.3 mmHg and 0° C. for 1 hour, and then solid-state polymerized at 0.3 mmHg and 2’10° C. for 1 hour. The intrinsic viscosity of the obtained polyester is 0
．． It was 67.

(Method for producing polyethylene naphthalate film) After drying the polymer obtained by the above method by a conventional method, the dichroic dye (Diamond Resin Yel) manufactured by Mitsubishi Kasei Co., Ltd.
low H2C) was triblended to a blending amount of 0.0/&wt%. This was melted and extruded at 29 parts Celsius using an extruder, and then rapidly solidified using an electrostatic cooling method on a cooling drum of about 50°C to obtain a substantially amorphous sheet having a thickness of θ0 μm. This sheet was guided to a group of preheating rolls heated to 73 parts C (surface speed Jm/min), and after being heated,
The film was stretched 5.5 times using stretching rolls arranged as shown in FIG. This stretching roll is equipped with the same electrostatic adhesion device used during stretching in Example/, the distance between each electrode and the roll surface is set to 10 parts MI, and the applied voltage is 6.0 parts MI. The sheet was brought into close contact with the roll in between. This stretched film was once wound up and then guided to a group of preheating rolls for heat fixing heated to 730°C (surface speed 2 m/min), and after heating, the electrostatic adhesion device used for heat fixing in Example was installed. Heat setting was carried out at 220° C. using a heating device (5). At this time, the distance between each electrode and the roll surface is 70
The film was brought into close contact with the film by applying an applied voltage of 0Kv, and the circumferential speed ratio between the rolls was set to / and θ.

The properties of the obtained film are shown in Table 1.

Pigment structural formula: N1h in polyethylene terephthalate as in Example/
onthreue Red FBB dis, pdr
An amorphous sheet with a thickness of 4t00 μm containing 0.10 wj% of , was obtained, and after performing two-step stretching in the same manner as in Example, it was heat-set at 0°C. However, a facing electrode roll (6) shown in Fig. 3 is installed on the stretching roll and heat setting roll, and the film is brought into close contact with the rolls (2) and (3) by contact pressure without applying voltage. method was adopted. A roll capable of applying pressure up to 7 Jcf/cm per width was used as the counter electrode roll, but during the second stage of stretching,
In roll (3), slippage was observed between the film and the roll surface, and even if the voltage was maximized, this slippage could not be stopped. In addition, slippage occurred even during heat setting.

The properties of the obtained film are shown in Table 1.

Comparative Example = An amorphous sheet with a thickness of 4ioθμm was obtained by blending 0.0/&w1% of Diarezi 7 Yellow H-2G with polyethylene naphthalate in the same manner as in Example C, and this was stretched in the same manner as in Example C. After that, it was heat-set at 22θ°C. However, for the stretching roll and the heat setting roll, a rubber-lined nip roll was installed in the same place instead of the opposed electrode roll used in Comparative Example. Slippage between the film and roll surface is only slightly observed during stretching.
There were not many scratches on the film surface, but there was considerable slippage on the heat-setting roll.

The properties of the obtained film are shown in Table 1.

Comparative Example 3 N1h was added to polyethylene terephthalate in the same manner as in Example
onthrene Red FBB dis, pdr
An amorphous sheet with a thickness of μm containing 0.10 wt% of
Heat fixation was performed at 0°C. However, the electrostatic adhesion device was not installed on the stretching roll, and instead, the nip roll used in Comparative Example 1 was installed at the same location. The electrostatic adhesion device used in Example was installed on the heat fixing roll. Using this apparatus, the second-stage stretching ratio was gradually increased from 0x to obtain a stretched film sample at the maximum stretching ratio that could be stretched without causing sagging.

The obtained film had almost no scratches on the surface, but the second stage stretching ratio was increased to 7.3 times (tota 13.9 times).
As a result, the film orientation was insufficient and the dye orientation coefficient (FD) was as low as 0.

Comparative Example: An amorphous sheet with a thickness of 00 μm was obtained by blending polyethylene naphthalate with 0.0/11 wt% of Diaresin Yel low H2G in the same manner as in Example λ, and after stretching it in the same manner as in Example A. Heat fixation was performed at 220°C. However, for heat fixation, the surface temperature was set to 220℃.
I used a book heat setting roll. However, as soon as the stretched film was passed through, severe adhesion occurred and the sample could not be collected due to wrapping around the roll.

The physical properties of the films obtained in Examples/, = and Comparative Examples/--g are summarized in Table -/.

<Effects of the Invention> According to the method of the present invention, it is possible to set a large stretching ratio with almost no roll scratches on the surface of the film, resulting in a film with good surface properties and excellent polarizing performance. polarizing film can be produced.

In addition, for heat fixing, a heating device is installed between the rolls,
In addition, by keeping the roll surface temperature below the stretching temperature, it is possible to suppress the adhesion of the film to the roll, and by installing an electrostatic adhesion device on the nuclear heat setting roll, it is possible to prevent the occurrence of scratches on the film during heat setting. be able to. As a result, it is possible to produce a polarizing film with good surface properties and excellent heat-resistant dimensional stability, and the method of the present invention is effective as a method for producing polarizing films.

[Brief explanation of the drawing]

FIG. 7, FIG. 2, and FIG. 3 are schematic explanatory diagrams showing an example of an apparatus for carrying out the present invention. In the figure, (1) is a film,
(2) and (3) are rolls, (4) is an electrode, (5) is a heating device, and (6) is a counter electrode roll. (B) is the point where the film leaves the roll, (
B') is a point forming a circumferential angle of 250 degrees opposite the direction of film movement. Applicant: Diafoil Co., Ltd. Agent: Patent attorney: Yo Hase - 7 others Kuzu 1 Kou No. 28

Claims (1)

[Claims] (1) A method of manufacturing a polarizing film by melt-extruding a polyester resin containing a photodichroic substance to form an amorphous sheet, then longitudinally stretching the amorphous sheet, and then heat-setting the amorphous sheet, the method comprising: A method for producing a polarizing film, characterized in that heat fixing is carried out while the film is brought into close contact with the roll using a roll equipped with an electrostatic adhesion device.