Plastic film for optical use, optical laminate using same, polarizing plate, and image display device

Abstract

The present application relates to a plastic film for optical use, and an optical laminate, a polarizing plate, and an image display device using the same. Provided is an optical plastic film capable of suppressing rainbow spots during observation with naked eyes and black screens during observation with polarized sunglasses without increasing in-plane phase differences and without requiring axial alignment.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of March 30, 2021, an invention title of "Plastic Film for Optics, and Optical Laminate, Polarizing Plate, and Image Display Device Using the Same", and an application number of 202180035179.2. Technical Field

[0002] The present invention relates to a plastic film for optics, and an optical laminate, a polarizing plate, and an image display device using the same. Background Art

[0003] In optical components such as image display devices, various plastic films for optics are used. For example, in an image display device having a polarizing plate on a display element, a plastic film for protecting a polarizing element constituting the polarizing plate is used. In this specification, the "plastic film for protecting a polarizing element" is sometimes referred to as a "polarizing element protection film".

[0004] The plastic film for an image display device typified by the polarizing element protection film preferably has excellent mechanical strength. Therefore, as the plastic film for an image display device, a stretched plastic film is preferably used.

[0005] When a stretched plastic film is disposed on a polarizing element, since the stretched plastic film disturbs the polarization state of linearly polarized light passing through the polarizing element, there is a problem that spots of a rainbow pattern are observed. To solve this problem, Patent Documents 1 to 3 and the like have been proposed. In this specification, the "spots of a rainbow pattern" are sometimes referred to as "rainbow spots".

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-300611

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2010-244059

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2011-107198 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In Patent Documents 1 and 2, the absorption axis of the polarizing element and the slow axis of the stretched plastic film are arranged in parallel or perpendicular, and rainbow spots can be suppressed.

[0013] However, when the polarizing element and the stretched plastic film are arranged as in the relationship between Patent Documents 1 and 2, there is a problem that the screen becomes black when observing the image display device with polarized sunglasses. In this specification, the above phenomenon is sometimes referred to as "black screen".

[0014] Patent Document 3 discloses a liquid crystal display device, which can eliminate iridescence and black screen by making the light source of the image display device a specific white light source, making the in-plane retardation of the stretched plastic film as high as 3000 nm or more and 30000 nm or less, and arranging the absorption axis of the polarizing element and the slow axis of the stretched plastic film at approximately 45 degrees.

[0015] However, Patent Document 3 requires the use of a stretched plastic film with a large in-plane retardation. And the stretched plastic film with a large in-plane retardation is usually uniaxially stretched, so it has problems such as being easily broken in the stretching direction.

[0016] In addition, Patent Document 3 needs to perform fine axis alignment of the absorption axis of the polarizing element and the slow axis of the stretched plastic film to suppress the black screen, so the operability is poor and it is difficult to improve the yield.

[0017] The subject of the present invention is to provide an optical plastic film that can suppress iridescence when observed with the naked eye and black screen when observed with polarized sunglasses without increasing the in-plane retardation and without requiring axis alignment; and to provide an optical laminate, a polarizing plate, and an image display device using the optical plastic film.

[0018] Means for Solving the Subject

[0019] The present inventors conducted in-depth research and found that in a plastic film with a reduced in-plane retardation, without making the angle of the slow axis of the plastic film uniform, but making the standard deviation σ of the above angle a specified value or more, the above subject can be solved.

[0020] The present invention provides the following optical plastic film, and an optical laminate, a polarizing plate, and an image display device using the plastic film.

[0021] [1] An optical plastic film that satisfies the following Condition 1 and Condition 2.

[0022] <Condition 1>

[0023] A large sample with a size of 200 mm × 300 mm is cut out from the plastic film. The above large sample is divided into 30 small samples of 40 mm × 50 mm. The 30 mm × 40 mm area after removing 5 mm from the edge of each small sample is subdivided into more than 47,000 areas, and then the in-plane phase difference of each subdivided area is measured. Among the above 30 small samples, the proportion of small samples with an average in-plane phase difference of each measurement area showing 50% or more of 50 nm or more and 1200 nm or less is 50% or more.

[0024] <Condition 2>

[0025] For the above 30 small samples, in the same manner as in the above Condition 1, the angles of the slow axes of each area after subdivision of each small sample are measured. Among the above 30 small samples, the proportion of small samples in which the standard deviation σ calculated from the angles of the slow axes of each measurement area shows 0.8 degrees or more is 50% or more.

[0026] [2] An optical laminate having a functional layer on the plastic film for optical use described in the above [1].

[0027] [3] A polarizing plate which is a polarizing plate having a polarizing element, a first transparent protective plate disposed on one side of the polarizing element, and a second transparent protective plate disposed on the other side of the polarizing element, wherein at least one of the first transparent protective plate and the second transparent protective plate includes the plastic film for optical use described in the above [1].

[0028] [4] An image display device which is an image display device having a display element and a plastic film disposed on the light exit surface side of the display element, wherein the plastic film is the plastic film for optical use described in the above [1].

[0029] Effects of the Invention

[0030] The plastic film for optical use of the present invention, and the optical laminate, polarizing plate, and image display device using the plastic film can suppress iridescence when observed with the naked eye and black screen when observed with polarized sunglasses without increasing the in-plane phase difference. Description of the Drawings

[0031] Figure 1 It is a top view for explaining a 40 mm × 50 mm sample in Condition 1 and Condition 2 and a 30 mm × 40 mm area after removing 5 mm from the edge of the above sample.

[0032] Figure 2 It is a diagram for explaining a sampling method of a roll-shaped plastic film.

[0033] Figure 3 It is a cross-sectional view showing an embodiment of the image display device of the present invention.

[0034] Figure 4 It is a cross-sectional view showing another embodiment of the image display device of the present invention.

[0035] Figure 5 It is a diagram schematically showing the situation of a continuous folding test.

[0036] Figure 6 It is a schematic cross-sectional view of a measuring device for the erosion rate of a plastic film.

[0037] Figure 7 It is an image of the state where the plastic film is worn by a test liquid containing pure water and spherical silica ejected from the ejection part. Detailed Embodiments

[0038] The embodiments of the present invention will be described below.

[0039] [Plastic Film for Optics]

[0040] The plastic film for optics of the present invention satisfies the following Condition 1 and Condition 2.

[0041] <Condition 1>

[0042] A large sample with a size of 200 mm × 300 mm is cut out from the plastic film. The above large sample is divided into 30 small samples of 40 mm × 50 mm. The 30 mm × 40 mm area after removing 5 mm from the edge of each small sample is subdivided into more than 47,000 regions, and then the in-plane phase difference of each subdivided region is measured. Among the above 30 small samples, the proportion of small samples in which the average value of the in-plane phase difference of each measurement region shows 50% or more in the range of 50 nm or more and 1200 nm or less is 50% or more.

[0043] <Condition 2>

[0044] For the above 30 small samples, in the same manner as in Condition 1, the angle of the slow axis of each region after subdivision of each small sample is measured. Among the above 30 small samples, the proportion of small samples in which the standard deviation σ calculated from the angle of the slow axis of each measurement region shows 0.8 degrees or more is 50% or more.

[0045] <Regarding Measurement>

[0046] The large sample with a size of 200 mm × 300 mm used in Condition 1 and Condition 2 is cut out from an arbitrary position of the plastic film.

[0047] In Condition 1 and Condition 2, the above large sample is divided into 30 small samples of 40 mm × 50 mm, and the 30 mm × 40 mm area after removing 5 mm from the edge of each small sample is measured. Figure 1Among them, the outer quadrilateral region represents a small sample with a size of 40 mm × 50 mm, and the inner quadrilateral region represents a region of 30 mm × 40 mm.

[0048] The reason for measuring the region after removing 5 mm from the edge of the small sample can be considered as follows: When cutting the large sample, stress is easily applied near the edge of the plastic film, so the optical axis near the edge of the small sample sometimes deforms.

[0049] Plastic films for optical use, for example, may be in a sheet form or a roll form. The plastic film in sheet form and the plastic film in roll form are preferably sampled from the large sample as follows. After cutting out 30 small samples from the large sample, the determination of Conditions 1 and 2 is carried out.

[0050] In the case where multiple large samples with a size of 200 mm × 300 mm can be collected from a sheet-like plastic film, it is preferable to sample with a layout that can obtain the largest number of large samples.

[0051] In the case where multiple large samples with a size of 200 mm × 300 mm can be collected from a sheet-like plastic film, it is sufficient if any one of the large samples satisfies Conditions 1 and 2. In order to more easily exhibit the effects of the present invention, among all the large samples, the proportion of the large samples that satisfy Conditions 1 and 2 is preferably 50% or more, more preferably 70% or more, further preferably 90% or more, and even more preferably 100%. The same applies to Condition 3 described later.

[0052] In the case of a roll-shaped plastic film, it is preferable to determine whether Conditions 1 and 2 are satisfied in the width direction of each roll as described in (1) to (4) below.

[0053] (1) In the width direction of the roll-shaped plastic film 10b, large samples with a flow direction of 200 mm × a width direction of 300 mm are cut out in the available quantity. For example, in the case where the roll width is 1200 mm, 4 large samples are cut out. In addition, in the case where the roll width is 1600 mm, 5 large samples are cut out. In the case where the roll width is 1600 mm, 100 mm remains in the width direction. Let the cut large samples be S1, S2, ··· Sn (refer to Figure 2 ).

[0054] (2) Cut out 30 small samples of 40 mm × 50 mm from the large sample S1, and perform the measurement regarding Conditions 1 and 2 to determine whether Conditions 1 and 2 are satisfied.

[0055] (3) The various physical properties of the rolled plastic film are liable to change in the width direction, but are almost the same in the flow direction. Therefore, when the large sample S1 meets conditions 1 and 2, for the part in the roll having the same position in the width direction as the large sample S1, it can be assumed that conditions 1 and 2 are met throughout the flow direction of the roll.

[0056] (4) The same operations as in (2) to (3) above are also performed on the large samples S2, ··· Sn to determine whether the large samples S2, ··· Sn meet conditions 1 and 2. Also, for the part in the roll having the same position in the width direction as the large samples among S2, ··· Sn that meet conditions 1 and 2, it is assumed that conditions 1 and 2 are met throughout the flow direction of the roll. The same applies to condition 3 described later.

[0057] In conditions 1 and 2, after subdividing a 30 mm × 40 mm area obtained by removing 5 mm from the edge of the small sample into more than 47,000 regions, it is necessary to measure the in-plane phase difference and the angle of the slow axis for each of the subdivided regions. If the number of subdivided regions is 47,000 or more, the value of the standard deviation σ is sufficiently reliable. Therefore, the number of subdivided regions can be, for example, around 47,000, around 70,000, or around 100,000. Of course, the sizes of the subdivided regions are roughly equal. Such measurement can be performed using, for example, a two-dimensional distribution evaluation device for birefringence.

[0058] As a two-dimensional distribution evaluation device for birefringence, a product named "WPA-200-L" by Photonic Lattice can be cited. When using the product named "WPA-200-L" by Photonic Lattice, the small sample is set on the workbench of the device, and the preview area is adjusted so that the number of pixels in the 30 mm × 40 mm area is 47,000 or more, whereby it is possible to measure the in-plane phase difference and the angle of the slow axis for each of the regions subdivided into more than 47,000 regions.

[0059] Regarding the in-plane phase difference of condition 1 and the phase difference in the thickness direction of condition 3 described later, they are represented by the refractive index nx in the slow axis direction, which is the direction with the maximum refractive index at each measurement site, the refractive index ny in the fast axis direction, which is the direction orthogonal to the above-mentioned slow axis direction at each measurement site, the refractive index nz in the thickness direction of the plastic film, and the thickness T [nm] of the plastic film, by the following formulas (1) and (2). In this specification, sometimes the "in-plane phase difference" is denoted as "Re", and the "phase difference in the thickness direction" is denoted as "Rth".

[0060] In-plane phase difference (Re) = (nx - ny) × T [nm] (1)

[0061] In-plane retardation (Rth) in the thickness direction = ((nx + ny) / 2 - nz) × T [nm] (2)

[0062] The plastic film for optics of the present invention needs to satisfy the following Condition 1.

[0063] <Condition 1>

[0064] A large sample with a size of 200 mm × 300 mm is cut out from the plastic film. The above large sample is divided into 30 small samples of 40 mm × 50 mm. A region of 30 mm × 40 mm after removing 5 mm from the edge of each small sample is subdivided into more than 47,000 regions, and then the in-plane retardation of each subdivided region is measured. Among the above 30 small samples, the proportion of small samples in which the average value of the in-plane retardation of each measurement region shows 50 nm or more and 1200 nm or less is 50% or more.

[0065] In this specification, Condition 1 and Condition 2 refer to the values at a wavelength of 543 nm.

[0066] When the average value of the in-plane retardation of the plastic film is less than 50 nm, it is difficult to suppress blackening of the screen. The reason is that a plastic film with an average value of in-plane retardation less than 50 nm can hardly disturb linearly polarized light and allows linearly polarized light to pass through directly.

[0067] On the other hand, when the average value of the in-plane retardation of the plastic film exceeds 1200 nm, iridescence when observed with the naked eye cannot be suppressed.

[0068] In addition, even if there are small samples in which the average value of the in-plane retardation shows 50 nm or more and 1200 nm or less, when the proportion is less than 50%, blackening of the screen cannot be suppressed, or iridescence when observed with the naked eye cannot be suppressed. Among the 30 small samples, the proportion of small samples in which the average value of the in-plane retardation of each measurement region shows 50 nm or more and 1200 nm or less is preferably 70% or more, more preferably 90% or more, and further preferably 100%.

[0069] Techniques such as making the in-plane retardation 3000 nm or more as in Patent Document 3 cannot suppress iridescence when the shape of the spectral distribution of the image display device is sharp. On the other hand, when the in-plane retardation is reduced as in the present invention, even when the shape of the spectral distribution of the image display device is sharp, iridescence can be eliminated.

