JP2018180405A - Film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film that has desired optical properties, and prevents the occurrence of an uneven color tone or the deterioration of surface quality.SOLUTION: A film has a variation in refractive index at wavelength 420 nm (d420 n) of 0.001 or more and 0.100 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a film.

  In various industrial applications, in order to impart various characteristics to a film, a lamination technique of laminating two or more types of resin layers is widely used. As an example utilizing such a lamination technology, for example, light interference which selectively cuts light of a specific wavelength by interference of light which is expressed by alternately laminating two or more kinds of resin layers having different refractive indexes. Multilayer films are known. Such a multilayer film can be used for various optical applications because various optical filter functions can be provided by setting the refractive index of the resin constituting each layer, the number of layers, and the thickness of each layer to a desired range. ing.

  As a method of producing a laminated film, a co-extrusion method using a plurality of extruders and a lamination method of laminating films 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, so it is widely used as a general laminated film manufacturing method There is. However, in the coextrusion method, when the melting point of the resin constituting the layer to be laminated, the glass transition temperature, the melt viscosity, and the affinity and the like are different, the thickness unevenness of the laminated film itself or the thickness unevenness of the laminated layers It tends to occur, and problems such as non-uniformity of film properties, color tone unevenness of the film surface, and deterioration of surface quality such as flow marks may occur.

  In order to reduce such problems, a method has been proposed in which the resin layer is laminated by a feed block in which two or more types of resin layers are laminated, and then extrusion is performed to improve the lamination accuracy (patented) Literature 1). Furthermore, by using a feed block in which the width of the slits forming the thick film layers at both ends is twice or more the width of the slits forming the other thin film layers, the deterioration of the lamination accuracy due to the increase in the number of layers is reduced. A method is also known (see Patent Document 2).

JP 2002-160339 A Unexamined-Japanese-Patent No. 2007-176154

  However, in the technique described in Patent Document 1, the laminated structure of the polymer may be disturbed before being discharged from the die due to the lamination disorder or the like caused by the decrease in the flow velocity of the wall surface. It becomes difficult and may lead to the occurrence of color tone unevenness and the deterioration of the surface quality. Further, in the technique described in Patent Document 2, by having a thick film layer in a portion in contact with the wall surface, it is possible to realize a desired multilayer structure with high accuracy at the time after extrusion from a die, The influence on the laminated structure in the stretching step of the film is not sufficiently considered. Therefore, it is difficult to obtain the desired optical properties after stretching.

  SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a film having the intended optical properties and reducing the occurrence of color tone unevenness and the deterioration of the surface quality.

  In order to solve the above-mentioned subject, the present invention consists of the following composition.

The film characterized in that the variation (d420 n) of the refractive index at a wavelength of 420 nm measured by an ellipsometer under the following measurement condition I is 0.001 or more and 0.100 or less.
Measurement condition I:
(Step 1)
Abrasive paper No. 240 specified in JIS-R6252 (2006) is pressed at a pressure of 0.2 MPa on the entire surface of a film of 50 mm (direction orthogonal to the main orientation axis) × 50 mm (direction of the main orientation axis), orthogonal to the main orientation axis Reciprocate 20 times parallel to the direction.
(Step 2)
The abrasive paper No. 240 is pressed against the entire surface of the abrasive paper No. 240 reciprocated in procedure 1 under the same conditions as the procedure 1, and reciprocated 20 times in parallel with the main orientation axis direction.
(Step 3)
In the procedures 1 and 2, the surface opposite to the surface treated with the abrasive paper No. 240 is used as the measurement surface, and the straight line obtained by drawing the center of gravity of the measurement surface from A1 and A1 perpendicularly to the film surface is from Z, A1 on the measurement surface And Y is a straight line drawn from A1 on the film surface so as to be perpendicular to X, Z and X, the angle between Z and the polarized beam on the XZ plane is 50 °. A polarized beam is irradiated from the point (XZ50), the point (XZ60) to be 60 °, and the point (XZ70) to be 70 °, and the phase difference Δ and the amplitude intensity ratio Ψ obtained from the reflected light are The parameters of the oscillator are determined by comparison with the model satisfying (1) to (5).
(1) A direction parallel to X, Y, and Z is X direction, Y direction, and Z direction, and a model in X direction is model X, a model in Y direction is model Y, and a model in Z direction is model Z And the models X, Y and Z are different models.
(2) Gaussian distribution is used for the vibrator, and the parameters of the vibrator are half width, energy position, and peak intensity.
(3) In each of the models X, Y, and Z, the energy positions of the vibrators are independent of each other.
(4) The energy positions of the vibrators are subordinate to each other among the models X, Y, and Z.
(5) The half-widths of the model X, the model Y, and the model Z are subordinate to each other.
(Step 4)
Arbitrary four points (A2, A3, A4, A5) located on the measurement surface and having a linear distance of 20 mm or more from A1 and a distance of 20 mm or more between the centers of the points. And determine the oscillator parameters at A2 to A5 according to Procedure 3.
(Step 5)
The refractive index at a wavelength of 420 nm at each point is determined from the parameters of the transducers in A1 to A5, and the difference between the maximum value and the minimum value is d420 n.

  According to the present invention, it is possible to provide a film having the intended optical properties and in which the occurrence of color tone unevenness and the reduction in surface quality are reduced. The film of the present invention can be suitably used for optical applications, and in particular, can be suitably used as a protective film of a screen using an LED as a light source.

A schematic diagram showing an example of an analysis method by ellipsometry that can be used in the present invention Top view showing an example of A2 to A5 selected in step 4 Schematic of the longitudinal stretching process

The film of the present invention is characterized in that the dispersion (d420n) of the refractive index at a wavelength of 420 nm measured by an ellipsometer under the following measurement condition I is 0.001 or more and 0.100 or less.
Measurement condition I:
(Step 1)
Abrasive paper No. 240 specified in JIS-R6252 (2006) is pressed at a pressure of 0.2 MPa on the entire surface of a film of 50 mm (direction orthogonal to the main orientation axis) × 50 mm (direction of the main orientation axis), orthogonal to the main orientation axis Reciprocate 20 times parallel to the direction.
(Step 2)
The abrasive paper No. 240 is pressed against the entire surface of the abrasive paper No. 240 reciprocated in procedure 1 under the same conditions as the procedure 1, and reciprocated 20 times in parallel with the main orientation axis direction.
(Step 3)
In the procedures 1 and 2, the surface opposite to the surface treated with the abrasive paper No. 240 is used as the measurement surface, and the straight line obtained by drawing the center of gravity of the measurement surface from A1 and A1 perpendicularly to the film surface is from Z, A1 on the measurement surface And Y is a straight line drawn from A1 on the film surface so as to be perpendicular to X, Z and X, the angle between Z and the polarized beam on the XZ plane is 50 °. A polarized beam is irradiated from the point (XZ50), the point (XZ60) to be 60 °, and the point (XZ70) to be 70 °, and the phase difference Δ and the amplitude intensity ratio Ψ obtained from the reflected light are The parameters of the oscillator are determined by comparison with the model satisfying (1) to (5).
(1) A direction parallel to X, Y, and Z is X direction, Y direction, and Z direction, and a model in X direction is model X, a model in Y direction is model Y, and a model in Z direction is model Z And the models X, Y and Z are different models.
(2) Gaussian distribution is used for the vibrator, and the parameters of the vibrator are half width, energy position, and peak intensity.
(3) In each of the models X, Y, and Z, the energy positions of the vibrators are independent of each other.
(4) The energy positions of the vibrators are subordinate to each other among the models X, Y, and Z.
(5) The half-widths of the model X, the model Y, and the model Z are subordinate to each other.
(Step 4)
Arbitrary four points (A2, A3, A4, A5) located on the measurement surface and having a linear distance of 20 mm or more from A1 and a distance of 20 mm or more between the centers of the points. And determine the oscillator parameters at A2 to A5 according to Procedure 3.
(Step 5)
The refractive index at a wavelength of 420 nm at each point is determined from the parameters of the transducers in A1 to A5, and the difference between the maximum value and the minimum value is d420 n.

