JP6884997B2 - Polyester film and polarizing plate protective film - Google Patents

Description

The present invention relates to a polyester film that can be suitably used as a polarizing plate protective film. The present invention also relates to a polarizing plate using the polyester film as a polarizing plate protective film. Further, the present invention relates to a polyester film that can be suitably used for an ITO (Indium Tin Oxide) base film.

Thermoplastic resin films, especially biaxially stretched polyester films, have excellent mechanical properties, electrical properties, dimensional stability, transparency, chemical resistance, etc., and therefore are used in many magnetic recording materials, packaging materials, etc. It is widely used as a base film in applications. Particularly in recent years, in the field of flat panel displays and touch panels, demand for various optical films such as polarizing plate protective films and transparent conductive films has been increasing. Among them, in the field of polarizing plate protective films, conventional ones have been used for the purpose of cost reduction. The replacement of the triacetyl cellulose (TAC) film with a polyester film is being actively studied.

Japanese Unexamined Patent Publication No. 2013-254186 Japanese Unexamined Patent Publication No. 2013-200435 Japanese Unexamined Patent Publication No. 2013-109285 However, unlike the TAC film, the biaxially stretched polyester film which has been conventionally studied generates residual stress due to the polymer orientation during stretching, and shrinks, curls and wrinkles occur during heat treatment. There was a problem that would end up. In order to solve this problem in the polarizing plate protective film, a method of reducing the heat shrinkage rate has been proposed, but there is an invention in which the biaxially stretched polyester film is a thin film, has a low phase difference, and can sufficiently suppress curl. No (for example, Patent Documents 1, 2, 3, 4). Further, even if the dimensional change due to heat can be suppressed by performing offline annealing after manufacturing the biaxially stretched polyester film, there remains a problem that the cost increases due to a decrease in product yield and an increase in processing steps. ing. Furthermore, the polarizing plate protective film used for the outermost layer of the upper polarizing plate of the liquid crystal panel is required to have high UV blocking properties, and there are problems such as cost increase, process contamination, and color change due to the addition of a large amount of ultraviolet absorber. It was.

An object of the present invention is to solve the above-mentioned problems. That is, although it is a biaxially stretched polyester film that can be thinned at low cost, it has high UV cut property and low retardation property, and is further converted into a polarizing plate as a polarizing plate protective film or post-processed as an ITO base film. An object of the present invention is to provide a polyester film having less curl and wrinkles due to heat treatment.

The above-mentioned problems are that the heat shrinkage rate at 85 ° C. in the longitudinal direction for 6 hours is 0.5% or less, the phase difference (Re) at an incident angle of 0 ° is 400 nm or less, and the Young's modulus in the longitudinal direction and the width direction is Both can be achieved by a polyester film having a breaking elongation of 50% or more in the longitudinal direction and the width direction, and a rising temperature of shrinkage stress at the time of TMA measurement of 90 ° C. or more.

The polyester film of the present invention can suppress the occurrence of curls and wrinkles due to long-term storage or heat treatment when it is bonded to a polarizing element as a polarizing plate protective film to form a polarizing plate or when it is post-processed as an ITO base film. It is possible, and the handling property is good, and the effect of excellent process passability is exhibited.

Hereinafter, the polyester film of the present invention will be described in detail.

The thermoplastic resin constituting the polyester film of the present invention needs to be polyester.
The polyester film of the present invention has a heat shrinkage rate of 0.5% or less at 85 ° C. in the longitudinal direction for 6 hours. The heat shrinkage at 85 ° C. for 6 hours in the longitudinal direction of the film is preferably 0.4% or less, more preferably 0.3% or less, further preferably 0.2% or less, and 0. It is particularly preferable if it is 1% or less. When the heat shrinkage rate in the longitudinal direction of the film at 85 ° C. for 6 hours exceeds 0.5%, the heat shrinkage with the polarizing plate protective film on the other side when bonded to PVA to form a polarizing plate as described later. There is a possibility that the quality may be significantly deteriorated due to curling due to the rate difference and further wrinkling. The method of controlling the heat shrinkage rate in the longitudinal direction at 85 ° C. for 6 hours can be achieved by controlling the longitudinal orientation of the film according to the raw material composition and the film forming conditions described later.

The polyester film of the present invention needs to have a phase difference (Re) of 400 nm or less at an incident angle of 0 °. The phase difference (Re) here means a phase difference in the in-plane direction, and its value is 0 to 400 nm. Further, the incident angle of 0 ° means light incident from a plane direct direction. Re is preferably 0 to 200 nm, preferably 0 to 150 nm, from the viewpoint of interference colors generally observed by cross Nicol and parallel Nicol observations, and rainbow unevenness observed with the naked eye on a liquid crystal display due to a birefringent such as a polyester film. If it is, it is more preferable, if it is 0 to 100 nm, it is further preferable, and if it is 0 to 50 nm, it is particularly preferable. Generally, Re is calculated from the product of the maximum value of the difference in refractive index in two orthogonal directions in the plane of the film and the thickness of the film, but in a polyester film like the present invention, it can be easily used as a film. Since the refractive index cannot be measured, the value calculated by an indirect method is used as the Re value. Specifically, the value measured by the phase difference measuring device KOBRA series manufactured by Oji Measuring Instruments Co., Ltd. shall be used. If Re exceeds 400 nm, interference color may occur when mounted on a liquid crystal display as a polarizing plate protective film. When Re is 200 nm or less, the interference color disappears and it is most preferable.
The polyester film of the present invention preferably has a thickness direction retardation (Rth) of 0 to 1500 nm. When Rth is 0 to 1000 nm, there is no rainbow unevenness and the interference color is almost colorless, so it is more preferable, and when it is 0 to 700 nm, it is further preferable. Since the interference color is completely colorless, 0 to 500 nm is particularly preferable. When Rth exceeds 1500 nm, when it is mounted on a liquid crystal display as a polarizing plate protective film and observed at an angle, the interference color becomes easy to see, which may deteriorate the quality of the display.
The method of controlling Re and Rth as described above can be achieved by controlling the birefringence of each layer according to the film forming conditions described later. Specifically, for example, the phase difference Re in the in-plane direction can be generally expressed by the product of the birefringence Δn and the film thickness, so in order to reduce the value, Δn should be brought close to 0. As a means to achieve this, in the case of a sequentially biaxially stretched film, the film forming conditions are adjusted so that the refractive indexes given by the vertical and horizontal orientations are equal. Alternatively, it is completely unoriented without imparting stretching that induces oriented crystallization. Since the thermoplastic resin B is once melted and non-oriented in the film manufacturing process, the birefringence representing the anisotropy of the refractive index in the layer B made of the thermoplastic resin B can be made almost zero. In this case, Re depends only on the product of the anisotropy of the refractive index of the A layer made of crystalline polyester and the total thickness of the A layer. It can be suppressed. On the other hand, for the phase difference Rth in the thickness direction, it is preferable to select a polymer material in which the molecular chains are as difficult to plane-orient as possible. For example, the thermoplastic resin B is a copolymerized polyethylene terephthalate or a copolymerized polyethylene naphthalate obtained by copolymerizing 5 to 60 mol% of spiroglycol, naphthalenedicarboxylic acid, polyetherimide, bisphenol A, fluorene, isosorbide and the like. If it is less than 5 mol%, orientation crystallization is likely to occur, and the phase difference in the thickness direction increases. On the other hand, if it exceeds 60 mol%, it exhibits amorphousness as a polymer, so that orientation crystallization is unlikely to occur, but it is not preferable because it affects dimensional stability, film forming property, and post-process when heat is applied. More preferably, it is a copolymerized polyethylene terephthalate obtained by copolymerizing 10 to 40 mol%, or a copolymerized polyethylene naphthalate.