[0070] In Condition 1, in order to more easily suppress blackening of the screen, the average value of the in-plane retardation is preferably 100 nm or more, more preferably 150 nm or more, more preferably 200 nm or more, more preferably 250 nm or more, more preferably 300 nm or more, more preferably 400 nm or more, more preferably 520 nm or more, more preferably 620 nm or more. It should be noted that if the average value of the in-plane retardation of the plastic film is too small, the standard deviation σ of the angle of the slow axis sometimes becomes too large. Therefore, from the aspect of preventing the standard deviation σ of the angle of the slow axis from becoming too large, it is also preferable to set the average value of the in-plane retardation to a specified value or more.

[0071] In addition, a small in-plane retardation of the plastic film means that the molecular orientation of the resin constituting the plastic film is insufficient and / or the thickness of the plastic film is thin. Therefore, by setting the average value of the in-plane retardation of the plastic film to a specified value or more, the pencil hardness of the plastic film can be improved. In order to improve the pencil hardness of the plastic film, the average value of the in-plane retardation of the plastic film is preferably 100 nm or more, more preferably 520 nm or more, and further preferably 620 nm or more.

[0072] In Condition 1, in order to easily suppress iridescence when observed with the naked eye, the average value of the in-plane retardation is preferably 1100 nm or less, more preferably 1000 nm or less, more preferably 950 nm or less. In addition, if the average value of the in-plane retardation is large, the bend resistance described later tends to decrease. By setting the average value of the in-plane retardation to 950 nm or less, it is possible to easily suppress the decrease in bend resistance.

[0073] In the components shown in this specification, when upper limit options and lower limit options of multiple numerical values are respectively shown, one selected from the upper limit options can be combined with one selected from the upper limit options as an embodiment of the numerical range.

[0074] For example, in the case of the average value of the in-plane phase difference described above, embodiments with numerical ranges of 50 nm or more and 1200 nm or less, 50 nm or more and 1100 nm or less, 50 nm or more and 1000 nm or less, 50 nm or more and 950 nm or less, 100 nm or more and 1200 nm or less, 100 nm or more and 1100 nm or less, 100 nm or more and 1000 nm or less, 100 nm or more and 950 nm or less, 150 nm or more and 1200 nm or less, 150 nm or more and 1100 nm or less, 150 nm or more and 1000 nm or less, 150 nm or more and 950 nm or less, 200 nm or more and 1200 nm or less, 200 nm or more and 1100 nm or less, 200 nm or more and 1000 nm or less, 200 nm or more and 950 nm or less, 250 nm or more and 1200 nm or less, 250 nm or more and 1100 nm or less, 250 nm or more and 1000 nm or less, 250 nm or more and 950 nm or less, 300 nm or more and 1200 nm or less, 300 nm or more and 1100 nm or less, 300 nm or more and 1000 nm or less, 300 nm or more and 950 nm or less, 400 nm or more and 1200 nm or less, 400 nm or more and 1100 nm or less, 400 nm or more and 1000 nm or less, 400 nm or more and 950 nm or less, 520 nm or more and 1200 nm or less, 520 nm or more and 1100 nm or less, 520 nm or more and 1000 nm or less, 520 nm or more and 950 nm or less, 620 nm or more and 1200 nm or less, 620 nm or more and 1100 nm or less, 620 nm or more and 1000 nm or less, 620 nm or more and 950 nm or less can be cited.

[0075] The standard deviation σ of the in-plane phase difference of each subdivided region is not particularly limited. The lower limit is preferably 5 nm or more, more preferably 10 nm or more, still more preferably 15 nm or more, and even more preferably 20 nm or more. The upper limit is preferably 100 nm or less, more preferably 70 nm or less, further preferably 50 nm or less.

[0076] As embodiments of the range of the standard deviation σ of the in-plane phase difference, 5 nm or more and 100 nm or less, 5 nm or more and 70 nm or less, 5 nm or more and 50 nm or less, 10 nm or more and 100 nm or less, 10 nm or more and 70 nm or less, 10 nm or more and 50 nm or less, 15 nm or more and 100 nm or less, 15 nm or more and 70 nm or less, 15 nm or more and 50 nm or less, 20 nm or more and 100 nm or less, 20 nm or more and 70 nm or less, 20 nm or more and 50 nm or less can be cited.

[0077] The plastic film for optics of the present invention needs to satisfy the following condition 2.

[0078] <Condition 2>

[0079] For the above 30 small samples, in the same manner as in the above Condition 1, the angles of the slow axes of the respective regions after subdivision of each small sample were measured. Among the above 30 small samples, the proportion of small samples in which the standard deviation σ calculated from the angles of the slow axes of the respective measurement regions showed 0.8 degrees or more was 50% or more.

[0080] The standard deviation σ of the angle of the slow axis being 0.8 degrees or more indicates that there is a deviation in the slow axis of the plastic film. When the standard deviation σ is less than 0.8 degrees, blackening of the screen cannot be suppressed.

[0081] In addition, even if there are small samples in which the standard deviation σ of the angle of the slow axis shows 0.8 degrees or more, when the proportion is less than 50%, the information on the display cannot be read due to local blackening of the screen. Among the 30 small samples, the proportion of small samples in which the standard deviation σ calculated from the angles of the slow axes of the respective measurement regions showed 0.8 degrees or more is preferably 70% or more, more preferably 90% or more, and further preferably 100%.

[0082] The existing plastic film for optics is designed such that the direction of the slow axis does not deviate, but the plastic film for optics of the present invention intentionally deviates the direction of the slow axis, which is different from the configuration of the existing optical film. In addition, it can be said that the plastic film for optics of the present invention is also characterized by focusing on the deviation of the slow axis in a relatively small region of 30 mm × 40 mm.

[0083] In addition, from the aspect of being able to improve the bend resistance of the plastic film, it is preferable to satisfy Condition 2.

[0084] On the other hand, for a general alignment film with a uniform slow axis, the film breaks after a bending test, or there are obvious bending marks remaining. Specifically, the uniaxially stretched film of Patent Document 3 breaks when a bending test is performed along the slow axis, and obvious bending marks remain when a bending test is performed along a direction orthogonal to the slow axis. In addition, obvious bending marks remain when a bending test is performed on a general biaxially stretched film along a direction orthogonal to the slow axis.

[0085] The plastic film of the present invention is preferable in that it can suppress the remaining of bending marks or breakage after a bending test regardless of the direction of bending.

[0086] In Condition 2, the standard deviation σ is preferably 0.9 degrees or more, more preferably 1.0 degrees or more, further preferably 1.2 degrees or more, and even more preferably 1.6 degrees or more. By making the standard deviation σ 1.6 degrees or more, the effect of suppressing blackening of the screen can be extremely good.

[0087] If the standard deviation σ of Condition 2 is too large, there is a tendency for the orientation of the plastic film to decrease, the mechanical strength and pencil hardness to decrease, and wrinkles to occur under environmental changes, which has an adverse effect on visibility. Therefore, in Condition 2, the standard deviation σ is preferably 20.0 degrees or less, more preferably 15.0 degrees or less, more preferably 10.0 degrees or less, more preferably 7.0 degrees or less, and more preferably 5.0 degrees or less.

[0088] As embodiments of the range of the standard deviation σ of Condition 2, there may be mentioned 0.8 degrees or more, 0.8 degrees or more and 20.0 degrees or less, 0.8 degrees or more and 15.0 degrees or less, 0.8 degrees or more and 10.0 degrees or less, 0.8 degrees or more and 7.0 degrees or less, 0.8 degrees or more and 5.0 degrees or less, 0.9 degrees or more and 20.0 degrees or less, 0.9 degrees or more and 15.0 degrees or less, 0.9 degrees or more and 10.0 degrees or less, 0.9 degrees or more and 7.0 degrees or less, 0.9 degrees or more and 5.0 degrees or less, 1.0 degrees or more and 20.0 degrees or less, 1.0 degrees or more and 15.0 degrees or less, 1.0 degrees or more and 10.0 degrees or less, 1.0 degrees or more and 7.0 degrees or less, 1.0 degrees or more and 5.0 degrees or less, 1.2 degrees or more and 20.0 degrees or less, 1.2 degrees or more and 15.0 degrees or less, 1.2 degrees or more and 10.0 degrees or less, 1.2 degrees or more and 7.0 degrees or less, 1.2 degrees or more and 5.0 degrees or less, 1.6 degrees or more and 20.0 degrees or less, 1.6 degrees or more and 15.0 degrees or less, 1.6 degrees or more and 10.0 degrees or less, 1.6 degrees or more and 7.0 degrees or less, 1.6 degrees or more and 5.0 degrees or less.

[0089] The plastic film for optics of the present invention preferably satisfies the following Condition 2'.

[0090] <Condition 2'>

[0091] For the above 30 small samples, in the same manner as in the above Condition 1, the angles of the slow axes of the respective regions obtained by subdividing each small sample are measured. Among the above 30 small samples, the proportion of small samples in which the standard deviation 3σ calculated from the angles of the slow axes of the respective measurement regions is 30.0 degrees or less is 50% or more.

[0092] If the standard deviation 3σ of Condition 2' is too large, the orientation of the plastic film sometimes becomes too low, and there is a tendency for the pencil hardness to decrease. Therefore, by making the standard deviation 3σ 30.0 degrees or less, it is possible to easily improve the pencil hardness of the plastic film. The standard deviation 3σ is more preferably 25.0 degrees or less, more preferably 20.0 degrees or less, more preferably 15.0 degrees or less, and more preferably 10.0 degrees or less.

[0093] If the standard deviation 3σ of condition 2' is too small, the orientation of the plastic film is too high, and thus the plastic film sometimes becomes brittle. Therefore, the standard deviation 3σ is preferably 2.4 degrees or more, more preferably 2.7 degrees or more, still more preferably 3.0 degrees or more, still more preferably 3.6 degrees or more, and still more preferably 4.8 degrees or more.

[0094] As embodiments of the range of the standard deviation 3σ of condition 2', there may be mentioned 2.4 degrees or more and 30.0 degrees or less, 2.4 degrees or more and 25.0 degrees or less, 2.4 degrees or more and 20.0 degrees or less, 2.4 degrees or more and 15.0 degrees or less, 2.4 degrees or more and 10.0 degrees or less, 2.7 degrees or more and 30.0 degrees or less, 2.7 degrees or more and 25.0 degrees or less, 2.7 degrees or more and 20.0 degrees or less, 2.7 degrees or more and 15.0 degrees or less, 2.7 degrees or more and 10.0 degrees or less, 3.0 degrees or more and 30.0 degrees or less, 3.0 degrees or more and 25.0 degrees or less, 3.0 degrees or more and 20.0 degrees or less, 3.0 degrees or more and 15.0 degrees or less, 3.0 degrees or more and 10.0 degrees or less, 3.6 degrees or more and 30.0 degrees or less, 3.6 degrees or more and 25.0 degrees or less, 3.6 degrees or more and 20.0 degrees or less, 3.6 degrees or more and 15.0 degrees or less, 3.6 degrees or more and 10.0 degrees or less, 4.8 degrees or more and 30.0 degrees or less, 4.8 degrees or more and 25.0 degrees or less, 4.8 degrees or more and 20.0 degrees or less, 4.8 degrees or more and 15.0 degrees or less, 4.8 degrees or more and 10.0 degrees or less.

[0095] In this specification, regarding the measurement of condition 1 and condition 2, and the atmosphere for other measurements such as condition 2', condition 3 to 6, and total light transmittance, unless otherwise specified, the temperature is set to 23°C ± 5°C and the relative humidity is 40% or more and 65% or less. In addition, unless otherwise specified, the sample is exposed to the above atmosphere for 30 minutes or more before each measurement.

[0096] The plastic film for optics of the present invention preferably satisfies the following condition 3.

[0097] <Condition 3>

[0098] For the above 30 small samples, the retardation in the thickness direction is measured at the center of the above 30 mm × 40 mm region. Among the above 30 small samples, the proportion of small samples in which the retardation in the thickness direction shows 2000 nm or more is 50% or more.

[0099] In this specification, condition 3 refers to the value at a wavelength of 589.3 nm.

[0100] By satisfying Condition 3, not only in the front direction but also the black screen when viewed obliquely can be easily suppressed. Among 30 small samples, the proportion of samples with a retardation in the thickness direction of 2000 nm or more is preferably 70% or more, more preferably 90% or more, and further preferably 100%.

[0101] In Condition 3, the retardation in the thickness direction is more preferably 3000 nm or more, further preferably 4000 nm or more, and even more preferably 5000 nm or more.

[0102] There is no particular limitation on the upper limit of the retardation in the thickness direction in Condition 3. In order to easily satisfy Condition 4 described later, it is preferably 15000 nm or less, more preferably 12000 nm or less, and further preferably 9000 nm or less.

[0103] As embodiments of the range of the retardation in the thickness direction of Condition 3, there can be mentioned 2000 nm or more, 2000 nm or more and 15000 nm or less, 2000 nm or more and 12000 nm or less, 2000 nm or more and 9000 nm or less, 3000 nm or more and 15000 nm or less, 3000 nm or more and 12000 nm or less, 3000 nm or more and 9000 nm or less, 4000 nm or more and 15000 nm or less, 4000 nm or more and 12000 nm or less, 4000 nm or more and 9000 nm or less, 5000 nm or more and 15000 nm or less, 5000 nm or more and 12000 nm or less, 5000 nm or more and 9000 nm or less.

[0104] The retardation in the thickness direction of Condition 3 can be measured, for example, using the product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd.

[0105] When measuring the retardation in the thickness direction and the like using the product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd., it is preferable to prepare for the measurement in the following order (A1) to (A4).

[0106] (A1) First, in order to stabilize the light source of RETS-100, after turning on the light source, it is left for 60 minutes or more. Then, the rotating analyzer method is selected, and the θ mode is selected. The θ mode is a mode for measuring the angular direction retardation and calculating Rth. By selecting this θ mode, the stage is an inclined rotating stage.

[0107] (A2) Next, the following measurement conditions are input into RETS-100.

[0108] (Measurement conditions)

[0109] · Delay measurement range: Rotating analyzer method

[0110] · Measure the spot diameter:

[0111] · Tilt angle range: 0°

[0112] · Wavelength range for measurement: above 400 nm and below 800 nm

[0113] · Average refractive index of the plastic film. For example, in the case of a PET film, N = 1.617.

[0114] · Thickness: Thickness measured separately using SEM

[0115] (A3) Next, without setting a sample in the device, background data is obtained. The device is a closed system, and (A1) to (A3) are implemented each time the light source is lit.