  Hereinafter, the measurement condition I of the present invention will be described in detail with reference to the drawings. The measurement condition I is to sequentially carry out the steps 1 to 5. FIG. 1 is a schematic view showing an example of an analysis method by ellipsometry that can be used in the present invention.

  In procedure 1, press the abrasive paper No. 240 specified in JIS-R6252 (2006) at a pressure of 0.2 MPa on the entire surface of the film of “50 mm (direction orthogonal to main orientation axis) × 50 mm (main orientation axis direction) Reciprocate 20 times in parallel with the direction orthogonal to the orientation axis. In procedure 2, “the abrasive paper 240 is applied to the entire surface on which the abrasive paper No. 240 is reciprocated in procedure 1 under the same conditions as procedure 1. The number is pressed and reciprocated 20 times in parallel with the main orientation axis direction.

  Here, the direction perpendicular to the main orientation axis refers to a direction perpendicular to the direction in which the molecular orientation is largest (main orientation axis direction) in the film plane and parallel to the film plane. The size of molecular orientation can be measured by a microwave type molecular orientation meter at a frequency of 4 GHz. As a molecular orientation meter, for example, a microwave molecular orientation meter made by KS Systems (now Oji Scientific Instruments) MOA-2001A etc. can be used. "One side of film" means one side selected arbitrarily. "Abrasive paper No. 240 (hereinafter sometimes referred to simply as" abrasive paper "as defined in JIS-R6252 (2006) is pressed against the entire surface of the film at a pressure of 0.2 MPa, and 20 times parallel to the direction orthogonal to the main orientation axis The term “reciprocate.” Means an operation of reciprocating 20 times in the direction orthogonal to the main orientation axis so that the whole is rubbed while pressing the polishing paper against the whole of one side of the film with a pressure of 0.2 MPa. The same operation as described in “Procedure 1 is performed by pressing the abrasive paper No. 240 and reciprocating 20 times in parallel with the main orientation axis direction” except that the direction in which the abrasive paper reciprocates changes.

  Procedures 3-5 of the present invention mean that the film is irradiated with polarized light with an ellipsometer and the reflected light is measured and analyzed, such analysis method is generally called ellipsometry. Ellipsometry is a method that can estimate the optical characteristics (refractive index etc.) and molecular structure of a film without contact, at high speed, with high precision, and simply, and it is possible to use an optical anisotropy represented by a polyester resin film. It is useful to the analysis of the film which it has.

In step 3, “the surface opposite to the surface treated with abrasive paper No. 240 in step 1 and step 2 is the measurement surface, and the center of gravity of the measurement surface is A1, the straight line drawn from A1 perpendicular to the film surface is Z, The angle between the polarized beam on the XZ plane and Z, where Y is the straight line drawn from A1 on the film surface so that the straight line drawn from A1 on the measurement surface is perpendicular to X, Z and X. The polarized light beam is irradiated to A1 from the point (XZ50) at which 50 ° becomes 50 °, the point at 60 ° (XZ60), and the point at 70 ° (XZ70), and the phase difference Δ and the amplitude intensity obtained from the reflected light The parameters of the oscillator are determined by comparing the ratio Ψ with a model satisfying the following (1) to (5).
(1) A direction parallel to X, Y, and Z is X direction, Y direction, and Z direction, and a model in X direction is model X, a model in Y direction is model Y, and a model in Z direction is model Z And the models X, Y and Z are different models.
(2) Gaussian distribution is used for the vibrator, and the parameters of the vibrator are half width, energy position, and peak intensity.
(3) In each of the models X, Y, and Z, the energy positions of the vibrators are independent of each other.
(4) The energy positions of the vibrators are subordinate to each other among the models X, Y, and Z.
(5) The half-widths of the model X, the model Y, and the model Z are subordinate to each other. ".

  As shown in FIG. 1, in procedure 3 of the present invention, that is, in ellipsometry, a straight line drawn perpendicularly to the measurement surface [a] from the center of gravity A1 [b] or A1 [b] of the measurement surface [a] is Z [ c), a straight line drawn arbitrarily from A1 [b] onto the measurement plane [a] is perpendicular to X [d], Z [c] and X [d] from the measurement plane [a] Let Y [e] be a straight line drawn upward. Also, when A1 [b] is irradiated with the polarized beam [f], the size of the angle formed between the polarized beam [f] and Z [c] is 50 °, 60 °, 70 ° on the XZ plane Three points (XZ50 [g1], XZ60 [g2], XZ70 [g3]) are selected. Regarding the positional relationship between XZ50 [g1], XZ60 [g2], and XZ70 [g3], three points are points on the XZ plane, and the requirement for the size of the angle formed by the polarized beam [f] and Z [c] is There is no particular limitation as long as the condition is satisfied, and it can be selected arbitrarily. Then, a polarized light beam [f] is irradiated in a circular or elliptical shape centered on A1 [b] from a light source installed at the position of XZ50 [g1], XZ60 [g2], XZ70 [g3], and the reflected light By detecting [h] by the detection unit [i], the phase difference Δ and the amplitude intensity ratio で あ る, which are parameters of the physical properties of the film, are measured. The radius of the circle or the minor axis of the ellipse when irradiated with the polarized beam [f] is 10 mm or less.

  Then, the parameters of the oscillator are determined by comparing the obtained values of the phase difference Δ and the amplitude intensity ratio と with the model satisfying the above (1) to (5).

  A model refers to a dielectric function comprised of one or more oscillators that show absorption and emission of light due to molecular vibration or electronic excitation when viewing a film. The oscillator is a dielectric function model, and in the present invention refers to a Gaussian distribution. By using a Gaussian distribution as the dielectric function model, calculation of peak area, calculation of the range of energy applied by the corresponding vibrator and its intensity, and comparison among their X model, Y model, and Z model become easy. As a result, structural analysis of the film becomes easy. “Model X, model Y, and model Z are different models” means that the values of the parameters constituting the vibrator differ by one or more among the X direction, the Y direction, and the Z direction. In the present invention, the parameters constituting the oscillator refer to the half width, energy position, and peak intensity in the Gaussian distribution.

  Since the oscillators show absorption and emission of light due to vibration or electronic excitation of molecules at a specific wavelength, the energy positions of the oscillators are independent of each other in each of the model X, model Y, and model Z. This is very important. “The energy positions of the transducers are independent of each other in each of the models X, Y, and Z.” means, for example, unique molecular vibrations or electronic transitions that differ from each other in each model. We say that we show form.

  In addition, since the oscillator shows molecular vibration or electronic excitation in the structure of a specific molecule, and the absorption wavelength does not depend on the direction in which the film is observed, among the models X, Y, and Z, It is important that the energy positions of the transducers be subordinate to one another. “The energy positions of the vibrators are subordinate to each other among the models X, Y, and Z.” means that the vibrators having the same energy position among the models have the same molecular vibration or It refers to showing an electronic transition form.

  Since the absorption wavelength band of a particular transducer is specific to the molecular structure and does not depend on the observation direction, it is important that the half-widths of the model X, the model Y, and the model Z be subordinate to each other. “The half width is dependent on each other among model X, model Y, and model Z” indicates that the transducers having the same half width between the models have the same absorption wavelength band. .