The polyester film of the present invention has a Young's modulus of 2 GPa or more in the longitudinal direction and the width direction. It is more preferably 2.5 GPa or more, still more preferably 3 GPa or more. From the viewpoint of heat resistance and post-processing, the Young's modulus in the longitudinal direction and the width direction is preferably 3.2 GPa or more, more preferably 3.5 GPa or more, further preferably 3.8 GPa or more, and even 4 GPa or more. Is particularly preferable. If the Young's modulus in either the longitudinal direction or the width direction is less than 2 GPa, the film may not be stiff and there may be a problem in handleability. The method of controlling the Young's modulus in the longitudinal direction and the width direction as described above can be achieved by appropriately adjusting the film forming conditions by the sequential biaxial stretching method using a crystalline polyester described later.
The polyester film of the present invention has a breaking elongation of 50% or more in the longitudinal direction and the width direction. The elongation at break in the longitudinal direction and the width direction is preferably 100% or more, more preferably 110% or more, further preferably 120% or more, and particularly preferably 130% or more. If the breaking elongation in either the longitudinal direction or the width direction is less than 50%, the film may become brittle and the film may break when tension is applied during the processing process. As a method of controlling the elongation at break in the longitudinal direction and the width direction as described above, it can be achieved by using the above-mentioned crystalline polyester and taking the film-forming conditions described later.

In the polyester film of the present invention, the rise of shrinkage stress at the time of TMA (Thermal Mechanical Analysis) measurement in the longitudinal direction is 90 ° C. or higher. The rise of shrinkage stress during TMA measurement in the longitudinal direction is preferably 95 ° C. or higher, more preferably 100 ° C. or higher, further preferably 105 ° C. or higher, and particularly preferably 110 ° C. or higher. If the rise of shrinkage stress during TMA measurement in the longitudinal direction is less than 90 ° C., curls and wrinkles may occur due to heat treatment during hard coating and polarizing plate formation. Controlling the rise of contraction stress during TMA measurement in the longitudinal direction as described above is only possible when the film forming conditions described later, particularly the lengthening of the longitudinal stretching section and the longitudinal relaxation treatment after transverse stretching are simultaneously performed. Can be achieved. High thermal dimensional stability is imparted by performing longitudinal stretching at 100 ° C. or higher, which is higher than the temperature applied in the manufacturing process of the polarizing plate. Further, if the glass transition point of the main component of the thermoplastic resin B to be the B layer is 88 ° C. or higher, shrinkage stress due to residual strain does not appear, so that high thermal dimensional stability can be maintained. More preferably, it is 93 ° C. or higher.

The polyester film of the present invention is preferably a polyester film in which three or more layers are laminated in the thickness direction. The number of laminated films is preferably 51 to 601 layers from the viewpoints of UV blocking property using interference reflection, low retardation property using amorphous resin, and total film thickness. More preferably, 151-351 layers and further 201-301 layers are particularly preferable. When the number of laminated films is less than three, when an amorphous resin is used as the thermoplastic resin B as described later, film formation failure due to adhesion to manufacturing equipment such as rolls and clips, and flatness of the laminated film surface Problems such as deterioration may occur. When the number of laminated films is one, that is, a single film, it is necessary to reduce the thickness in order to control the phase difference, and the handleability may be deteriorated. Further, when the number of laminated films is less than 51, the UV cut property may be insufficient. The relationship between the UV cut property and the number of layers in the thickness direction will be described later. On the other hand, when the number of laminated films exceeds 601 layers, the total thickness of the film may become too thick. The thickness of the layer is preferably 60 nm or less from the viewpoint of causing an interference reflection phenomenon in the wavelength of light having a wavelength of less than 400 nm in the UV region. More preferably, it is 50 to 30 nm.
The polyester film of the present invention is preferably formed by alternately laminating layers A containing crystalline polyester as a main component and layers B containing a thermoplastic resin B different from the crystalline polyester as a main component. Crystallinity is a resin having a glass transition temperature Tg and a melting point Tm, and a resin having a melting enthalpy change ΔHm> 0. More preferably, it is 15 (J / g) or more. The "main component" means that the ratio of the specific component to all the components is 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 90% by mass or more. It means that it is 95% by mass or more. The thermoplastic resin B different from the crystalline polyester A used for the A layer refers to a resin having different thermal characteristics from the crystalline polyester A used for the A layer, and specifically, differential scanning calorimetry (differential scanning calorimetry). DSC) that shows different melting points and glass transition points. Further, "alternately laminated" here means that layers made of different thermoplastic resins are laminated in a regular arrangement in the thickness direction, for example, two thermoplastic resins A having different refractive indexes and In the case of B, if each layer is expressed as an A layer and a B layer, they are laminated in a regular arrangement of A (BA) n (n is a natural number). By alternately laminating resins having different thermal characteristics in this way, it is possible to highly control the orientation state of each layer when manufacturing a biaxially stretched film, which in turn improves the phase difference and UV cut property. It can be controlled.

In the polyester film of the present invention, it is preferable that the A layer made of crystalline polyester is the outermost layer. In this case, since the crystalline polyester is the outermost layer, it is possible to obtain a biaxially stretched film similar to a crystalline polyester film such as a polyethylene terephthalate film or a polyethylene naphthalate film. When the thermoplastic resin A is made of, for example, a non-crystalline resin, when a biaxially stretched film is obtained in the same manner as a general sequential biaxially stretched film described later, film formation defects due to adhesion to manufacturing equipment such as rolls and clips In addition, problems such as deterioration of the flatness of the surface of the laminated film may occur. As the crystalline polyester used in the present invention, a polyester obtained by polymerization of a monomer containing an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main constituents is preferable. Here, as the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyl Examples thereof include dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, and 4,4'-diphenylsulfone dicarboxylic acid. Examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dimer acid, dodecandioic acid, cyclohexanedicarboxylic acid and their ester derivatives. Of these, terephthalic acid and 2,6-naphthalenedicarboxylic acid, which exhibit a high refractive index, are preferable. Only one of these acid components may be used, two or more of them may be used in combination, and an oxyacid such as hydroxybenzoic acid may be partially copolymerized.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. , 1,6-Hexanediol, 1,2-Cyclohexanedimethanol, 1,3-Cyclohexanedimethanol, 1,4-Cyclohexanedimethanol, Diethylene glycol, Triethylene glycol, Polyalkylene glycol, 2,2-Bis (4-) Hydroxyethoxyphenyl) propane, isosorbate, spiroglycol and the like can be mentioned. Of these, ethylene glycol is preferably used. Only one of these diol components may be used, but two or more thereof may be used in combination.
The resin that can be added to the crystalline polyester used in the present invention, and the thermoplastic resin B includes ring-opening of chain polyolefins such as polyethylene, polypropylene, poly (4-methylpentene-1), and polyacetal, and norbornenes. Metathesis polymerization, addition polymerization, biodegradable polymers such as alicyclic polyolefin, polylactic acid, polybutylsuccinate, which are addition copolymers with other olefins, nylon 6, nylon 11, nylon 12, nylon 66, etc. Polyamide, aramid, polymethylmethacrylate, polyvinylchloride, polyvinylidene chloride, polyvinyl alcohol, polyvinylbutyral, vinylethylene acetate copolymer, polyacetal, polyglucolic acid, polystyrene, styrene copolymer polymethylmethacrylate, polycarbonate, polypropylene terephthalate, Polypropylene terephthalate, polybutylene terephthalate, polyester such as polyethylene-2,6-naphthalate, polyether sulfone, polyether ether ketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide, polyarylate, ethylene tetrafluoride resin, Ethylene trifluoride resin, ethylene chloride trifluoride resin, ethylene tetrafluoride-6 propylene fluoride copolymer, polyvinylidene fluoride and the like can be used. Among these, the thermoplastic resin B, which is different from the crystalline polyester from the viewpoint of strength, heat resistance, transparency and versatility, has not only strength, heat resistance, transparency and versatility, but also adhesion to crystalline polyester. -It is preferable to use polyester from the viewpoint of stackability. These may be copolymers or mixtures.