[0116] (A4) After that, a sample is set on the stage in the device for measurement.

[0117] The plastic film for optics of the present invention preferably satisfies the following Condition 4.

[0118] <Condition 4>

[0119] Among the above 30 small samples, the proportion of small samples in which the average value of the in-plane phase difference with respect to the phase difference in the thickness direction is 0.20 or less is 50% or more.

[0120] The average value of the in-plane phase difference with respect to the phase difference in the thickness direction is "the average value of the in-plane phase difference / the phase difference in the thickness direction". A small value of the average value of the in-plane phase difference / the phase difference in the thickness direction means that the stretching degree of the plastic film for optics is close to uniform biaxiality. Therefore, by making the above ratio 0.20 or less, it is possible to easily improve the mechanical strength and pencil hardness of the plastic film, and in addition, it is possible to suppress the formation of wrinkles in the plastic film under environmental changes and have an adverse effect on visibility. Among the 30 small samples, the proportion of small samples in which the above ratio is 0.20 or less is preferably 70% or more, more preferably 90% or more, and further preferably 100%.

[0121] The ratio of Condition 4 is more preferably 0.17 or less, and further preferably 0.15 or less.

[0122] The lower limit of the ratio of Condition 4 is not particularly limited. The lower limit of the ratio of Condition 4 is usually around 0.01.

[0123] Examples of the implementation manner of the range of the ratio of Condition 4 include 0.20 or less, 0.01 or more and 0.20 or less, 0.01 or more and 0.17 or less, 0.01 or more and 0.15 or less.

[0124] In order to easily obtain the above effects brought about by satisfying Condition 4, the average value of the in-plane phase difference of Condition 1 is preferably 100 nm or more.

[0125] <Condition 5>

[0126] For the above 30 small samples, the erosion rate of the plastic film constituting the small sample from the surface to a depth of 20 μm is measured at the center of the above-mentioned 30 mm × 40 mm area. The average value of the erosion rate of the plastic film constituting the small sample from the surface to a depth of 20 μm is defined as E. 0-20 When, among the above 30 small samples, 0-20 the proportion of small samples with E of 1.4 μm / g or more is 50% or more.

[0127] In this specification, E 0-20 is measured under the following measurement conditions.

[0128] <Measurement Conditions>

[0129] Pure water, a dispersion liquid, and spherical silica with an average particle size within ±8% based on 4.2 μm are mixed in a mass ratio of 968:2:30, and the mixed test liquid is stored in a container. The above test liquid in the above container is sent to a nozzle. Compressed air is supplied into the above nozzle, the above test liquid is accelerated in the above nozzle, and a specified amount of the above test liquid is vertically sprayed from the ejection hole at the front end of the above nozzle onto the above plastic film, causing the spherical silica in the above test liquid to collide with the above plastic film. The cross-sectional shape of the above nozzle is a 1 mm × 1 mm square, and the distance between the above ejection hole and the above plastic film is 4 mm. In addition, the flow rates of the above test liquid and the above compressed air supplied to the above nozzle, the pressure of the above compressed air, and the pressure of the above test liquid in the above nozzle are specified values adjusted through calibration described later.

[0130] After spraying a specified amount of the above test liquid, the spraying of the above test liquid is temporarily stopped.

[0131] After temporarily stopping the spraying of the above test liquid, the cross-sectional profile is measured at the part of the above plastic film where the spherical silica in the above test liquid collides.

[0132] The steps of ejecting a prescribed amount of the test liquid from the above-mentioned ejection port, temporarily stopping the ejection of the test liquid after ejecting the prescribed amount of the test liquid, and measuring the cross-sectional profile after temporarily stopping the ejection of the test liquid are regarded as one cycle, and the above operations are performed until the depth of the cross-sectional profile exceeds 20 μm. And, in each cycle until the depth of the cross-sectional profile reaches 20 μm, the erosion rate (μm / g) of the plastic film is calculated by dividing the depth (μm) of the cross-sectional profile developed in each cycle by the ejection amount (g) of the test liquid in each cycle. The erosion rates of the plastic film in each cycle until the depth of the cross-sectional profile reaches 20 μm are averaged to calculate the above E 0-20 。

[0133] <Calibration>

[0134] The above test liquid is stored in the above container. The test liquid in the above container is sent to the above nozzle. Compressed air is supplied into the above nozzle to accelerate the test liquid in the above nozzle, and an arbitrary amount of the above test liquid is vertically ejected from the ejection hole at the front end of the above nozzle onto an acrylic plate with a thickness of 2 mm, so that the spherical silica in the above test liquid collides with the above acrylic plate. The cross-sectional shape of the above nozzle is a square with a size of 1 mm × 1 mm, and the distance between the above ejection hole and the above acrylic plate is 4 mm.

[0135] After ejecting an arbitrary amount of the above test liquid, the ejection of the above test liquid is temporarily stopped. After temporarily stopping the ejection of the above test liquid, the cross-sectional profile is measured at the part of the above acrylic plate where the above spherical silica collides in the above test liquid.

[0136] The erosion rate (μm / g) of the acrylic plate is calculated by dividing the depth (μm) of the cross-sectional profile by the above arbitrary amount (g).

[0137] The qualified condition for the erosion rate of the above acrylic plate is within the range of ±5% based on 1.88 (μm / g). In the manner that the erosion rate of the above acrylic plate is within the above range, the flow rates of the above test liquid and the above compressed air, the pressure of the above compressed air, and the pressure of the above test liquid in the above nozzle are adjusted and calibrated.

[0138] Hereinafter, refer to Figure 6 to explain the measurement conditions of the erosion rate and the technical meaning of the erosion rate calculated based on the above measurement conditions. As Figure 6 the erosion rate measurement device, for example, the part number “MSE-A203” of the MSE test device of Palmeso Co., Ltd. can be cited.

[0139] In the measurement conditions of the erosion rate of the present invention, first, pure water, a dispersant, and spherical silica with an average particle size within ±8% based on 4.2 μm are mixed at a mass ratio of 968:2:30, and the mixed test liquid is stored in a container (110). Inside the container (110), it is preferable to stir the test liquid.

[0140] As the pure water, general pure water can be used. The resistivity value of the pure water is usually 0.1 MΩ·cm or more and 15 MΩ·cm or less.

[0141] The dispersant is not particularly limited as long as it can disperse the spherical silica. As the dispersant, for example, the product name “DEMOL N (DemolN)” of Wako Pure Chemical Industries, Ltd. can be cited.

[0142] In other words, “the average particle size within ±8% based on 4.2 μm” means that the average particle size is 3.864 μm or more and 4.536 μm or less.

[0143] In addition, in the measurement conditions of the erosion rate in this specification, the “average particle size of the spherical silica” is measured as the volume average value d50 in the particle size distribution measurement using the laser diffraction method, which refers to the so-called “median diameter”.

[0144] Regarding the above spherical silica, in the result of the above particle size distribution measurement, when the frequency of the particle size showing the maximum is normalized to 100, the width of the particle size showing a frequency of 50 is preferably within ±10% based on 4.2 μm. Regarding the “width of the particle size showing a frequency of 50”, when “defining the particle size that is the particle size showing a frequency of 50 and is located in the more positive direction than the particle size showing a frequency of 100” as X and “defining the particle size that is the particle size showing a frequency of 50 and is located in the more negative direction than the particle size showing a frequency of 100” as Y, it is represented by “X - Y (μm)”. It should be noted that in this specification, the “width of the particle size showing a frequency of 50” is sometimes referred to as the “full width at half maximum of the particle size distribution”.

[0145] As the spherical silica with an average particle size within ±8% based on 4.2 μm, the model “MSE - BS - 5 - 3” specified by Palmeso Co., Ltd. can be cited. As the spherical silica conforming to the model “MSE - BS - 5 - 3” specified by Palmeso Co., Ltd., for example, the part number “BS5 - 3” of Potters - Ballotini Co., Ltd. can be cited.

[0146] The test liquid in the container is fed into the nozzle (510). The test liquid can be sent to the nozzle through, for example, the piping for the test liquid (210). A flow meter (310) for measuring the flow rate of the test liquid is preferably arranged between the container (110) and the nozzle (510). The flow rate of the test liquid is a value adjusted through the above-mentioned correction.

[0147] It should be noted that Figure 6 in, the nozzle (510) is arranged inside the housing (520) constituting the ejection part (500).

[0148] Compressed air is fed into the nozzle (510). The compressed air is sent to the nozzle through, for example, the piping for the compressed air (220). Inside the nozzle, the position where the compressed air is fed is preferably more upstream than the position where the test liquid is fed. The upstream side refers to the side away from the ejection hole of the nozzle.

[0149] Before the compressed air reaches the nozzle (510), a flow meter (320) for measuring the flow rate of the compressed air and a pressure gauge (420) for measuring the pressure of the compressed air are preferably arranged. The compressed air can be supplied by an air compressor (not shown) or the like.

[0150] The flow rate and pressure of the compressed air are values adjusted through the above-mentioned correction.

[0151] When compressed air is fed into the nozzle (510), the test liquid is accelerated while being mixed with the compressed air. And after the accelerated test liquid is ejected from the ejection hole at the front end of the nozzle (510), it collides perpendicularly with the plastic film (10). The plastic film is mainly worn by the spherical silica particles in the test liquid.

[0152] It should be noted that a pressure gauge (410) for measuring the pressure of the test liquid inside the nozzle is preferably arranged inside the nozzle (510). The pressure gauge (410) is preferably more downstream than the position where the compressed air is fed and the position where the test liquid is fed.

[0153] The pressure of the test liquid inside the nozzle (510) is a value adjusted through the above-mentioned correction.

[0154] The test liquid ejected from the ejection hole at the front end of the nozzle (510) is mixed with air and ejected in a mist form. Therefore, the collision pressure of the spherical silica particles against the plastic film can be reduced. Thereby, the amount of wear of the plastic film caused by one spherical silica particle can be suppressed to a very small amount. Figure 7 is an image of the state where the plastic film (10) is worn by the test liquid containing pure water (A1) and spherical silica (A2) ejected from the ejection part (500). Figure 7 in, the symbol A3 represents air, and the symbol A4 represents the worn plastic film.

[0155] In addition, since the test liquid contains water with excellent cooling effect, deformation and deterioration of the plastic film caused by heat during collision can be substantially eliminated. That is, abnormal wear of the plastic film can be substantially eliminated. In addition, water also has the function of cleaning the surface of the worn plastic film and achieving stable wear. In addition, water has the function of accelerating spherical silica particles or controlling the fluid of the test liquid.

[0156] In addition, since a large number of spherical silica collide with the plastic film, the influence brought by the subtle physical property differences of each spherical silica particle can be eliminated.

[0157] Furthermore, regarding the measurement conditions of the present invention, the flow rate of the test liquid supplied to the nozzle, the flow rate of the compressed air supplied to the nozzle, the pressure of the compressed air supplied to the nozzle, and the pressure of the test liquid in the nozzle are values adjusted by the above-mentioned calibration. At the same time, the cross-sectional shape of the nozzle is specified as a square of 1 mm × 1 mm, and the distance between the injection hole and the plastic film is specified as 4 mm, thereby specifying the factors that affect the wear amount of the plastic film. It should be noted that the above distance is Figure 6 the distance indicated by "d", which refers to the perpendicular distance between the front end of the nozzle, i.e., the injection hole, and the plastic film.

[0158] From the above results, it can be said that the measurement conditions of the present invention are measurement conditions that can form statistically stable wear marks on the plastic film.

[0159] The plastic film (10) only needs to be installed on the specimen mounting table (810) of the measuring device (900). It should be noted that it is preferable to fabricate a laminate in which the plastic film is adhered to a support (820) such as a stainless steel plate, and install the laminate on the specimen mounting table (810).

[0160] The test liquid sprayed onto the plastic film (10) is preferably recovered by the receiver (120) and returned to the container (110) through the return pipe (230).

[0161] In the measurement conditions of the present invention, the following are the conditions: after spraying a specified amount of the test liquid, the spraying of the test liquid is temporarily stopped; and after temporarily stopping the spraying of the test liquid, the cross-sectional profile of the part of the plastic film where the spherical silica in the test liquid collides is measured.

[0162] The cross-sectional profile refers to the cross-sectional shape of the plastic film worn by the test liquid. The plastic film is mainly worn by the spherical silica particles in the test liquid.

[0163] The cross-sectional profile can be measured, for example, by a cross-sectional profile acquisition unit (600) such as a stylus-type surface shape measurement device and a laser interferometer-type surface shape measurement device. It should be noted that the cross-sectional profile acquisition unit (600) is usually arranged at a position far from the plastic film (10) when the test liquid is ejected. Therefore, it is preferable that at least one of the plastic film (10) and the cross-sectional profile acquisition unit (600) is movable.

[0164] In the part number "MSE-A203" of the MSE test device of Palmeso Co., Ltd., the means for measuring the cross-sectional profile is of the stylus type.

[0165] Furthermore, in the measurement conditions of the present invention, three steps, namely, the step of ejecting a predetermined amount of the test liquid from the ejection port, the step of temporarily stopping the ejection of the test liquid after ejecting the predetermined amount of the test liquid, and the step of measuring the cross-sectional profile after temporarily stopping the ejection of the test liquid, are regarded as one cycle, and the operation is performed until the depth of the cross-sectional profile exceeds 20 μm.

[0166] By performing the above operations, the erosion rate of the plastic film in each cycle can be measured, and furthermore, the deviation of the erosion rate of the plastic film can be calculated.

[0167] The above cycle can continue after the depth of the cross-sectional profile exceeds 20 μm, but it is preferably terminated at the moment when the depth of the cross-sectional profile exceeds 20 μm. In addition, the reason for measuring "from the surface to a depth of 20 μm of the plastic film" is considered to be that the physical properties of the plastic film tend to change easily near the surface and become more stable towards the inside.

[0168] In this specification, the erosion rate of each cycle can be expressed by the following [Equation 1].

[0169] Erosion rate of each cycle (μm / g) = Depth of the cross-sectional profile developed in each cycle (μm) / Injection amount of the test liquid in each cycle (g) [Equation 1]

[0170] In Equation 1, "Depth of the cross-sectional profile developed in each cycle (μm)" refers to the value represented by "y - x" when the depth of the cross-sectional profile in the nth cycle is defined as x (μm) and the depth of the cross-sectional profile in the (n + 1)th cycle is defined as y (μm). In addition, for the first cycle, the depth of the cross-sectional profile in the first cycle (μm) corresponds to "Depth of the cross-sectional profile developed in each cycle (μm)".

