JP6440992B2 - Uniaxially oriented laminated polyester film, laminate comprising the same, and polarizing plate - Google Patents

Description

  The present invention relates to a uniaxially oriented laminated polyester film, a laminate comprising the uniaxially oriented laminated polyester film, and more specifically, a uniaxially oriented laminated polyester film having excellent film forming properties while having excellent optical properties used in a liquid crystal display device. , And a laminate and a polarizing plate comprising the same. In particular, the present invention relates to a uniaxially oriented laminated polyester film that can be suitably used as a polarizer protective film for polarizing plates used in liquid crystal display devices.

  A polarizing plate, which is indispensable for a liquid crystal display device, protects the polarizer on both sides of a polarizer composed of a polyvinyl alcohol (PVA) film that has been dyed with a dichroic dye and stretched and oriented in an aqueous boric acid solution. A protective film (also referred to as a polarizer protective film) for adhesion is used. As a material for such a polarizer protective film, it is common to use a triacetyl cellulose (TAC) film that is excellent in optical properties and easy to adhere to PVA.

  TAC film, on the other hand, is a material that easily absorbs and permeates moisture, and under high-temperature and high-humidity environments, the degree of polarization and the deterioration of the polarizer are remarkable. In addition, there is a need to meet the demands for thinning the members accompanying the recent thinning of the liquid crystal display device itself, and studies are being conducted to realize a polarizer protective film with a material that has excellent moisture and heat resistance and can be made thin. It has been broken.

Furthermore, with the explosive spread of liquid crystal displays, the demand for cost reduction of components has become very strong, and there is a movement to replace TAC film, which is relatively low in productivity and expensive, with other inexpensive materials. It is getting into full swing.
As candidate materials for TAC substitution, many materials such as polystyrene resins, acrylic resins, polycarbonate resins, polyolefin resins, norbornene resins, polyester resins such as polyethylene terephthalate (PET) and polylactic acid have been proposed. However, film materials using acrylic resins, polyester resins, and the like are particularly studied from the viewpoints of film transparency, mechanical strength, adhesion to the coating layer, and availability.

  Among them, since acrylic films are easy to adjust retardation, have high transparency, and are relatively inexpensive, various proposals have been made for a long time as materials suitable for polarizer protective films (Patent Document 1). However, acrylic resin, which is a typical amorphous resin, has low toughness and is difficult to handle during processing. As described above, the thinning of displays has been progressing in recent years, and the polarizer protective film has been required to be thinner than before. Especially, thin acrylic films of 50 μm or less are broken during the process. It is easy to handle, and it has difficult aspects to handle, such as requiring very precise adjustments for equipment in the transport system.

  On the other hand, polyester films, particularly PET films, have a high degree of transparency, high toughness and toughness, and are excellent in handling properties during processing under normal processing conditions. Conventionally, polyester films, which are difficult to adjust for retardation, have been considered difficult to apply because they tend to emit iridescent interference colors when used as a polarizer protective film. As light emitting diodes (LEDs) have become widespread, interference colors due to retardation are less likely to occur, and an environment where a polyester film can be applied optically has been established. In particular, it has also been proposed that interference colors can be suppressed by applying a uniaxially oriented film having a retardation increased to 3000 nm or more to the outer surface of the polarizer (Patent Document 2).

JP 7-56017 A International Publication No. 2011-162198 Pamphlet

  As described above, optical restrictions when applying a polyester film to a polarizer protective film are decreasing, but because it has a feature of highly enhancing orientation, it is orthogonal to uniaxial orientation like an acrylic film. When trying to obtain a uniaxially oriented polyester film having low toughness in the direction and higher retardation, a new problem of breaking at the time of handling and roll pulling has arisen.

  The object of the present invention is to solve the above-mentioned problems, while having excellent optical properties used in a liquid crystal display device, has excellent film forming properties, and also has uniaxial orientation with adhesion to a mating material. The object is to provide a laminated polyester film.

  As a result of intensive studies to solve such problems, the present inventors have made the aromatic polyester forming the polyester film have a higher intrinsic viscosity characteristic than the conventional one in a uniaxially oriented polyester film having a high retardation. The film break elongation in the non-oriented direction is improved, while having excellent optical properties used in a liquid crystal display device, it can have excellent film forming properties, and by having a coating layer on at least one surface, The inventors have found that a uniaxially oriented laminated polyester film having adhesiveness with a mating material to be bonded is obtained, and the present invention has been completed.

That is, an object of the present invention is a uniaxially oriented laminated polyester film having a coating layer on at least one surface of an aromatic polyester layer, wherein the aromatic polyester has an acid-glycol unit component of 100 mol%, 85 More than mol% is polyethylene terephthalate or polyethylene-2,6-naphthalate whose ethylene terephthalate component or ethylene-2,6-naphthalate component, and the intrinsic viscosity of the uniaxially oriented laminated polyester film is 0.60 or more and 1.0 or less The uniaxially oriented laminated polyester film is characterized in that the film breaking elongation in the direction orthogonal to the uniaxial orientation direction is 10% or more and the retardation in the uniaxial orientation direction is 4000 nm or more in the entire width.

