JP2017132990A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film that is free from irregular tone when the film is obliquely observed, has excellent surface quality, and can be suitable for optical applications.SOLUTION: The present invention provides a polyester film in which variations Rψ60 in maximum values of ψ in measurement wavelengths of 235-255 nm at measurement angle 60° measured with the Woollam ellipsometer M-2000D are 0.10 or more and 5.00 or less.SELECTED DRAWING: None

Description

  The present invention relates to a polyester film having no uneven color tone and excellent surface quality.

  Conventionally, the technique of a laminated film in which two or more kinds of resins are laminated is capable of imparting various properties to the film and has been widely used in various industrial applications. For example, optical interference that selectively cuts light of a specific wavelength by using the light interference phenomenon that occurs by alternately laminating two or more types of resins with different refractive indexes at the layer thickness of the wavelength of light. Multilayer films are known. Such a multilayer film is used for various optical applications because an optical filter having various performances can be achieved by setting the refractive index, the number of layers, and the thicknesses of each resin to a desired optical design. ing.

  As a method for producing a laminated film, a co-extrusion method using a plurality of extruders and a laminating method in which films are laminated are known. Among them, the co-extrusion method is capable of laminating a large number of layers in one step, and is very advantageous in terms of productivity and cost. Therefore, it is widely used as a general laminated film manufacturing method. Yes. However, in the coextrusion method, when two or more kinds of laminated resins have different characteristics such as melting point, glass transition temperature, melt viscosity, affinity, etc., uneven thickness of the laminated film and uneven thickness of each laminated layer are likely to occur. There are problems of uniformity in film characteristics and surface quality deterioration such as uneven color tone and flow marks on the film surface.

  Under such circumstances, in order to solve the above problems, a feed block used for laminating at least two kinds of resins in multiple layers has a configuration using two or more slit plates. A method for obtaining a laminated film by controlling the above has been proposed (see Patent Document 1).

JP 2007-176154 A

  The laminated film obtained by the method described in Patent Document 1 defines the structure of the feed block and realizes a multilayer structure with high lamination accuracy by including a thick film layer in the laminated structure of the laminated film. be able to. However, the laminated film obtained by the method described in Patent Document 1 does not take into consideration the influence on the laminated structure due to stretching unevenness in the stretching process during film production. Therefore, the laminated film obtained by the method described in Patent Document 1 has a problem that uneven color tone is not seen when the laminated film is observed from the lick, although uneven color tone is not seen when the laminated film is observed from the front. is there.

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a polyester film having excellent surface quality without uneven color tone when the film is observed from the lick.

  The present invention employs the following means in order to solve such problems. That is, it is a polyester film in which the variation Rψ60 of the maximum value of ψ at a measurement wavelength of 235 to 255 nm at a measurement angle of 60 ° measured using an ellipsometer M-2000D manufactured by Woollam is 0.10 or more and 5.00 or less. Is intended.

  According to the present invention, there is provided a polyester film which has no uneven color tone and has excellent surface quality when the film is observed particularly from the lick. The polyester film of the present invention can be suitably used for optical applications, and in particular, can be suitably used for a screen protective film using an LED as a light source.

Schematic diagram of longitudinal stretching process

  The polyester film of the present invention has an amplitude ratio at a measurement wavelength of 235 to 255 nm at a measurement angle of 60 ° measured using an ellipsometer M-2000D manufactured by Woollam in order to suppress uneven color tone when the film is viewed from the lick. The variation Rψ60 of the maximum value of the change ψ needs to be 0.10 or more and 5.00 or less. Here, an ellipsometer is a device that enters polarized light into a sample, measures changes in the polarized state reflected and interacted with the sample, and analyzes the fine structure of the material. The method of structural analysis is called ellipsometry. The change in the polarization state reflected and interacted with the sample is expressed by a change Δ in the phase difference of the reflected light and a change ψ in the amplitude ratio. In ellipsometry, the measurement sensitivity is highest at the Brewster angle. For example, polyethylene terephthalate, which is a typical polyester, has a Brewster angle of about 60 ° with respect to the normal of the film plane. Therefore, in a polyethylene terephthalate film, a minute structural change when observing the film from the lick can be captured by measuring at a measurement angle of 60 °. In addition, polyethylene terephthalate has a π → π * transition peak of the benzene ring, which is a constituent element of polyethylene terephthalate, in the vicinity of 245 nm (235 to 255 nm), which greatly affects the optical characteristics in the visible light region. By reducing the variation of the amplitude ratio ψ at 60 ° (hereinafter also referred to as Rψ60) in the vicinity of 245 nm (235 to 255 nm) with an ellipsometer, it is possible to suppress uneven color tone when the film is observed from the lick. In addition, that Rψ60 is small indicates that the optical elements such as the molecular structure, orientation, density, and thickness of each laminated film are uniform when the film is viewed from the lick. If Rψ60 is greater than 5.0, unevenness in the color of the film surface when the film is viewed obliquely occurs. On the other hand, when Rψ60 is smaller than 0.1, the uneven color tone is good, but streaks occur under the crossed Nicols condition. Therefore, when it uses for the optical use which uses LED as a light source, it becomes a problem. Rψ60 is preferably 0.1 or more and 4.0 or less, more preferably 0.1 or more and 4.0 or less.