  Procedure 4 “The four points (A2, A3, A4, etc. are located on the measurement surface, the linear distance from A1 is 20 mm or more, and all the distances between the centers of the points are 20 mm or more) A5) is arbitrarily selected, and the parameters of the oscillator in A2 to A5 are determined according to Procedure 3. Hereinafter, A2, A3, A4, and A5 may be collectively referred to as A2 to A5.

  Here, “the four points located on the measurement plane, such that the linear distance from A1 is 20 mm or more and the distance between the centers of the respective points is all 20 mm or more” are each points When drawing a circle with a radius of 20 mm as the center, it means four points selected so that other points are not included in each circle. That is, four points satisfying the requirement are A2 to A5. At this time, it is not always necessary that the distance from each point to the end of the measurement surface is 20 mm or more.

  Although the aspect shown, for example to A-C of FIG. 2 is mentioned as an example of A2-A5, for example, It is not necessarily limited to these. In FIG. 2, [j] represents A2 to A5, and [k] represents a circle having a radius of 20 mm centering on each point of A1 to A5. A circle [k] of 20 mm in radius centered on each point ([b] and [j]) of A1 to A5 does not include any point other than the point centered on any of them.

  After selecting A2 to A5, the phase difference Δ and the amplitude intensity ratio で あ る, which are parameters of the physical properties of the film, are measured in the same manner as in procedure 3 except that the measurement points are set to A2 to A5, respectively, and the oscillator parameters Decide.

  Procedure 5 is “determine the refractive index of the wavelength 420 nm at each point from the parameters of the transducers in A1 to A5, and set the difference between the maximum value and the minimum value as d420 n”.

It is known that the dielectric function consisting of the phase difference Δ and the amplitude intensity ratio 表現 expressed by the model X to Z composed of the determined parameters of the oscillator can be converted into the refractive index and the absorbance (second version spectral ellipsometry Measurement Hiroyuki Fujiwara (2011), hereinafter referred to as Reference 1. In ellipsometry, transformation of the dielectric function can be performed using analysis software, for example, as described in J. A. Woollam analysis software: "CompleteEASE" (registered trademark) can be easily implemented from GraphType in the Analysis tab. The above conversion is carried out for each of the determined A1 to A5 X model, Y model, and Z model, and the refractive index of 420 nm for each of A1 to A5, X420ni, Y420ni, and Z420ni (1 ≦ i ≦ 5, i Is an integer and indicates the measurement number), and Xd 420 n, Y d 420 n, and Z d 420 n are determined by using the formulas (II) to (IV) so that d 420 n of the formula (I) becomes maximum. When the refractive index can not be read at 420 nm, the refractive index can be read, and the refractive index of the wavelength closest to 420 nm is taken as the refractive index of 420 nm.
d420 n = (X d 420 n + Y d 420 n + Z d 420 n) ÷ 3 (I)
Xd420n = X420nj-X420nk (II)
Yd420n = Y420nj-Y420nk (III)
Zd 420 n = Z 420 n j-Z 420 nk (IV)
(1 ≦ j ≦ 5, 1 ≦ k ≦ 5, j ≠ k, j and k are integers and indicate measurement numbers.)
The details are as follows. First, the values of X420n1 to X420n5, Y420n1 to Y420n5, and Z420n1 to Z420n5 are read by an ellipsometry measurement device. Then all the X420 nj-X 420 nk (X 420 n 1-X 420 n 2, X 420 n 1-X 420 n 3, X 420 n 1-X 420 n 4, X 420 n 1-X 420 n 5, X 420 n 2-X 420 n 1, X 420 n 2-X 420 n 3, X 420 n 2-X 420 n 4, X 420 n 2-X 420 n 5, X 420 n 3- X 420 x 4 Calculate X Y 420 n Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y n , All Z4 0nj-Z420nk be calculated to determine the d420n from the obtained values. For example, in the case of j = 1 and k = 2, the calculation formula of d420 n is d420 n = ((X 420 n 1 −X 420 n 2) + (Y 420 n 1 −Y 420 n 2) + (Z 420 n 1 − Z 420 n 2)) ÷ 3. Similarly, d420n is calculated for all combinations, and the one with the largest value is extracted, and X420nj-X420nk, Y420nj-Y420nk, and Z420nj-Z420nk at this time become Xd420n, Yd420n, and Zd420n, respectively.

  In the film of the present invention, it is important that the dispersion (d420n) of the refractive index at a wavelength of 420 nm measured by an ellipsometer under measurement condition I is 0.001 or more and 0.100 or less. By adopting such an embodiment, it is possible to reduce blue color unevenness when the film is observed from the vertical direction and the oblique direction with respect to the film surface.

  In general, a complex cell, which is a type of photoreceptor that is abundant in the central part of the retina and the macula of the eye, absorbs light and senses color by sending a signal to the brain. Complex cells are classified according to a sensitive wavelength (color) region, and in the case of a human, they have three types of complex cells from the short wavelength side: blue complex, green complex, and red complex. In particular, short-wavelength light such as blue is sensed by the blue complex, and the blue complex is known to have a large absorption peak around 420 nm. And the film for LED protection has a function which selectively reflects an ultraviolet and blue wavelength by the light interference by the multilayer laminated structure in a film, and permeate | transmits visible light. At this time, when the refractive index of the film varies in the film plane, the reflected wavelength band in the film plane also varies, and blue color unevenness occurs in the film. Therefore, by controlling d420 n, which is the dispersion of the refractive index at the wavelength most sensitive to blue complexes of 420 nm, to 0.100 or less, preferably 0.060 or less, more preferably 0.020 or less, color unevenness in the blue region Can be effectively reduced. On the other hand, the lower limit value of d420 n is 0.001 from the viewpoint of productivity. If it is attempted to control d420n to less than 0.001, productivity may be reduced due to film breakage at an excessive drawing rate in the longitudinal drawing process described later, and appearance defects may be caused due to high pressure of the nip roll.

  For example, it is known that polyethylene terephthalate has several large absorption peaks in the range of 300 nm or less, and in particular, has a π-π * excitation band having a polarization in a direction parallel to the alignment direction present near 250 nm. (I. Ouchi et al./ Nucl. Instr. And Meth. In Phys. Res. B 199 (2003) 270-274, hereinafter referred to as Reference 2). Since this 250 nm peak most affects the refractive index of 420 nm, it is important to make the strength and direction of the π-π * bond uniform in order to set d420 n to 0.001 or more and 0.100 or less.

  The method for making the strength and direction of the π-π * bond uniform and setting d420n to 0.001 or more and 0.100 or less or the above-mentioned preferable range is not particularly limited as long as the effects of the present invention are not impaired. There is a method of making the stretching stress applied to the film more uniform when stretching the film. In particular, in the case of performing sequential biaxial stretching in which the film is stretched in the longitudinal direction and then stretched in the width direction, it is better to make the stretching stress in the longitudinal direction in which the base structure of the film can be more uniform. The longitudinal direction means the running direction of the film, and the width direction means the direction parallel to the film surface and perpendicular to the longitudinal direction.

  When sequential biaxial stretching is performed, stretching in the longitudinal direction can be performed by the peripheral speed difference of a plurality of stretching rolls. Specifically, as shown in FIG. 3, the upstream stretching roll 1 (hereinafter sometimes referred to as a first stretching roll) and the downstream stretching roll 2 having a rotational speed faster than that of the first stretching roll 1 (hereinafter Film 3 may be stretched in the longitudinal direction by the second stretching roll). At this time, the stretching stress in the longitudinal direction can be made more uniform by making a plurality of nip rolls 4 close to the first drawing roll 1 and a plurality of nip rolls 5 close to the second drawing roll 2 as well. Unevenness in stretching is suppressed.

