JP2003121818A - Oriented polyester film for liquid crystal display plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an adhesive property, moisture resistance and a blocking property in a film used as a component of a liquid crystal display plate in a liquid crystal display device. SOLUTION: An oriented film is composed of polyethylene terephthalate. A difference between the maximum refractive index and the minimum refractive index of the film is >=0.08. Variation of principal orientation axis is <=5 deg.. Total light transmittance is >=80%. A coating film is laminated on at least one surface thereof. The coating film contains a copolyester (A), a water soluble polymer compound (B) and fine particles (C). (A) has the ratio of a dicarboxylic acid component with a sulfonic acid base group to the total dicarboxylic acid component ranging from 1 to 16 mol % and has 20-90 deg.C second order transition temperature. (C) has 20-80 nm average particle diameter. Respective contents in the coating film are 30-80 wt.% (A), 10-45 wt.% (B) and 3-25 wt.% (C). Surface energy of the coating film is 50-70 dyne/cm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oriented polyester film used as a constituent element of a liquid crystal display panel.

[0002]

2. Description of the Related Art Conventionally, as a film for a liquid crystal display panel, a triacetate film formed by a casting method has been used.
No polyethylene terephthalate film was used. The reason is that the biaxially oriented polyethylene terephthalate film is not uniform in the direction of the optical orientation axis, and therefore, when used as a polarizing plate protective film used for a liquid crystal display plate, the optical characteristics become uneven, which is inconvenient. Is. In addition, the property required for the protective film of the polarizing film is that it is optically non-oriented, that is, the change in the amount of transmission is small even if the film is rotated in-plane in crossed Nicols, or it is oriented in one direction. (However, it is important that they are oriented in the vertical direction or the horizontal direction when viewed from the bonding work surface).

If these conditions are not satisfied, the ratio of the amount of transmitted light is small when an electric field is applied to the liquid crystal between the orthogonal polarizers and when there is no electric field, and the function as a display plate is lost. . Therefore, a casting unstretched film which is a non-oriented film, for example, a triacetate film is optically suitable, and a biaxially oriented polyester film in which the orientation axis direction is not constant is unsuitable.

[0004]

In recent years, liquid crystal display panels have come to be used in various fields. As a result, some applications, such as display devices for automobile dashboards, are
In applications where the humidity is high, the deterioration of triacetate due to heat and moisture, especially the generation of bubbles, becomes a drawback.
As a countermeasure against this, a film made of a material having a wet heat deterioration superior to that of the triacetate film is desired.

Further, a polyester film used as a base film when a polarizing film with a protective film is prepared by laminating an oriented polyethylene terephthalate film and a polyvinyl alcohol uniaxially oriented film having adsorbed iodine, which is a polarizer, with each other in the flow direction thereof. Has poor adhesion to.

The object of the present invention is to obtain a clear extinction property under crossed Nicols while maintaining the dimensional stability and long-term wet heat deterioration resistance of the oriented polyethylene teralate film, and also to provide a uniaxial polarizer. It is an object of the present invention to provide a film suitable for a protective film of a polarizer for a liquid crystal display plate, a transparent electrode of a liquid crystal element, a surface protective plate, etc., which has dramatically improved adhesiveness to oriented polyvinyl alcohol.

[0007]

The oriented polyester film for a liquid crystal display panel of the present invention is an oriented film composed of polyethylene terephthalate in a film used as a constituent element of a liquid crystal display panel in a liquid crystal display device, and has a maximum refractive index of the film. The difference between the refractive index N _MAX and the minimum refractive index N _{M IN} (N _MAX −N _MIN ) is 0.08 or more, and in the film sampled in 50 cm square, the variation of the orientation main axis with respect to the linear axis set in any direction is 5 at all positions.
The total light transmittance within 80 ° and in the visible light wavelength range of the film is 80% or more, a coating film is laminated on at least one side of the film, and the coating film is a copolyester (A) and a water-soluble polymer compound ( B) and fine particles (C) are contained, and the copolyester (A) has a ratio of the dicarboxylic acid component having a sulfonate group to the total dicarboxylic acid component of 1 to 16 mol% and a second-order transition temperature of 20 to 90 ° C. The average particle diameter of the fine particles (C) is 20 to 80 nm, and the content of the fine particles (C) in the coating film is 30 to 80% by weight of the copolyester (A),
The water-soluble polymer compound (B) is 10 to 45% by weight, the fine particles (C) are 3 to 25% by weight, and the surface energy of the coating film is 50 to 70 dyne / cm.