  Rψ60 in the present invention can be measured by the ellipsometry method of Examples described later. In the polyester film of the present invention, the variation Rψ60 of the maximum value of ψ at a measurement wavelength of 235 to 255 nm at a measurement angle of 60 ° measured using an ellipsometer M-2000D manufactured by Woollam is 0.10 or more and 5.00 or less. There is no particular limitation on the method for satisfying this. Rψ60 can be reduced by reducing the stretching unevenness when the polyester film is stretched. As a method of reducing stretching unevenness when stretching a polyester film, when stretching a polyester film by a method of stretching by utilizing a peripheral speed difference of stretching rolls, for example, as shown in FIG. In the stretching process in which a film is stretched using a roll 5 (hereinafter referred to as a first stretching roll) and a downstream stretching roll 6 (hereinafter referred to as a second stretching roll), the film is close to the first stretching roll. Two or more nip rolls (example: 1, 2 in FIG. 1) and two or more nip rolls close to the second stretching roll (example: 3, 4 in FIG. 1) are used. If the number of nip rolls adjacent to the first stretching roll is less than two and the number of nip rolls adjacent to the second stretching roll is less than two, the film cannot be sufficiently fixed during film stretching, and stretching unevenness is likely to occur. Stretching unevenness can be reduced by using two or more nip rolls for each of the upstream stretching roll and the downstream stretching roll. On the other hand, if the number of nip rolls is excessively increased, Rψ60 becomes too small. Therefore, the number of nip rolls is preferably 2 or more and 4 or less for each of the upstream stretching roll and the downstream stretching roll.

  Further, the total pressure of the nip rolls (the total pressure applied by all the nip rolls close to the upstream drawing roll and the downstream drawing roll) is preferably 0.1 MPa or more and 1.0 MPa or less. Even when the total pressure of the nip rolls is smaller than 0.1 MPa, the film cannot be sufficiently fixed during film stretching, and stretching unevenness is likely to occur. On the other hand, if the total pressure of the nip rolls is greater than 1.0 MPa, the nip roll marks may be attached to the film, resulting in poor appearance. Preferably, the total pressure of the nip rolls is not less than 0.2 MPa and not more than 0.6 MPa.

  The polyester used in the polyester film of the present invention is preferably a polyester obtained by polymerization from a monomer mainly composed of an aromatic dicarboxylic acid or aliphatic dicarboxylic acid and a diol. 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′- Examples thereof include diphenyl dicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 4,4′-diphenyl sulfone dicarboxylic acid, and the like. Examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid and ester derivatives thereof. Among them, terephthalic acid and 2,6-naphthalenedicarboxylic acid having a high refractive index are preferable. Only one kind of these acid components may be used, or two or more kinds may be used in combination, and further, 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-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4- Hydroxyethoxyphenyl) propane, isosorbate, spiroglycol and the like. Of these, ethylene glycol is preferably used. These diol components may use only 1 type and may use 2 or more types together.

  Among the polyesters, polyethylene terephthalate and copolymers thereof, polyethylene naphthalate and copolymers thereof, polybutylene terephthalate and copolymers thereof, polybutylene naphthalate and copolymers thereof, and polyhexamethylene terephthalate and copolymers thereof. It is preferable to use a polymer, polyhexamethylene naphthalate, a copolymer thereof, and the like.

  The polyester film of the present invention is preferably a laminated polyester film having a layer composed of polyester resin A (hereinafter referred to as A layer) and a layer composed of polyester resin B (hereinafter referred to as B layer).

  A preferable combination of the polyester resin A and the polyester resin B is preferably a resin containing the same basic skeleton as one of the resins. Here, the “basic skeleton” referred to in the present invention refers to a repeating unit constituting a resin. For example, when one resin is polyethylene terephthalate, ethylene terephthalate is the basic skeleton. Examples of the polymer include a polymer (copolymer) composed of an ethylene terephthalate unit and a cyclohexane 1,4-dimethylene terephthalate unit. As another example, when one resin is polyethylene, ethylene is a basic skeleton. When the resin having the same basic skeleton is used, problems such as stacking faults such as flow marks and peeling between layers are less likely to occur in the formation of a laminated film.