The crystalline polyester preferably used in the present invention and the thermoplastic resin B different from the crystalline polyester are, for example, among the polyesters, polyethylene terephthalate and its polymer, polyethylene naphthalate and its copolymer, polybutylene terephthalate and its polymer. It is preferable to use a copolymer, polybutylene naphthalate and its copolymer, polyhexamethylene terephthalate and its copolymer, polyhexamethylene naphthalate and its copolymer and the like. Further, from the viewpoint of suppressing curls and wrinkles due to heat treatment of the polarizing plate, it is particularly preferable to contain spiroglycol, naphthalenedicarboxylic acid, polyetherimide, bisphenol A, and fluorene components. The preferred component may be copolymerized as the thermoplastic resin B in the polymer, or may be blended with the thermoplastic resin B as another polymer.

As a preferable combination of the crystalline polyester preferably used for the polyester film of the present invention and the thermoplastic resin B different from the crystalline polyester, the absolute value of the difference in SP value of each thermoplastic resin is 1.0 or less. Is particularly preferable. When the absolute value of the difference between the SP values is 1.0 or less, delamination is less likely to occur. More preferably, the crystalline polyester and the thermoplastic resin B are made of a combination having the same basic skeleton. The basic skeleton referred to here is a repeating unit constituting the resin. For example, when polyethylene terephthalate is used as one of the thermoplastic resins, it is the same as polyethylene terephthalate from the viewpoint of easily realizing a highly accurate laminated structure. It is preferable that ethylene terephthalate, which is the basic skeleton of the above, is contained in the other thermoplastic resin. When the crystalline polyester and the thermoplastic resin B are resins containing the same basic skeleton, it is possible to obtain a laminated structure having high lamination accuracy and less delamination at the lamination interface.

Further, as a preferable combination of the crystalline polyester used for the polyester film of the present invention and the thermoplastic resin B different from the crystalline polyester, the glass transition temperature difference between the crystalline polyester and the thermoplastic resin B is 30 ° C. or less. Is preferable. If the glass transition temperature difference is larger than 30 ° C., the thickness uniformity in manufacturing the laminated film becomes poor, which may cause variations in the phase difference. Further, when molding the laminated film, problems such as overstretching are likely to occur. More preferably, it is 20 ° C. or lower. Further, it is preferable that the glass transition temperature of the thermoplastic resin B is lower than that of the thermoplastic resin A before stretching in which orientation crystallization is imparted to the crystalline polyester from the viewpoint of imparting higher dimensional stability.

In the B layer of the polyester film of the present invention, it is preferable that the thermoplastic resin B, which is different from the crystalline polyester used for the A layer, is made of an amorphous resin. Since the amorphous resin is less likely to be oriented when the biaxially stretched film is produced as compared with the crystalline resin, it is possible to suppress an increase in the phase difference of the B layer made of the thermoplastic resin B, and by extension, the phase difference of the film. It becomes easy to suppress the non-uniformity. In particular, this effect becomes remarkable when a heat treatment step is provided when the biaxially stretched film is produced. Specifically, the orientation generated in the layer made of amorphous resin in the stretching step in the longitudinal direction and the width direction of the film can be completely relaxed in the heat treatment step, and the A layer made of substantially crystalline polyester can be obtained. This is because only the resulting phase difference affects the phase difference as a laminated film. The amorphous resin referred to here refers to a resin that does not show a peak corresponding to the melting point in differential scanning calorimetry or has a melting enthalpy of 10 (J / g) or less.

As an example of the combination of resins for satisfying the above conditions, in the polyester film of the present invention, the crystalline polyester is a polyester containing polyethylene terephthalate or polyethylene naphthalate, and the thermoplastic resin B is a polyester containing spiroglycol. Is preferable. The polyester containing spiroglycol refers to a copolyester in which spiroglycol is copolymerized, a homopolyester, or a polyester in which they are blended. Polyesters containing spiroglycol are preferable because they have a small glass transition temperature difference from polyethylene terephthalate and polyethylene naphthalate, and thus are less likely to be overstretched during molding and are less likely to be delaminated. More preferably, the crystalline polyester is a polyester containing polyethylene terephthalate or polyethylene naphthalate, and the thermoplastic resin B is a polyester containing spiroglycol and cyclohexanedicarboxylic acid. When the polyester contains spiroglycol and cyclohexanedicarboxylic acid, the crystallinity can be lowered, so that the phase difference can be easily suppressed. In addition, since the glass transition temperature difference from polyethylene terephthalate and polyethylene naphthalate is small and the adhesiveness is excellent, overstretching is unlikely to occur during molding, and delamination is also difficult to occur.

Further, in the polyester film of the present invention, it is also preferable that the crystalline polyester is a polyester containing polyethylene terephthalate or polyethylene naphthalate, and the thermoplastic resin B different from the crystalline polyester is a polyester containing cyclohexanedimethanol. The polyester containing cyclohexanedimethanol refers to a copolyester obtained by copolymerizing cyclohexanedimethanol, a homopolyester, or a polyester blended thereto. Polyester containing cyclohexanedimethanol can easily suppress the phase difference because its crystallinity can be lowered, and since the glass transition temperature difference from polyethylene terephthalate or polyethylene naphthalate is small, it is molded. It is preferable because sometimes it is difficult to overstretch and it is difficult to delaminate. More preferably, the thermoplastic resin B is an ethylene terephthalate polycondensate having a copolymerization amount of cyclohexanedimethanol of 15 mol% or more and 60 mol% or less. By doing so, in addition to being able to suppress the phase difference because the state can be made substantially amorphous, the change in the phase difference due to heating or aging is particularly small, and peeling between layers is less likely to occur. The ethylene terephthalate polycondensate having a copolymerization amount of cyclohexanedimethanol of 15 mol% or more and 60 mol% or less adheres very strongly to polyethylene terephthalate. In addition, the cyclohexanedimethanol group has a cis isomer or a trans isomer as a geometric isomer, and a chair type or a boat type as a conformation isomer. Therefore, even if it is co-stretched with polyethylene terephthalate, it is difficult to orientally crystallize. It is unlikely to cause blurring during manufacturing.

Further, in the polyester film of the present invention, it is also preferable that the crystalline polyester is a polyester containing polyethylene terephthalate or polyethylene naphthalate, and the thermoplastic resin B different from the crystalline polyester is a polyester containing isophthalic acid. The polyester containing isophthalic acid refers to a copolyester in which isophthalic acid is copolymerized, a homopolyester, or a polyester in which they are blended. Polyester containing isophthalic acid can easily suppress the phase difference because its crystallinity can be lowered, and since the glass transition temperature difference with polyethylene terephthalate or polyethylene naphthalate is small, it is during molding. It is preferable because it is unlikely to be overstretched and delamination is also difficult to occur. More preferably, the thermoplastic resin B is an ethylene terephthalate polycondensate having an isophthalic acid copolymerization amount of 10 mol% or more and 25 mol% or less.
In addition, various additives such as antioxidants, heat-resistant stabilizers, weather-resistant stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, and charges are contained in the thermoplastic resin. An inhibitor, a nucleating agent, or the like may be added to such an extent that the characteristics are not deteriorated.
The concentration of the ultraviolet absorber (UVA) preferably added to the polyester film of the present invention is preferably 0.5 to 2% by mass, more preferably 0.7 to 1.8% by mass, and 0.8 to 0.8 to. 1.5% by mass is more preferable, and 1.0 to 1.5% by mass is particularly preferable. If the concentration of UVA is less than 0.5% by mass, the UV blocking property may be inferior. On the other hand, when the concentration of UVA exceeds 2% by mass, process contamination, color change, and decrease in mechanical strength may occur. As UVA, 2,2'-methylenebis [6- (2H benzotriazole-2-yl) -4- (1,1,3,3) is used from the viewpoint of UV absorption in the region of 300 to 400 nm. -Tetramethylbutyl) phenol], 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine, 2,2'-(1,4-phenylene) ) Bis (4H-3,1-benzoxazodine-4-one), 2- (4,6- (4-biphenyl) -1,3,5-triazine-2-yl) -5- (2-) Ethylhexyloxy) -phenol, 2- (4,6-diphenyl-1,3,5-triazine-2-yl) -5- [2- (2-ethylhexanoyloxy) ethoxy] phenol and mixtures thereof. It can be preferably used.