[0171] It should be noted that in this specification, the depth of the cross-sectional profile in the nth cycle refers to the depth of the deepest position of the cross-sectional profile in the nth cycle. n is an integer of 1 or more.

[0172] In Formula 1, the "spraying amount (g) of the test liquid for each cycle" is quantitatively determined in principle, but it may vary slightly in each cycle.

[0173] The spraying amount of the test liquid for each cycle is not particularly limited. The lower limit is preferably 0.5 g or more, more preferably 1.0 g or more, and the upper limit is preferably 3.0 g or less, more preferably 2.0 g or less.

[0174] Under the measurement conditions of the present invention, the erosion rate (μm / g) is calculated for each cycle up to a depth of 20 μm of the cross-sectional profile. Then, the erosion rates for each cycle up to a depth of 20 μm of the cross-sectional profile are averaged to calculate E 0-20 .

[0175] The above cycles are carried out until the depth of the cross-sectional profile exceeds 20 μm, and the data for the cycles with a cross-sectional profile depth exceeding 20 μm are excluded from the calculation of E 0-20 .

[0176] Generally, a plastic film is easily damaged when it is soft and not easily damaged when it is hard. The present inventors studied using values obtained from evaluations including the depth direction of the Martens hardness, indentation hardness, elastic recovery work, etc. by PICODENRTOR as an index of pencil hardness. However, the above parameters such as Martens hardness, indentation hardness, and elastic recovery work cannot be used as an index of pencil hardness.

[0177] In addition, a plastic film has a tendency to increase in strength when stretched. Specifically, compared with an unstretched plastic film, a uniaxially stretched plastic film has a tendency to have good pencil hardness, and compared with a uniaxially stretched plastic film, a biaxially stretched plastic film has a tendency to have good pencil hardness. However, even a biaxially stretched plastic film sometimes has insufficient pencil hardness.

[0178] As an index of the pencil hardness of a plastic film, the present inventors studied the erosion rate. As described above, a plastic film is easily damaged when it is soft and not easily damaged when it is hard, so it is considered that good pencil hardness can be achieved when the erosion rate is small. However, the present inventors found that, on the contrary, by making the erosion rate E 0-20 greater than 1.4 μm / g, the pencil hardness of the plastic film can be improved. In addition, the present inventors found that regarding the erosion rate of a plastic film, a biaxially stretched plastic film shows a larger value than a uniaxially stretched plastic film, and the quality of the pencil hardness in a biaxially stretched plastic film can be judged by the erosion rate.

[0179] It should be noted that, as described above, the molecular orientation of the resin constituting the plastic film also affects the pencil hardness of the plastic film. In addition, a plastic film has a tendency to have good mechanical strength such as pencil hardness when σ and 3σ are not too large.

[0180] The reason why the erosion rate of the plastic film is related to the pencil hardness can be considered as follows.

[0181] As described above, in the measurement conditions of the present invention, a test solution containing water and spherical silica is mixed with air and sprayed in a mist form. Therefore, the collision pressure of the spherical silica particles against the plastic film is suppressed to a relatively low level. Thus, it is considered that when the plastic film is soft, the stress at the time of collision between the spherical silica and the plastic film is easily dispersed, so the plastic film is not easily worn and the erosion rate is reduced. On the other hand, when the plastic film is hard, since the stress at the time of collision between the spherical silica and the plastic film is difficult to be dispersed, it is considered that the plastic film is easily worn and the erosion rate increases.

[0182] In addition, it is considered that the difference in the erosion rate in the biaxially stretched plastic film is caused by differences in the elongation of molecular chains, differences in the degree of molecular orientation, etc. For example, in principle, the molecules in the biaxially stretched plastic film are stretched in the plane, but there are also molecules that are not fully stretched locally in the plane. Thus, it is considered that if the proportion of molecules that are not fully stretched locally in the plane increases, the biaxially stretched plastic film becomes locally soft and the erosion rate decreases. In addition, it is considered that even for biaxially stretched plastic films with the same in-plane phase difference, different erosion rates will be shown due to different local molecular orientations.

[0183] Among 30 small samples, the proportion of small samples with E 0-20 of 1.4 μm / g or more is preferably 70% or more, more preferably 90% or more, and further preferably 100%.

[0184] In Condition 5, in order to further improve the pencil hardness, the E of the plastic film 0-20 is more preferably 1.6 μm / g or more, more preferably 1.8 μm / g or more, more preferably 1.9 μm / g or more, and more preferably 2.0 μm / g or more.

[0185] In order to make the plastic film not easily break, E 0-20 is preferably 3.0 μm / g or less, more preferably 2.5 μm / g or less, and further preferably 2.2 μm / g or less.

[0186] E 0-20Examples of preferred numerical ranges of implementation include, for example, 1.4 μm / g or more and 3.0 μm / g or less, 1.4 μm / g or more and 2.5 μm / g or less, 1.4 μm / g or more and 2.2 μm / g or less, 1.6 μm / g or more and 3.0 μm / g or less, 1.6 μm / g or more and 2.5 μm / g or less, 1.6 μm / g or more and 2.2 μm / g or less, 1.8 μm / g or more and 3.0 μm / g or less, 1.8 μm / g or more and 2.5 μm / g or less, 1.8 μm / g or more and 2.2 μm / g or less, 1.9 μm / g or more and 3.0 μm / g or less, 1.9 μm / g or more and 2.5 μm / g or less, 1.9 μm / g or more and 2.2 μm / g or less, 2.0 μm / g or more and 3.0 μm / g or less, 2.0 μm / g or more and 2.5 μm / g or less, 2.0 μm / g or more and 2.2 μm / g or less.

[0187] Before measuring the above erosion rate, the above correction is carried out.

[0188] For example, the correction can be carried out as follows.

[0189] <Correction>

[0190] The above test liquid is stored in the above container. The above test liquid in the above container is sent to the above nozzle. Compressed air is supplied into the above nozzle, the above test liquid is accelerated in the above nozzle, and an arbitrary amount of the above test liquid is vertically sprayed from the injection hole at the front end of the above nozzle onto an acrylic plate with a thickness of 2 mm, so that the spherical silica in the above test liquid collides with the above acrylic plate. The cross-sectional shape of the above nozzle is a square of 1 mm × 1 mm, and the distance between the above injection hole and the above acrylic plate is 4 mm.

[0191] After spraying an arbitrary amount of the above test liquid, the spraying of the above test liquid is temporarily stopped. After temporarily stopping the spraying of the above test liquid, the cross-sectional profile of the part of the above acrylic plate where the above spherical silica in the above test liquid collides is measured.

[0192] Calculate the erosion rate (μm / g) of the acrylic plate by dividing the depth (μm) of the cross-sectional profile by the above arbitrary amount (g).

[0193] The qualified condition for the erosion rate of the above acrylic plate is within the range of ±5% based on 1.88 (μm / g). In the manner that the erosion rate of the above acrylic plate is within the above range, the flow rates of the above test liquid and the above compressed air, the pressure of the above compressed air, and the pressure of the above test liquid in the above nozzle are adjusted and corrected.

[0194] The test liquid used in the correction is the same as the test liquid used in the measurement conditions implemented later.

[0195] In addition, the measuring device used in calibration is the same as the measuring device used in the measurement conditions implemented later.

[0196] The difference between the calibration and the measurement conditions implemented later is that, for example, an acrylic plate with a thickness of 2 mm is used as a standard specimen in the calibration, while a plastic film is used as a specimen in the measurement conditions.

[0197] The acrylic plate with a thickness of 2 mm as the standard specimen is preferably a polymethyl methacrylate plate. In addition, the acrylic plate with a thickness of 2 mm as the standard specimen is preferably such that when the average value of the erosion rate of the acrylic plate measured under the following measurement condition A is defined as AcE, AcE is 1.786 μm / g or more and 1.974 μm / g or less. In addition, as the spherical silica in the following measurement condition A, the model "MSE-BS-5-3" specified by Palmeso Co., Ltd. can be cited. As the spherical silica conforming to the model "MSE-BS-5-3" specified by Palmeso Co., Ltd., for example, the part number "BS5-3" of Potters-Ballotini Co., Ltd. can be cited.

[0198] <Measurement Condition A>

[0199] Pure water, a dispersant, and spherical silica with an average particle size within ±8% based on 4.2 μm are mixed in a mass ratio of 968:2:30, and the mixed test solution is stored in a container. The test solution in the above container is sent to a nozzle. Compressed air is supplied into the above nozzle to accelerate the test solution in the above nozzle, and a specified amount of the test solution is vertically sprayed from the injection hole at the front end of the above nozzle onto the above acrylic plate, so that the spherical silica in the test solution collides with the above acrylic. The cross-sectional shape of the above nozzle is a square of 1 mm × 1 mm, and the distance between the above injection hole and the above acrylic is 4 mm. In addition, for the flow rate of the test solution and the compressed air supplied to the above nozzle, the pressure of the compressed air, and the pressure of the test solution in the above nozzle, the flow rate of the test solution is 100 ml / min or more and 150 ml / min or less, the flow rate of the compressed air is 4.96 L / min or more and 7.44 L / min or less, the pressure of the compressed air is 0.184 MPa or more and 0.277 MPa or less, and the pressure of the test solution in the nozzle is 0.169 MPa or more and 0.254 MPa or less.

[0200] After spraying 4 g of the above test solution, the spraying of the above test solution is temporarily stopped.

[0201] After temporarily stopping the injection of the above test liquid, measure the cross-sectional profile of the part of the above acrylic plate that is hit by the above spherical silica in the above test liquid.

[0202] Then, calculate the erosion rate AcE of the acrylic plate by dividing the depth (μm) of the cross-sectional profile by the injection amount 4 g of the test liquid. The unit of AcE is "μm / g".

[0203] During calibration, the qualified condition for the erosion rate of the above acrylic plate is within the range of ±5% based on 1.88 (μm / g). In the manner that the erosion rate of the above acrylic plate is within the above range, perform the operation of adjusting the flow rates of the above test liquid and the above compressed air, the pressure of the above compressed air, and the pressure of the above test liquid in the above nozzle.

[0204] It should be noted that, in other words, "the erosion rate is within ±5% based on 1.88 (μm / g)" means that the erosion rate is 1.786 (μm / g) or more and 1.974 (μm / g) or less.

[0205] <Condition 6>

[0206] For the above 30 small samples, measure the erosion rate from the surface to a depth of 20 μm of the plastic film constituting the small sample at the center of the above 30 mm × 40 mm area. Define the deviation of the erosion rate calculated from the erosion rate of the plastic film constituting the small sample from the surface to a depth of 20 μm as σ 0-20 When, among the above 30 small samples, σ 0-20 / E 0-20 is 0.100 or less, the proportion of small samples is 50% or more.

[0207] In this specification, σ 0-20 can be calculated from the erosion rate of each cycle from the depth of the cross-sectional profile to 20 μm under the above measurement conditions.

[0208] σ 0-20 / E 0-20 represents the coefficient of variation of the erosion rate. σ 0-20 / E 0-20 being small means that the erosion rate is not likely to vary in the thickness direction of the plastic film. By making σ 0-20 / E 0-20 be 0.100 or less, the erosion rate in the thickness direction is stable, and it is possible to easily further improve the pencil hardness.

[0209] In addition, by making σ 0-20 / E 0-20is 0.100 or less, and can make the film quality in the thickness direction of the plastic film homogeneous. The film quality homogeneity in the thickness direction of the plastic film is related to the homogeneity of the film quality of the plastic film itself. When the film quality homogeneity in the thickness direction of the plastic film is low, it may be difficult to stably form a functional layer on the plastic film. Therefore, by satisfying Condition 6, it is possible to easily improve the quality of the optical laminate having a functional layer on the plastic film.

[0210] Among 30 small samples, the proportion of small samples in which σ 0-20 / E 0-20 is 0.100 or less is preferably 70% or more, more preferably 90% or more, and further preferably 100%.

[0211] In Condition 6, the upper limit of σ 0-20 / E 0-20 is more preferably 0.080 or less, further preferably 0.070 or less, further preferably 0.060 or less, and further preferably 0.055 or less.

[0212] σ 0-20 / E 0-20 The smaller the value of, the more homogeneous the film quality in the thickness direction of the plastic film means. When the film quality in the thickness direction of the plastic film is homogeneous, there is a tendency for stress to easily propagate in the thickness direction. Therefore, σ 0-20 / E 0-20 is preferably 0.020 or more, more preferably 0.035 or more.

[0213] σ 0-20 / E 0-20 Examples of the preferred numerical range of can be cited as 0.020 or more and 0.100 or less, 0.020 or more and 0.080 or less, 0.020 or more and 0.070 or less, 0.020 or more and 0.060 or less, 0.020 or more and 0.055 or less, 0.035 or more and 0.100 or less, 0.035 or more and 0.080 or less, 0.035 or more and 0.070 or less, 0.035 or more and 0.060 or less, 0.035 or more and 0.055 or less.

[0214] In order to make the erosion rate of the plastic film within the above range, it is preferable to stretch the molecules evenly in the plane of the plastic film.

[0215] The plastic film can be manufactured, for example, by general sequential biaxial stretching. In the stretching in the flow direction of sequential biaxial stretching, if the stretching time is shortened, the erosion rate tends to decrease, and if the stretching time is prolonged, the erosion rate tends to increase. The reason is considered that if the stretching time is short, the molecules in the plane of the plastic film are difficult to be evenly elongated, and if the stretching time is long, the molecules in the plane of the plastic film are easy to be evenly elongated. That is, in order to make E 0-20is 1.4 μm / g or more, and it is preferable to extend the stretching time. Further, by increasing the stretching ratio appropriately to the extent of physical property imbalance while extending the stretching time, it is possible to more easily make E 0-20 is 1.4 μm / g or more.

[0216] <Relationship between the width direction of the plastic film and the slow axis>

[0217] The plastic film for optical use preferably has high orientation in the entire width direction. The state where the plastic film has high orientation in the entire width direction means that in a 1000-mm-wide plastic film, the vibration amplitude of the slow axis in the entire width direction is 24.0 degrees or less. The vibration amplitude is half of the difference between the minimum value and the maximum value of the angle of the slow axis in the entire width direction.