  As the polyester resin A constituting the A layer in the present invention, it is preferable to use polyethylene terephthalate or polyethylene naphthalate from the viewpoint of maintaining high lamination accuracy.

  As polyester resin B which comprises B layer in this invention, it is preferable to contain 1, 4- hexanedimethanol as a diol component from a viewpoint of suppressing the raise of a refractive index. Further, a copolymer of the above polyester resin A containing cycloisophthalic acid, naphthalene dicarboxylic acid, diphenyl acid, cyclohexane dicarboxylic acid as an acid component, or containing spiroglycol, cyclohexanedimethanol, bisphenoxyethanol fluorene, bisphenol A component The polyester resin A may be mixed or used alone.

  The polyester film of the present invention preferably has a structure in which the above-described polyester A layer and polyester B layer are alternately laminated in a thickness direction in a total of 30 layers or more. More preferably, a total of 250 or more layers are alternately stacked in the thickness direction, and a more preferable structure is a stack of 800 or more layers. In the case of less than 30 layers, it may become impossible to control the reflection wavelength, the reflectance, and the transmittance. Further, considering the decrease in wavelength selectivity accompanying the decrease in stacking accuracy due to the increase in the size of the stacking device and the increase in the number of stacks, it is realistic that the number of layers is 1000 layers or less.

  In the polyester film of the present invention, the difference in in-plane average refractive index between the A layer and the B layer is preferably 0.01 or more and 0.20 or less. When the difference in in-plane average refractive index between the A layer and the B layer exceeds 0.20, the coloring of transmitted light may increase. When the difference in the in-plane average refractive index between the A layer and the B layer is less than 0.01, the average transmittance increases in a short wavelength region of visible light such as a wavelength band of 400 to 460 nm, and the screen is protected using an LED as a light source. In some cases, the blue light wavelength cannot be cut.

  As means for achieving the in-plane average refractive index difference between the A layer and the B layer of 0.01 or more and 0.20 or less, as the polyester resin A constituting the A layer, polyethylene terephthalate is used, and the B layer is constituted. As the glycol component of the polyester resin B, the cyclohexanedimethanol component is preferably contained in an amount of 5 mol% to 25 mol% with respect to the acid component. When the cyclohexanedimethanol component is less than 5 mol%, the density difference between the A layer and the B layer is small, and the difference in refractive index between the A layer and the B layer may be insufficient. When the cyclohexanedimethanol component exceeds 25 mol%, adhesion may be insufficient and delamination may occur. Moreover, since the polyester film of this invention suppresses shrinkage | contraction of the film at the time of bonding to a display member and drying after bonding, the thermal contraction rate in 100 degreeC of MD direction and TD direction is all 1.00. % Or less is preferable. Preferably, the thermal shrinkage rate at 100 ° C. in the MD direction and the TD direction are both 0.70% or less. On the other hand, from the viewpoint of the flatness of the film, it is preferable that the thermal shrinkage rates at 100 ° C. in the MD direction and the TD direction are both 0.01% or more. If the thermal shrinkage rate is less than 0.01%, the flatness of the film may deteriorate due to the deflection of the film within the film production process. Preferably, the thermal shrinkage at 100 ° C. in the MD direction and the TD direction are both 0.03% or more.

  Examples of a method for adjusting the thermal shrinkage at 100 ° C. in the MD direction and the TD direction to 0.01% or more and 1.00% or less include a method of adjusting the heat treatment conditions of the film after biaxial stretching. When the treatment temperature is high, orientation relaxation occurs and the thermal shrinkage tends to be reduced, but the heat treatment temperature after biaxial stretching is 170 ° C. to 240 ° C. from the viewpoint of dimensional stability and film quality. If it is preferable, it is more preferable if it is 175 to 230 ° C, and most preferable if it is 180 to 220 ° C.

  The polyester film of the present invention preferably has non-uniformity of thermal shrinkage at 100 ° C. in the MD direction of 0.01% or more and 0.30% or less in order to suppress poor appearance after being bonded to the display member. . Preferably, the heat shrinkage unevenness at 100 ° C. in the MD direction is 0.01% or more and 0.10% or less. When the thermal shrinkage unevenness at 100 ° C. in the MD direction is larger than 0.30%, appearance defects such as wrinkles may occur on the film depending on the use environment after the members are bonded. Moreover, when trying to make the thermal shrinkage unevenness at 100 ° C. in the MD direction smaller than 0.01%, it is necessary to increase the nip roll pressure at the time of stretching between the rolls in the polyester film production process, resulting in poor appearance due to the nip roll pressure. May occur.