When the polyester film of the present invention has an A layer and a B layer as a preferred embodiment, the lamination ratio of the A layer and the B layer (total thickness of the A layer / total thickness of the B layer) is 0.5 to 1.5. It is preferably in the range. The lamination ratio of the A layer and the B layer is more preferably 0.6 to 1.4, further preferably 0.7 to 1.3, and particularly preferably 0.8 to 1.2. When the lamination ratio is less than 0.5, the heat resistance may be deteriorated, especially when an amorphous resin is used for the B layer. When the lamination ratio exceeds 1.5, the phase difference may increase too much, especially when an amorphous resin is used for the B layer.

In the polyester film of the present invention, the variation of Re is preferably 18% or less in the width direction. The variation of Re is more preferably 15% or less, further preferably 12% or less, and particularly preferably 10% or less. The variation of Re at this time is that when the film width of the polyester film is 400 mm or more, after sampling at intervals of 50 mm in the entire width direction of the film, Re in the center of each sample is measured, and the maximum value of Re is used. The value displayed as% by dividing the difference between the minimum values by the average value. In the case of a roll-shaped film, the winding direction of the roll is the longitudinal direction of the film, and the direction perpendicular to the winding direction corresponds to the width direction. On the other hand, in the case of a cut sheet, Re is measured at both ends (25 mm away from both ends) in the direction orthogonal to the long side direction and the long side direction of the film, and the difference from the center of the film. The direction in which is larger is the width direction of the film referred to in the present invention. When the variation of Re exceeds 18% in the width direction, color unevenness may occur when the polarizing plate protective film is mounted on a large liquid crystal display, and the quality may be deteriorated. As a method of controlling the variation in the width direction of Re as described above, it can be achieved by taking the film forming conditions described later.

The polyester film of the present invention preferably has a film thickness of 40 μm or less. This is because the phase difference is represented by the product of the thickness and the birefringence Δn. The film thickness is more preferably 5 to 30 μm, further preferably 7 to 25 μm, and particularly preferably 10 to 20 μm. When the film thickness exceeds 40 μm, the phase difference becomes high, and when used as a polarizing plate protective film, the polarizing plate becomes thick, so that the weight may increase or the size may increase when mounted on a liquid crystal display.

The polyester film of the present invention preferably has a film width of 400 mm or more. The width of the film is more preferably 600 mm or more, further preferably 1300 mm or more, and particularly preferably 1500 mm or more. If the width of the film is less than 400 mm, it may not be possible to mount it as a large liquid crystal display.

The polyester film of the present invention preferably has a glass transition point of 90 ° C. or higher. The glass transition point of the film is more preferably 92 ° C. or higher, further preferably 94 ° C. or higher, and particularly preferably 96 ° C. or higher. If the glass transition point of the film is less than 90 ° C, the polarizing plate may curl or wrinkles may occur at the interface between the film and the polarizer in the durability test such as the manufacturing process of the polarizing plate and long-term storage. is there. The method of controlling the glass transition point of the film as described above is achieved by including any one of the spiroglycol, naphthalenedicarboxylic acid, polyetherimide, bisphenol A, fluorene, and isosorbide component in the thermoplastic resin B as described above. can do. The amount of these copolymerizations is preferably 5 mol% or more and 60 mol% or less. If it is 5 mol% or less, the glass transition point does not reach 90 ° C. or higher. Further, if it is too large, 60 mol% or more, the glass transition point exceeds 120 ° C., so that co-stretching with the layer A containing the crystalline polyester made of the thermoplastic resin A as the main component becomes difficult, and thickness unevenness or the like occurs. It becomes impossible to obtain a film that is sequentially biaxially stretched. More preferably, it is 10 mol% or more and 45 mol% or less.
The polyester film of the present invention preferably has a coefficient of linear expansion in the longitudinal direction from 25 ° C. to 85 ° C. of 5.0 × 10 ⁻⁵ / ° C. or less. The coefficient of linear expansion of the film ^{is more preferably 4.5 × 10-5} / ° C. or less, further preferably 4.2 × ^10-5 / ° C. or less, and 4.0 × ^10-5 / ° C. or less. Is particularly preferable. If the coefficient of linear expansion of the film ^{exceeds 5.0 × 10-5} / ° C, the polarizing plate may be curled or wrinkled at the interface between the film and the polarizer in the durability test of the polarizing plate. is there. As a method for controlling the linear expansion coefficient of the film as described above, the thermoplastic resin B contains any one of spiroglycol, naphthalenedicarboxylic acid, polyetherimide, bisphenol A, fluorene, and isosorbide component as described above, and will be described later. It can be achieved by taking the film forming conditions.

The polyester film of the present invention preferably has a light transmittance of 0 to 30% at a wavelength of 380 nm from the viewpoint of UV blocking property. It is more preferably 25% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance at a wavelength of 380 nm exceeds 30%, the polarizer and the liquid crystal may be deteriorated by ultraviolet rays when mounted on a liquid crystal display as a polarizing plate protective film. In order to control the light transmittance at a wavelength of 380 nm within a preferable range, it can be realized by increasing the difference in the in-plane refractive index of two or more kinds of resins having different optical characteristics. The laminated film may be a laminated film in which layers mainly composed of polyester, which is a property, and layers mainly composed of a thermoplastic resin, which retains amorphousness during stretching or is melted in a heat treatment step, are alternately laminated. Specifically, it can be achieved by laminating the polyester and the thermoplastic resin B as described above in a desired number of layers. Further, as described above, it is more preferable to contain the ultraviolet absorber (UVA) in a preferable range.

The polyester film of the present invention preferably has an average transmittance of 5% or less at a wavelength of 240 to 360 nm from the viewpoint of UV blocking property. It is more preferably 4% or less, further preferably 3% or less, and particularly preferably 2% or less. When the average transmittance at a wavelength of 240 to 360 nm exceeds 5%, the polarizer and the liquid crystal may be deteriorated by ultraviolet rays when mounted on a liquid crystal display as a polarizing plate protective film. In order to control the average transmittance at a wavelength of 240 to 360 nm within a preferable range, it can be realized by increasing the difference in the in-plane refractive index of two or more kinds of resins having different optical characteristics. May be a laminated film in which a layer containing a crystalline polyester as a main component and a layer containing a thermoplastic resin as a main component, which retains amorphousness during stretching or is melted in a heat treatment step, are alternately laminated. Specifically, it can be achieved by laminating the polyester and the thermoplastic resin B as described above in a desired number of layers.

Next, a preferable method for producing the polyester film of the present invention will be described below. Of course, the present invention is not construed as being limited to such an example. Further, the laminated structure of the polyester film used in the present invention can be easily realized by the same method as that described in columns [0053] to [0063] of JP-A-2007-307893. In the present invention, by reducing the number of layers, one slit plate can be used to form multiple layers, which is preferable from the viewpoint of stacking accuracy in the width direction as compared with using three slit plates. .. Poor stacking accuracy in the width direction means that the UV cut property differs depending on the position of the film.