  The number of the nip rolls 4 adjacent to the first stretching roll 1 and the number of the nip rolls 5 approaching the second stretching roll 2 are preferably 2 or more and 4 or less from the viewpoint of equalizing stretching stress and installation space. (The example in FIG. 3 is two).

The stretching speed is preferably 3.5 × 10 ⁴ % / min or more and 6.5 × 10 ⁴ % / min or less. By adopting such an embodiment, uneven stretching and film breakage during stretching can be reduced. From the above viewpoint, the stretching rate is more preferably 4.0 × 10 ⁴ % / min or more and 6.0 × 10 ⁴ % / min or less, and still more preferably 4.5 × 10 ⁴ % / min or more. It is 5 × 10 ⁴ % / min or less.

  The film drawing rate is calculated by dividing the distance between rolls 6 (m) by the rotation speed (m / min) of the second draw roll 2 to calculate the time (min) required for drawing, and the film drawing rate (%) ) Can be calculated by dividing by time (min) required for stretching. The inter-roll distance 6 refers to the distance between the center of the first stretching roll and the center of the second stretching roll. The stretch ratio of a film refers to a value obtained by dividing the length of a film increased by stretching by the length of the film before stretching and expressing it in percentage. For example, the stretch ratio of the film when not stretched is 0%, and the stretch ratio of the film when stretched twice is 100%.

  The sum of the pressures of the nip rolls (the sum of the pressures applied by the stretching rolls on the upstream side and all the nip rolls close to the stretching rolls on the downstream side) is preferably 0.1 MPa or more and 1.0 MPa or less. By adopting such an aspect, not only the stress becomes more uniform, but it is also possible to reduce the occurrence of nip roll marks caused by pressing the nip rolls. 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 still more preferably 0.4 MPa or more and 0.5 MPa or less.

  Moreover, it is preferable that the thickness ratio of the width direction center part and edge part of the film (Hereafter, it may be mentioned a non-oriented film.) Before extending | stretching is 1.1 or more and 2.5 or less. By setting this ratio to 2.5 or less, the film is sufficiently fixed at the time of film stretching, and the occurrence of stretching unevenness is reduced. On the other hand, when the ratio is 1.1 or more, the clip can sufficiently hold the film end in the stretching in the width direction with the stenter performed after the stretching in the longitudinal direction, and the productivity is lowered. It is reduced. From the above reasons, the thickness ratio of the widthwise center portion to the end portion of the non-oriented film is more preferably 1.3 or more and 2.3 or less, and still more preferably 1.6 or more and 1.9 or less. The thickness ratio between the widthwise center portion and the end portion can be calculated by dividing the average value of the thicknesses at both widthwise end portions (5 mm inside each end portion) by the thickness at the widthwise center portion. At this time, the thickness can be measured by the method described in JIS-C-2330 (2001) 7.4.1.1. The detailed measurement method will be described later.

  In the film of the present invention, the type of resin constituting the film is not limited as long as the effects of the present invention are not impaired. Examples of the resin constituting the film of the present invention include polyolefins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyamide, polycarbonate, polystyrene, polyvinyl alcohol, saponified ethylene vinyl acetate copolymer, Various resins such as polyacrylonitrile and polyacetal may be mentioned.

  From the viewpoint of heat resistance, dimensional stability, and economy, the film of the present invention preferably contains a polyester resin as a main component. In the present invention, having a polyester resin as a main component means containing 50% by mass or more of the polyester resin when the entire resin component constituting the film is 100% by mass. At this time, the polyester resin may be one kind or a mixture of plural kinds, and in the latter case, the content is calculated by adding all the polyester resins. In the following, the term "main component" can be interpreted in the same manner.

  Polyester resin is a general term for polymer compounds having an ester bond continuously in the main chain, and usually a dicarboxylic acid or a derivative thereof (hereinafter sometimes referred to as a dicarboxylic acid etc.) and a diol or a derivative thereof (hereinafter a diol) Etc.) can be obtained by polycondensation reaction. In the film of the present invention, when the total amount of the dicarboxylic acid and the like is 100% by mole, it is preferable to make the amount of the aromatic dicarboxylic acid or the aliphatic dicarboxylic acid more than 50% by mole.

  As an 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'-diphenyldicarboxylic acid And 4,4'-diphenyl ether dicarboxylic acid, and 4,4'-diphenyl sulfone dicarboxylic acid. Examples of aliphatic dicarboxylic acids include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexane dicarboxylic acid, and ester derivatives of these. Among them, terephthalic acid having high crystallinity and 2,6-naphthalene dicarboxylic acid are preferably used. These aromatic dicarboxylic acids and aliphatic dicarboxylic acids may be a single type or a mixture of two or more types as long as the effects of the present invention are not impaired, and even if an oxy acid such as hydroxybenzoic acid is mixed, etc. Good.

  Further, as the diol etc., for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 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- Examples include hydroxyethoxyphenyl) propane, isosorbate, and spiro glycol. Among them, ethylene glycol is preferably used. These diols may be used alone or in combination of two or more, as long as the effects of the present invention are not impaired.

  Examples of the polyester resin in the film of the present invention include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polyhexamethylene terephthalate, polyhexamethylene naphthalate, and copolymers of these alone or the like. It can be used in combination.

  The film of the present invention has a layer (A layer) containing polyester resin A as a main component and a layer (B layer) containing resin B, which is a resin other than polyester resin A, as a main component. 30 layers or more are preferably laminated alternately in the thickness direction, more preferably 200 layers or more, and still more preferably 800 layers or more. By adopting such an embodiment, layers having different molecular orientations are alternately stacked, so that it is possible to adjust the light transmittance. When the number of layers is less than 30, it may be difficult to control the reflection wavelength, the reflectance and the transmittance. The upper limit of the number of layers is not particularly limited as long as the effects of the present invention are not impaired. However, considering the increase in the size of the stacking device and the deterioration of wavelength selectivity due to the decrease in stacking accuracy due to an excessive number of layers, 1 4,000 layers are realistic. The thickness direction refers to a direction perpendicular to the main alignment axis and a direction perpendicular to the main alignment axis.

  Furthermore, it is preferable that the polyester resin A is a crystalline polyester resin and the resin B is an amorphous polyester resin. By adopting such an embodiment, crystallization of the B layer is less likely to occur even under high temperature, so it is possible to reduce whitening of the film and the like.

  Amorphous polyester resin refers to a polyester resin having a heat of crystal fusion of less than 0.1 mJ / mg when heated at a temperature rising rate of 5 ° C./min in differential thermal analysis (DSC), and is a crystalline polyester resin The term "polyester resin" does not correspond to this.

  The crystalline polyester resin (polyester resin A) and the non-crystalline polyester resin (resin B) are preferably combined in such a way that the basic skeletons of the respective resins become the same. The basic skeleton refers to a repeating unit that constitutes a resin. As a specific example, in polyethylene terephthalate, ethylene terephthalate is a basic skeleton, and in polyethylene, ethylene is a basic skeleton. As a preferable combination of the crystalline polyester resin and the noncrystalline polyester resin, for example, a weight in which the crystalline polyester resin is polyethylene terephthalate and the noncrystalline polyester resin is composed of ethylene terephthalate units and cyclohexane 1,4-dimethylene terephthalate units The example which is a combination (copolymer) is mentioned. By setting it as such an aspect, in film forming of a lamination film, problems, such as lamination failure of a flow mark etc., exfoliation between layers, etc. can be reduced.