  As a method for achieving the above, in the drawing step using the rolls described above, the total pressure of the nip rolls (the total pressure applied by all the nip rolls adjacent to the upstream drawing roll and the downstream drawing roll) is 0.1 MPa or more. It is preferably 1.0 MPa or less. By setting it as such an aspect, not only can stress become more uniform, but generation | occurrence | production of the nip roll trace resulting from pressing a nip roll can be reduced. From the above viewpoint, the total pressure of the nip rolls is more preferably 0.2 MPa or more and 0.6 MPa or less, and further preferably 0.4 MPa or more and 0.5 MPa or less.

Moreover, it is preferable that the Young's modulus of MD direction and TD direction is 2.5 GPa or more and 4.5 GPa or less in the polyester film of this invention. By setting the Young's modulus to 2.5 GPa or more, it is possible to suppress a minute film deformation due to a tension at the time of conveyance when being bonded to a display member, and it is possible to suppress an appearance defect. Further, when the Young's modulus is 4.5 GPa or less, it is possible to suppress the relaxation of molecules over time, and to suppress uneven color tone and poor appearance. More preferably, it is 3.0 GPa or more and 4.2 GPa or less.
The method of satisfying that the Young's modulus in the MD direction and the TD direction of the laminated polyester film of the present invention satisfies 2.5 GPa or more and 4.5 GPa or less is not particularly limited, but the method of adjusting the draw ratio when stretching in the longitudinal direction or the longitudinal direction And a method of adjusting the temperature of the heat treatment and a method of adjusting the temperature of the heat treatment after transverse stretching.

  Next, the preferable manufacturing method of the polyester film of this invention is demonstrated below for the example using two types of polyester resins. Of course, the present invention is not construed as being limited to such examples. Moreover, the formation itself of the laminated structure of the multilayer laminated polyester film can be realized by referring to the description in [0053] to [0063] stages of JP-A-2007-307893.

  Prepare polyester resin in the form of pellets. The pellets are dried in hot air or under vacuum as necessary, and then supplied to a separate extruder. In the extruder, the resin melted by heating to a temperature equal to or higher than the melting point is made uniform in the amount of resin extruded by a gear pump or the like, and foreign matter or denatured resin is removed through a filter or the like. These resins are formed into a desired shape by a die and then discharged. And the sheet | seat laminated | stacked in the multilayer discharged | emitted from die | dye is extruded on cooling bodies, such as a casting drum, and is cooled and solidified, and a casting film is obtained. At this time, it is preferable to use a wire-like, tape-like, needle-like, or knife-like electrode to be brought into close contact with a cooling body such as a casting drum by an electrostatic force and rapidly solidify. Also preferred is a method in which air is blown out from a slit-like, spot-like, or planar device to be brought into close contact with a cooling body such as a casting drum and rapidly cooled and solidified, or brought into close contact with a cooling body with a nip roll and rapidly cooled and solidified.

  Moreover, when producing the multilayer laminated polyester film which consists of a some polyester resin, several resin is sent out from a different flow path using two or more extruders, and is sent into a multilayer lamination apparatus. As the multi-layer laminating apparatus, a multi-manifold die, a feed block, a static mixer, etc. can be used. In particular, in order to efficiently obtain the configuration of the present invention, at least two members having a large number of fine slits are separately provided. It is preferable to use the feed block including the above. When such a feed block is used, since the apparatus does not become extremely large, there is little foreign matter due to thermal degradation, and high-precision lamination is possible even when the number of laminations is extremely large. Also, the stacking accuracy in the width direction is significantly improved as compared with the prior art. It is also possible to form an arbitrary layer thickness configuration. In this apparatus, since the thickness of each layer can be adjusted by the shape (length, width) of the slit, any layer thickness can be achieved.

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

  The casting film thus obtained is preferably biaxially stretched. Here, biaxial stretching refers to stretching in the longitudinal direction and the width direction. Stretching may be performed sequentially in two directions or simultaneously in two directions. Further, re-stretching may be performed in the longitudinal direction and / or the width direction.