Prepare the thermoplastic resin in the form of pellets or the like. The pellets are, if necessary, dried in hot air or under vacuum before being fed to a separate extruder. In the extruder, the resin heated and melted above the melting point is homogenized in the amount of resin extruded by a gear pump or the like, and foreign substances, modified resin and the like are removed through a filter or the like. These resins are formed into a desired shape by a die and then discharged. Then, the sheet discharged from the die is extruded onto a cooling body such as a casting drum and cooled and solidified to obtain a casting film. At this time, it is preferable to use a wire-shaped, tape-shaped, needle-shaped, or knife-shaped electrode to bring it into close contact with a cooling body such as a casting drum by electrostatic force to quench and solidify it. Further, it is also preferable to blow air from a slit-shaped, spot-shaped, or planar device to bring it into close contact with a cooling body such as a casting drum to quench and solidify it, or to bring it into close contact with a cooling body with a nip roll to quench and solidify it.

Further, a plurality of resins of crystalline polyester, which is the main component of the A layer, and thermoplastic resin B, which is different from the crystalline polyester, are sent out from different flow paths by using two or more extruders, and are sent to the multilayer stacking apparatus. As the multi-layer stacking device, a multi-manifold die, a feed block, a static mixer, or the like can be used, but in particular, in order to efficiently obtain the configuration of the present invention, a feed block having three or more fine slits is used. Is preferable. When such a feed block is used, the apparatus does not become extremely large, so that there are few foreign substances due to thermal deterioration, and even when the number of layers is extremely large, high-precision lamination is possible. In addition, the stacking accuracy in the width direction is also significantly improved as compared with the conventional technique. Further, in this device, since the thickness of each layer can be adjusted by the shape (length, width) of the slit, it is possible to achieve an arbitrary layer thickness.

The molten multilayer laminate formed in the desired layer structure in this manner is guided to the die, and the casting film is obtained as described above.

The casting film thus obtained is preferably biaxially stretched. Here, biaxial stretching means stretching in the longitudinal direction and the width direction. The stretching may be sequentially stretched in two directions, or may be stretched in two directions at the same time. Further, re-stretching may be performed in the longitudinal direction and / or the width direction.

The case of sequential biaxial stretching will be described first. Here, the stretching in the longitudinal direction means stretching to give the film a molecular orientation in the longitudinal direction, and is usually applied by the difference in peripheral speed of the rolls, and this stretching may be performed in one step. , Multiple roll pairs may be used in multiple stages. The stretching ratio varies depending on the type of resin, but is usually preferably 2 to 15 times, and when polyethylene terephthalate is used as one of the resins constituting the laminated film, 2 to 7 times is preferably used. It is preferably 3 to 5 times, more preferably 3 to 4 times, and particularly preferably 3 to 3.5 times from the viewpoint of suppressing the variation of Re in the width direction. The stretching temperature is preferably from the glass transition temperature to the glass transition temperature of the resin constituting the film + 100 ° C, more preferably 80 to 120 ° C, further preferably 90 to 115 ° C, and the variation of Re in the width direction. From the viewpoint of suppression, 95 to 110 ° C. is particularly preferable. _Regarding the relationship between the stretched section ( _LMD ) and the film width ( _{LAF) of the casting film, LA AF} / L _MD is 0 from the viewpoint of suppressing the occurrence of curls and wrinkles due to heat treatment in the durability test after using a polarizing plate. The range of .1 to 2.0 is preferable, the range of 0.5 to 2.0 is more preferable, the range of 0.7 to 2.0 is further preferable, and the range of 0.7 to 1.8 A range is particularly preferable.

The uniaxially stretched film thus obtained is subjected to surface treatment such as corona treatment, frame treatment, and plasma treatment as necessary, and then has functions such as slipperiness, adhesiveness, and antistatic property. It may be applied by in-line coating.

Subsequently, the stretching in the width direction means stretching for giving the film orientation in the width direction, and usually, a tenter is used to carry the film while gripping both ends with clips to stretch the film in the width direction. The stretching ratio varies depending on the type of resin, but is usually preferably 2 to 15 times, and when polyethylene terephthalate is used as one of the resins constituting the film, 2 to 6 times is preferably used, more preferably. Is 3 to 6 times, more preferably 3 to 5.5 times, and 3.5 to 5 times is particularly preferable from the viewpoint of suppressing variations in Re and Rth, and the film is stretched at a magnification higher than the longitudinal stretching ratio. That is still preferable. Further, the stretching temperature is preferably from the glass transition temperature to the glass transition temperature of the resin constituting the film to + 120 ° C., and it is preferable to give an inclination to the temperature from the viewpoint of suppressing the variation of Re in the width direction. It is preferable that the temperature increases, and specifically, when the transverse stretching section is divided into two, the difference between the upstream temperature and the downstream temperature is preferably 20 ° C. or more. It is more preferably 30 ° C. or higher, further preferably 35 ° C. or higher, and particularly preferably 40 ° C. or higher. The stretching temperature of the first stage is more preferably 80 to 120 ° C, further preferably 90 to 110 ° C, and particularly preferably 95 to 105 ° C.

Further, in the polyester film of the present invention, it is preferable to provide a difference in the transverse stretching speed from the viewpoint of suppressing the variation of Re in the width direction. The stretched amount of the film (film width at the measurement point-film width before stretching) is preferably 60% or more, more preferably 70% or more, still more preferably 75% of the stretching amount at the end of the transverse stretching section. As mentioned above, it is particularly preferably 80% or more.

The biaxially stretched polyester film is preferably heat-treated in a tenter at a stretching temperature or higher and a melting point or lower in order to impart flatness and dimensional stability. Specifically, 160 to 250 ° C. is preferable, 160 to 240 ° C. is more preferable, and 180 to 240 ° C. is further preferable. When the heat treatment temperature exceeds 230 ° C, the Boeing phenomenon known as unevenness of physical properties in the film width direction is likely to occur in the tenter, and birefringence becomes large, so that the absolute values of Re and Rth and the variation of Re in the width direction vary. growing. Therefore, 190 to 210 ° C. is particularly preferable from the viewpoint of suppressing these. The heat treatment improves the dimensional stability of the film. After being heat-treated in this manner, it is uniformly slowly cooled, cooled to room temperature, and wound up. From the viewpoint of suppressing the occurrence of curls and wrinkles due to the process heat treatment of polarizing plate formation, it is preferable to use a relaxation treatment in combination with the heat treatment and slow cooling. As a method of relaxation treatment, the relaxation method in the width direction can be performed by narrowing the width of the tenter, and in the longitudinal direction, a tenter equipped with a mechanism for shrinking the clip in the longitudinal direction can be used, or the peripheral speed difference between rolls can be reduced. It can be used and implemented. The order of relaxation treatment is as follows: width direction, longitudinal direction, width direction, regardless of whether the relaxation in the longitudinal direction is performed after the relaxation in the width direction or the relaxation in the width direction is performed after the relaxation in the longitudinal direction. Although it may be carried out step by step, it is preferable to carry out the relaxation in the longitudinal direction after the relaxation in the width direction from the viewpoint of simplifying the process. The relaxation rate in the width direction during heat treatment is preferably 0.5 to 5%, more preferably 0.5 to 3%, further preferably 0.8 to 2.5%, and dimensional stability and suppression of Re variation in the width direction. From the viewpoint of compatibility between the above, 1 to 2% is particularly preferable. Further, the relaxation rate in the width direction during slow cooling is preferably 0.5 to 3%, more preferably 0.5 to 2%, further preferably 0.5 to 1.5%, and dimensional stability and Re in the width direction. 0.5 to 1% is particularly preferable from the viewpoint of suppressing the variation of the above. The temperature at the time of slow cooling is preferably 90 to 180 ° C., more preferably 90 to 170 ° C., further preferably 100 to 160 ° C., and particularly preferably 100 to 150 ° C. from the viewpoint of dimensional stability and film flatness. The temperature at the time of relaxation in the longitudinal direction is preferably 90 to 180 ° C., more preferably 90 to 170 ° C., further preferably 100 to 160 ° C., and particularly preferably 100 to 150 ° C. from the viewpoint of dimensional stability and film flatness. The relaxation rate in the longitudinal direction is preferably 0.5 to 5%, more preferably 1 to 4%, further preferably 1.5 to 3.5%, from the viewpoint of achieving both dimensional stability and suppression of Re variation in the width direction. 2 to 3.5% is particularly preferable. By performing the relaxation treatment in the longitudinal direction at a film temperature of around 85 ° C., there is an effect that the heat yield at 85 ° C. is greatly reduced.