[0218] For general biaxially stretched plastic films for optical use such as PET with a thickness of 15 μm or more and 100 μm or less, due to the bowing phenomenon, the vibration amplitude of the slow axis in the entire width direction of the plastic film increases. Specifically, the vibration amplitude of the slow axis in the entire width direction of a general 1000-mm-wide biaxially stretched plastic film for optical use approaches 30.0 degrees. (Condition 2 of the plastic film for optical use of the present invention specifies the deviation of the slow axis in a small area of 30 mm × 40 mm. On the other hand, the vibration amplitude of the slow axis in the entire width direction of the above plastic film specifies the vibration amplitude of the slow axis in a large area, which is different in this regard.)

[0219] By making the vibration amplitude of the slow axis in the entire width direction of the plastic film 24.0 degrees or less, it is possible to easily suppress the deviation of physical properties such as pencil hardness in the width direction of the plastic film. The above vibration amplitude is more preferably 20.0 degrees or less, and further preferably 17.0 degrees or less.

[0220] It should be noted that if the above vibration amplitude is too small, the plastic film may not be sufficiently biaxially stretched. Therefore, the above vibration amplitude is preferably 4.0 degrees or more, more preferably 6.0 degrees or more, and further preferably 8.0 degrees or more.

[0221] The slope of the slow axis of the plastic film for optical use with respect to the width direction or the flow direction is preferably 24.0 degrees or less, more preferably 20.0 degrees or less. When cutting out a quadrilateral plastic film from a large plastic film, it is mostly cut out along the width direction and the flow direction of the large plastic film. The smaller the slope of the slow axis of the plastic film with respect to the width direction, the smaller the difference between the width direction of the cut-out plastic film and the slow axis direction of the plastic film. Therefore, it is possible to easily and stably apply the optical characteristics when the plastic film for optical use is applied to an image display device. It should be noted that, in order to easily suppress blackening of the screen, a technique of increasing the slope of the slow axis of the plastic film with respect to the width direction has also been studied. However, the plastic film for optical use of the present invention can suppress blackening of the screen by satisfying condition 2, so there is no need to increase the slope of the slow axis of the plastic film with respect to the width direction.

[0222] The slow axis of the plastic film can be measured as the "orientation angle (degrees)", for example, in the product named "RETS-100" manufactured by Otsuka Electronics Co., Ltd.

[0223] <Plastic film>

[0224] The laminated structure of the plastic film may include a single-layer structure and a multi-layer structure. Among them, a single-layer structure is preferred.

[0225] In order to suppress iridescence while improving mechanical strength, the plastic film is preferably a stretched plastic film with a small in-plane retardation. And, in order to reduce the in-plane retardation of the stretched plastic film, it is important to perform fine stretching control such that the stretching in the flow direction and the width direction is equally close. In a single-layer structure, the physical properties in the thickness direction are substantially uniform, and it is easier to perform fine stretching control compared to a multi-layer structure, and thus it is preferred from this aspect.

[0226] Examples of the resin component constituting the plastic film include polyester, triacetyl cellulose (TAC), diacetyl cellulose, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, polymethyl methacrylate, polycarbonate, polyurethane, and amorphous olefin (Cyclo-Olefin-Polymer (COP)). Among these, polyester is preferred from the aspect of easily improving mechanical strength and pencil hardness. That is, the plastic film for optical use is preferably a polyester film.

[0227] As described above, the polyester film can easily improve the pencil hardness and the like, and thus can be suitably used as a surface material of an image display device.

[0228] On the other hand, most polycarbonate films and amorphous olefin films have a pencil hardness of B or lower on their own. Therefore, in order to improve the pencil hardness of polycarbonate films and amorphous olefin films, efforts are needed to increase the film thickness, provide a very thick functional layer, or further cover with a sputtered film, etc. In this way, polycarbonate films and amorphous olefin films have drawbacks such as thickening when the pencil hardness is increased, and thus it is difficult to be used as the surface material of an image display device.

[0229] The following research was also conducted: As the resin constituting the plastic film, by using resins such as triacetyl cellulose, cycloolefin resins, and polymethyl methacrylate that are easy to impart optical isotropy, even when the plastic film is stretched, the in-plane retardation can be made infinitesimal. However, the stretched plastic films using triacetyl cellulose, cycloolefin resins, and polymethyl methacrylate are difficult to control the manufacturing conditions, and thus tend to have difficulty in adjusting optical properties such as the deviation range of the in-plane retardation and the slow axis to the preferred range of the optical properties of the plastic film for optics of the present invention.

[0230] Examples of the polyester constituting the polyester film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT). Among these, PET is preferred from the aspect of low intrinsic birefringence and easy reduction of the in-plane retardation.

[0231] The plastic film may also contain additives such as ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, anti-gelation agents, and surfactants.

[0232] In order to improve the mechanical strength, the thickness of the plastic film is preferably 10 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, and still more preferably 30 μm or more.

[0233] In order to easily satisfy Condition 1 and to improve the bending resistance, the thickness of the plastic film is preferably 75 μm or less, more preferably 60 μm or less, further preferably 55 μm or less, and still more preferably 50 μm or less.

[0234] Examples of the implementation modes of the thickness range of the plastic film include 10 μm or more and 75 μm or less, 10 μm or more and 60 μm or less, 10 μm or more and 55 μm or less, 10 μm or more and 50 μm or less, 20 μm or more and 75 μm or less, 20 μm or more and 60 μm or less, 20 μm or more and 55 μm or less, 20 μm or more and 50 μm or less, 25 μm or more and 75 μm or less, 25 μm or more and 60 μm or less, 25 μm or more and 55 μm or less, 25 μm or more and 50 μm or less, 30 μm or more and 75 μm or less, 30 μm or more and 60 μm or less, 30 μm or more and 55 μm or less, 30 μm or more and 50 μm or less.

[0235] The haze of the plastic film for optical use according to JIS K7136:2000 is preferably 3.0% or less, more preferably 2.0% or less, and further preferably 1.0% or less.

[0236] The total light transmittance of the plastic film for optical use according to JIS K7361-1:1997 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more.

[0237] In order to improve the mechanical strength and pencil hardness, the plastic film is preferably a stretched plastic film, more preferably a stretched polyester film. In addition, the stretched polyester film is more preferably a single-layer structure of a polyester resin layer.

[0238] The stretched plastic film can be obtained by stretching a resin layer containing the components constituting the plastic film. Examples of the stretching method include biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching, and uniaxial stretching such as longitudinal uniaxial stretching. Among these, biaxial stretching, which is easy to reduce the in-plane retardation and easy to improve the mechanical strength and pencil hardness, is preferred. That is, the stretched plastic film is preferably a biaxially stretched plastic film. Among the biaxially stretched plastic films, biaxially stretched polyester films are preferred, and biaxially stretched polyethylene terephthalate films are more preferred.

[0239] -Sequential biaxial stretching-

[0240] In sequential biaxial stretching, after the cast film is stretched in the flow direction, it is stretched in the width direction of the film.

[0241] The stretching in the flow direction is usually carried out using the circumferential speed difference of stretching rolls, and it can be carried out in one stage or in multiple stages using multiple pairs of stretching rolls. In order to suppress excessive deviation of optical properties such as in-plane retardation, it is preferred to make multiple pinch rolls close to the stretching rolls. The stretching ratio in the flow direction is usually 2 times or more and 15 times or less. In order to suppress excessive deviation of optical properties such as in-plane retardation, it is preferably 2 times or more and 7 times or less, more preferably 3 times or more and 5 times or less, and further preferably 3 times or more and 4 times or less.

[0242] In order to suppress excessive deviation of optical properties such as in-plane retardation, the stretching temperature is preferably above the glass transition temperature of the resin and below the glass transition temperature + 100°C. In the case of PET, it is preferably 70°C or more and 120°C or less, more preferably 80°C or more and 110°C or less, and further preferably 95°C or more and 110°C or less. By quickly raising the temperature of the film, etc., and shortening the stretching interval at low temperature, the average value of the in-plane retardation tends to become smaller.

[0243] During heating during stretching or cooling after stretching, it is preferable to blow wind containing turbulence onto the film. By blowing wind containing turbulence, a temperature difference is generated in a minute area within the film surface, and as a result, due to the above temperature difference, it becomes easy for a minute deviation of the orientation axis to occur, and thus it becomes possible to easily satisfy Condition 2.

[0244] Functions such as slipperiness, adhesiveness, antistatic property, etc. can be imparted to the film stretched in the flow direction by on-line coating. In addition, before on-line coating, surface treatments such as corona treatment, flame treatment, plasma treatment, etc. can be carried out as needed.

[0245] The thickness of the coating film formed in this way during on-line coating is extremely thin, about 10 nm or more and 2000 nm or less. The above coating film is stretched thinner by stretching treatment. In this specification, such a thin layer is not counted as the number of layers constituting the plastic film.

[0246] Regarding stretching in the width direction, generally, the tenter frame method is used, and while holding both ends of the film with jigs and conveying it, stretching is carried out in the width direction. The stretching ratio in the width direction is usually 2 times or more and 15 times or less. In order to suppress excessive deviation of optical properties such as in-plane retardation, the stretching ratio in the width direction is preferably 2 times or more and 5 times or less, more preferably 3 times or more and 5 times or less, and further preferably 3 times or more and 4.5 times or less. In addition, compared with the longitudinal stretching ratio, it is more preferable to increase the width stretching ratio.

[0247] The stretching temperature is preferably above the glass transition temperature of the resin and below the glass transition temperature + 120°C, and the temperature is preferably increased from the upstream to the downstream. Specifically, in the case where the stretching section in the width direction is divided into two parts, the temperature difference between the upstream temperature and the downstream temperature is preferably 20°C or more, more preferably 30°C or more, further preferably 35°C or more, and still further preferably 40°C or more. In the case of PET, the stretching temperature in the first stage is preferably 80°C or more and 120°C or less, more preferably 90°C or more and 110°C or less, and further preferably 95°C or more and 105°C or less.

[0248] For the plastic film that has been subjected to stepwise biaxial stretching as described above, in order to impart planarity and dimensional stability, it is preferable to perform heat treatment at a temperature above the stretching temperature and less than the melting point in a tenter frame. Specifically, in the case of PET, it is preferably heat-fixed in the range of 150°C or more and 255°C or less, and more preferably 200°C or more and 250°C or less. In addition, in order to suppress excessive deviation of optical properties such as in-plane retardation, it is preferable to perform additional stretching of 1% or more and 10% or less in the first half stage of the heat treatment.

[0249] Before the above heat treatment after the stepwise biaxial stretching, it is preferable to cool the plastic film with air containing turbulence. Through the above cooling process, a temperature difference is generated in a minute area within the film surface, and thus, due to the above temperature difference, it is easy to cause a minute deviation of the orientation axis, and therefore it is possible to easily satisfy Condition 2.

[0250] After the heat treatment of the plastic film, it is slowly cooled to room temperature and then wound up. Additionally, if necessary, relaxation treatment or the like can be applied during the heat treatment or slow cooling. In order to suppress excessive deviation of optical properties such as in-plane retardation, the relaxation rate during the heat treatment is preferably 0.5% or more and 5% or less, more preferably 0.5% or more and 3% or less, further preferably 0.8% or more and 2.5% or less, and still further preferably 1% or more and 2% or less. Also, in order to suppress excessive deviation of optical properties such as in-plane retardation, the relaxation rate during slow cooling is preferably 0.5% or more and 3% or less, more preferably 0.5% or more and 2% or less, further preferably 0.5% or more and 1.5% or less, and still further preferably 0.5% or more and 1.0% or less. In order to improve planarity, the temperature during slow cooling is preferably 80°C or more and 150°C or less, more preferably 90°C or more and 130°C or less, further preferably 100°C or more and 130°C or less, and still further preferably 100°C or more and 120°C or less.

[0251] -Simultaneous biaxial stretching-

[0252] In simultaneous biaxial stretching, the cast film is introduced into a simultaneous double-screw tenter, and while holding both ends of the film with clamps, it is conveyed, and stretching is performed synchronously and / or stepwise in the flow direction and the width direction. As the simultaneous biaxial stretching machine, there are the pantograph method, the screw method, the drive motor method, and the linear motor method, but the drive motor method or the linear motor method that can arbitrarily change the stretching ratio and can perform relaxation treatment at an arbitrary location is preferred.

[0253] The stretching ratio in simultaneous biaxial stretching is usually 6 times or more and 50 times or less in terms of the area ratio. In order to suppress excessive deviation of optical properties such as in-plane retardation, it is preferably 8 times or more and 30 times or less, more preferably 9 times or more and 25 times or less, further preferably 9 times or more and 20 times or less, and still further preferably 10 times or more and 15 times or less.

[0254] In addition, in the case of simultaneous biaxial stretching, in order to suppress the in-plane orientation difference, it is preferable that the stretching ratios in the flow direction and the width direction are the same and the stretching speeds are also substantially equal.

[0255] In order to suppress excessive deviation of optical properties such as in-plane phase difference, the stretching temperature in synchronous biaxial stretching is preferably above the glass transition temperature of the resin and below the glass transition temperature + 120°C. In the case of PET, it is preferably 80°C or higher and 160°C or lower, more preferably 90°C or higher and 150°C or lower, and still more preferably 100°C or higher and 140°C or lower.

[0256] For the film subjected to synchronous biaxial stretching, in order to impart planarity and dimensional stability, it is preferable to continue heat treatment at a temperature above the stretching temperature and less than the melting point in the heat setting chamber in the tenter. The conditions of the above heat treatment are the same as those after stepwise biaxial stretching.

[0257] <Dimensions>

[0258] The plastic film for optics can be in the form of a single leaf cut into a specified size, or in the form of a roll obtained by winding a long sheet. The size of the single leaf is not particularly limited, and the maximum diameter is about 14.2 inches or more and 500 inches or less. The "maximum diameter" refers to the maximum length when connecting any two points of the plastic film for optics. For example, when the plastic film for optics is rectangular, the diagonal of the rectangle is the maximum diameter. When the plastic film for optics is circular, the diameter of the circle is the maximum diameter.