  Hereinafter, a production method by sequential biaxial stretching will be described. In order for the Young's modulus in the MD direction and TD direction to be 2.5 GPa or more and 4.5 GPa or less, the draw ratio is preferably 2.5 to 4.0 times, more preferably 2.7 times in the longitudinal direction. More than 3.5 times is adopted. Usually, stretching is performed by the difference in peripheral speed between the two rolls, but the maximum value of ψ at a measurement wavelength of 235 to 255 nm at a measurement angle of 60 ° measured using an ellipsometer M-2000D manufactured by Woollam Co., Ltd. In order for the variation Rψ60 to be not less than 0.10 and not more than 5.00, the first stretching roll is used for the upstream stretching roll (hereinafter referred to as the first stretching roll) and the downstream stretching roll (hereinafter referred to as the second stretching roll). It is preferable that there are two or more nip rolls close to the roll, that is, two or more nip rolls close to the second stretching roll, and the total pressure of the nip rolls is 0.1 MPa or more and 1.0 MPa or less. By setting the number of nip rolls and the pressure as described above, the film can be uniformly stretched in the width direction during stretching in the longitudinal direction. When the number of nip rolls is less than the above, or when the total pressure of the nip rolls is less than 0.1 MPa, the stretching point cannot be fixed in the width direction, causing uneven stretching, and uneven color due to inhomogeneous molecular structure in the surface. It may cause. Further, when the total pressure of the nip roll is larger than 1.0 MPa, the nip roll marks are transferred to the film to cause poor appearance, or the life of the nip roll is shortened and the productivity is lowered. The stretching temperature in the longitudinal direction is preferably a glass transition temperature of the resin constituting the laminated polyester film from −10 ° C. to a glass transition temperature of + 50 ° C. As the stretching temperature, when polyethylene terephthalate is used for the polyester resin A, the stretching temperature Is preferably 70 ° C. or higher and 90 ° C. or lower.

  The uniaxially stretched film thus obtained is subjected to surface treatment such as corona treatment, flame treatment, and plasma treatment as necessary, and then functions such as slipperiness, easy adhesion, and antistatic properties are provided. It may be applied by in-line coating.

  The stretching in the width direction refers to stretching for giving the film an orientation in the width direction. Usually, the tenter is used to convey the film while holding the both ends with clips and stretch in the width direction. The stretching ratio varies depending on the type of resin, but usually 2 to 15 times is preferable, and when polyethylene terephthalate is used for any of the resins constituting the multilayer laminated film, 2 to 7 times is particularly preferably used. . Moreover, as extending | stretching temperature, the range of the glass transition temperature of the resin which comprises a multilayer laminated film-glass transition temperature +120 degreeC is preferable.

  The biaxially stretched film is subjected to heat treatment at 170 ° C. to 240 ° C. in the tenter so that the thermal shrinkage at 100 ° C. in the MD direction and TD direction is 0.10% or more and 1.00% or less. Is more preferable if it is 175 to 230 ° C, and most preferable if it is 180 to 220 ° C. By performing the heat treatment, the dimensional stability of the film is improved. After being heat-treated in this way, it is gradually cooled down uniformly, then cooled to room temperature and wound up. Moreover, you may use a relaxation process etc. together in the case of annealing from heat processing as needed.

  The polyester film of the present invention can be preferably used as an optical film because it has excellent surface quality without unevenness in color even when observed from the licking direction and optically excellent transparency. In particular, it can be suitably used as a film for screen protection used for protecting a screen using an LED as a light source.

  EXAMPLES Hereinafter, although this invention is demonstrated along an Example, this invention is not restrict | limited by these Examples. Various characteristics were measured by the following methods.

(1) Number of laminated films The layer structure of the film was determined by observation with an electron microscope for a sample obtained by cutting a cross section using a microtome. That is, using a transmission electron microscope H-7100FA type (manufactured by Hitachi, Ltd.), the cross section of the film was magnified 40000 times at an acceleration voltage of 75 kV, a cross-sectional photograph was taken, and the layer configuration and each layer thickness were measured. In some cases, in order to obtain high contrast, a staining technique using a known RuO ₄ or OsO ₄ may be used.

(2) The main orientation axis of the film and the axis perpendicular to it (TD direction, MD direction)
A sample is cut out with a size of 100 mm × 100 mm at an arbitrary point of the film, and a main orientation axis in the plane of the polyester film is obtained using a microwave molecular orientation meter MOA-2001A (frequency 4 GHz) manufactured by KS Systems (currently Oji Scientific Instruments). Was determined as the TD direction, and the direction perpendicular thereto was defined as the MD direction.

(3) Refractive index Polyester resin A and polyester resin B were each used alone, and a single film was formed under the same film forming conditions as the laminated polyester film. In this case, the unstretched film was formed by the same method up to casting. Next, a sample is cut out from the unstretched film into a size of 100 mm × 100 mm, stretched using a biaxial stretching apparatus (Toyo Seiki Co., Ltd.), and the obtained stretched film is further attached to a 200 mm × 200 mm metal frame. Then, heat treatment was performed using a tunnel oven (manufactured by Taishin Manufacturing Co., Ltd.) to obtain a single film. In addition, when the heat treatment temperature at the time of film formation was a temperature at which the thermoplastic resin was melted, it was sandwiched by a support such as a polyimide film and subjected to heat treatment in a tunnel oven. A sample is cut out from the central part of the obtained single film in the film width direction with a dimension of length 40 m × width 35 mm, and the refractive indexes of MD and TD are obtained using an Abbe refractometer 4T (manufactured by Atago Co., Ltd.). It was. As a light source, a sodium D line wavelength of 589 nm was used. The average refractive index of MD and TD was defined as the in-plane refractive index, and the difference in the in-plane average refractive index between the polyester resin A and the polyester resin B was determined as the in-plane refractive index difference (absolute value) (| polyester resin A In-plane average refractive index-polyester resin B in-plane average refractive index |). As the immersion liquid, methylene iodide and a test piece having a refractive index of 1.74 were used.