<Polyester Film> Polyethylene terephthalate is used for the oriented polyester film in the present invention, but other components may be copolymerized within a range not impairing the effects of the present invention. As other copolymerization components, as acid components, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, isophthalic acid, 2-6 naphthalenedicarboxylic acid, 2-7 naphthalenedicarboxylic acid, 1-5 Aromatic dicarboxylic acids such as naphthalene dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid and anthracene dicarboxylic acid can be preferably mentioned. Preferred examples of the alcohol component include aliphatic diols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol and hexanediol, and polyalkylene glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol. These may be used alone or in combination of two or more.

In order to improve the winding property of the polyester during the production of the film and the transportability of the film when the coating layer is applied, the polyester may contain organic or inorganic fine particles as a lubricant, if necessary. May be included. It is important that the added amount is not too large in consideration of the light transmittance. Examples of such fine particles include calcium carbonate, calcium oxide, aluminum oxide, kaolin, silicon oxide, zinc oxide, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, urea resin particles, melamine resin particles and crosslinked silicone resin particles. In addition to the fine particles, other resins such as colorants, antistatic agents, antioxidants, lubricants, catalysts, polyethylene, polypropylene, ethylene-propylene-polymers, olefinic ionomers and the like are also used within a range that does not impair transparency. It can be optionally contained.

Since a film having a thickness of about 30 to 100 μm is usually used, in order to secure a light transmittance of 80% or more, the particle size of the inorganic fine particles is 1 μm or less and the addition amount is 0.01% by weight or less. desirable. If the addition amount is more than 0.1% by weight, the light transmittance often becomes less than 80%, the contrast of displayed figures and characters becomes weak, and the display quality deteriorates.

In the present invention, the oriented polyethylene phthalate has a difference (N _MAX -N _MIN ) between the maximum refractive index N _MAX and the minimum refractive index N _MIN of the film of 0.08 or more. This is preferably 0.09 or more, more preferably 0.10 or more. N _MAX -N _MIN is colored to be smaller than the range on the liquid crystal display image occurs. Further, when a sample is taken from a conventional film roll, the film is formed in the film forming direction (longitudinal direction), and is cut out based on the direction perpendicular to the film forming direction, and the refractive index is not always the maximum or minimum value of the sample refractive index. Was not. The polarizer is usually based on a longitudinally uniaxially stretched film of a polyvinyl alcohol film, and it is desirable that the polarizing direction of the film is the same as that of the polyester film which is the protective film. The birefringence value in the present invention is defined as the value obtained by subtracting the minimum value from the maximum value of the refractive index of the cut sample, that is, the value obtained by subtracting the minimum value from the maximum value of the index ellipsoid. By sticking the direction of maximum refractive index and the uniaxial stretching direction of polyvinyl alcohol, it is possible to match the polarization direction with the polarizer more efficiently than the conventional technology in which the film width direction and the alignment direction of polyvinyl alcohol are matched. it can.

Further, the variation of the orientation main axis with respect to the linear axis set in an arbitrary direction of the film sampled in 50 cm square is within 5 ° at all locations. This is preferably within 4 °, more preferably within 3 °. If there is a place where the variation of the orientation main axis exceeds 5 °, an interference color is generated when the liquid crystal display device is constructed by using this film, and the display quality is significantly impaired.

The film of the present invention has a total light transmittance of 80% or more, preferably 83% in the visible light wavelength range.
Or more, More preferably, it is 86% or more. If the total light transmittance is less than 80%, the contrast of display, figures and characters is weakened and the display quality is deteriorated.

The film of the present invention preferably has a heat shrinkage of 1% or less when held at 150 ° C. for 30 minutes. It is more preferably 0.5% or less. This value is 1%
Anything that shrinks beyond will shrink due to the heat at the time of commercialization,
It may not be a product. A stretched film having such a heat shrinkage can be obtained, for example, by heat-setting after stretching or heat treatment at a temperature of Tg or higher of polyester so that the density of the film becomes 1.390 g / cm ³ or higher.