Moreover, the uniaxially oriented laminated polyester film of the present invention has a preferred embodiment that the uniaxially oriented laminated polyester film has a light transmittance of 10% or less at a wavelength of 380 nm, and the uniaxially oriented laminated polyester film transmits light in a wavelength range of 550 nm or more. It has a light transmission characteristic of 80% or more, a thickness unevenness in a direction orthogonal to the uniaxial orientation direction of the uniaxially oriented laminated polyester film is 5% or less, and the coating layer is made of either an acrylic resin or a polyester resin. What comprises at least any one of being comprised and for polarizer protective films is also included.
Further, in the present invention, a laminate in which an active energy ray-curable adhesive is laminated on the coating layer of the uniaxially oriented laminated polyester film of the present invention, and further, via the laminate and the active energy ray-curable adhesive layer A polarizing plate comprising a bonded polarizer is also included.

The uniaxially oriented laminated polyester film of the present invention has excellent optical properties used in liquid crystal display devices and adhesiveness with a mating material, and further has excellent film forming properties. Since it can use suitably for a protective film etc. and can substitute the conventional TAC film, a polarizing plate can be provided cheaply.
Furthermore, when the laminated polyester film of the present invention is used as a polarizer protective film, it is possible to provide a polarizing plate that adheres well to the PVA polarizer and has high adhesive strength between the polarizer and the polarizer protective film.

Hereinafter, the present invention will be described in detail.
[Aromatic polyester layer]
The uniaxially oriented laminated polyester film of the present invention has an aromatic polyester layer and a coating layer on at least one surface thereof.

(Aromatic polyester)
The aromatic polyester constituting the aromatic polyester layer of the present invention is preferably polyethylene terephthalate or polyethylene-2,6-naphthalate. The main component of the polyethylene terephthalate is an ethylene terephthalate component, the polyethylene-2,6-naphthalate is a main component of an ethylene-2,6-naphthalate component, and “main” means an acid-glycol unit constituting a polyester. It means that 85 mol% or more, preferably 90 mol% or more is an ethylene terephthalate component or an ethylene-2,6-naphthalate component, where the component is 100 mol%.

  The polyester in the present invention can contain other polyester components as copolymerization components as long as the properties of polyethylene terephthalate or polyethylene-2,6-naphthalate are not essentially lost. Examples of the copolymer component include terephthalic acid (when the main component is naphthalene-2,6-dicarboxylic acid), naphthalene-2,6-dicarboxylic acid (when the main component is terephthalic acid), and naphthalene-2,7-dicarboxylic acid. Aromatic dicarboxylic acid component derived from acid, naphthalene-1,5-dicarboxylic acid, phthalic acid, isophthalic acid, diphenylsulfone dicarboxylic acid, benzophenone dicarboxylic acid, 4,4′-diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, etc .; succinic acid Aliphatic dicarboxylic acid components derived from oxalic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, etc .; Alicyclic dicarboxylic acid components derived from hexahydroterephthalic acid, 1,3-adamantanedicarboxylic acid, etc .; p-oxybenzoic acid Oxycals derived from acids, p-oxyethoxybenzoic acid, etc. Phosphate component diethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, may be mentioned glycol component derived from 1,4-cyclohexanedimethanol and the like.

  The intrinsic viscosity of the aromatic polyester in the present invention is preferably 0.7 or more and 1.2 or less. If the intrinsic viscosity of the aromatic polyester is less than the lower limit, the intrinsic viscosity of the uniaxially oriented laminated polyester film after film formation is less than 0.60. Therefore, the elongation at break in the direction perpendicular to the uniaxial orientation direction when uniaxially oriented is used. The degree cannot be secured. On the other hand, if the intrinsic viscosity of the aromatic polyester exceeds the upper limit, the flowability at the time of melting of the polyester resin is lowered and it is difficult to melt by extrusion. For example, a filter is installed in the process for the purpose of removing foreign substances in the polyester resin, and the resin When the filter is passed, the pressure at the filter increases and the extrudability decreases.

(Additive)
In order to make the uniaxially oriented laminated polyester film of the present invention excellent in transparency and slipperiness, an embodiment in which particles are not contained or is used in a very small range (100 ppm or less) when particles are contained is preferable. Here, the particles in the present invention preferably have an average particle diameter of 100 nm or more and 5 μm or less. For the purpose of improving slipperiness or adjusting transparency, inorganic particles such as silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, titanium oxide, barium sulfate, crosslinked silicone resin, crosslinked Organic particles made of a heat-resistant polymer such as polystyrene resin, cross-linked acrylic resin, urea resin, melamine resin or the like can be contained alone or in combination.

  In addition, an ultraviolet absorber can be added to the uniaxially oriented laminated polyester film in the present invention. Although a well-known thing can be used for a ultraviolet absorber, in order to provide the light transmittance of 10% or less at wavelength 380nm mentioned later as content of a ultraviolet absorber, the mass of a uniaxially-oriented laminated polyester film is a reference | standard. It is preferable that it is 0.1-10 mass%.