(4) Young's modulus A film was cut into a rectangular shape with a length of 150 mm and a width of 10 mm in the MD direction and the TD direction, and used as a sample. Using a tensile tester (Orientec Tensilon UCT-100), the initial tension chuck distance was 50 mm, the temperature was 25 ° C., and the humidity was 65% RH. . The Young's modulus was measured in accordance with ASTM D-882-67 from the rising slope of the start point in the stress-strain curve recorded in the tensile test, and the unit was expressed in MPa. In addition, evaluation evaluated the average value of the measured value of 3 samples for MD direction and TD direction, respectively, as Young's modulus of MD direction and TD direction.

(5) Thermal shrinkage (100 ° C)
The film was cut into rectangles each having a length of 150 mm and a width of 10 mm in the MD direction and the TD direction as samples. A marked line was drawn on the sample at an interval of 100 mm (positions at 50 mm from the center to both ends), and a heat treatment was performed by suspending a 3 g weight in a hot air oven heated to 100 ° C. for 30 minutes. The distance between the marked lines after the heat treatment was measured, and the thermal contraction rate was calculated from the change in the distance between the marked lines before and after heating by the following formula. In addition, evaluation made the average value of the measured value of 3 samples of MD direction and TD direction each as the thermal contraction rate of the film MD direction and TD direction in 100 degreeC.
Thermal contraction rate (%) = {(distance between marked lines before heat treatment) − (distance between marked lines after heat treatment)} / (distance between marked lines before heat treatment) × 100
(6) Uneven thermal shrinkage in MD direction (100 ° C)
Each film was cut out in the MD direction into a length of 150 mm and a width of 100 mm, and 10 rectangles of 150 mm and a width of 10 mm were cut out as samples. A marked line was drawn on the sample at an interval of 100 mm (positions at 50 mm from the center to both ends), and a heat treatment was performed by suspending a 3 g weight in a hot air oven heated to 100 ° C. for 30 minutes. Measure the distance between marked lines after heat treatment, calculate the thermal contraction rate for each of 10 samples from the change in the distance between marked lines before and after heating by the same formula as (5), The difference between the minimum values was uneven heat shrinkage in the MD direction at 100 ° C.

(7) R60ψ
A sample is cut out at a point of 50 mm × 50 mm at an arbitrary point on the film, and an angle between the normal of the film plane and incident light is 60 ° at an arbitrary position on the sample using an ellipsometer M-2000D manufactured by Woollam. The sample was set so that the reflected intensity of the measured reflected light was 0.20 or more, and the measurement was performed 10 times in the standard measurement mode. Then, the incident light direction at the time of the first measurement is set as direction A, and then the sample is moved so that the light is incident from the center of the measurement location in an arbitrary direction at least 10 mm and from the direction A, and the same measurement is performed. The measurement was repeated four times (measured at arbitrary five points), and the maximum value of the ψ value at the measurement wavelength of 235 to 255 nm was obtained at each point. R60ψ was determined as the difference between the maximum value and the minimum value of the five measured values obtained by measuring in a 50 mm × 50 mm sample.

(8) Uneven color tone A sample was cut out with a size of 100 mm × 100 mm at an arbitrary point on the film, and a CM-3600d manufactured by Konica Minolta Co., Ltd. was used, and the angle between the normal line of the film plane and the incident light was 60 A sample was set so that the temperature would be °, and the chromaticity a ^* , chromaticity b ^* , and lightness L ^* at any location on the sample were measured with transmitted light under the condition of a target mask having a measurement diameter of φ25.4 mm. . Thereafter, the sample was moved so as to be 30 mm or more away from the center of the measurement location, and the same measurement was repeated four times (measurement was performed at five arbitrary points). Next, the color difference ΔE was obtained using the formula ΔE = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^1/2 . For uneven color tone, the difference between the maximum value and the minimum value of five color differences ΔE obtained by measuring at a distance of 30 mm in a 100 mm × 100 mm sample was evaluated according to the following criteria: ○: very good, Δ: good , X: Impossible.
○: 4.0 or less Δ: greater than 4.0 and 5.0 or less x: greater than 5.0 (9) Bonding inspection The following urethane-based thermosetting adhesion to a polyester film surface with a tension of 200 N on a 100 mm width polyester film The coating agent was applied at a wet thickness of 5 g / m 2, dried at a drying temperature of 90 ° C. for 1 minute, and using a PET film (manufactured by Toray Industries, Inc., trade name: Lumirror, type U35, product number 188), nip pressure 0.4 MPa temperature Lamination was performed using a nip roll at 50 ° C. to obtain a laminated film. The obtained laminated film was evaluated according to the following criteria, and ○: extremely good, Δ: good, ×: not possible.
○: No streak or wrinkle was generated on the film.