In the oriented polyester film for a liquid crystal display panel produced by a known stretching method which is a conventional technique, the bowed portion of the edge is rarely used as a product. However, in the present invention, even if the product is cut out from the bowing portion of the edge, the product can be collected if the physical properties are within the range of the present invention, so that the product can be collected efficiently and efficiently over the entire width. .

Next, an example of the method for producing the film of the present invention will be described. The extrusion film-forming process can be carried out by a tenter method as usual. In this case, the longitudinal direction means a film forming direction (longitudinal direction) of the film, and the lateral direction means a direction perpendicular to the film forming direction of the film. In the biaxially stretched film formation of the present invention,
The direction in which the draw ratio is high may be either the longitudinal direction or the transverse direction, but more preferred is a method in which the draw ratio in the transverse direction is increased and the film is drawn.

The stretched polyethylene terephthalate film in the present invention achieves the birefringence, the dispersion angle of the orientation main axis in the vicinity of the center and the edge portion over the entire width of the film as described above, so that the stretching ratio thereof is less than 2.0 in the longitudinal direction. It is preferably less than 1.8, more preferably less than 1.6, and 4.0 or more in the lateral direction, preferably 4.2 or more, and more preferably 4.4 or more. A film formed at a magnification outside this range can achieve the birefringence near the center with respect to the width direction of the film and the dispersion angle of the orientation main axis with respect to the linear axis set arbitrarily, but the range is narrow,
Most of the range does not satisfy the performance required for this application, resulting in poor productivity.

<Coating film> In the present invention, the film includes a copolyester (A), a water-soluble polymer compound (B), fine particles (C), and preferably a crosslinking agent (D) represented by the following formula (I). A coating film containing as a component is laminated.

[0019]

[Chemical 5]

(However, R in the structural formula (I) is any of the following structural formulas (II) to (IV).)

[0021]

[Chemical 6]

[0022]

[Chemical 7]

[0023]

[Chemical 8]

The copolyester (A) used as a component for forming this coating film is a polyester in which the ratio of the dicarboxylic acid component having a sulfonate group to the total dicarboxylic acid component in the molecule is 1 to 16 mol%. . Such copolyesters include terephthalic acid, isophthalic acid, 2,6-
Naphthalene dicarboxylic acid, hexahydroterephthalic acid,
Carboxylic acid components such as 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, adipic acid, sebacic acid, 5-sulfoisophthalic acid, trimellitic acid, dimethylolpropionic acid and 5-Nasulfoisophthalic acid, 5-K A dicarboxylic acid component having a sulfonate group such as sulfoisophthalic acid and 5-K sulfoterephthalic acid;
Hydroxy compounds such as ethylene glycol, diethylene glycol, neopentylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, glycerin, trimethylolpropane and bisphenol-A alkylene oxide adducts A polyester composed of components and used as an aqueous solution, an aqueous dispersion or an emulsion.

In the copolyester (A), the dicarboxylic acid component having a sulfonate group for imparting hydrophilicity is 1 to 16 mol% based on all dicarboxylic acid components in the molecule.
Must be This is preferably 1.5 to 14 mol%. If the dicarboxylic acid component having a sulfonate group is less than 1 mol%, the hydrophilicity of the copolyester will be insufficient, while if it exceeds 16 mol%, the moisture resistance of the coating film will be reduced, such being undesirable. The second-order transition temperature (Tg) of the copolyester (A) needs to be 20 to 90 ° C. If the Tg is less than 20 ° C, the film tends to be blocked, while if it exceeds 90 ° C, the adhesiveness of the film decreases, which is not preferable.

Preferred examples of the water-soluble polymer compound (B) include polyvinyl alcohol and polyvinylpyrrolidone. Among these, the saponification degree is 75-
It is preferred to use 95 mol% polyvinyl alcohol. If the degree of saponification is less than 75 mol%, the moisture resistance of the coating film will decrease, while if it exceeds 95 mol%, the adhesion to polyvinyl alcohol will decrease, which is not preferable. Furthermore, polyvinyl alcohol is cation-modified,
It is preferable because it has good adhesiveness. When polyvinylpyrrolidone is used, it preferably has a K value of 26 to 100. When the K value is less than 26, the strength of the coating film is weak, which is not preferable. Further, when the K value exceeds 100, the adhesiveness to polyvinyl alcohol used for the polarizer decreases, which is not preferable. Further, if the average molecular weight of the water-soluble polymer compound (B) is 40,000 or less, the abrasion resistance of the coating film of the film decreases, which is not preferable.