[Characteristics of uniaxially oriented laminated film]
(Intrinsic viscosity)
The intrinsic viscosity of the uniaxially oriented laminated polyester film of the present invention needs to be 0.60 dl / g or more and 1.0 dl / g or less, preferably 0.61 or more and 0.95 or less, more preferably 0.62 or more. 0.90 or less. If the intrinsic viscosity of the uniaxially oriented laminated polyester film is less than the lower limit, the film forming property is affected, and even if film formation is possible, the uniaxially oriented laminated polyester film breaks in the direction perpendicular to the uniaxially oriented direction. Sufficient elongation cannot be secured.

It is considered that the film forming property and the elongation at break in such a direction depend on the entanglement of the aromatic polyester polymer chain. In the case of a uniaxially oriented laminated polyester film, it is generally uniaxially stretched in the width direction (hereinafter sometimes referred to as the transverse direction or the TD direction). That is, in order to achieve a high degree of orientation in the width direction, it is difficult to apply stretch molding in the longitudinal direction (hereinafter sometimes referred to as film forming direction, continuous film forming direction, longitudinal direction, MD direction), and an unstretched state. Therefore, the molecular chains in the vertical direction are not sufficiently entangled, and it is difficult to obtain sufficient elongation.
Therefore, in the film oriented in the width direction, in order to ensure the elongation at break in the longitudinal direction, the molecular weight of the aromatic polyester is increased, thereby increasing the number of entanglements with respect to the molecular chains relatively oriented in the width direction. It is considered that the breaking elongation in the direction orthogonal to the uniaxial orientation direction can be secured. On the other hand, in the range exceeding the upper limit of the intrinsic viscosity of the film, the stretching stress load at the time of film formation becomes large and the film forming property is lowered.

(Elongation at break)
The uniaxially oriented laminated polyester film of the present invention needs to have a film breaking elongation of 10% or more in a direction orthogonal to the uniaxial orientation direction, preferably 11% or more, particularly preferably 12% or more. . If the film breaking elongation in such a direction is less than the lower limit, problems such as the film cannot be pulled out because the breaking elongation is small with respect to an external force such as tension when the film wound in a roll shape is pulled out. Moreover, since a film cannot be pulled out, it becomes difficult to add secondary processing, for example, when film productivity falls, for example, when coating is applied to the uniaxially oriented laminated polyester film of the present invention. The upper limit of the elongation at break is not particularly limited, but is preferably 60% or less, more preferably 50% or less in relation to the production equipment.

(Phase difference)
The retardation (retardation) of the uniaxially oriented laminated polyester film of the present invention is not practically limited, but the retardation in the uniaxial orientation direction has a full width in order to suppress interference colors when observed from the vicinity of the Brewster angle. In this case, it is necessary to be 4000 nm or more, more preferably 4300 nm or more, and further preferably 4500 nm or more. Further, the variation in retardation in such a direction is preferably 1000 nm or less, and more preferably 500 nm or less, with a maximum difference in the range of 1.0 to 2.5 m in the uniaxial orientation direction. Furthermore, also in the direction orthogonal to the uniaxial orientation direction, the difference between the maximum value and the minimum value measured at 10 points at regular intervals for each continuous 10 m is preferably 1000 nm or less, and more preferably 500 nm or less.

The difference in the orientation angle in the uniaxial orientation direction (difference between the maximum value and the minimum value of the orientation angle) is preferably 20 degrees or less, more preferably 10 degrees or less in the range of 1.0 to 2.5 m in the uniaxial orientation direction. is there. Here, the orientation angle is an angle formed by a direction (0 degree) extending uniaxially and the main orientation direction. In the present invention, a film side parallel to a uniaxial orientation direction when a cut film is used as a uniaxially stretched direction may be used as a reference of 0 degree.
The main orientation direction in the present invention is a main orientation direction in the film plane, and is a direction defined by a direction in which the polymer main chain is statistically most oriented.

  Such uniaxial retardation characteristics can be achieved by uniaxially stretching in the width direction under certain stretching conditions. In a normal stretching process, uniaxial stretching in the width direction is performed by introducing an unstretched film into the tenter. In order to achieve the above retardation characteristics, the tenter preferably stretches an unstretched film heated above the glass transition temperature of the polyester at least 3.5 times to 5.5 times in the width direction, more preferably Is 3.6 times to 5.0 times, particularly preferably 3.8 times to 5.0 times. When the draw ratio is less than the lower limit, the increase in the refractive index in the main alignment direction is insufficient, and the retardation characteristic (retardation) of the present invention is not exhibited. When the stretching ratio exceeds the upper limit, the elongation at break in the direction perpendicular to the uniaxial orientation direction is not sufficient, and the film breaks when attempting to transport the film in the direction perpendicular to the uniaxial orientation direction, that is, in the longitudinal direction. Film formation is not possible.

(Film thickness)
The uniaxially oriented laminated polyester film of the present invention has a film thickness of preferably 10 to 100 μm, more preferably 20 to 50 μm. By setting it as such thickness, the rigidity suitable when using as a polarizer protective film can be provided, and it is preferable. Moreover, since a polarizing plate can be thinned, it is preferable.