      Δ: Although streaks or wrinkles were generated on the film, the thickness was less than 3 mm and the length was less than 10 mm.

X: One or more streaks or wrinkles having a thickness of 3 mm or more or a length of 10 mm or more can be confirmed on the film.
[adhesive]
5 parts by weight of urethane prepolymer solution “Takenate A-971” manufactured by Mitsui Chemicals Polyurethane Co., Ltd. and 0.5 part by weight of urethane prepolymer solution “Takelac A-3” manufactured by Mitsui Chemicals Polyurethane Co., Ltd. are dissolved in 5 parts by weight of ethyl acetate. Used.

(10) Cross Nicol Inspection A sample was cut out at a size of 100 mm × 100 mm at an arbitrary point on the film, the appearance of the film was confirmed under the crossed Nicol condition, and evaluated according to the following criteria: ○: very good, Δ: good , X: Impossible.
○: No streak was generated on the film.
Δ: The film has streaks but is less than 3 mm in thickness and less than 10 mm in length.
X: One or more streaks having a thickness of 3 mm or more or a length of 10 mm or more can be confirmed on the film.

(11) Glass plate adhesion inspection A film was cut out with a size of 100 mm × 100 mm, and a glass plate was prepared using an optical adhesive film “Panaclean” (registered trademark) (thickness: 50 μm, product number: PD-S1) manufactured by Panac Corporation. The film was laminated on top to obtain a film glass plate laminate. Then, it left still for 1 hour in the oven heated at 100 degreeC. Thereafter, it was cooled to room temperature, the appearance of the film glass plate laminate was confirmed, and evaluated according to the following criteria: ○: extremely good, Δ: good, ×: not possible.
○: Wrinkles were not generated on the film.
Δ: The film has wrinkles but is less than 3 mm in thickness and less than 10 mm in length.
X: One or more wrinkles having a thickness of 3 mm or more or a length of 10 mm or more can be confirmed on the film.

Example 1
Polyethylene terephthalate having an intrinsic viscosity of 0.8 was used as two types of polyester resins having different optical characteristics. (Hereinafter also referred to as PET, the in-plane refractive index of the film after stretching and heat treatment was about 1.66). As the amorphous polyester resin B, a blend chip in which 59 wt% of copolyester in which 30 mol% of cyclohexanedimethanol was copolymerized and 41 wt% of PET was uniformly dispersed was used (hereinafter, sometimes referred to as PETG, after stretching / heat treatment). The in-plane refractive index of the film was 1.59, and the total amount of cyclohexanedimethanol in layer B was 18 mol%). These polyester resin A and polyester resin B were each dried and then supplied to an extruder.

  The polyester resin A and the polyester resin B thus prepared are each melted at 280 ° C. by a twin screw extruder with a vent, and then merged in a 909-layer feed block through a gear pump and a filter. It was. Both surface layer portions were made of the polyester resin A, and the layer thicknesses of the layer A made of the polyester resin A and the layer B made of the polyester resin B were made substantially the same. Subsequently, after being joined by a 909 layer feed block, led to a T-die and formed into a sheet shape, it was rapidly cooled and solidified on a casting drum maintained at a surface temperature of 25 ° C. by electrostatic application to obtain a cast film. . The discharge amount was adjusted so that the weight ratio of the polyester resin A and the polyester resin B was about 1: 1 so that the thickness ratio of the adjacent layers was about 1.

  The obtained casting film was heated with a roll group set at 85 ° C. to 100 ° C., and the longitudinal direction was 3.0 times in the process in which the first stretching roll and the second stretching roll were each two nip-rolled. Stretched. The total nip roll pressure was 0.5 MPa. Thereafter, the uniaxially stretched film was guided to a tenter device, preheated with hot air at 100 ° C., stretched 3.5 times in the width direction at a temperature of 110 ° C., and then heat-treated at a temperature of 220 ° C. with the tenter device. Thereafter, heat treatment was performed with hot air having a relaxation rate of 3% and 150 ° C., and after gradually cooling to room temperature, the film was wound with a winder to obtain a laminated polyester film having a thickness of 42 μm. The results are shown in Table 1.