The fine particles (C) are organic or inorganic fine particles having a particle size of 20 to 80 nm. Examples of such fine particles include calcium carbonate, calcium oxide, aluminum oxide, kaolin, silicon oxide, zinc oxide, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, melamine resin particles and crosslinked silicone resin particles. If the particle size of the fine particles is less than 20 nm, the film tends to be blocked, while if it exceeds 80 nm, the sharpness decreases, which is not preferable.

Further preferably, by using a compound represented by the following formula (I) as a cross-linking agent (D) as a component for forming the coating film, the adhesiveness between the coating curtain and the polyvinyl alcohol which is the polarizer is Becomes extremely strong.

[0029]

[Chemical 9]

(However, R in the structural formula (I) is any of the following structural formulas (II) to (IV).)

[0031]

[Chemical 10]

[0032]

[Chemical 11]

[0033]

[Chemical 12]

In the present invention, the copolyester (A),
The blending ratio of the water-soluble polymer (B) and the fine particles (C) in the coating film is 30 to 80% by weight of the copolyester (A),
10 to 45% by weight of water-soluble polymer (B), fine particles (C)
Is 3 to 35% by weight. If the proportion of the component (A) is less than 30% by weight, the adhesiveness to the polyester film will be insufficient, while if it exceeds 80% by weight, the adhesiveness to polyvinyl alcohol, which is a polarizer, will be reduced, which is not preferable.
When the proportion of the component (B) is less than 10% by weight, the adhesiveness to polyvinyl alcohol which is a polarizer is insufficient, while when it exceeds 45% by weight, blocking resistance is deteriorated, which is not preferable. When the ratio of the component (C) is less than 3% by weight,
The slipperiness (transportability) of the film is insufficient, while if it exceeds 25% by weight, the sharpness is deteriorated, which is not preferable. Further, when the cross-linking agent (D) is added to the coating film, if the proportion of the component (D) is less than 5% by weight, the adhesiveness to polyvinyl alcohol which is a polarizer is insufficient, while if it exceeds 20% by weight, blocking resistance is increased. It is not preferable because it lowers the property and the adhesiveness with the polyester film.

The coating film of the present invention must have a surface energy of 50 to 70 dyne / cm. Particularly, it is preferably from 52 to 65 dyne / cm. If the surface energy is less than 50 dyne / cm, the coatability and adhesiveness of the coating layer will be poor,
If it exceeds 70 dyne / cm, the adhesion with the polyester film as the substrate may be insufficient, or the moisture resistance of the coating film may be insufficient, which is not preferable. Surface energy is 5
A coating film having a copolyester (A), a water-soluble polymer (B) and a fine particle (C), preferably a cross-linking agent (D), in the range of 0 to 70 dyne / cm is, for example, 0. It can be obtained by laminating with a thickness of 02 to 1 μm.

In the present invention, other than the above-mentioned components, other resins such as melamine resin, antistatic agents, colorants, surfactants, and ultraviolet absorbers can be used as the components for forming the coating film.

<Lamination of Coating Film> In the present invention, a coating film comprising the above components is laminated on at least one surface of the polyester film. This is a stretchable polyester film, after applying an aqueous liquid containing the components that form a coating film,
It can be laminated by drying, stretching, and heat treatment if necessary. The solid content concentration of this aqueous liquid is preferably 30% by weight or less, more preferably 10% by weight or less.

The above-mentioned stretchable polyester film is an unstretched polyester film, a uniaxially stretched polyester film or a biaxially stretched polyester film.
Of these, a longitudinally stretched polyester film that is uniaxially stretched in the extrusion direction (longitudinal direction) of the film is particularly preferable.

When an aqueous liquid is applied to a polyester film, if it is carried out in a usual coating process, that is, in a process separated from the manufacturing process of the film on the polyester film which is biaxially stretched and heat-fixed, it is easy to entrap dirt, dust and the like. Not preferable. From this viewpoint, application in a clean atmosphere, that is, application in the film manufacturing process is preferable. Then, according to this coating, the adhesion of the coating film to the polyester film is further improved.