  The polyester resin A is not particularly limited as long as the effects of the present invention are not impaired, but it is preferable to use polyethylene terephthalate or polyethylene naphthalate from the viewpoint of maintaining high lamination accuracy.

  As the resin B, it is preferable to contain a 1,4-hexanedimethanol unit as a diol unit from the viewpoint of reducing an excessive increase in crystallinity. Further, a copolymer having the same main constituent unit as polyester resin A and containing cycloisophthalic acid unit, naphthalenedicarboxylic acid unit, diphenyl acid unit, cyclohexanedicarboxylic acid unit as an acid unit, and a main constituent unit of polyester As in the resin A, a copolymer containing a spiroglycol unit, a cyclohexanedimethanol unit, a bisphenoxyethanol fluorene unit, and a bisphenol A unit as a diol unit may be used.

  Further, in consideration of forming a laminated film with a uniform thickness, it is preferable that the polyester resin A and the resin B be a combination in which the difference between the glass transition temperatures of the both is 20 ° C. or less. If the difference between the glass transition temperatures of the two is greater than 20 ° C., the thickness at the time of film formation tends to be nonuniform, and the stability of the optical properties when formed into a laminated film may be impaired. In some cases, overstretching may occur.

  The layers A and B in the present invention should contain particles such as colloidal silica, titanium oxide and crosslinked polystyrene in order to impart functions such as winding properties, rigidity and optical properties as long as the effects of the present invention are not impaired. it can. The content of these resins and particles in the layer A or the layer B is not particularly limited as long as the effects of the present invention are not impaired, but preferably 10% by mass or less when the entire layer is 100% by mass. Moreover, A layer and B layer are various additives, for example, an antioxidant, an antistatic agent, a crystal nucleating agent, a viscosity reducing agent, a thermal stabilizer, a lubricant, an infrared absorber, as long as the effects of the present invention are not impaired. It may contain a UV absorber, a dopant for adjusting the refractive index, and the like.

The film of the present invention preferably has a correlation coefficient (nR) of refractive index wavelength dispersion at a wavelength of 196 nm to 800 nm measured by an ellipsometer under measurement condition II of 0.600 or more and 0.995 or less. It is more preferably 750 or more and 0.995 or less, and still more preferably 0.900 or more and 0.995 or less.
Measurement condition II:
(Procedure 1) to (Procedure 4) are the same as the measurement condition I.
(Step 5)
The refractive index of the wavelength of 196 nm to 800 nm at each point is determined from the parameters of the transducers in A1 to A5, the correlation coefficient between them is calculated, and the combination with the smallest correlation coefficient is nR.

  Hereinafter, measurement conditions II of the present invention will be described in detail. The measurement conditions II sequentially carry out the steps 1 to 5 and the steps 1 to 4 are the same as the measurement conditions I.

  Procedure 5 of the measurement condition II of the present invention “calculates the refractive index of the wavelength from 196 nm to 800 nm at each point from the parameter of the vibrator in A1 to A5, calculates the correlation coefficient between each other, and the correlation coefficient is minimized Let the combination be nR.

  The details of step 5 are as follows. First, conversion of the refractive index of the dielectric function is performed on the X model and the Y model of A1 to A5 determined by the ellipsometry measurement device, and the refractive indexes in the X direction and Y direction of wavelengths 196 nm to 800 nm (A1Xn to A5Xn , A1Yn to A5Yn). Then, all the AjXn-AkXn (A1Xn-A2Xn, A1Xn-A2Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A3Xn, A1Xn-A4Xn, A1Xn-A3Xn, A1Xn-A4Xn, A1Xn-A4Xn; A3Xn-A5Xn, A4Xn-X1Xn, A4Xn-A2Xn, A4Xn-A3Xn, A4Xn-A5Xn, A5Xn-X1Xn, A5Xn-A2Xn, A5Xn-A3Xn, and A5Xn-A4X5 x 1x 5x5 <1 <. j ≠ k, j and k indicate integers and measurement numbers))) calculate correlation coefficients when the refractive indices of the same wavelength are used as variables, and similarly calculate AjYn-AkYn. The correlation coefficient which becomes the minimum among calculated AjXn-AkXn and AjYn-AkY is set to nR.

  In polyethylene terephthalate, the refractive index has a σ-π * excitation band at 196 nm or less and the excitation band is broad toward the long wavelength side, and affects the visible light region from the ultraviolet region of 196 nm to 800 nm. Is known (Reference 1). That is, the uniformity of the σ-π * bond is important as well as the uniformity of the π-π * bond in order to suppress color tone unevenness in the blue light region and the visible light region, and by measuring nR, σ-π * The uniformity of binding can be estimated.

  The method for setting nR to 0.600 or more and 0.995 or less is not particularly limited, but for example, a method using two or more nip rolls in the stretching roll as in the method for setting d420 n to 0.001 or more and 0.100 or less A method of controlling the stretching speed, a method of adjusting the total pressure of the nip rolls, and a method of adjusting the thickness ratio of the unstretched film are used.

  The film of the present invention can be preferably used as an optical film because it has an excellent surface quality without color tone unevenness. In particular, it can be suitably used as a protective film for a screen using an LED as a light source.

  Next, although the preferable manufacturing method of the polyester film of this invention is demonstrated based on the example which used 2 types of polyester resins, this invention is limited to the example concerned and is not interpreted. In addition, the formation itself of the laminated structure of the multilayer laminated polyester film can be realized with reference to the description in paragraphs [0053] to [0063] of JP-A-2007-307893.

  First, a polyester resin to be a raw material of the layer A and a polyester resin to be a raw material of the layer B are respectively prepared in the form of pellets, and dried in hot air or under vacuum as necessary. Particles and additives are added to each dried resin pellet as required, and the mixture is supplied to a vented twin-screw extruder for melt extrusion. At this time, it is preferable to control the oxygen concentration to 0.7% by volume or less and the resin temperature to 265 ° C. to 295 ° C. in a flowing nitrogen atmosphere from the viewpoint of suppressing the oxidative decomposition of the resin.

  Next, removal of foreign substances and adjustment of extrusion amount are performed by a filter or gear pump, and the obtained resin compositions are alternately laminated by a multilayer laminating apparatus to form a sheet having a multilayer structure, and a casting drum etc. from a die Push onto the cooling body of the The extruded sheet is cooled and solidified to form a casting film. Under the present circumstances, it is preferable to closely_contact | adhere to cooling bodies, such as a casting drum etc., by electrostatic force using a wire-like, tape-like, needle-like or knife-like electrode, and to make it harden rapidly. It is also preferable to blow air from a slit-like, spot-like or plane-like device to adhere closely to a cooling body such as a casting drum to cause rapid solidification, or to closely adhere to a cooling body with a nip roll to cause rapid solidification.

  As a multi-layer laminating apparatus, a multi-manifold die, a feed block, a static mixer, etc. can be used, but in particular, in order to efficiently obtain the film of the present invention, at least two separate members having a large number of fine slits. It is preferable to use a feed block including the above. When such a feed block is used, the apparatus does not increase in size extremely, so foreign matter due to thermal deterioration is small, and highly accurate lamination can be performed even if the number of layers increases. Furthermore, the lamination accuracy in the width direction is also significantly improved as compared with the prior art, and it becomes easy to form an arbitrary layer thickness configuration.

  Moreover, in order to make dispersion (d420n) of the refractive index of wavelength 420nm when setting it as a biaxially oriented film 0.001 or more and 0.100 or less, the width direction center part and both ends of a non-oriented film The thickness ratio (edge thickness / center thickness) is preferably 1.0 or more and 2.5 or less. By adopting such an embodiment, uniform stretching is possible in the subsequent longitudinal stretching step without impairing the appearance and productivity.