(Thickness unevenness)
The uniaxially oriented laminated polyester film of the present invention preferably has a thickness unevenness of 5% or less, more preferably 4%, in the direction orthogonal to the uniaxial orientation direction, that is, when the film width direction is the uniaxial stretching direction. Hereinafter, it is more preferably 3% or less. If the thickness unevenness exceeds the upper limit, the film appearance may be impaired. The thickness unevenness of the film in the present invention is preferably smaller within such a range, and the lower limit is not particularly limited.

In the present invention, when the film is highly oriented in the width direction and the film is not stretched in the longitudinal direction, the thickness produced in the casting of the resin from the die cannot be reduced because the longitudinal thickness cannot be reduced by the longitudinal stretching. It is considered that thick spots remain as they are without eliminating the spots.
In order to eliminate such vertical thickness unevenness, the position of the cooling drum when the molten resin discharged from the extruder is landed on the cooling drum, the optimization of the pinning position, the speed of the resin flowing from the die and the speed of the cooling drum are adjusted. By adjusting the draft ratio that is the ratio, the thickness unevenness in the vertical direction can be improved.

(Light transmittance at a wavelength of 380 nm)
The uniaxially oriented laminated polyester film of the present invention preferably has a light transmittance at a wavelength of 380 nm of 10% or less, more preferably 9% or less, and particularly preferably 8% or less. If the optical characteristics exceed this range, it cannot be said that the ability to absorb ultraviolet rays is sufficient, and for example, the characteristics of PVA used in a liquid crystal display device may be deteriorated. More specifically, such a problem tends to occur when the polarizing plate is used on the upper side of the two polarizing plates arranged on both sides of the liquid crystal panel, and preferably has the light transmittance characteristics described above.
In order to obtain a uniaxially oriented laminated polyester film having such light transmittance characteristics, existing ultraviolet absorbers such as hindered amines, triazines, benzophenones, and benzotriazoles are preferably used. An ultraviolet absorber having heat resistance is preferably used.

(Light transmittance at a wavelength of 550 nm or more)
The uniaxially oriented laminated polyester film of the present invention preferably has a light transmission property with a light transmittance of 80% or more in a wavelength range of 550 nm or more, more preferably 85% or more, and particularly preferably 89% or more. In order to improve the total light transmittance, it is also a preferable aspect that a low reflection coating layer is laminated on the surface on the backlight side particularly when used as a polarizer protective film. By appropriately controlling the refractive index and thickness of the low-reflection coating layer, it is possible to effectively suppress loss due to light reflection on the film surface and improve the total light transmittance. As such a low reflection coating layer, it is preferable to use a coating liquid mainly composed of an acrylic resin or a polyester resin.

[Coating layer]
The uniaxially oriented laminated polyester film of the present invention has a coating layer on at least one surface of the aromatic polyester layer.
A thermoplastic resin is used as the binder component of the coating layer in the present invention, and the type thereof is not particularly limited as long as the object of the present invention is not impaired. The binder component of the coating layer is not particularly limited as long as appropriate plasticity and elasticity can be imparted to the coating layer and the adhesiveness with the mating material can be improved.
Examples of the binder component of the coating layer include water-soluble natural polymers such as polysaccharides, water-soluble polyvinyl alcohol (preferably having a saponification degree of 95% or more), acrylic resins, polyester resins, and urethane resins. The The thermoplastic resin preferably has a glass transition temperature lower than the stretching temperature of the polyester film. Specifically, the glass transition temperature of the thermoplastic resin is preferably 120 ° C. or lower.

  Among these, a thermoplastic resin having high affinity with the polyester film as the base film is preferable, and for example, either an acrylic resin or a polyester resin is preferable. In addition, a water-soluble thermoplastic resin having a high affinity with the polyester film is preferable from the viewpoint of improving adhesiveness. From this viewpoint, an acrylic resin obtained by copolymerizing a predetermined amount or more of a monomer unit having a hydrophilic group as an acrylic resin. The polyester resin is preferably a copolymer polyester resin obtained by copolymerizing a predetermined amount or more of an acid component or glycol component having a hydrophilic group to make it water-soluble, and particularly preferably the copolymer polyester resin.

When the acrylic resin has a copolymer component having a hydrophilic group, preferred examples of the monomer unit having a hydrophilic group include acrylic acid and a 2-hydroxyethyl methacrylate component. In order to obtain a water-soluble acrylic resin, it is preferable to contain 10 mol% or more, and more preferably 20 mol% or more of such components with respect to 100 mol% of all monomer units of the acrylic polymer. By containing a large amount of these components, water solubility is improved and further excellent adhesiveness can be obtained.
In addition, it is also a preferable aspect to use a thermoplastic resin having a functional group that exhibits an electrical bonding force and the like with a functional group of the polyester film as a binder component. From such a viewpoint, for example, an acrylic resin having a nitrogen atom, Mention may be made of urethane resins.