(Example 2)
A laminated polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 3.7 times. The results are shown in Table 1.

(Example 3)
A laminated polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 2.5. The results are shown in Table 1.

Example 4
A laminated polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 2.7 times and the total nip roll pressure was 0.6 MPa. The results are shown in Table 1.

(Example 5)
A laminated polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 2.8 times and the total nip roll pressure was 0.4 MPa. The results are shown in Table 1.

(Example 6)
A laminated polyester film was obtained in the same manner as in Example 1 except that the heat treatment temperature was 180 ° C. The results are shown in Table 1.

(Example 7)
A laminated polyester film was obtained in the same manner as in Example 1 except that the heat treatment temperature was 240 ° C. The results are shown in Table 1.

(Example 8)
A laminated polyester film was obtained in the same manner as in Example 1 except that the total nip roll pressure was 0.15 MPa. The results are shown in Table 1.

Example 9
A laminated polyester film was obtained in the same manner as in Example 1 except that the total pressure of the nip rolls was 0.8 MPa. The results are shown in Table 1.

(Example 10)
As the amorphous polyester resin B, a blend chip in which 20% by weight of copolymerized polyester in which 30 mol% of cyclohexanedimethanol was copolymerized and 80% by weight of PET was uniformly dispersed (hereinafter, sometimes referred to as PETG, after stretching and heat treatment) was used. A laminated polyester film was obtained in the same manner as in Example 1 except that the in-plane refractive index of the film was 1.64 (total amount of cyclohexanedimethanol in layer B was 6 mol%). The results are shown in Table 1.

(Example 11)
Example except that a copolymer of polyethylene terephthalate copolymerized with 20 mol% of spiroglycol component (non-crystalline polyester resin B, the in-plane refractive index of the film after stretching and heat treatment was 1.51) was used. In the same manner as in Example 1, a laminated polyester film was obtained. The results are shown in Table 1.

(Example 12)
A feed of 33 layers using a copolymer of polyethylene terephthalate copolymerized with 20 mol% of spiroglycol component as amorphous polyester resin B (the in-plane refractive index of the film after stretching and heat treatment was 1.51) A laminated polyester film was obtained in the same manner as in Example 1 except that the block was used. The results are shown in Table 1.

(Comparative Example 1)
A laminated polyester film was obtained in the same manner as in Example 1 except that the total nip roll pressure was 1.2 MPa. The results are shown in Table 1.

(Comparative Example 2)
A laminated polyester film was obtained in the same manner as in Example 1 except that the total nip roll pressure was 0.05 MPa. The results are shown in Table 1.

(Comparative Example 3)
A laminated polyester film was obtained in the same manner as in Example 1 except that only the second nip roll was used as the nip roll on the second stretching roll and the heat treatment temperature was 250 ° C. The results are shown in Table 1.

(Comparative Example 4)
A laminated polyester film was obtained in the same manner as in Example 1 except that only the first nip roll was used as the nip roll on the first stretching roll and the heat treatment temperature was 180 ° C. The results are shown in Table 1.

  The laminated polyester film of the present invention can be suitably used for optical applications that have no uneven color tone when the film is observed from the lick, and has a superior surface quality. This film can be used particularly for screen protection using LED as a light source.

1: 0th nip roll 2: 1st nip roll 3: 2nd nip roll 4: 3rd nip roll 5: 1st drawing roll 6: 2nd drawing roll 7: polyester film

Claims (8)

A polyester film having a maximum variation Rψ60 of an amplitude ratio change ψ of 0.10 or more and 5.00 or less at a measurement angle of 60 ° and a measurement wavelength of 235 to 255 nm measured using an ellipsometer M-2000D manufactured by Woollam. Layers of polyester resin A (hereinafter referred to as A layer) and layers of polyester resin B (hereinafter referred to as B layer) are alternately laminated in the thickness direction by 30 layers or more, and the polyester resin A and the polyester resin B are laminated. The polyester film according to claim 1, wherein the difference in refractive index is from 0.01 to 0.20. The polyester film according to claim 1 or 2, wherein the thermal shrinkage rate at 100 ° C in the MD direction and the TD direction is both 0.01% or more and 1.00% or less. The polyester film according to any one of claims 1 to 3, wherein the unevenness of thermal shrinkage at 100 ° C in the MD direction is 0.01% or more and 0.30% or less. The polyester film according to claim 1, wherein the Young's modulus in the MD direction and the TD direction are both 2.5 GPa or more and 4.5 GPa or less. The polyester film according to any one of claims 1 to 5, which is used for optical film applications. The polyester film according to any one of claims 1 to 6, which is used for a film for protecting a screen having an LED as a light source. The film for screen protection using the polyester film in any one of Claims 1-7.

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