  Then, the film of the present invention can be obtained by stretching the cast film in the longitudinal direction (longitudinal stretch) and further stretching in the width direction (transverse stretch). The longitudinal stretching ratio is not particularly limited as long as the effect of the present invention is not impaired, but is preferably 2.8 times or more and 3.8 times or less, more preferably 3.1 times or more and 3.5 times or less. Further, the film temperature at the time of longitudinal stretching is preferably 80 ° C. or more and 110 ° C. or less.

Furthermore, from the viewpoint of longitudinally stretching the film uniformly without impairing the appearance and productivity, in the longitudinal stretching step, there are two or more nip rolls adjacent to the upstream stretching roll, and a nip roll proximate to the downstream stretching roll It is important that is two or more. From the same point of view, it is important that the total sum of the nip roll pressures is 0.1 MPa or more and 1.0 MPa or less. The pressure of the nip roll is a value obtained by dividing the load for pressing the nip roll against the film by the surface length of the nip roll. Furthermore, from the same viewpoint, it is important that the drawing speed is 3.5 × 10 ⁴ % / min or more and 6.5 × 10 ⁴ % / min or less. By setting it as such an aspect, nonuniformity of molecular structure resulting from drawing unevenness is controlled, and not only molecular structure unevenness in a film is reduced but also occurrence of film breakage etc. is reduced.

  The transverse stretching ratio is not particularly limited as long as the effect of the present invention is not impaired, but is preferably 3.1 times or more and 4.5 times or less, more preferably 3.5 times or more and 4.2 times or less. Lateral stretching is preferably performed by dividing the temperature into a plurality of zones and raising the temperature stepwise. As a specific example of such a method, for example, the first half stretching temperature is 90 ° C. or more and 120 ° C. A method of setting the temperature at the first half temperature to 100 ° C. to 130 ° C. and setting the temperature of the second half of the stretching to 110 ° C. to 150 ° C. at the drawing middle temperature may be mentioned.

  Furthermore, it is preferable to heat-treat a film after transverse stretching. The heat treatment can be performed by a conventionally known method using a stenter, a heated roll or the like. The heat treatment temperature may be a temperature equal to or lower than the crystal melting peak temperature of the polyester resin, preferably 200 ° C. or more and 240 ° C. or less, more preferably 210 ° C. or more and 235 ° C. or less, and still more preferably 215 ° C. or more and 230 ° C. or less . The heat treatment temperature mentioned here means the temperature which becomes the highest temperature in the heat treatment performed after biaxial stretching. The heat treatment time may be arbitrary within a range that does not deteriorate the characteristics, and is preferably 5 seconds to 60 seconds, more preferably 10 seconds to 40 seconds, and most preferably 15 seconds to 30 seconds.

  Further, a heat treatment method in which the temperature is increased and / or decreased stepwise in a plurality of zones and a method in which the film is slightly stretched in the width direction in the heat treatment step are preferably employed. It is also preferable to carry out the heat treatment while relaxing by 1% or more and 10% or less in the latter half in order to lower the heat shrinkage of the film. Furthermore, after the heat treatment step, it is preferable to include a cooling step of relaxing by 0.2% or more and 3.0% or less at 80 ° C. or more and 120 ° C. or less.

  The biaxially oriented film thus obtained is once wound up as an intermediate product by a wide winding machine, and then cut into an appropriate width and length by a slitter to obtain a final product.

  Hereinafter, the present invention will be described according to examples, but the present invention is not limited by these examples. Various properties were measured by the following methods. Usually, the main orientation axis is determined by measuring the size of the orientation of molecules, but all the films of this example are produced by stretching in the longitudinal direction and then stretching in the width direction, and the stretching It is clear from the conditions that the width direction is the main orientation axis direction. Therefore, the measurement was performed by regarding the width direction as the main orientation axis direction.

(1) Number of layers of film The layer configuration of the film was determined by electron microscopic observation on a sample whose cross section was cut out using a microtome. That is, using a transmission electron microscope H-7100 FA type (manufactured by Hitachi, Ltd.), the cross section of the film is observed at 40,000 magnifications at an accelerating voltage of 75 kV, the cross section photograph is taken, and the layer configuration and thickness of each layer are measured. did. In the case where confirmation of the layer configuration is difficult, in order to obtain high contrast, a dyeing technique using known RuO ₄ or OsO ₄ or the like was used.

(2) Thickness ratio of the film end of the non-oriented film to the thickness ratio of the central portion 5 mm from the widthwise end of the non-oriented film and the central portion in the width direction JIS-C-2330 (2001) The micrometer thickness was measured by the method described in 7.4.1.1. The end of one side was measured 5 times each 5 mm from the widthwise end of the film, and the average of 10 points was taken as the film end thickness. The widthwise central portion thickness was taken as the average value of five measurements. Further, the thickness ratio was calculated by dividing the average value of the film end thickness by the width direction central portion thickness.

(3) Dispersion of refractive index at wavelength 420 nm (d 420 n)
[Sample processing (steps 1 and 2 of measurement condition I)]
A film sample is cut out in 50 mm (longitudinal direction) × 50 mm (width direction), and a pressure of 0.2 MPa is applied to the entire surface of the film with abrasive paper No. 240 (JIS-R6252: 2006, base material: Cw, material of abrasive: garnet ( G) Adhesive: Glue (G / G) was pressed and reciprocated 20 times in parallel with the longitudinal direction. Next, the abrasive paper No. 240 was pressed against the entire surface of the abrasive paper No. 240, and was reciprocated 20 times in parallel with the width direction under the same conditions as the longitudinal processing.

[Measurement by ellipsometer (up to irradiation of polarized beam in procedures 3 and 4 of measurement condition I)]
On the sample base of the spectroscopic ellipsometer (M-2000D manufactured by JA Woollam Co., Ltd., analysis software: “CompleteEASE” (registered trademark)), the surface opposite to the surface treated with the abrasive paper No. 240 is the measurement surface Set the sample as follows. Then, in the standard measure mode, the magnitudes of the angles formed by the straight line (Z) drawn perpendicular to the measurement plane from the center of gravity (A1) in the sample and the polarized beam irradiated to A1 are 50 °, 60 ° and 70 respectively. Three light sources were arranged on the same plane so as to obtain an angle, and measurements were performed by irradiating polarized light beams from A1 to A1 (Procedure 3). When the angle between the straight line Z and the polarized beam was set to 70 °, the intensity of the reflected light was 0.200 or more when the intensity of the incident light was 1.000. Thereafter, four measurement points (A2 to A5) are arbitrarily selected so that the linear distance from A1 is 20 mm or more and the distances between the centers of the respective points are all 20 mm or more, under the same conditions. The measurement was performed (Procedure 4).

[Analytical method using an ellipsometer (Procedure 5 and 5 after irradiation with polarized beam in procedures 3 and 4 of measurement condition I)]
In the Analsys mode, select and launch a Blank model in the window of Model, set the layer configuration of the model as Substrate indicating a single layer, set the initial model as a Gen-Osc model representing dielectric functions from multiple oscillators, model In this case, Biaxial capable of representing optical anisotropy in three directions was used as Type exhibiting optical anisotropy of (Satisfying (1) in Step 3)
Then, as shown in Table 1, a total of four transducers were added and parameters were set. In Table 1, Gaussian indicates Gaussian distribution (fills step 2 (2)), Amp indicates peak intensity, Br indicates half width (unit: eV), En indicates energy position of the oscillator (unit: eV) . In the model in the X direction, En is not dependent on each other but is independent (for vibrator numbers 1 to 4, En is 6.200, 4.900, 4.200, 18 in order). .000 satisfies step 3 (3)).