Among these thermoplastic resins, polyester resin, acrylic resin, and urethane resin are preferable from the viewpoint of excellent adhesion to a polyester film. Among them, acrylic resin that has high transparency and excellent adhesion to an active energy ray-curable adhesive. Polyester resin is particularly preferable. By using such a resin as the binder component of the coating layer, it is possible to obtain a uniaxially oriented laminated polyester film that has excellent appearance and excellent adhesion to the active energy ray-curable adhesive.
In addition to the binder component, the coating layer may contain a crosslinking agent, a surfactant, a filler and the like. The binder component is 80 to 100% by mass and the crosslinking agent is 0 to 0% with respect to the composition of the coating layer. 5% by mass, 0 to 10% by mass of surfactant, and 0 to 5% by mass of filler are preferable.

(Thickness of coating layer)
The thickness of the coating layer in the present invention is preferably 0.01 μm or more, more preferably 0.05 μm or more, and further preferably 0.08 μm or more from the viewpoint of adhesiveness. On the other hand, if the coating layer is too thick, the curing of the coating layer tends to be weakened, which may reduce the effect of improving adhesiveness. From this viewpoint, the upper limit of the thickness of the coating layer is preferably 1 μm or less, more preferably 0.5 μm or less, and still more preferably 0.2 μm or less.

[Film Production Method]
The uniaxially oriented laminated polyester film of the present invention can be produced by a conventionally known melt extrusion method. Specifically, the dried polyester resin composition pellets are supplied to an extruder, a method of extruding a molten resin from a slit die such as a T die, or a vent device is set in an extruder that has supplied polyester resin composition pellets, A method of extruding a molten resin from a slit die such as a T die while discharging moisture and various gas components generated during melt extrusion can be mentioned.

  The molten resin extruded from the slit die is cast and cooled and solidified. Any conventionally known method may be used for cooling and solidifying, but a method of casting a molten resin on a rotating cooling roll to form a sheet is preferably used. The surface temperature of the cooling roll is preferably set in the range of (Tg-100) ° C. to (Tg + 20) ° C. with respect to the glass transition temperature (Tg) of the polyester constituting the resin composition. It is preferable to set in the range of 70) ° C. to (Tg-5) ° C. When the surface temperature of the cooling roll exceeds the upper limit, the molten resin may stick to the roll before solidifying. Further, when the surface temperature of the cooling roll is less than the lower limit, solidification is too fast and the roll surface slides, and the flatness of the obtained sheet may be impaired.

  When casting on the chill roll, a metal wire is stretched near the position where the molten resin lands on the chill roll, and an electric field is generated by passing an electric current to charge the resin and onto the metal surface of the chill roll. It is also effective from the viewpoint of improving the flatness of the film by eliminating thickness unevenness in the longitudinal direction of the film. In that case, you may add an electrolyte substance in the resin composition in the range which does not exceed the meaning of this invention.

  The sheet-like material obtained by melt extrusion casting can be matched with the object of the present invention by stretching in at least one direction, and is suitable as a polarizer protective film. Stretching may be uniaxial stretching that extends in either the longitudinal direction or the transverse direction, or biaxial stretching that extends in either the longitudinal direction or the transverse direction, but it increases the retardation and reduces the influence of interference colors. Therefore, uniaxial stretching is most preferable, and it is particularly preferable to stretch only in the transverse direction from the viewpoint of productivity.

As the stretching method, a conventionally known method can be used. For example, when stretching in the longitudinal direction, a method of stretching using a peripheral speed difference of two or more rolls, and when stretching in the lateral direction, An example is a method of stretching in a tenter oven that grips the end with a clip or the like with a difference in the gap between the inlet and outlet clip transport rails. Furthermore, if necessary, the film may be stretched in two directions, the longitudinal direction and the lateral direction.In that case, the stretching ratio in the direction orthogonal to the uniaxial orientation direction is relatively small relative to the stretching ratio in the uniaxial orientation direction. By doing so, the phase difference characteristic of a uniaxial orientation direction can be improved more. As a biaxial stretching method, stretching may be performed by a method of sequentially stretching in both the longitudinal and lateral directions or a method of stretching in the longitudinal and lateral directions at the same time.
In the stretching method using a roll, examples of the heating method of the sheet (unstretched film) include a method of induction heating with a roll through a heating medium, and a method of heating from the outside with an infrared heater, etc. Several methods may be taken.

The film stretching temperature in the present invention is preferably Tg to (Tg + 60 ° C.). When the stretching temperature of the film is less than Tg, stretching itself is difficult, while when the stretching temperature exceeds (Tg + 40 ° C.), the stress required for stretching becomes extremely low, so the orientation of the molecular chain is In some cases, the phase difference characteristics of the present invention cannot be secured. A more preferable range of the stretching temperature is Tg to (Tg + 40 ° C.).
In the stretching, in the case of uniaxial stretching, longitudinal stretching is not substantially performed, and the transverse stretching ratio is 3.5 to 5.5 times, preferably 4.0 to 5.0 times, and more preferably 4. 0 to 4.5 times.

  In addition, in order to improve the variation in the degree of orientation and orientation angle in the lateral direction, it is important to suppress bowing and minimize stretching unevenness as much as possible, for example, uniform temperature distribution in the oven, heat setting Measures such as lowering the temperature by lowering the temperature and applying a tension after stretching to align the orientation are effective.