The polyester film of the present invention obtained as described above has high dimensional stability and can generate curls and wrinkles due to the heat treatment in the polarizing plate forming step, and therefore can be suitably used as a polarizing plate protective film. Further, the polarizing plate protective film can be suitably used as a polarizing plate by being bonded to a PVA sheet prepared by containing and orienting iodine in commercially available PVA. Further, when it is used for an ITO film substrate application, it is excellent in heat resistance and handleability even in the processing process.

Since the polyester film of the present invention has a low phase difference in both Re and Rth, the rainbow unevenness seen in the biaxially stretched polyethylene terephthalate film and the interference color are not visible when wearing polarized sunglasses. It is also suitable as a material film.

The polyester film of the present invention is preferably used for a touch panel. The touch sensor unit is composed of at least a cover glass and a conductive layer. The touch panel of the present invention may be of a resistive film type, an optical type, or a capacitance type. The capacitance type can be roughly divided into a projection type and a surface type. The projected capacitance type is most preferable from the viewpoint of enabling multi-touch. The conductive layer is a metal such as gold, silver, platinum, palladium, rhodium, indium, copper, aluminum, nickel, chromium, titanium, iron, cobalt, tin, and alloys thereof, tin oxide, indium oxide, titanium oxide, etc. It can be formed by a metal oxide film such as antimony oxide, zinc oxide, cadmium oxide, indium tin oxide (ITO), or a composite film such as copper iodide. For these transparent conductive films, a thin film can be obtained by vacuum deposition, sputtering, reactive RF ion plating, spray thermal decomposition method, chemical plating method, electroplating method, CVD method, coating method or a combination method thereof. Other conductive polymers include polypyrrole, polyaniline, polyacetylene, polythiophene, polyphenylene vinylene, polyphenylene sulfide, poly-p-phenylene, polyhetellocycle vinylene, and particularly preferably (3,4-ethylenedioxythiophene). ) (PEDOT). In addition, carbon nanotubes and nanosilver are also preferable because they exhibit high conductivity. These can be applied to the base material by a coating method by dissolving them in an organic solvent. As the coating method, various methods can be adopted in the same manner as the method of the hard coat layer. ITO is preferable from the viewpoint of versatility.

Out-cell type touch sensors can be broadly divided into glass sensors and film sensors. Examples of the glass sensor type include GG, GG2, G2, and G1M. GG is cover glass / ITO / glass / ITO, GG2 is cover glass / glass / ITO / insulating layer / ITO, G2 (OGS) is cover glass / ITO / insulating layer / ITO, and G1M is cover glass / ITO. Is the basic configuration.

On the other hand, as the film sensor type, there are GFF, GF2, G1F, GF1, PFF, and PF1, and any of them may be used. GFF is cover glass / ITO / film / ITO / film, GF2 is cover glass / ITO / film / ITO, or cover glass / ITO / insulating layer / ITO / film, and G1F is cover glass / ITO / ITO. / Film, GF1 is a cover glass / ITO / film, PFF is a cover plastic / ITO / film / ITO / film, and P1M cover plastic / ITO is the basic configuration. The thickness of the polyester film as a base material is preferably 40 μm or less, more preferably 30 μm or less, from the viewpoint of thinning. If it is too thin, it is preferably 20 μm or more and 30 μm or less from the viewpoint of film handleability. The GF1 type is preferable as a touch sensor due to the recent trend toward thinning of displays.

Hereinafter, the present invention will be described in detail with reference to Examples. The characteristics were measured and evaluated by the following methods.

(1) Number of Laminates The number of laminated films was determined by observing a transmission electron microscope (TEM) for a sample whose cross section was cut out using a microtome. That is, using a transmission electron microscope H-7100FA (manufactured by Hitachi, Ltd.), the cross section of the film was observed under the condition of an acceleration voltage of 75 kV, a cross section photograph was taken, and the number of layers was measured. In some cases, in order to obtain high contrast, a dyeing technique using _{RuO 4} or OsO _{4 was used.} Further, according to the thickness of the thinnest layer (thin film layer) among all the layers that can be captured in one image, if the thin film layer thickness is less than 50 nm, it is 100,000 times, and the thin film layer thickness is 50 nm or more and 500 nm. Observation was carried out at a magnification of 40,000 times when it was less than, and at a magnification of 10,000 times when it was 500 nm or more.

(2) Re, Rth
A phase difference measuring device (KOBRA-21ADH) manufactured by Oji Measuring Instruments Co., Ltd. was used. A sample was cut out at a size of 3.5 cm × 3.5 cm from the center in the film width direction, installed in the device so that the film width direction had an angle of 0 ° defined by this measuring device, and Re and Rth at a wavelength of 590 nm. Was measured. Rth was calculated by a quadratic approximation of each phase difference value when the incident angle was 0 to 50 ° (every 10 °).

(3) Variation in the width direction of Re In a laminated film having a film width of 400 mm or more, sampling is performed at intervals of 50 mm over the entire width direction of the film by the method described in item (2) above, and then Re in the center of each sample. Was measured, the difference between the maximum value and the minimum value of Re was divided by the average value, and the value displayed as% was taken as the variation in the width direction of Re of the present laminated film. In the case of a roll-shaped laminated film, the winding direction of the roll is the longitudinal direction of the film, and the direction perpendicular to the winding direction corresponds to the width direction. On the other hand, in the case of a cut sheet, Re is measured at both ends (25 mm away from both ends) in the direction orthogonal to the long side direction and the long side direction of the film, and the difference from the center of the film. Is the width direction of the laminated film referred to in the present invention.

(4) Young's modulus and elongation at break The sample was cut out from the center of the film in the width direction at 15 cm in the longitudinal direction and 1.5 cm in the width direction, and used as a sample for measuring Young's modulus in the longitudinal direction. Similarly, a sample for measuring Young's modulus in the width direction was cut out at 15 cm in the width direction and 1.5 cm in the longitudinal direction. Young's modulus and elongation at break were measured at a temperature of 23 ° C. and a humidity of 65% RH using a robot Tencilon RTA (manufactured by Orientec) in the measurement according to JIS-K7127-1999. The pulling speed was set to 300 mm / min.

(5) Film thickness The film thickness was measured with a contact-type film thickness meter Mitutoyo Lightmatic VL-50A (10.5 mmφ cemented carbide spherical surface stylus, measuring load 0.06 N). The measurement was performed 10 times at different locations, and the average value was taken as the thickness of the laminated film.

(6) Rising temperature of shrinkage stress during TMA measurement A sample was cut out from the center in the width direction of the film at a length of 50 mm in the longitudinal direction x 4 mm in the width direction, and TMA / 6000 manufactured by Seiko Instruments Co., Ltd. was used to adjust the temperature from 25 ° C to 200 ° C. TMA was measured under the conditions of a temperature range, a heating rate of 5 ° C./min, a hold of 5 minutes, a measurement length of 15 mm, and a constant tensile length. The load at the time of length measurement was set to 19.6 mN. The rising temperature of the contraction stress was set to the temperature at which the value obtained by subtracting the initial load from the measurement result load exceeded 10 mN for the first time.