  Furthermore, Br and En used Parameter Coupling to make the values of model Y and model Z respectively dependent on the values of model X as in Table 1 (for example, "= x 1 Br" in Table 1 is in the x direction) Indicates that Br and the parameter value are equal in oscillator 1. (4) in step 3 is satisfied. In addition, since Br and En are specific to the molecular bond form, range designation is performed as shown in Table 1, and for Amp, the bond amount and strength are not 0 or more because they are not smaller than 0. Also, UV pole Amp, UV pole En and IR pole Amp were fixed at 0.

  Next, parameters for performing parameter fitting were set as shown in Table 2, and measurements were performed by irradiating polarized beams from three directions so that the angles formed by the polarized beam and the straight line Z would be 50 °, 60 °, and 70 °, respectively. Parameter fitting was performed on the values of the amplitude intensity ratio Ψ and the phase difference Δ at 20 to 6.40 eV. The mean square error was 30.0 or less to quantify the difference between the measured data and the data calculated from the model. Moreover, fitting was implemented about the parameter shown by "(circle)" in Table 2, and since parameter Coupling was implemented about the parameter shown by "-", fitting was not implemented separately. As described above, UV pole Amp, UV pole En and IR pole Amp were fixed at 0.

Next, conversion of dielectric function to refractive index was performed. J. A. Woollam analysis software: "CompleteEASE" (registered trademark) can be easily implemented from GraphType in the Analysis tab, and can obtain a refractive index profile at a wavelength. d420 n implements the above conversion for each of the determined A1 to A5 X model, Y model, and Z model, and in A1 to A5, the refractive index of 420 nm, X 420 ni, Y 420 ni, Z 420 ni (1 ≦ i ≦ 5, respectively) i is an integer and indicates the measurement number), and using formulas (II) to (IV), using formulas (II) to (IV) so as to maximize d420 n of formula (I), Xd 420 n, Y d 420 n , Zd 420 n determined by determining. When the refractive index can not be calculated at 420 nm, the refractive index of the wavelength closest to 420 nm is treated as the refractive index of 420 nm (satisfying (5) in Procedure 3).
d420 n = (X d 420 n + Y d 420 n + Z d 420 n) ÷ 3 (I)
Xd420n = X420nj-X420nk (II)
Yd420n = Y420nj-Y420nk (III)
Zd 420 n = Z 420 n j-Z 420 nk (IV)
(1 ≦ j ≦ 5, 1 ≦ k ≦ 5, j ≠ k, j and k are integers and indicate measurement numbers).

(4) Correlation coefficient of refractive index wavelength dispersion (nR)
The refractive index for each wavelength of 196 nm to 800 nm of A1 determined by (3) is variable nA1, similarly, the refractive index for each wavelength of 196 nm to 800 nm of A2, A3, A4, A5 is variable nA2, nA3, When nA4 and nA5 are used, the correlation coefficient is determined from the covariance and standard deviation between all two combinations of nA1 to nA5, and the correlation coefficient of the combination showing the smallest value is nR.

(5) Color tone unevenness (ΔE)
A sample is cut out with dimensions of 50 mm × 50 mm at any point on the film, and the sample is set so that the normal of the film plane matches the incident light, using a spectrophotometer Konica Minolta CM-3600A. The chromaticity a ^* , the chromaticity b ^* , and the lightness L ^* at an arbitrary position on the sample were measured in transmitted light under target mask conditions of a measurement diameter Φ 8 mm. Thereafter, the sample was moved so as to leave 20 mm or more from the center of the measurement point, and the same measurement was repeated four times. The color tone unevenness ΔE was determined using Formulas (VII) to (X) in combination of the chromaticity a ^* , the chromaticity b ^* , and the lightness L ^* at which ΔE becomes maximum among five measurements. Based on the obtained color difference ΔE, evaluation was made according to the following criteria, and AA to B were regarded as passing.
ΔL ^* = L ^* l−L ^* m (VII)
Δa ^* = a ^* l-a ^* m (VIII)
Δ b ^* = b ^* l-b ^* m (IX)
ΔE = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^1/2 (X)
(1 ≦ l ≦ 5, 1 ≦ m ≦ 5, l ≠ m, l and m indicate integers and measurement numbers.)
AA: ΔE is 2.0 or less.
A: ΔE is greater than 2.0 and less than or equal to 4.0.
B: ΔE is greater than 4.0 and 5.0 or less.
C: ΔE is larger than 5.0.

(6) Appearance (cross nicol inspection)
After cutting out a sample with dimensions of 100 mm × 100 mm at any point of the film, the appearance of the film was confirmed under cross nicol conditions and evaluated according to the following criteria. As for the appearance, A was the best, and B or more was accepted.
A: There were no streaks.
B: A streak occurred, but the thickness was less than 3 mm and the length was less than 10 mm.
C: A streak corresponding to any one of thickness 3 mm or more and length 10 mm or more was generated.
(7) Productivity The productivity was evaluated from the film formation continuation time from the start of commercialization to the interruption of product collection due to film breakage. In addition, A was the most excellent in productivity, and B or more was taken as pass.
A: The film was formed for 6 hours and no film breakage occurred.
B: Film formation was carried out for 6 hours and film breakage occurred once.
C: Film formation was performed for 6 hours, and film breakage occurred twice or more.

(Polyester resin)
(Resin A1) To a mixture of 100 parts by mass of dimethyl terephthalate and 60 parts by mass of ethylene glycol, 0.09 parts by mass of magnesium acetate and 0.03 parts by mass of antimony trioxide are added with respect to the amount of dimethyl terephthalate. The temperature was raised by heating to carry out the transesterification reaction. Next, 0.020 parts by mass of an aqueous solution of 85% phosphoric acid was added to the transesterification reaction product with respect to the amount of dimethyl terephthalate, and then the mixture was transferred to a polycondensation reaction layer. Further, the reaction system was gradually depressurized while heating under heating to carry out a polycondensation reaction at 290 ° C. under a reduced pressure of 1 mmHg to obtain a polyethylene terephthalate of IV = 0.63. Refractive index 1.60.
(Resin A2) Polyethylene naphthalate of IV = 0.43 obtained by polycondensation of naphthalene 2,6-dicarboxylic acid dimethyl ester with ethylene glycol. Refractive index 1.65.
As resin B, the following were prepared.
(Resin B1) Polyethylene terephthalate copolymerized with IV = 0.75 (25 mol% of cyclohexanedimethanol (CHDM)). Refractive index 1.57.
(Resin B2) Polyethylene terephthalate copolymerized with IV = 0.73 (cyclohexanedimethanol (CHDM) 10 mol%). Refractive index 1.59.
(Resin B3) Polyethylene terephthalate copolymerized with IV = 0.78 (20 mol% of spiro glycol component). Refractive index 1.55.

  The refractive index of each resin was measured by forming a casting film under the same conditions as in Example 1 described later. Specifically, a sample of 40 mm (longitudinal direction) × 35 mm (width direction) is cut out from the central portion in the width direction of the casting film, and an Abbe refractometer 4T (manufactured by Atago Co., Ltd.) is used to cut the sample in the longitudinal direction and width direction. The refractive index of each was measured three times. The average value of the total of six measurements obtained was taken as the refractive index of the resin that constitutes the film. In the measurement, a sodium D line (wavelength: 589 nm) was used as a light source, methylene iodide was used as an immersion liquid, and a test piece having a refractive index of 1.74 was used.