  The coating layer in the present invention can be formed by applying in-line during the process of forming a polyester film, and productivity and adhesion quality can be improved by applying in-line. Coating can be performed by a conventionally known method, such as a roll coating method, a gravure coating method, a micro gravure coating method, a reverse coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method, etc. May be applied alone or in combination. Among these methods, the gravure coating method is particularly preferable because of excellent coating uniformity.

  In order to obtain better adhesion, the application timing is important, and it is preferable to apply before the stretching is completely completed. Specifically, it is preferable to carry out after casting and cooling. Thereby, it can apply before the polyester film surface becomes inactive by orientation, and the adhesiveness of a polyester film and an application layer can be made high. Moreover, bridge | crosslinking fully progresses by receiving a high temperature heat history in an extending | stretching and a heat setting process, a firm coating layer is formed, and adhesiveness improves.

[Active energy ray-curable adhesive]
In the present invention, an active energy ray-curable adhesive layer can be laminated on the coating layer of the above-described uniaxially oriented laminated polyester film and used as a laminate.
In the present invention, the active energy ray-curable adhesive is an adhesive that can be cured by active energy rays such as ultraviolet rays and electron beams to exhibit adhesiveness. The UV curable adhesive is preferable from the viewpoint of the safety of exposure work and the simplicity of the apparatus.
In particular, when the laminated film of the present invention is used for a polarizer protective film, it is preferably excellent in adhesiveness with a PVA polarizer, and an epoxy adhesive containing an epoxy group or an oxetanyl adhesive containing an oxetanyl group is used. preferable. By using such an adhesive, it is excellent in adhesiveness with a polarizer such as PVA, in particular, an acrylic resin or a polyester resin is used as a binder component of the coating layer of the present invention, and the active energy ray-curable adhesive is used. It is preferable to use an agent because the adhesiveness with the PVA polarizer is further enhanced.
Specific examples of the active energy ray-curable adhesive that can be preferably used in the present invention include adhesion described in JP2011-236389A, JP20127080A, and JP2012-172026A. Agents can be exemplified.

[Polarizer]
A polarizing plate can be produced by using the uniaxially oriented laminated polyester film of the present invention as a support substrate (polarizer protective film) for a polarizer and by combining with a polarizer through the coating layer of the present invention. More preferably, the coating layer is combined with a polarizer via an active energy ray-curable adhesive.
Specifically, a laminate in which an active energy ray-curable adhesive is laminated on the coating layer of the uniaxially oriented laminated polyester film of the present invention, and a polarizer is bonded onto the active energy ray-curable adhesive layer. The aspect made into a polarizing plate is mentioned.

As the polarizer, a polyvinyl alcohol resin film dyed with a dichroic material and uniaxially stretched is used. The polymerization degree of polyvinyl alcohol constituting this polyvinyl alcohol resin film is preferably 500 or more, and more preferably 1000 or more. Polyvinyl alcohol having such a polymerization degree can also be applied to water-soluble polyvinyl alcohol used in the coating layer.
The polyvinyl alcohol resin film can be formed by a known method. For example, the polyvinyl alcohol resin film can be formed by a casting method or a casting method in which a solution obtained by dissolving a resin in water or an organic solvent is cast. The dichroic molecule is not particularly limited, but polyiodine ions are generally used.

  Moreover, when using the uniaxially oriented laminated polyester film of the present invention as a polarizer protective film, the film of the present invention may be used for only one of the support substrates to be bonded to both sides of the polarizer when bonded to the polarizer, Moreover, you may use for both. Among these, the aspect used for the light source side among the substrates on both sides of the polarizing plate on the light source side is preferable, and further, the light source side among the substrates on both sides of the polarizing plate on the light source side and the substrates on both sides of the polarizing plate on the viewer side. Of these, the embodiment used on the viewer side is also preferably exemplified.

  Hereinafter, the present invention will be described more specifically with reference to examples. In the examples, the following methods were used.

1. Intrinsic viscosity (unit: dl / g)
The intrinsic viscosity of the polyester resin and the polyester resin constituting the aromatic polyester layer of the obtained film is measured at o-chlorophenol at 35 ° C. When it is difficult to dissolve uniformly with o-chlorophenol, It measured and measured at 35 degreeC using the mixed solvent of p-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio).
When particles were included, the intrinsic viscosity was determined based on the weight of the composition obtained by removing the particles from the solution using a centrifuge and subtracting the particles.

2. Film elongation at break A test piece with a sample width of 10 mm and a length of 15 cm is prepared so that the direction perpendicular to the uniaxial orientation direction of the film is the length direction, and an instron type universal tensile test with a chuck interval of 100 mm. A tensile test was performed with an apparatus at a tensile speed of 100 mm / min, and the elongation at the point at which the film was broken was measured on the resulting load-elongation curve.