(7) Coefficient of linear expansion A sample is cut out from the center in the width direction of the film in a length direction of 50 mm and a width direction of 4 mm, and using TMA / 6000 manufactured by Seiko Instruments, Inc., a temperature range of 25 ° C. to 150 ° C. and a heating rate. TMA was measured under the conditions of 5 ° C./min, hold for 5 minutes, load of 29.4 mN, measurement length of 15 mm, and constant tensile load. The load at the time of length measurement was also set to 29.4 mN, which was the same as at the time of measurement. From the measurement results, the coefficient of linear expansion in the longitudinal direction from 25 ° C. to 85 ° C. was calculated.

(8) Dimensional stability test during post-processing Curable urethane acrylic resin (Shikou UV-1700B manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was diluted to a concentration of 30% using a methyl ethyl ketone solvent, and the outermost surface of the polyester film was diluted. Apply evenly on top using a bar coater, and use a condensing high-pressure mercury lamp (H04-L41 manufactured by Eye Graphics Co., Ltd.) with an irradiation intensity of 120 W / cm2 to achieve an integrated irradiation intensity of 180 mJ / cm2. After irradiating and curing, a polyester film having a hard coat with a thickness of 2 μm was prepared by heat treatment at 90 ° C., and a sample cut out from the central portion in the width direction in a size of 30 mm × 30 mm was visually described below. It was evaluated according to the criteria of.

⊚: A level at which curls and wrinkles do not occur, or curls are weak enough not to form a cylinder.

◯: Curled into a tubular shape, but no wrinkles occurred.

X: Curled into a cylinder and wrinkled.

(9) Handleability The Young's modulus and breaking elongation measured in the above item (4) were evaluated as handleability according to the following criteria.

⊚: Young's modulus in the longitudinal direction and the width direction is 3 GPa or more and elongation at break is 50% or more ◯: Young's modulus in the longitudinal direction and the width direction is 2 GPa or more and less than 3 GPa, and elongation at break is 50% or more ×: Young's modulus in the longitudinal direction Alternatively, Young's modulus in the width direction is less than 2 GPa, or elongation at break is less than 50% (10) Glass transition point (Tg) of the film.
The dynamic viscoelasticity of the film was measured using DMS-6100 manufactured by Seiko Instruments Inc. under the following conditions.

Sample length: 20 mm (width 5 mm)
Minimum load: 50mN
Frequency: 1Hz
Displacement: 5 μm
Temperature program: 25 ℃ start → 250 ℃ end 5min holding (2 ℃ / min)
Next, the α relaxation temperature was obtained from the obtained temperature dependence diagram of tan δ. The α relaxation temperature of the polyester film of the present invention is a peak observed near the glass transition point of the resin A layer and the B layer, and when two α relaxation temperatures are confirmed, the lower one is set as the glass transition point. Adopted.

(11) Glass transition temperature (Tg) of thermoplastic resin B, melting point (Tm) of thermoplastic resin A
Immediately after discharge, the melt-kneaded polyester chip cooled with cold water of 10 ° C. or lower is heated at 5 ° C./min from 25 ° C. to 290 ° C. using differential calorimetry (DSC), and the transition point appearing at this time is JIS. -Measured and calculated according to K-7122 (1987).
Equipment: "EXTRA DSC6220" manufactured by SII Nanotechnology Co., Ltd. (former Seiko Electronics Co., Ltd.)
Sample mass: 5 mg.

(12) Heat Shrinkage A film sample having a width direction of 150 mm and a longitudinal direction of 150 mm was collected from the central portion of the film roll in the width direction. A pair of marks were added to the central portion of each sample so as to have an interval of 100 mm as the original length (L0) in each of the longitudinal direction and the width direction. The sample was treated in an oven at 85 ° C. for 6 hours and then cooled to room temperature, and the distance between the pair of marks was measured and used as the length (L1) after the treatment. The heat shrinkage rate at each position and direction was calculated according to 100 × (L0-L1) / L0. The average value of the obtained results was calculated in each of the longitudinal direction and the width direction, and used as the heat shrinkage rate of the film.

(Example 1)
As the crystalline polyester, polyethylene terephthalate (PET) having a melting point of 258 ° C. was used. As the thermoplastic resin B, ethylene terephthalate (PE / SPG · T / CHDC) obtained by copolymerizing 30 mol% of spiroglycol and 15 mol% of cyclohexanedicarboxylic acid, which are amorphous resins having no melting point, was used. 98% by mass of PE / SPG / T / CHDC and 2% by mass of 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine as UVA in this ratio. Raw materials are supplied from the weighing hopper to the twin-screw extruder so that they are mixed, melt-kneaded at 280 ° C, discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C, and cut into chips. A thermoplastic resin composition (A) was obtained.

The prepared PET and the composition A were dried under a sufficiently vacuum high temperature so as not to contain water, and then put into two single-screw extruders and melt-kneaded at 280 ° C. Next, after passing through five FSS type leaf disc filters, the stacking ratio of each layer composed of composition A and each layer composed of composition B (total thickness of A / total thickness of B) becomes 1.0. On a cast drum whose surface temperature is controlled to 25 ° C., it is extruded from a T-die as a laminated body in which 251 layers are alternately laminated in the thickness direction by merging with a laminating device having 251 slits while weighing with a gear pump. I cast it on and got a casting film. The method for forming the laminated body was carried out according to the description in columns [0053] to [0056] of JP-A-2007-307893. Here, the slit length and the interval are all constant. The obtained laminate had 126 layers of PET and 125 layers of composition A, and had a laminated structure in which they were alternately laminated in the thickness direction. Further, the value obtained by dividing the length in the film width direction of the base lip, which is the widening ratio inside the base, by the length in the film width direction at the inlet of the base is set to 2.5.

The obtained casting film is heated in a roll group set at 105 ° C., and then _{rapidly heated from both sides of the film with a radiation heater at L AF} / L _MD 0.8 while keeping the film temperature at 110 ° C. in the longitudinal direction of the film. It was stretched 3.3 times and then cooled once. Subsequently, both sides of this uniaxially stretched film are subjected to corona discharge treatment in air to set the wetting tension of the base film to 55 mN / m, and the treated surfaces on both sides of the film (polyester resin having a glass transition temperature of 18 ° C.) / (Polyester resin having a glass transition temperature of 82 ° C.) / A laminated film coating liquid composed of silica particles having an average particle size of 100 nm was applied to form a transparent, easy-slip, and easy-adhesion layer.