As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brushing method, a spray coating method, an air knife coating method, an impregnation method and a curtain coating method can be used alone or in combination. The coating amount is 0.5 to ²⁰ g per 1 m ² of the running film, and further 1
10g is preferable. The aqueous liquid is preferably used as an aqueous dispersion or emulsion.

The stretchable polyester film coated with the aqueous liquid is guided to the drying and stretching treatment steps, and such treatment can be carried out under the conditions conventionally accumulated in the art. As preferable conditions, the drying condition is 90 to 13
It is 2-10 seconds at 0 degreeC. Stretching temperature is 90-130 ° C
Is preferred. The stretching ratio in the machine direction is less than 2.0, preferably less than 1.8, more preferably 1.6 in order to achieve a variation angle of the orientation main axis with respect to a linear axis set in an arbitrary direction of a film sampled in a 50 cm square. Less than 4.0 in the lateral direction, preferably 4.2 or more,
It is more preferably 4.4 or more. When heat-fixing, 170-240 degreeC and 2-20 second are preferable. The thickness of the polyester film after such treatment is 30 to 150 μm, and the thickness of the coating film is 0.0.
It is preferably 2-1 μm.

[0042]

EXAMPLES The present invention will be further described below with reference to examples and comparative examples. Various physical properties and evaluation characteristics in the present invention are measured and evaluated as follows.

(1) Film thickness Using a dot-type film thickness system, the thickness was measured at 50 arbitrary locations in the film width direction and 50 locations in the longitudinal direction near the center of the film width, for a total of 100 locations. The number average value of is the film thickness. In addition, in the film as the sample, the thickness unevenness in the width direction and the longitudinal direction is +
A material within 20 to -20% thickness is used. A film having a thickness unevenness exceeding this range is not preferable for a liquid crystal display plate because it causes poor display contrast and poor display quality.

(2) A birefringence Abbe refractometer was used to measure 18 cm with respect to the linear axis set in an arbitrary direction of the film sampled in 50 cm square.
The maximum refractive index N of the film was measured by measuring the refractive index over 0 °.
The difference between _MAX and the minimum refractive index N _MIN (N _MAX −N _MIN ) was defined as the value of birefringence (Δn).

(3) A straight line is drawn on a linear axis set in an arbitrary direction of a film sampled in a 50 cm square orientation axis and observed under a polarizing microscope. At that time, the line drawn on the film should be overlapped with the cross line in the field of view of the polarizing microscope. Next, the stage of the polarization microscope is rotated clockwise, and the rotation angle of the stage when the field of view becomes darkest is read from the scale and used as the tilt of the alignment axis.

(4) Total light transmittance Using an integrating sphere type haze meter manufactured by Nippon Seimitsu Optical Co., Ltd., the total light transmittance in the visible light wavelength range was measured.

(5) Stretching ratio The longitudinal stretching ratio was defined as the ratio of the rotation speed of the rolls before and after the longitudinal stretching zone. The lateral draw ratio was defined as the ratio of the width of the entrance to the width of the lateral draw zone.

(6) Heat Shrinkage The heat shrinkage of the polyester film after heat treatment at 150 ° C. for 30 minutes was measured at a gauge length of 30 cm.

(7) Polyvinyl alcohol adhesiveness (tape peeling evaluation) Spherical silica (average particle size 18
μm, average pore diameter 20 nm, average pore volume 1.5 cc /
g) An aqueous slurry obtained by mixing 70% by weight and 30% by weight of polyvinyl alcohol (trade name “PVA117” manufactured by Kuraray) was applied so that the dry thickness would be 20 μm. In addition, an adhesive tape having a width of 12.7 mm and a length of 150 mm (trade name “Scotch Tape No. 60, manufactured by 3M Co., Ltd.
0 ") was adhered to prevent air bubbles from entering. Further, this was leveled with a manual load roll described in JIS C2701 (1975) to be in close contact. After that, it was cut into a tape width. When the pressure-sensitive adhesive tape was peeled off from the sample thus prepared, the peeled state from the polyester film was observed, and the adhesiveness with polyvinyl alcohol was evaluated as follows. ⊚ (Good): No peeling was observed and the adhesion was good. ◯ (Slightly good): Peeling was slight and slightly good. Poor (poor): Peeling was remarkable and poor.