[0259] The width and length of the roll are not particularly limited. Generally, the width is 300 mm or more and 9000 mm or less, and the length is 100 m or more and 5000 m or less. The plastic film for optics in the form of a roll can be cut into single leaves for use according to the size of an image display device or the like. When cutting, it is preferable to exclude the roll ends where the physical properties are unstable.

[0260] The shape of the single leaf is not particularly limited either. For example, it can be a polygon such as a triangle, quadrilateral, pentagon, etc., it can be circular, or it can be a random amorphous shape.

[0261] <Applications>

[0262] The plastic film for optics of the present invention can be suitably used as the plastic film of an image display device.

[0263] In addition, as described above, the plastic film of the present invention can suppress the residual bending marks or breakage after the bending test regardless of the bending direction, and thus can be more suitably used as the plastic film for a foldable image display device, a rollable image display device, or an image display device having a curved surface shape.

[0264] In addition, the plastic film for optics of the present invention can be suitably used as the plastic film disposed on the light exit surface side of the display element of an image display device. At this time, it is preferable to have a polarization element between the display element and the plastic film for optics of the present invention.

[0265] As a plastic film for an image display device, a plastic film can be cited as a base material for various functional films such as a protective film for a polarization element, a surface protective film, an antireflection film, and a conductive film constituting a touch panel.

[0266] [Optical laminate]

[0267] The optical laminate of the present invention has a functional layer on the above-mentioned plastic film for optical use of the present invention.

[0268] As the functional layer, one or more selected from a hard coat layer, an antireflection layer, an antiglare layer, a retardation layer, an adhesive layer, a transparent conductive layer, an antistatic layer, and an antifouling layer can be cited. Among the above functional layers, a retardation layer represented by a liquid crystal layer has a tendency of weak physical properties such as pencil hardness and insufficient light resistance. Therefore, when the optical laminate has a retardation layer, in an image display device, it is preferable to arrange the retardation layer side of the optical laminate toward the display element side based on the plastic film.

[0269] The functional layer of the optical laminate preferably includes an antireflection layer. The antireflection layer is preferably disposed on the outermost surface of the side of the plastic film having the functional layer.

[0270] By having an antireflection layer as the functional layer of the optical laminate, iridescence can be further suppressed.

[0271] The plastic film for optical use constituting the optical laminate of the present invention can easily improve the pencil hardness by satisfying the above-mentioned specified preferred conditions. Therefore, the optical laminate of the present invention can also easily improve the pencil hardness. Thus, the optical laminate of the present invention can be suitably used as a surface material for an image display device. It should be noted that when the optical laminate of the present invention is used as a surface material for an image display device, it does not have a retardation layer as the functional layer on the observation side.

[0272] The functional layer more preferably includes a hard coat layer and an antireflection layer. When the functional layer includes a hard coat layer and an antireflection layer, it is preferable to sequentially arrange a hard coat layer 41 and an antireflection layer 42 on the plastic film 10( Figure 3 ). When the functional layer includes a hard coat layer and an antireflection layer, the suitability as a surface material for an image display device can be improved.

[0273] Examples of the antireflection layer include: a single-layer structure of a low refractive index layer; a two-layer structure of a high refractive index layer and a low refractive index layer; a multilayer structure of three or more layers;

[0274] The low refractive index layer is preferably disposed on the outermost surface of the side of the plastic film having the functional layer.

[0275] The lower limit of the refractive index of the low refractive index layer is preferably 1.10 or more, more preferably 1.20 or more, still more preferably 1.26 or more, still more preferably 1.28 or more, still more preferably 1.30 or more, and the upper limit is preferably 1.48 or less, more preferably 1.45 or less, still more preferably 1.40 or less, still more preferably 1.38 or less, still more preferably 1.32 or less.

[0276] As embodiments of the range of the refractive index of the low refractive index layer, 1.10 or more and 1.48 or less, 1.10 or more and 1.45 or less, 1.10 or more and 1.40 or less, 1.10 or more and 1.38 or less, 1.10 or more and 1.32 or less, 1.20 or more and 1.48 or less, 1.20 or more and 1.45 or less, 1.20 or more and 1.40 or less, 1.20 or more and 1.38 or less, 1.20 or more and 1.32 or less, 1.26 or more and 1.48 or less, 1.26 or more and 1.45 or less, 1.26 or more and 1.40 or less, 1.26 or more and 1.38 or less, 1.26 or more and 1.32 or less, 1.28 or more and 1.48 or less, 1.28 or more and 1.45 or less, 1.28 or more and 1.40 or less, 1.28 or more and 1.38 or less, 1.28 or more and 1.32 or less, 1.30 or more and 1.48 or less, 1.30 or more and 1.45 or less, 1.30 or more and 1.40 or less, 1.30 or more and 1.38 or less, 1.30 or more and 1.32 or less can be cited.

[0277] In this specification, the refractive index of the layer constituting the antireflection layer such as the low refractive index layer and the high refractive index layer refers to the value at a wavelength of 589.3 nm.

[0278] The lower limit of the thickness of the low refractive index layer is preferably 80 nm or more, more preferably 85 nm or more, still more preferably 90 nm or more, and the upper limit is preferably 150 nm or less, more preferably 110 nm or less, still more preferably 105 nm or less.

[0279] As embodiments of the range of the thickness of the low refractive index layer, 80 nm or more and 150 nm or less, 80 nm or more and 110 nm or less, 80 nm or more and 105 nm or less, 85 nm or more and 150 nm or less, 85 nm or more and 110 nm or less, 85 nm or more and 105 nm or less, 90 nm or more and 150 nm or less, 90 nm or more and 110 nm or less, 90 nm or more and 105 nm or less can be cited.

[0280] As a method for forming a low refractive index layer, it can be roughly classified into a wet method and a dry method. As the wet method, examples include: a method of forming by a sol-gel method using a metal alkoxide or the like; a method of forming by coating a low refractive index resin such as a fluororesin; a method of forming by coating a coating liquid for forming a low refractive index layer containing low refractive index particles in a resin composition. As the dry method, examples include a method of forming a low refractive index layer by physical vapor deposition or chemical vapor deposition. As materials, examples include SiO2, SiO x (x is 1 or more and 2 or less), MgF2, etc.

[0281] From the viewpoints of production efficiency, suppression of oblique reflection color tone, and chemical resistance, the wet method is superior to the dry method. In the present embodiment, among the wet methods, from the viewpoints of adhesion, water resistance, abrasion resistance, and reduction of refractive index, it is preferably formed by a coating liquid for forming a low refractive index layer containing low refractive index particles in a binder resin composition. In other words, the low refractive index layer preferably contains a binder resin and low refractive index particles.

[0282] The binder resin of the low refractive index layer preferably contains a cured product of a curable resin composition. The proportion of the cured product of the curable resin composition is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and most preferably 100% with respect to all the binder resins of the low refractive index layer.

[0283] As the curable resin composition of the low refractive index layer, a thermosetting resin composition or a radiation curable resin composition can be cited. Curable resin compositions such as thermosetting resin compositions or radiation curable resin compositions can use general compositions.

[0284] The low refractive index particles preferably contain one or more selected from hollow particles and non-hollow particles. In order to balance low reflection and abrasion resistance, it is preferable to use one or more selected from hollow particles in combination with one or more selected from non-hollow particles.

[0285] The materials of the hollow particles and the non-hollow particles can be any of inorganic compounds such as silica and magnesium fluoride and organic compounds. For reasons of reduction of refractive index and strength, silica is preferred. That is, the low refractive index layer preferably contains hollow silica particles and non-hollow silica particles as the low refractive index particles.

[0286] When considering optical properties and mechanical strength, the lower limit of the average particle size of the hollow particles is preferably 50 nm or more, more preferably 60 nm or more, and the upper limit is preferably 100 nm or less, more preferably 80 nm or less. As embodiments of the range of the average particle size of the hollow particles, 50 nm or more and 100 nm or less, 50 nm or more and 80 nm or less, 60 nm or more and 100 nm or less, and 60 nm or more and 80 nm or less can be cited.

[0287] When considering dispersibility while preventing aggregation of non-hollow particles, the lower limit of the average particle size of the non-hollow particles is preferably 5 nm or more, more preferably 10 nm or more, and the upper limit is preferably 20 nm or less, more preferably 15 nm or less. As embodiments of the range of the average particle size of the non-hollow particles, 5 nm or more and 20 nm or less, 5 nm or more and 15 nm or less, 10 nm or more and 20 nm or less, and 10 nm or more and 15 nm or less can be cited.

[0288] The more the content of the hollow particles, the higher the filling rate of the hollow particles in the binder resin and the lower the refractive index of the low refractive index layer. Therefore, the content of the hollow particles is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, relative to 100 parts by mass of the binder resin.

[0289] On the other hand, if the content of the hollow particles relative to the binder resin is too large, the hollow particles exposed from the binder resin increase, and the binder resin between the combined particles becomes less, resulting in a tendency for the mechanical strength such as scratch resistance of the low refractive index layer to decrease. Therefore, the content of the hollow particles is preferably 400 parts by mass or less, more preferably 300 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0290] As embodiments of the range of the content of the hollow particles relative to 100 parts by mass of the binder resin, 100 parts by mass or more and 400 parts by mass or less, 100 parts by mass or more and 300 parts by mass or less, 150 parts by mass or more and 400 parts by mass or less, and 150 parts by mass or more and 300 parts by mass or less can be cited.

[0291] When the content of the non-hollow particles is small, even if non-hollow particles are present on the surface of the low refractive index layer, it sometimes has no effect on the increase in hardness. On the other hand, when the content of the non-hollow particles is large, the influence of uneven shrinkage caused by the polymerization of the binder resin becomes smaller, and thus the unevenness generated on the surface of the low refractive index layer after resin curing becomes smaller, so that the scratch resistance can be more easily improved. Therefore, the content of the non-hollow particles is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or more, more preferably 100 parts by mass or more, relative to 100 parts by mass of the binder resin.

[0292] On the other hand, when the content of non-hollow particles is excessive, since non-hollow particles tend to aggregate and cause uneven shrinkage of the binder resin, the surface unevenness becomes large. Therefore, the content of non-hollow particles is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0293] As embodiments of the range of the content of non-hollow particles relative to 100 parts by mass of the binder resin, examples include 10 parts by mass or more and 200 parts by mass or less, 10 parts by mass or more and 150 parts by mass or less, 50 parts by mass or more and 200 parts by mass or less, 50 parts by mass or more and 150 parts by mass or less, 70 parts by mass or more and 200 parts by mass or less, 70 parts by mass or more and 150 parts by mass or less, 100 parts by mass or more and 200 parts by mass or less, 100 parts by mass or more and 150 parts by mass or less.

[0294] The high refractive index layer is preferably disposed closer to the plastic film side than the lower refractive index layer. In the case of having a hard coat described later, the high refractive index layer is preferably formed between the hard coat and the low refractive index layer.

[0295] The lower limit of the refractive index of the high refractive index layer is preferably 1.53 or more, more preferably 1.54 or more, still more preferably 1.55 or more, still more preferably 1.56 or more, and the upper limit is preferably 1.85 or less, more preferably 1.80 or less, still more preferably 1.75 or less, still more preferably 1.70 or less.

[0296] As embodiments of the range of the refractive index of the high refractive index layer, examples include 1.53 or more and 1.85 or less, 1.53 or more and 1.80 or less, 1.53 or more and 1.75 or less, 1.53 or more and 1.70 or less, 1.54 or more and 1.85 or less, 1.54 or more and 1.80 or less, 1.54 or more and 1.75 or less, 1.54 or more and 1.70 or less, 1.55 or more and 1.85 or less, 1.55 or more and 1.80 or less, 1.55 or more and 1.75 or less, 1.55 or more and 1.70 or less, 1.56 or more and 1.85 or less, 1.56 or more and 1.80 or less, 1.56 or more and 1.75 or less, 1.56 or more and 1.70 or less.

[0297] The upper limit of the thickness of the high refractive index layer is preferably 200 nm or less, more preferably 180 nm or less, still more preferably 150 nm or less, and the lower limit is preferably 50 nm or more, more preferably 70 nm or more.

[0298] As an embodiment of the range of the thickness of the high refractive index layer, examples include 200 nm or less, 50 nm or more and 200 nm or less, 50 nm or more and 180 nm or less, 50 nm or more and 150 nm or less, 70 nm or more and 200 nm or less, 70 nm or more and 180 nm or less, 70 nm or more and 150 nm or less.

[0299] When forming the high refractive index hard coat, it is preferably based on the thickness of the hard coat.

[0300] The high refractive index layer can be formed, for example, from a coating liquid for forming a high refractive index layer containing a binder resin composition and high refractive index particles. That is, the high refractive index layer preferably contains a binder resin and high refractive index particles.

[0301] The binder resin of the high refractive index layer preferably contains a cured product of a curable resin composition. The proportion of the cured product of the curable resin composition is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and most preferably 100% with respect to all the binder resins of the high refractive index layer.

[0302] As the curable resin composition of the high refractive index layer, a thermosetting resin composition or a radiation curable resin composition can be cited. Curable resin compositions such as thermosetting resin compositions or radiation curable resin compositions can use general compositions.

[0303] Examples of the high refractive index particles include antimony pentoxide (refractive index: about 1.79), zinc oxide (refractive index: about 1.90), titanium oxide (refractive index: about 2.3 or more and 2.7 or less), cerium oxide (refractive index: about 1.95), indium tin oxide doped with tin (refractive index: about 1.95 or more and 2.00 or less), antimony doped tin oxide (refractive index: about 1.75 or more and 1.85 or less), yttrium oxide (refractive index: about 1.87), and zirconium oxide (refractive index: about 2.10).

[0304] The average particle size of the high refractive index particles is preferably 2 nm or more, more preferably 5 nm or more, and further preferably 10 nm or more. In addition, for the reasons of suppressing whitening and transparency, the average particle size of the high refractive index particles is preferably 200 nm or less, more preferably 100 nm or less, still more preferably 80 nm or less, still more preferably 60 nm or less, and still more preferably 30 nm or less.