3. Phase difference Using KOBRA manufactured by Oji Scientific Instruments Co., Ltd., the phase difference in the uniaxial orientation direction of the obtained uniaxially oriented laminated polyester film was measured at intervals of 50 mm across the entire width, and the phase difference was determined from the average value. .
The minimum value of the phase difference was evaluated according to the following criteria.
X: Minimum value of phase difference is less than 4000 nm ○: Minimum value of phase difference is 4000 nm or more

4). Light transmittance In accordance with JIS K7361, the total light transmittance (unit:%) of the film was measured using a haze meter (NDH-2000) manufactured by Nippon Denshoku Industries Co., Ltd., and light at 380 nm, 550 nm, and 800 nm. The transmittance was read. In addition, in the wavelength range of 550 nm to 800 nm, all were evaluated as ○ if the light transmittance was 80% or more, and × if there was a light transmittance that was less than 80%.

5. Film thickness unevenness The film was cut out by 2 m so that the direction perpendicular to the uniaxial orientation direction of the film was the measurement direction, and the thickness was measured with an electronic micro thickness gauge at a pitch of 1 mm. With respect to the average value of the measured thickness, the thickness fluctuation width was calculated as a ratio to obtain a thickness unevenness.

6). Adhesion Using a sample in which the adhesive described below is applied onto the coating layer of the laminated film, a cross cut (100 squares of 1 mm ² ) is applied to the adhesive layer, and a cellophane tape having a width of 24 mm is formed thereon. (Nichiban Co., Ltd.) was affixed and peeled off rapidly at a peeling angle of 90 °, and then the peeled surface was observed and evaluated according to the following criteria.
○: Peeling area is less than 20% ·········· Good adhesion Δ: Peeling area is 20% or more to less than 50% ·· Adhesion is somewhat good ×: Peeling area is 50% or more ··· Poor adhesion

[Coating solution]
The following components were used as the composition constituting the coating layer. The types and composition ratios of the compositions are shown in Table 1. In Table 1, the ratio of each component was described with the total amount of each component as 100% by mass.

(Binder component of coating layer: Acrylic resin)
An acrylic resin composed of the following copolymer components was used as a binder component of the coating layer (described as BA in Table 1).
Methyl methacrylate 40 mol% / ethyl acrylate 45 mol% / acrylonitrile 10 mol% / N-methylolacrylamide 5 mol%.

(Binder component of the coating layer: polyester resin)
A polyester resin composed of the following copolymer components was used as a binder component of the coating layer (described as BP in Table 1).
The carboxylic acid component is 85 mol% terephthalic acid / 15 mol% sulfoisophthalic acid, and the glycol component is 90 mol% ethylene glycol / 10 mol% diethylene glycol.

(Crosslinking agent)
Cross-linking agent 1: Trade name “Epocross WS-700” manufactured by Nippon Shokubai Co., Ltd. was used. In Table 1, it is written as OX.
Cross-linking agent 2: Trade name “Denacol EX-310” manufactured by Nagase Chemical Industries, Ltd. was used. In Table 1, it is written as OE.
Crosslinking agent 3: Trade name “TETRAD-X” manufactured by Mitsubishi Gas Chemical Co., Ltd. was used. In Table 1, it is written as OT.

(Surfactant)
Surfactant 1: Trade name “E-420” manufactured by Kao Corporation was used. In Table 1, it is written as SE.
Surfactant 2: The trade name “SS-70” manufactured by Sanyo Chemical Industries, Ltd. was used. In Table 1, it is described as SS.

(Filler)
Filler 1: A trade name “Snowtex” (average particle size 40 nm) manufactured by Nissan Chemical Industries, Ltd. was used. In Table 1, it is described as FL.
Filler 2: Trade name “Eposter MX200W” manufactured by Nippon Shokubai Co., Ltd. was used. In Table 1, it is described as FX.

[Example 1]
<Manufacture of uniaxially oriented laminated polyester film>
Polyethylene terephthalate (Tg = 78 ° C.) pellets having an intrinsic viscosity of 0.85 dl / g, and polyester pellets containing a triazine-based compound as an ultraviolet absorber, the ultraviolet absorber content in the film is 0.5% by weight. %, And pre-dried at a temperature of 120 ° C., melted at a temperature of 290 ° C. using an extruder, and extruded onto a cooling drum through a slit die to cool. The position of the cooling drum was adjusted so that the landing angle of the resin cast from the die was an obtuse angle.
The obtained unstretched film was continuously sent to the stretching step, and the coating liquid composition in Table 1 was diluted with ion-exchanged water to make a solid content concentration of 4% by mass without stretching in the machine direction. It applied to the single side | surface of an unstretched film using the gravure roll coater. The coating thickness was adjusted to 0.1 μm after drying.
Subsequently, after gripping both ends of the film coated with the coating liquid with clips and preheating at 80 ° C., the film is stretched 4.5 times in the transverse direction under a temperature atmosphere of 90 ° C., and then heat-fixed at 180 ° C. A uniaxially oriented film (laminated film) having a coating layer was obtained. The thickness of the obtained laminated film was 40 μm.

<Roll handling evaluation>
When the obtained uniaxially oriented film was once wound on a roll and then pulled out from the roll to evaluate roll handling properties, no breakage occurred when the roll was pulled out.