(8) Surface energy W. A. Zisman: "Contact Aug
le, Wettability and Adheses
Ion ", Am. Chem. Soc., (196
According to 4), the surface energy was defined as the critical surface tension γc measured.

(9) Secondary transition point differential calorimeter (Thermal Anal manufactured by DuPont)
yst 2000 type) at a heating rate of 20 ° C./min.

(10) Blocking property Two films cut to a width of 50 mm are stacked, and 50 kg /
cm ² load, temperature 40 ℃, relative humidity 50% RH
Hold for 17 hours. Then, the peel strength (g / 50 mm) of the portion to which the load was applied was measured with a tensile tester.
The value of peel strength was evaluated as follows. ⊚ (Good): Peel strength ≦ 10 g / 50 mm ○ (Slightly good): 10 g / 50 mm <Peel strength ≦ 30 g
/ 50 mm x (poor): 30 g / 50 mm <peeling strength.

(11) Moisture resistance The peel strength was measured by the same method as in the evaluation of blocking property (10). However, the holding conditions were changed to a temperature of 60 ° C. and a relative humidity of 70% RH. The measurement results were evaluated as follows. ⊚ (Good): Peel strength ≦ 10 g / 50 mm ○ (Slightly good): 10 g / 50 mm <Peel strength ≦ 30 g
/ 50 mm x (poor): 30 g / 50 mm ≤ peel strength.

(12) The water-dispersible coating agent was diluted with water to give a 0.2% by weight aqueous dispersion,
Using a quartz cell, the light transmittance was measured with a double beam spectrophotometer (Model 228A manufactured by Hitachi, Ltd.). The measurement results were evaluated as follows. ⊚ (good): light transmittance ≧ 50% ◯ (somewhat good): 50%> light transmittance ≧ 30% × (bad): 30%> light transmittance.

(13) Coefficient of Friction According to ASTM D1894-63, using a slipper measuring device manufactured by Toyo Tester Co., Ltd., the front and back surfaces of the film were aligned, and a static friction coefficient was measured by applying a load of 1 kg. If the friction coefficient exceeds 0.6, the film transportability will be impaired.

[Examples 1-44 and Comparative Examples 1-26]
A polyester composed of a terephthalic acid component and an ethylene glycol component is supplied to an extruder hopper, melt-mixed at a melting temperature of 280 to 300 ° C., and extruded onto a cooling drum having a surface temperature of 20 ° C. using a single layer die, and rapidly cooled, Thickness 18
An unstretched film of 0 to 190 μ was obtained.

The unstretched film thus obtained is preheated to 80 ° C. and stretched in the machine direction at a stretching temperature of 90 to 100 ° C. by using an IR heater between low-speed rolls and high-speed rolls. Example 2 is 1.1 times, Example 3 is 1.5 times,
Comparative Example 1 was 3.3 times, and the others were 1.3 times).

Thereafter, 91% by weight of the material having the composition shown in Tables 1 to 3 and 9% by weight of polyoxyethylene lauryl ether as a surface active agent were added to form a coating material.
Adjust this to an aqueous liquid with a solids concentration of 4% by weight,
It was applied with a roll coater.

The types of copolyester (A) shown in Table 1 or Table 2 have the composition shown in Table 3. The types of water-soluble polymer (B) and fine particles (C) shown in Table 1 or Table 2 are the following materials. Furthermore, Table 1
Alternatively, the types Y and Z of the crosslinking agent (D) shown in Table 2 are compounds of the following formula (V) and formula (VI), respectively. P: Polyvinyl alcohol having a saponification degree of 86 to 89 mol% Q: Polyvinyl alcohol having a saponification degree of 74 to 82 mol% R: Polyvinyl alcohol having a saponification degree of 91 to 95 mol% T: K value of 26 to 23, average molecular weight of 40,000 Polyvinylpyrrolidone U: K value 90 to 100, polyvinylpyrrolidone W having an average molecular weight of 1200000 W: cation-modified polyvinyl alcohol having a saponification degree of 74 to 80 mol% X: cation-modified polyvinyl alcohol having a saponification degree of 86 to 95 mol%: crosslinking Acrylic particles: Colloidal silica particles

[0060]

[Chemical 13]

[0061]

[Chemical 14]

For example, in Example 1, the acid component was terephthalic acid (60 mol%), isophthalic acid (36 mol%), and 5-Nasulfoisophthalic acid (4 mol%), and the glycol component was ethylene glycol (60 mol%). ) And neopentyl glycol (40 mol%), a copolymerized polyester (Tg = 30 ° C.) 65% by weight, a saponification degree of 86 to 8
As a coating material, a composition comprising 16% by weight of 9 mol% of polyvinyl alcohol, 10% by weight of crosslinked acrylic resin particles having an average particle size of 40 nm, and 9% by weight of polyoxyethylene lauryl ether as a surfactant was used. An aqueous solution having a solid content concentration of 4% by weight was prepared and applied with a roll coater.