[0305] As an embodiment of the range of the average particle diameter of the high refractive index particles, examples include 2 nm or more and 200 nm or less, 2 nm or more and 100 nm or less, 2 nm or more and 80 nm or less, 2 nm or more and 60 nm or less, 2 nm or more and 30 nm or less, 5 nm or more and 200 nm or less, 5 nm or more and 100 nm or less, 5 nm or more and 80 nm or less, 5 nm or more and 60 nm or less, 5 nm or more and 30 nm or less, 10 nm or more and 200 nm or less, 10 nm or more and 100 nm or less, 10 nm or more and 80 nm or less, 10 nm or more and 60 nm or less, 10 nm or more and 30 nm or less.

[0306] The average particle diameter of the high refractive index particles or the low refractive index particles can be calculated by the following operations (y1) to (y3).

[0307] (y1) Take a cross-section of the high refractive index layer or the low refractive index layer using STEM. The acceleration voltage of the STEM is preferably 10 kV or more and 30 kV or less, and the magnification is preferably 50,000 times or more and 300,000 times or less. As a commercially available product of STEM, "Part number: S-4800" of the field emission type scanning electron microscope of Hitachi High-Technologies Corporation can be cited.

[0308] (y2) After extracting any 10 particles from the observation image, calculate the particle diameter of each particle. The particle diameter is measured as the distance between the two straight lines in the combination of the two straight lines that reach the maximum when the cross-section of the particle is clamped by any two parallel straight lines. In the case of particle aggregation, the aggregated particles are regarded as one particle for measurement.

[0309] (y3) Perform the same operation 5 times on the observation image of another frame of the same sample, and use the value obtained from the arithmetic mean of the 50 particle diameters as the average particle diameter of the high refractive index particles or the low refractive index particles.

[0310] The hard coat preferably contains a cured product of a curable resin composition such as a thermosetting resin composition or a radiation-curable resin composition as a main component. As the thermosetting resin composition or the radiation-curable resin composition and other curable resin compositions, general compositions can be used.

[0311] The main component means 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more of the resin component constituting the hard coat.

[0312] The lower limit of the thickness of the hard coat is preferably 0.5 μm or more, more preferably 1 μm or more, and the upper limit is preferably 30 μm or less, more preferably 10 μm or less.

[0313] As an embodiment of the range of the thickness of the hard coat, examples include 0.5 μm or more and 30 μm or less, 0.5 μm or more and 10 μm or less, 1 μm or more and 30 μm or less, and 1 μm or more and 10 μm or less.

[0314] <Size>

[0315] The optical laminate may be in the form of a single sheet cut to a specified size or in a roll form in which a long sheet is wound into a roll. The size of the single sheet is not particularly limited, and the maximum diameter is about 14.2 inches or more and 500 inches or less. The "maximum diameter" refers to the maximum length when connecting any two points of the optical laminate. For example, when the optical laminate is rectangular, the diagonal of the rectangle is the maximum diameter. When the optical laminate is circular, the diameter of the circle is the maximum diameter.

[0316] The width and length of the roll form are not particularly limited. Generally, the width is 300 mm or more and 9000 mm or less, and the length is 100 m or more and 5000 m or less. The optical laminate in roll form can be cut into single sheets for use according to the size of an image display device or the like. When cutting, it is preferably except for the roll ends with unstable physical properties.

[0317] The shape of the single sheet is not particularly limited either. For example, it can be a polygon such as a triangle, quadrilateral, pentagon, etc., it can be circular, or it can be a random amorphous shape.

[0318] [Polarizer]

[0319] The polarizer of the present invention is a polarizer having a polarizing element, a first transparent protective plate disposed on one side of the polarizing element, and a second transparent protective plate disposed on the other side of the polarizing element, wherein at least one of the first transparent protective plate and the second transparent protective plate contains the optical plastic film of the present invention.

[0320] The polarizer is used, for example, to impart antireflectivity by combining the polarizer with a λ / 4 retardation plate. In this case, the λ / 4 retardation plate is disposed on the display element of the image display device, and the polarizer is disposed on the side closer to the observer than the λ / 4 retardation plate.

[0321] When the polarizer is used for a liquid crystal display device, the polarizer is used to impart the function of a liquid crystal light valve. In this case, the liquid crystal display device is configured in the order of the lower polarizer, the liquid crystal display element, and the upper polarizer, and the absorption axes of the polarizing elements of the lower polarizer and the upper polarizer are arranged orthogonally. In the above configuration, it is preferable to use the polarizer of the present invention as the upper polarizer.

[0322] <Transparent protective plate>

[0323] The polarizing plate of the present invention includes the above-mentioned plastic film for optical use of the present invention as at least one of the first transparent protective plate and the second transparent protective plate. In a preferred embodiment, both the first transparent protective plate and the second transparent protective plate include the above-mentioned plastic film for optical use of the present invention.

[0324] When one of the first transparent protective plate and the second transparent protective plate includes the above-mentioned plastic film for optical use of the present invention, the other transparent protective plate is not particularly limited, and an optically isotropic transparent protective plate is preferred.

[0325] In this specification, optical isotropy means that the in-plane retardation is 20 nm or less, preferably 10 nm or less, more preferably 5 nm or less. An acrylic film or a triacetyl cellulose (TAC) film is likely to impart optical isotropy.

[0326] When one of the first transparent protective plate and the second transparent protective plate includes the above-mentioned plastic film for optical use of the present invention, it is preferred that the transparent protective plate on the light-emitting side includes the above-mentioned plastic film for optical use of the present invention.

[0327] The polarizing plate of the present invention also preferably uses the above-mentioned optical laminate of the present invention as at least one of the first transparent protective plate and the second transparent protective plate.

[0328] <Polarizing element>

[0329] Examples of the polarizing element include sheet-type polarizing elements such as a polyvinyl alcohol film, a polyvinyl formal film, a polyvinyl acetal film, and a saponified ethylene-vinyl acetate copolymer film that are dyed with iodine or the like and stretched; a wire grid-type polarizing element composed of a large number of parallel metal wires; a coating-type polarizing element coated with a lyotropic liquid crystal or a dichroic host-guest material; a multilayer thin film-type polarizing element, etc. These polarizing elements may be reflective polarizing elements having a function of reflecting non-transmitted polarized components.

[0330] The angle formed by the direction of the absorption axis of the polarizing element and the average of the directions of the slow axes of the plastic films for optical use is not particularly limited, and it is preferably arranged to be substantially parallel or substantially perpendicular. In this specification, substantially parallel means within ±5 degrees of 0 degree, preferably within ±3 degrees of 0 degree, more preferably within ±1 degree of 0 degree. In this specification, substantially perpendicular means within ±5 degrees of 90 degrees, preferably within ±3 degrees of 90 degrees, more preferably within ±1 degree of 90 degrees. Usually, when the angle formed by the direction of the absorption axis of the polarizing element and the direction of the slow axis of the plastic film for optical use is substantially parallel or substantially perpendicular, it is difficult to suppress black screen. However, since the polarizing plate of the present invention uses the plastic film for optical use of the present invention, even if the above angle is substantially parallel or substantially perpendicular, black screen can be suppressed. In addition, by making the above angle substantially parallel or substantially perpendicular, the yield of the polarizing element and the plastic film for optical use can be easily improved.

[0331] <Dimensions>

[0332] The polarizing plate can be in the form of a single leaf cut into a specified size or in a roll form in which a long sheet is wound into a roll. The size of the single leaf is not particularly limited, and the maximum diameter is about 14.2 inches or more and 500 inches or less. The "maximum diameter" refers to the maximum length when connecting any two points of the polarizing plate. For example, in the case where the polarizing plate is rectangular, the diagonal of the rectangle is the maximum diameter. In the case where the polarizing plate is circular, the diameter of the circle is the maximum diameter.

[0333] The width and length of the roll form are not particularly limited. Generally, the width is about 300 mm or more and 9000 mm or less, and the length is about 100 m or more and 5000 m or less. The polarizing plate in roll form can be cut into single leaf form for use according to the size of an image display device or the like. When cutting, it is preferable to exclude the roll ends where the physical properties are unstable.

[0334] The shape of the single leaf is not particularly limited either. For example, it can be a polygon such as a triangle, a quadrilateral, or a pentagon, it can be circular, or it can be a random amorphous shape.

[0335] [Image display device]

[0336] The image display device of the present invention is an image display device having a display element and a plastic film disposed on the light-emitting surface side of the display element, wherein the plastic film is the plastic film for optical use of the present invention.

[0337] Figure 3 And Figure 4 is a cross-sectional view showing an embodiment of the image display device 100 of the present invention.

[0338] Figure 3 And Figure 4 The image display device 100 of has an optical plastic film 10 on the light-emitting surface side of the display element 20. Figure 3 And Figure 4 The upper side of is the light-emitting surface side of the display element. Figure 3 And Figure 4 The image display devices 100 of both have a polarizing element 31 between the display element 20 and the optical plastic film 10. Figure 3 And Figure 4 In, a first transparent protection plate (32) and a second transparent protection plate (33) are laminated on both sides of the polarizing element 31. Figure 4 In the image display device of, the optical plastic film 10 is used as the first transparent protection plate (32).

[0339] When there is a polarization element between the display element and the plastic film for optics, the angle formed by the average of the direction of the absorption axis of the polarization element and the direction of the slow axis of the plastic film for optics is not particularly limited, and it is preferably arranged to be substantially parallel or substantially perpendicular.

[0340] The image display device 100 is not limited to Figure 3 and Figure 4 the manner of. For example, in Figure 3 and Figure 4 each component constituting the image display device 100 is arranged at a prescribed interval, but each component may also be integrated through an adhesive layer or the like. The image display device may also have components not shown in the figure.

[0341] <Display element>

[0342] As the display element, examples include liquid crystal display elements, organic EL display elements, and inorganic EL display elements such as EL display elements, plasma display elements, and further, LED display elements such as Micro LED display elements and micro LED display elements.

[0343] When the display element of the display device is a liquid crystal display element, a backlight is required on the surface of the liquid crystal display element opposite to the resin sheet.

[0344] The display element is preferably an element with a wide color gamut width. As described later, the spectral distributions of RGB of the display element with a wide color gamut width are sharp respectively. Moreover, if the shape of the spectral distribution of the display element is sharp, it is difficult to suppress iridescence by increasing the in-plane retardation. Since the in-plane retardation of the plastic film for optics of the present invention is small, it is easy to suppress iridescence even when the color gamut width of the display element is wide, and it is preferable from this aspect.

[0345] The color gamut that can be reproduced by mixing three colors of RGB is represented by a triangle on the CIE-xy chromaticity diagram. The above triangle is formed by determining the vertex coordinates of each color of RGB and connecting the vertices.

[0346] When the spectral distributions of RGB are sharp respectively, in the CIE-xy chromaticity diagram, the x value of the vertex coordinate of R is large and the y value is small, the x value of the vertex coordinate of G is small and the y value is large, and the x value of the vertex coordinate of B is small and the y value is small. That is, when the spectral distributions of RGB are sharp respectively, the area of the triangle formed by connecting the vertex coordinates of each color of RGB in the CIE-xy chromaticity diagram becomes large, and the width of the color gamut that can be reproduced becomes wide. In addition, widening the color gamut width leads to an improvement in the appeal and sense of presence of dynamic images.

[0347] As a standard for expressing a color gamut, there are "ITU-R Recommendation BT.2020-2 (hereinafter referred to as "BT.2020-2")" and the like. ITU-R is an abbreviation for "International Telecommunication Union - Radiocommunication Sector", and ITU-R Recommendation BT.2020-2 is an international standard for the color gamut of ultra-high definition revised in October 2015. When the coverage rate of BT.2020-2 based on the CIE-xy chromaticity diagram represented by the following formula is within the range described later, it is possible to easily improve the appeal and sense of presence of moving images.

[0348] <Formula for expressing the coverage rate of BT.2020-2>

[0349] [Area overlapping with the CIE-xy chromaticity diagram of BT.2020-2 in the area of the CIE-xy chromaticity diagram of the light emitted from the display element / Area of the CIE-xy chromaticity diagram of BT.2020-2] × 100 (%)

[0350] Regarding the "area of the CIE-xy chromaticity diagram of the light emitted from the display element" required for calculating the coverage rate of BT.2020-2, the x value and y value of the CIE-Yxy chromaticity system are measured respectively for red display, green display, and blue display, and can be calculated from the "red vertex coordinates", "green vertex coordinates", and "blue vertex coordinates" obtained from the above measurement results. The x value and y value of the CIE-Yxy chromaticity system can be measured, for example, using the spectral radiance meter CS-2000 manufactured by Konica Minolta, Inc.

[0351] It is preferable that the coverage rate of BT.2020-2 calculated by the above formula for the display element is 60% or more, and more preferably 65% or more. Since the optical plastic film of the present invention has a small in-plane retardation, even if the coverage rate of BT.2020-2 of the display element is 60% or more, it is easy to suppress iridescence, and is preferable in this regard.

[0352] The image display device can be an image display device having a touch panel function.

[0353] As the touch panel, there are methods such as a resistive film type, a capacitive type, an electromagnetic induction type, an infrared type, and an ultrasonic type.

[0354] The touch panel function can be a function added to the display element like an in-cell touch panel liquid crystal display element, or a touch panel can be mounted on the display element.

[0355] As described above, the plastic film for optics of the present invention can suppress the remaining of bending marks or the occurrence of breakage after the bending test. Therefore, the image display device of the present invention is preferably used in the case of a foldable image display device (a foldable image display device), a rollable image display device (a rollable image display device that can be deformed from a curved surface shape to a flat surface shape), or an image display device having a curved surface shape, since more remarkable effects can be exerted from this point of view.

[0356] When the image display device is a foldable image display device, a rollable image display device, or an image display device having a curved surface shape, the display element is preferably an organic EL display element.

[0357] <Plastic film>

[0358] The image display device of the present invention has the plastic film for optics of the present invention on the light-emitting surface side of the display element. In the image display device, the plastic film for optics of the present invention may be only one sheet, or may be two or more sheets.

[0359] As the plastic film for optics disposed on the light-emitting surface side of the display element, there can be mentioned a plastic film for optics that serves as a base material for various functional films such as a polarization element protective film, a surface protective film, an antireflection film, and a conductive film constituting a touch panel.

[0360] <Other plastic films>

[0361] The image display device of the present invention may have other plastic films within a range not impairing the effects of the present invention. Other plastic films refer to plastic films that do not satisfy the conditions of the plastic film for optics of the present invention.