This uniaxially stretched film was guided to a tenter, preheated with hot air at 95 ° C., and then stretched 4.0 times in the film width direction at a temperature of 105 ° C. for the first stage and 145 ° C. for the second stage. Here, when the transverse stretching section is divided into two, the stretching amount of the film at the midpoint of the transverse stretching section (film width at the measurement point-film width before stretching) is 80% of the stretching amount at the end of the transverse stretching section. It was stretched in two steps as described above. The laterally stretched film is directly heat-treated in a tenter with hot air at 190 ° C., followed by relaxation treatment of 1% in the width direction under the same temperature conditions, further quenching to 150 ° C., and then 1% in the width direction. After that, the relaxation treatment was performed, and then the peripheral speed difference between the rolls was reduced by 3.5% in the longitudinal direction while maintaining the temperature of 150 ° C. Finally, it was wound with a winder to obtain a polyester film. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 2)
96% by mass of ethylene terephthalate (PE / SPG / T / CHDC) copolymerized with 20 mol% of spiroglycol, which is an amorphous resin having no melting point, and 30 mol% of cyclohexanedicarboxylic acid, and 2,2'-methylenebis [6] as UVA. -(2H Benzotriazole-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol] 4% by mass is supplied from the weighing hopper to the twin-screw extruder so as to be mixed in this ratio. Then, the mixture was melt-kneaded at 280 ° C., discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C., and cut into chips to obtain a thermoplastic resin composition (B).
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that Composition B was used instead of Composition A and the relaxation rate in the longitudinal direction was set to 0.5%. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 3)
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the transverse stretching ratio was 5 times and the heat treatment temperature was 230 ° C. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 4)
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the temperature during the longitudinal relaxation treatment was 90 ° C. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 5)
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the PET2 layer and the composition A1 layer were formed by using a laminating device having three slits. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 6)
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the PET301 layer and the composition A300 layer were formed by using a laminating device having 601 slits. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 7)
As the thermoplastic resin B, polyethylene terephthalate (PET / N) copolymerized with 30 mol% of 2,6-naphthalenedicarboxylic acid, which is an amorphous resin having no melting point, was used. The above PET / N98% by mass and 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine 2% by mass as UVA are mixed in this ratio. The raw material is supplied from the measuring hopper to the twin-screw extruder, melt-kneaded at 280 ° C, discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C, and cut into chips to form a thermoplastic resin composition. The thing (C) was obtained.

In Example 1, a polyester film was obtained in the same manner as in Example 1 except that Composition C was used instead of Composition A. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 8)
As the thermoplastic resin B, polyethylene terephthalate (PETG) obtained by copolymerizing 30 mol% of 1,4-cyclohexanedimethanol, which is an amorphous resin having no melting point, was used. 93% by mass of PETG, 5% by mass of polyetherimide (PEI), and 2% by mass of 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine as UVA. The raw material is supplied from the weighing hopper to the twin-screw extruder so that the mixture is mixed at this ratio, melt-kneaded at 280 ° C, discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C, and chip-shaped. The thermoplastic resin composition (D) was obtained.

In Example 1, a polyester film was obtained in the same manner as in Example 1 except that Composition D was used instead of Composition A. The evaluation results of the obtained polyester film are shown in Table 1.

(Example 9)
As the thermoplastic resin B, polycyclohexane terephthalate (PCT), which is an amorphous resin having no melting point, was used. 93% by mass of PETG, 5% by mass of polycarbonate (PC), and 2% by mass of 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine as UVA. Raw materials are supplied from the weighing hopper to the twin-screw extruder so that they are mixed in a ratio, melt-kneaded at 280 ° C, discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C, and cut into chips. The thermoplastic resin composition (E) was obtained.

In Example 1, a polyester film was obtained in the same manner as in Example 1 except that Composition E was used instead of Composition A. The evaluation results of the obtained polyester film are shown in Table 2.

(Example 10)
As the thermoplastic resin B, polyethylene terephthalate (PET / I ・ FO) obtained by copolymerizing 20 mol% of isophthalic acid and 25 mol% of fluorene, which are amorphous resins having no melting point, was used. 98% by mass of PET / I · FO and 2% by mass of 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine as UVA are mixed in this ratio. Raw materials are supplied from the weighing hopper to the twin-screw extruder, melt-kneaded at 280 ° C, discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C, cut into chips, and thermoplastic. A resin composition (F) was obtained.

In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the composition F was used instead of the composition A. The evaluation results of the obtained polyester film are shown in Table 2.

(Example 11)
As the thermoplastic resin B, polyethylene terephthalate (PET / ISB / CHDM) copolymerized with 15 mol% isosorbide, which is an amorphous resin having no melting point, and 20 mol% cyclohexanedimethanol, and polyethylene terephthalate (25 mol% isophthalic acid) are copolymerized. PET / I) was used. PET / ISB / CHDM 49% by mass, PET / I 49% by mass, UVA 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine 2% by mass The raw material is supplied from the weighing hopper to the twin-screw extruder so that the mixture is mixed at this ratio, melt-kneaded at 280 ° C, discharged from the die in a strand shape, cooled and solidified in a water tank at 25 ° C, and chip-shaped. The thermoplastic resin composition (G) was obtained.

In Example 1, the composition G was used instead of the composition A, stretched 3.3 times in the longitudinal direction of the film while keeping the film temperature at 110 ° C., and heat-treated with hot air at 215 ° C. in the tenter. A polyester film was obtained in the same manner as in Example 1. The evaluation results of the obtained polyester film are shown in Table 2.

(Example 12)
In Example 11, a laminating device having 601 slits was used, and as the thermoplastic resin A, a thermoplastic resin composition (I) in which PET / ISB / CHDM was mixed at a ratio of 25% by mass was used as the thermoplastic resin A. A polyester film was obtained in the same manner as in Example 11 except that the composition I301 layer and the composition G300 layer were used. The evaluation results of the obtained polyester film are shown in Table 2.

(Comparative Example 1)
In Example 2, a polyester film was obtained in the same manner as in Example 1 except that the temperature during the longitudinal relaxation treatment was set to 80 ° C. The evaluation results of the obtained polyester film are shown in Table 2.

(Comparative Example 2)
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the transverse stretching ratio was set to 6.2 times. The evaluation results of the obtained polyester film are shown in Table 2.

(Comparative Example 3)
As the thermoplastic resin B, PETG, which is an amorphous resin having no melting point, was used. Weighed so that 98% by mass of PETG and 2% by mass of 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methylphenyl) -1,3,5-triazine as UVA are mixed in this ratio. The raw material is supplied from the hopper to the twin-screw extruder, melt-kneaded at 280 ° C., discharged from the die in the form of strands, cooled and solidified in a water tank at 25 ° C., cut into chips, and the thermoplastic resin composition ( H) was obtained.

In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the composition G was used instead of the composition A and the film was stretched 3.3 times in the longitudinal direction of the film while keeping the film temperature at 90 ° C. The evaluation results of the obtained polyester film are shown in Table 2.

Since the polyester film of the present invention has a low heat shrinkage rate, can suppress the occurrence of curls and wrinkles, and has excellent handleability, it is a polarizing plate protective film or a touch panel of a polarizing plate built in a display device such as a liquid crystal display. It can be suitably used as an ITO base film used in the above.

Claims (7)

The thermal shrinkage rate at 85 ° C. in the longitudinal direction at 6 hours is 0.5% or less, the phase difference (Re) at an incident angle of 0 ° is 400 nm or less, and the Young's modulus in both the longitudinal direction and the width direction is 2 GPa or more. elongation at break in the longitudinal direction and the width direction are both 50% or more, der rising temperature of 90 ° C. or more longitudinal TMA measurement during contraction stress is, and the film width is 400mm or more, the variation of Re is in the width direction The polyester film has three or more layers A containing crystalline polyethylene terephthalate as a main component and layers B containing a thermoplastic resin B different from the crystalline polyethylene terephthalate as a main component alternately in the thickness direction. A polyester film which is laminated and the thermoplastic resin B contains any one of a spiroglycol, a naphthalenedicarboxylic acid, a fluorene, and an isosorbide component . The polyester film according to claim 1 , wherein the thermoplastic resin B is an amorphous resin . The polyester film according to claim 1 or 2 , wherein the glass transition point is 90 ° C. or higher. The polyester film according to any one of claims 1 to 3 , wherein the coefficient of linear expansion in the longitudinal direction from 25 ° C. to 85 ° C. is 5.0 × 10 ⁻⁵ / ° C. or less. The polyester film according to any one of claims 1 to 4 , wherein the number of layers is 51 to 601 layers. The polyester film according to any one of claims 1 to 5 , which is used as a polarizing plate protective film. An ITO base film for a touch panel using the polyester film according to any one of claims 1 to 5.