In the next step, the longitudinally stretched film coated with the aqueous liquid was supplied to a stenter and stretched in the transverse direction while being dried at 90 to 110 ° C. (The stretching ratio is 3.
3 and 4.5 times other than that), and then heat setting was performed at 170 ° C. Thus, a biaxially oriented polyester film having a thickness of 38 μm (coating surface thickness was 0.03 μm) was obtained. The physical properties and evaluation results of the obtained film are shown in Table 4 to
8 shows.

[Examples 1 to 3] A high birefringence and a low orientation angle are achieved over the entire width of the formed film.
An oriented polyester film for a liquid crystal display plate suitable for laminating a polarizing plate having a high light transmittance, a retardation polarizing plate, and a retardation plate was obtained.

[Comparative Example 1] A biaxially oriented polyester film having a draw ratio in a normal balance region (that is, a longitudinal draw ratio and a transverse draw ratio are equal) has a somewhat high heat shrinkage ratio and is biaxially drawn during heat bonding. The polyester film shrank and could not be used as a product.

Comparative Example 2 A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the cooling step in the cold air section after the transverse stretching was omitted in Example 1. In the vicinity of the center, although a good film for this application can be obtained for this application,
The range was narrow and the productivity was very poor.

[Comparative Example 3] A biaxially stretched film was obtained in the same manner as in Example 1 except that the heat setting temperature was 230 ° C.
Although a good film can be obtained for this application near the center,
The range was narrow and the productivity was very poor.

Comparative Example 4 A biaxially stretched film was obtained in the same manner as in Example 1 except that the aqueous liquid was not applied. The surface energy was low and did not satisfy the constituent requirements of the film of the present invention.

[Examples 4 to 21] Biaxially oriented polyester films were obtained in the same manner as in Example 1 except that the types and ratios of coating agents were changed as shown in Tables 1 and 3. As is clear from the results shown in Table 7, the oriented polyester film for liquid crystal display panel of the present invention has excellent adhesiveness.

[Examples 22 to 25 and Comparative Examples 5 to 6]
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the type of copolyester (A) was changed as shown in Tables 1 to 3 and a copolyester having a different Tg was used. As is clear from the results shown in Tables 7 and 8, the polyester film for liquid crystal display panel of the present invention is excellent in blocking resistance and adhesiveness. In Comparative Example 5, the adhesive property is good, but the second-order transition temperature (Tg) of the copolyester (A) is less than 20 ° C., which is poor in blocking resistance.

[Examples 26 to 30 and Comparative Examples 7 to 8]
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the proportion of the dicarboxylic acid component containing a sulfonate group of the copolyester (A) was changed as shown in Tables 1 to 3. As is clear from the results shown in Tables 7 to 8, the polyester film for liquid crystal display panel of the present invention is excellent in both moisture resistance and water dispersibility.

[Examples 31 to 38 and Comparative Examples 9 to 2]
0] In the same manner as in Example 1 except that the ratios of the copolyester (A), the water-soluble polymer (B), the fine particles (C) and the crosslinking agent (D) were changed as shown in Tables 1 to 3. An axially stretched polyester film was obtained. As is clear from the results shown in Tables 7 to 8, the polyester film for a liquid crystal display panel of the present invention is excellent in adhesiveness, and the coefficient of friction does not exceed 0.6 (μs) and is excellent in transportability.

[Examples 39-40 and Comparative Examples 21-2]
2] A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the average particle size of the fine particles (C) was changed as shown in Tables 1 and 2. As is clear from the results shown in Tables 7 to 8, the polyester film for liquid crystal display panel of the present invention has excellent blocking resistance. In Comparative Example 22, although the blocking resistance is good, the average particle size of the fine particles (C) exceeds 80 nm, and the sharpness is poor.