<Manufacture of laminates>
Apply the active energy ray-curable adhesive described in Example 1 of JP2012-172026A on the coating layer of the uniaxially oriented film using a bar coater so that the coating thickness is 3 μm. It was cured by irradiating with a metal halide lamp so as to have an irradiation amount of 1000 mJ / cm ² and cured to obtain a laminate in which an adhesive layer was provided on the laminated film. After aging for 2 hours after UV irradiation, the adhesion evaluation described in Measurement Method (6) was performed. The results are shown in Table 1.

The active energy ray-curable adhesive was obtained as follows.
For 100 parts by mass of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (“2021P” manufactured by Daicel Chemical Industries, Ltd.), a photocationic polymerization initiator (“CPI-110P” manufactured by San Apro Co., Ltd.), p. -Phenylthiophenyl diphenylsulfonium PF6 salt) was mixed with 2 parts by mass, and the acrylic polymer as described below was mixed with 0.3 parts by mass of the following acrylic polymer to obtain a cation curable active energy ray curable adhesive.

(Acrylic polymer)
A four-necked flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas blowing tube was charged with 100 parts by mass of methyl isobutyl ketone, and the temperature was maintained at 105 ° C. while stirring while introducing nitrogen gas. A mixture of 10 parts by weight of methacrylate, 40 parts by weight of 2-ethylhexyl acrylate, 50 parts by weight of n-butyl acrylate, and 3 parts by weight of benzoyl peroxide was added dropwise over 2 hours. Thereafter, the mixture was reacted at 105 ° C. for 1 hour, 1 part of benzoyl peroxide was added, and further reacted for 1 hour to obtain an acrylic polymer solution having a nonvolatile content of 50%.

In addition, an active energy ray-curable adhesive is applied on the coating layer of the obtained uniaxially oriented laminated polyester film, and a PVA polarizer is bonded thereon, so that the irradiation amount is 1000 mJ / cm ² by a metal halide lamp. The adhesive was cured by irradiating with UV rays to obtain a polarizing plate. After UV irradiation, a cellophane tape having a width of 24 mm (manufactured by Nichiban Co., Ltd.) was attached and a 90 ° peel test was performed. No peeling was confirmed.

[Examples 2 to 9, Comparative Examples 1 to 4]
A monoaxially oriented laminated polyester film and laminate were obtained in the same manner as in Example 1 except that the type and intrinsic viscosity of the aromatic polyester, the type of coating layer, and the film forming conditions were changed to the modes described in Table 1, respectively. Thickness spots, breaking elongation, retardation, light transmittance and adhesion were evaluated. The results are shown in Table 1.
Also, for these examples and comparative examples, the roll handling properties were evaluated in the same procedure as in Example 1. As a result, Comparative Example 2 was broken at least once in the evaluation of 100 m length when the roll was drawn. In Examples and Comparative Examples, no breakage occurred when the roll was pulled out.

The uniaxially oriented laminated polyester film of the present invention has excellent optical properties used in liquid crystal display devices and adhesiveness with a mating material, and further has excellent film forming properties. Since it can use suitably for a protective film etc. and can substitute the conventional TAC film, a polarizing plate can be provided cheaply.
Furthermore, when the laminated polyester film of the present invention is used as a polarizer protective film, it is possible to provide a polarizing plate that adheres well to the PVA polarizer and has high adhesive strength between the polarizer and the polarizer protective film.

Claims (8)

A uniaxially oriented laminated polyester film having a coating layer on at least one surface of an aromatic polyester layer, wherein the aromatic polyester is composed of an acid-glycol unit component of 100 mol%, and 85 mol% or more is an ethylene terephthalate component Alternatively, it is polyethylene terephthalate or polyethylene-2,6-naphthalate which is an ethylene-2,6-naphthalate component, and the intrinsic viscosity of the uniaxially oriented laminated polyester film is 0.60 or more and 1.0 or less, and is orthogonal to the uniaxial orientation direction. A uniaxially oriented laminated polyester film having a film breaking elongation in the direction of 10% or more and a retardation in the uniaxial orientation direction of 4000 nm or more in the entire width.   The uniaxially oriented laminated polyester film according to claim 1, wherein the uniaxially oriented laminated polyester film has a light transmittance of 10% or less at a wavelength of 380 nm.   The uniaxially oriented laminated polyester film according to claim 1 or 2, wherein the uniaxially oriented laminated polyester film has a light transmission property with a light transmittance of 80% or more in a wavelength range of 550 nm or more.   The uniaxially oriented laminated polyester film according to any one of claims 1 to 3, wherein thickness unevenness in a direction perpendicular to the uniaxially oriented direction of the uniaxially oriented laminated polyester film is 5% or less.   The uniaxially oriented laminated polyester film according to any one of claims 1 to 4, wherein the coating layer is composed of either an acrylic resin or a polyester resin. The uniaxially oriented laminated polyester film according to any one of claims 1 to 5 , which is used for a polarizer protective film. The laminated body which laminated | stacked the active energy ray hardening-type adhesive agent on the coating layer of the uniaxially-oriented laminated polyester film in any one of Claims 1-6 . A polarizing plate comprising the laminate according to claim 7 and a polarizer bonded through the active energy ray-curable adhesive layer.