Example 1
After drying each of resin A1 (hereinafter resin A) and resin B1 (hereinafter resin B) as two types of polyester resins having different optical properties, they are respectively brought to a molten state of 280 ° C. in a vented twin-screw extruder, A feed block of 909 layers was joined and alternately laminated via a gear pump and a filter so that both film surface portions became resin A. The lamination method was performed according to description of Unexamined-Japanese-Patent No. 2007-307893 [0053]-[0056] stage. After being introduced into a T-die and formed into a sheet, it was quenched and solidified on a casting drum kept at a surface temperature of 25 ° C. by electrostatic application to obtain a non-oriented film having 909 layers. At this time, the discharge amount was adjusted so that the mass ratio of the resin A and the resin B was 1.0: 1.0.

Then, the film temperature is raised by a heating roll before stretching in the longitudinal direction, and the first stretching roll and the second stretching roll both include two nip rolls, and the stretching is performed by a roll stretching machine having a distance between rolls of 350 mm. ^3. At a film temperature of 90 ° C., the stretching speed in the longitudinal direction is 4.9 × 10 ⁴ % / min (the film forming speed after stretching is 78 m / min, the time required for stretching is 4.49 × 10 ³ min). The film was stretched twice to obtain a uniaxially oriented film. In addition, the sum total of the nip pressure in a 1st extending | stretching roll and a 2nd extending | stretching roll was 0.5 Mpa. The resulting uniaxially oriented film was immediately cooled with a controlled metal roll at 40 ° C. Next, in a stenter, the uniaxially oriented film is stretched 3.7 times in the width direction under temperature conditions of a first half temperature of drawing 95 ° C., a middle temperature of drawing 105 ° C., and a second half temperature of drawing 140 ° C. The heat treatment was performed at a temperature of 200 ° C. and a heat treatment middle plate temperature of 225 ° C. At this time, heat treatment was performed while performing 5% slight stretching in the width direction in the first half of the heat treatment. Then, heat treatment was performed while applying 3.0% relaxation in the width direction at a temperature of 180 ° C. in the second half of the heat treatment to obtain a film having a film thickness of 42 μm. Further, at the end of film formation, the thickness ratio of the end portion to the central portion of the film was determined from the film obtained by collecting the non-oriented film by emergency stop. The evaluation results of the obtained film are shown in Table 3.

(Examples 2 to 19, Comparative Examples 1 to 6)
A biaxially oriented film was obtained in the same manner as in Example 1 except that the longitudinal stretching conditions, the number of layers, and the composition of each layer were changed as shown in Table 3. The evaluation results are shown in Table 3. In Examples 18 and 19, the melt temperature of the resin A is extruded at 300 ° C., the stretched film temperature in the longitudinal direction is 110 ° C., the first half temperature, middle temperature and second half temperature in the stenter are 120 ° C. The temperature was 130 ° C and 150 ° C.

  According to the present invention, it is possible to provide a film having the intended optical properties and in which the occurrence of color tone unevenness and the reduction in surface quality are reduced. The film of the present invention can be suitably used for optical applications, particularly for the protection of screens using an LED as a light source.

a Measurement plane b Center of gravity of measurement plane (A1)
c A straight line (Z) drawn perpendicular to the measurement surface from A1
d A straight line drawn from A1 on the measurement surface (X)
e A straight line drawn from A1 on the measurement surface so as to be perpendicular to Z and X (Y)
f Polarized beam g1 XZ50
g2 XZ60
g3 XZ70
h Reflected light i Detection unit j A2 to A5
k Circle with a radius of 20 mm centering on each point of A1 to A5: first drawing roll 2: second drawing roll 3: film 4: nip roll 5 close to first drawing roll: nip roll close to second drawing roll 6: distance between rolls

Claims (8)

The film characterized in that the variation (d420 n) of the refractive index at a wavelength of 420 nm measured by an ellipsometer under the following measurement condition I is 0.001 or more and 0.100 or less.
Measurement condition I:
(Step 1)
Abrasive paper No. 240 specified in JIS-R6252 (2006) is pressed at a pressure of 0.2 MPa on the entire surface of a film of 50 mm (direction orthogonal to the main orientation axis) × 50 mm (direction of the main orientation axis), orthogonal to the main orientation axis Reciprocate 20 times parallel to the direction.
(Step 2)
The abrasive paper No. 240 is pressed against the entire surface of the abrasive paper No. 240 reciprocated in procedure 1 under the same conditions as the procedure 1, and reciprocated 20 times in parallel with the main orientation axis direction.
(Step 3)
In the procedures 1 and 2, the surface opposite to the surface treated with the abrasive paper No. 240 is used as the measurement surface, and the straight line obtained by drawing the center of gravity of the measurement surface from A1 and A1 perpendicularly to the film surface is from Z, A1 on the measurement surface And Y is a straight line drawn from A1 on the film surface so as to be perpendicular to X, Z and X, the angle between Z and the polarized beam on the XZ plane is 50 °. A polarized beam is irradiated from the point (XZ50), the point (XZ60) to be 60 °, and the point (XZ70) to be 70 °, and the phase difference Δ and the amplitude intensity ratio Ψ obtained from the reflected light are The parameters of the oscillator are determined by comparison with the model satisfying (1) to (5).
(1) A direction parallel to X, Y, and Z is X direction, Y direction, and Z direction, and a model in X direction is model X, a model in Y direction is model Y, and a model in Z direction is model Z And the models X, Y and Z are different models.
(2) Gaussian distribution is used for the vibrator, and the parameters of the vibrator are half width, energy position, and peak intensity.
(3) In each of the models X, Y, and Z, the energy positions of the vibrators are independent of each other.
(4) The energy positions of the vibrators are subordinate to each other among the models X, Y, and Z.
(5) The half-widths of the model X, the model Y, and the model Z are subordinate to each other.
(Step 4)
Arbitrary four points (A2, A3, A4, A5) located on the measurement surface and having a linear distance of 20 mm or more from A1 and a distance of 20 mm or more between the centers of the points. And determine the oscillator parameters at A2 to A5 according to Procedure 3.
(Step 5)
The refractive index at a wavelength of 420 nm at each point is determined from the parameters of the transducers in A1 to A5, and the difference between the maximum value and the minimum value is d420 n.   The film according to claim 1, wherein the film comprises a polyester resin as a main component.   A layer (A layer) containing polyester resin A as a main component and a layer (B layer) containing resin B, which is a resin other than polyester resin A, are provided, and layers A and B are alternately arranged in the thickness direction. The film according to claim 1 or 2, wherein 30 or more layers are laminated.   The film according to any one of claims 1 to 3, wherein the polyester resin A is a crystalline polyester resin, and the resin B is an amorphous polyester resin. The correlation coefficient (nR) of refractive index wavelength dispersion at a wavelength of 196 nm to 800 nm measured by an ellipsometer under measurement condition II is 0.600 or more and 0.995 or less. Film described in.
Measurement condition II:
(Procedure 1) to (Procedure 4) are the same as the measurement condition I.
(Step 5)
The refractive index of the wavelength of 196 nm to 800 nm at each point is determined from the parameters of the transducers in A1 to A5, the correlation coefficient between them is calculated, and the combination with the smallest correlation coefficient is nR.   The film according to any one of claims 1 to 5, which is an optical film.   The film according to claim 6, wherein the optical film is a protective film for a screen having an LED as a light source. In the longitudinal stretching step, there are two or more nip rolls in proximity to the upstream stretching roll, two or more nip rolls in proximity to the downstream stretching roll, and a stretching speed of 3.5 × 10 ⁴ % / min or more The method for producing a film according to any one of claims 1 to 7, characterized in that it is 6.5 x 10 ⁴ % / min or less and the total sum of the nip pressures is 0.1 MPa or more and 1.0 MPa or less. .