[Examples 41 to 44 and Comparative Examples 23 to 2]
6] In the same manner as in Example 1 except that the ratios of the copolyester (A), the water-soluble polymer (B), the fine particles (C) and the crosslinking agent (D) were changed as shown in Tables 1 to 2. An axially stretched polyester film was obtained. As is clear from the results shown in Tables 7 to 8, the polyester film for a liquid crystal display panel of the present invention has an excellent coefficient of friction, which does not exceed 0.6 (μs). Although Comparative Examples 24 and 26 are good in terms of the coefficient of friction, the content of the fine particles (C) exceeds 25% by weight, and the sharpness is poor.

[0075]

[Table 1]

[0076]

[Table 2]

[0077]

[Table 3]

[0078]

[Table 4]

[0079]

[Table 5]

[0080]

[Table 6]

[0081]

[Table 7]

[0082]

[Table 8]

[0083]

INDUSTRIAL APPLICABILITY The polyester film of the present invention can obtain a film for a liquid crystal display plate extremely efficiently over the entire area of the oriented film constituting the film for a liquid crystal display plate, and has been used conventionally. It is more excellent in moist heat resistance. Further, it has clear optical anisotropy different from conventional polyester oriented films, and has improved surface adhesiveness, and is suitable as a protective film for liquid crystal display devices and a transparent conductive film base. Furthermore, since it can be produced using a conventional polyester biaxially oriented film producing apparatus, it is excellent in economic effect.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Asada             3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture             People DuPont Films Co., Ltd. Sagamihara Research Center             In the center F-term (reference) 2H090 JA06 JB03 JB09 JB10 JB12                       JC07 JD01 JD15 JD17 LA09                 2H091 FA08X FA08Z FC09 GA01                       GA16 LA02 LA04 LA17                 4F006 AA35 AA55 AA56 AB13 AB15                       AB16 AB20 AB35 AB37 AB64                       AB73 AB74 AB76 BA01 BA04                       CA00 CA05 DA04                 4F100 AK21B AK41A AL01B BA02                       BA03 CA02B CA23B CC00B                       DE01B EH46B EJ37A JB09B                       JN01A JN18A YY00A

Claims (3)

[Claims] 1. A film used as a constituent element of a liquid crystal display plate in a liquid crystal display device, which is an oriented film made of polyethylene terephthalate, and is a difference (N _MAX −) between a maximum refractive index N _MAX and a minimum refractive index N _MIN of the film.
N _MIN ) is 0.08 or more and the variation of the orientation main axis with respect to the linear axis set in an arbitrary direction in the film sampled in a 50 cm square is within 5 ° in all places,
And the total light transmittance of the film in the visible light wavelength range is 80.
% Or more, a coating film is laminated on at least one side of the film, and the coating film contains the copolyester (A), the water-soluble polymer compound (B) and the fine particles (C), and the copolyester (A) is The ratio of the dicarboxylic acid component having a sulfonate group to the total dicarboxylic acid component is 1 to 16 mol%, the second-order transition temperature is 20 to 90 ° C., and the fine particles (C) have an average particle diameter of 20 to 80 nm. In the coating film, the content of the copolyester (A) is 30 to 80% by weight, the content of the water-soluble polymer compound (B) is 10 to 45% by weight, and the content of the fine particles (C) is 3.
-25% by weight, and the surface energy of the coating film is 50-7.
An oriented polyester film for a liquid crystal display panel, which is 0 dyne / cm. 2. The water-soluble polymer compound (B) has a saponification degree of 8.
0 to 90 mol% of polyvinyl alcohol, the polyvinyl alcohol content in the coating film is 15 to 45% by weight
The coating film further contains 5 to 20% by weight of a crosslinking agent (D) represented by the following structural formula (I), and the coating film has a surface energy of 50 to 65 dyne / cm. Item 2. An oriented polyester film for liquid crystal display panel according to item 1. [Chemical 1] (However, R in the structural formula (I) is the following structural formula (II)-
It is one of (IV). ) [Chemical 2] [Chemical 3] [Chemical 4] 3. The oriented polyester film for a liquid crystal display panel according to claim 1, wherein the film has a heat shrinkage ratio of 1% or less when held at 150 ° C. for 30 minutes.