[0362] As other plastic films, those having optical isotropy are preferred. In the present specification, optical isotropy means that the in-plane retardation is 20 nm or less.

[0363] <Dimensions>

[0364] The size of the image display device is not particularly limited, and the maximum diameter is about 14.2 inches or more and 500 inches or less. The "maximum diameter" means the maximum length when connecting any two points of the image display device. For example, in the case where the image display device is rectangular, the diagonal of the rectangle is the maximum diameter. In the case where the image display device is circular, the diameter of the circle is the maximum diameter.

[0365] The shape of the image display device is not particularly limited. For example, it may be a polygon such as a triangle, a quadrilateral, or a pentagon, it may be circular, or it may be a random amorphous shape.

[0366] Examples

[0367] Next, the present invention will be described in more detail by way of examples, but the present invention is not limited by any of these examples.

[0368] 1. Measurement and evaluation

[0369] The atmosphere for the following measurement and evaluation is a temperature of 23°C ± 5°C and a relative humidity of 40% or more and 65% or less. In addition, before the measurement and evaluation, the sample is exposed to the above atmosphere for 30 minutes or more. In addition, each sample is sampled from a portion of the optical plastic film and the functional layer without defects.

[0370] 1-1. In-plane retardation (Re), direction of the slow axis

[0371] Seven large samples with a flow direction of 200 mm × a width direction of 300 mm are cut out from the roll-shaped optical plastic films of Examples 1 to 10 and Comparative Example 6 with a width of 2100 mm prepared in "2" below. The large sample at the center in the width direction is used as Sample 1 of each example, the large sample at the first position to the right compared to the center in the width direction is used as Sample 2 of each example, the large sample at the second position to the right compared to the center in the width direction is used as Sample 3 of each example, and the large sample at the right end of the third position to the right compared to the center in the width direction is used as Sample 4 of each example. Since the physical properties of the positions symmetric about the center in the width direction of the optical plastic film can be said to be substantially equal, the measurement on the left side of the center in the width direction is omitted. Among them, only Samples 2 to 3 are collected in Example 4, only Samples 1 to 3 are collected in Example 5, only Sample 1 is collected in Examples 7 to 9, only Samples 1 to 2 are collected in Example 10, and only Samples 1 to 2 are collected in Comparative Example 6.

[0372] Thirty small samples of 40 mm × 50 mm are cut out from Samples 1 to 4 of the four large samples respectively to obtain measurement samples.

[0373] On the other hand, one large sample of 200 mm × 300 mm is cut out from the optical plastic films of Comparative Examples 1 to 5 prepared in "2" below, and thirty small samples of 40 mm × 50 mm are cut out from the above large sample to obtain measurement samples.

[0374] Next, in a 30 mm × 40 mm area after removing 5 mm from the edge of the 40 mm × 50 mm measurement samples of the examples and comparative examples, the in-plane retardation and the angle of the slow axis are measured. The measuring device used is the product named "WPA-200-L" of Photonic Lattice Company. The measurement conditions are as follows. Through this measurement, the in-plane retardation and the angle of the slow axis of each area after subdividing the 30 mm × 40 mm area into more than 47,000 areas can be measured.

[0375] Based on the measurement results, for the 30 small samples that make up a large sample, the average value of the in-plane phase difference and the standard deviation σ of the angle of the slow axis are calculated respectively, and then it is determined whether each large sample meets Conditions 1-2. When the conditions are met, it is marked as "A", and when not met, it is marked as "C". The results are shown in Table 1 or 2.

[0376] In addition, based on the average value of the in-plane phase difference, the standard deviation σ of the in-plane phase difference, and the standard deviation σ of the angle of the slow axis calculated from each small sample, the average value of the 30 small samples is calculated. The results are shown in Table 3.

[0377] It should be noted that the product name "WPA-200-L" of Photonic Lattice cannot measure the in-plane phase difference above 3000 nm. Therefore, only the standard deviation σ of the angle of the slow axis of the measurement sample in Comparative Example 5 was measured using the product name "WPA-200-L" of Photonic Lattice. In addition, the in-plane phase difference of the measurement sample in Comparative Example 5 was measured using the product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd. to measure the in-plane center value of the sample.

[0378] <Specifications of WPA-200-L>

[0379] · Number of birefringence pixels: 384×288 pixels

[0380] · Lens: Standard lens (f1.25)

[0381] <Measurement steps>

[0382] (1) Turn on the power of the device and start the software (WPA-view), and then wait for at least 30 minutes to make it stable.

[0383] (2) After placing the measurement sample on the light source stage, while adjusting the height of the camera unit, place the measurement sample in the area reflected by the light source stage within the camera preview window. At this time, make sure that the measurement sample does not float from the light source stage. In addition, visually confirm that no external light is reflected in the preview window. The area reflected by the light source stage within the camera preview window is divided into 384×288 pixels (110,592 pixels). It should be noted that in the camera preview window, it is preferable to make the above adjustments so that there is a certain gap between the outer edge of the measurement sample and the outer edge of the area reflected by the light source stage. The above gap is preferably about 3 mm in actual size.

[0384] (3) While turning the scale dial of the lens, focus on the measurement sample. In the measurement of the example, align the scale of the scale dial to "4".

[0385] (4) In the user settings, set the following conditions. Then, temporarily remove the measurement sample and measure the baseline. Measure the baseline for each sample.

[0386] (5) Re - configure the sample and then perform the measurement.

[0387] (6) On the analysis screen, after selecting the area where the actual area of the sample is equivalent to 30 mm × 40 mm, calculate the average value of the in - plane phase difference, the standard deviation σ of the in - plane phase difference, and the standard deviation σ of the angle of the slow axis.

[0388] <User settings>

[0389] In the user settings, check the following items.

[0390] · Auto - exposure adjustment: Perform auto - exposure adjustment during measurement

[0391] · Noise filter: Automatically applied

[0392] · Masking process for dark areas: Perform masking process (10.0%)

[0393] · Axis direction setting: Slow axis

[0394] · Measurement accuracy: High precision

[0395] · Measurement mode: 3 - wavelength measurement

[0396] · Material coefficient: Automatic

[0397] 1 - 2. Phase difference in the thickness direction (Rth)

[0398] Measure the phase difference in the thickness direction at the center of the 30 mm × 40 mm area obtained by removing 5 mm from the edge of the 30 measurement samples of 40 mm × 50 mm prepared in 1 - 1 from the examples and comparative examples. The measuring device uses the product named "RETS - 100" manufactured by Otsuka Electronics Co., Ltd.

[0399] Based on the measurement results, determine whether the large sample meets Condition 3. If it meets the condition, mark it as "A"; if it does not meet the condition, mark it as "C". The results are shown in Table 1 or 2.

[0400] In addition, based on the phase difference in the thickness direction calculated from each small sample, calculate the average value of the 30 small samples. The results are shown in Table 3.

[0401] 1 - 3. Erosion rate

[0402] At the center of the 30 mm × 40 mm area obtained by removing 5 mm from the edge of each of the 30 measurement samples of 40 mm × 50 mm prepared in 1-1 for the examples and comparative examples, the erosion rate of the plastic film constituting the sample from the surface to a depth of 20 μm was measured. Then, the average value E of the erosion rate of the plastic film constituting the sample from the surface to a depth of 20 μm was calculated from the obtained erosion rates. 0-20 The method for measuring the erosion rate is as described in the main text of the specification.

[0403] Based on the measurement results, it was determined whether the large sample satisfied Condition 5. When the condition was satisfied, it was marked as "A", and when it was not satisfied, it was marked as "C". The results are shown in Table 1 or 2.

[0404] 1-4. Iris spot 1 (Liquid crystal display device with a plastic film alone and a white LED as the light source)

[0405] On the viewing-side polarizer of the image display device 1 having the following configuration, the large samples of 200 mm × 300 mm prepared in 1-1 for the examples and comparative examples were arranged. The arrangement was such that the direction of the absorption axis of the polarization element of the viewing-side polarizer was on average parallel to the direction of the slow axis of the large sample. Then, with the image display device lit in a darkroom environment, it was observed with the naked eye from various angles along the slow axis of the measurement sample from a distance of about 1 m, and the presence or absence of an iris spot was evaluated based on the following criteria. The evaluators were 20 healthy people aged 20 to 59 with a corrected visual acuity of 1.0 or more, 5 from each age group, for a total of 20 people.

[0406] A: 16 or more people answered that they could not observe an iris spot.

[0407] B: 11 or more and 15 or fewer people answered that they could not observe an iris spot.

[0408] C: 10 or fewer people answered that they could not observe an iris spot.

[0409] <Configuration of Image Display Device 1>

[0410] (1) Backlight: White LED

[0411] (2) Display element: Liquid crystal display element with a color filter

[0412] (3) Light-source-side polarizer: Having a TAC film as protective films on both sides of the polarization element composed of PVA and iodine. The arrangement was such that the direction of the absorption axis of the polarization element was perpendicular to the horizontal direction of the screen.

[0413] (4) Image display unit: Liquid crystal unit

[0414] (5) Observation side polarizer: A polarizer using a TAC film as a protective film for a polarizing element composed of PVA and iodine. It is configured such that the direction of the absorption axis of the polarizing element is parallel to the horizontal direction of the screen.

[0415] (6) Dimensions: Diagonal 21.5 inches

[0416] The coverage rate of BT.2020-2 based on the CIE-xy chromaticity diagram of the image display device 1 is 49%.

[0417] 1-5. Rainbow spot 2 (plastic film alone, organic EL display device)

[0418] Except for changing the image display device 1 to the following image display device 2, the rainbow spot is evaluated in the same manner as in 1-4.

[0419] <Configuration of image display device 2>

[0420] (1) Display element: A three-color independent type organic EL display element having a microcavity structure

[0421] (2) Light source side polarizer: None

[0422] (3) Observation side polarizer: A polarizer using a TAC film as a protective film for a polarizing element composed of PVA and iodine. It is configured such that the direction of the absorption axis of the polarizing element is parallel to the horizontal direction of the screen.

[0423] (4) Dimensions: Diagonal 21.5 inches

[0424] The coverage rate of BT.2020-2 based on the CIE-xy chromaticity diagram of the image display device 2 is 77%.

[0425] 1-6. Rainbow spot 3 (optical laminate, liquid crystal display device with white LED light source)

[0426] Change the plastic films of the examples and comparative examples disposed on the observation side polarizer to the optical laminates of the examples and comparative examples fabricated in the following "3", and evaluate the rainbow spot in the same manner as in 1-4 except for this.

[0427] 1-7. Rainbow spot 4 (optical laminate, organic EL display device)

[0428] Change the plastic films of the examples and comparative examples disposed on the observation side polarizer to the optical laminates of the examples and comparative examples fabricated in the following "3", and evaluate the rainbow spot in the same manner as in 1-5 except for this.

[0429] 1-8. Black screen 1 (vertically configured)

[0430] On the viewing-side polarizer of the image display device 1 having the configuration shown in 1-4, large samples of 200 mm × 300 mm of the examples and comparative examples prepared in 1-1 are arranged. Each sample is arranged such that the average direction of the slow axis of the sample is perpendicular to the horizontal direction of the screen. In other words, it is arranged such that the angle formed by the absorption axis of the polarizing element of the viewing-side polarizer and the average direction of the slow axis of the sample is 90 degrees.

[0431] Next, at the center of the image display device on which the sample is arranged, three characters with a font size of 16 are displayed at a display magnification of 100% using the trade name "WORD (registered trademark)" of Microsoft Corporation, and then observed from the front through polarized sunglasses. The direction of the absorption axis of the polarized sunglasses during observation is a direction orthogonal to the absorption axis of the polarizing element of the viewing-side polarizer. When the characters can be easily distinguished, it is recorded as 3 points; when the characters cannot be easily distinguished due to a black screen, it is recorded as 1 point; when neither of them is met, it is recorded as 2 points. The evaluation is performed by 5 subjects in each age group from 20 years old to 59 years old, for a total of 20 subjects. Calculate the average score of the evaluations of the 20 people, and rank them according to the following criteria. All 20 subjects are healthy people with a visual acuity of 1.0 or more. The above visual acuity includes corrected visual acuity.

[0432] <Evaluation Criteria>

[0433] AAA: The average score is 2.85 or more

[0434] AA: The average score is 2.70 or more and less than 2.85

[0435] A: The average score is 2.50 or more and less than 2.70

[0436] B: The average score is 2.00 or more and less than 2.50

[0437] C: The average score is 1.50 or more and less than 2.00

[0438] D: The average score is less than 1.50

[0439] 1-9. Black Screen 2 (45-degree Configuration)

[0440] On the viewing-side polarizer of the image display device 1 having the configuration shown in 1-4, large samples of 200 mm × 300 mm of the examples and comparative examples prepared in 1-1 are arranged. Each sample is arranged such that the average direction of the slow axis of the sample is at 45 degrees to the horizontal direction of the screen. In other words, it is arranged such that the angle formed by the absorption axis of the polarizing element of the viewing-side polarizer and the average direction of the slow axis of the sample is 45 degrees.

[0441] Next, at the central part of the image display device configured with the sample, three characters with a font size of 16 are displayed at a display magnification of 100% using the trade name "WORD (registered trademark)" of Microsoft Corporation. After that, observe from the front through polarized sunglasses, and at the same time, evaluate using the same method as in 1-8. The direction of the absorption axis of the polarized sunglasses during observation is the direction orthogonal to the absorption axis of the polarization element of the observation-side polarizer.

[0442] 1-10. Flexural resistance

[0443] <Slow axis direction>

[0444] Cut out a strip-shaped sample with a width of 30 mm in the width direction and a length of 100 mm in the flow direction from the central part in the width direction of the 200 mm × 300 mm large samples of Examples 1 to 10 and Comparative Example 6 prepared in 1-1. The central part in the width direction of the optical plastic films of Examples 1 to 10 and Comparative Example 6 generally represents the average direction of the slow axis.

[0445] In addition, cut out a strip-shaped sample with a width of 30 mm in the slow axis direction and a length of 100 mm in the fast axis direction from the optical plastic films of Comparative Examples 1 to 5 prepared in "2" described later.

[0446] After fixing both ends on the short side of the sample to a durability testing machine (product name "DLDMLH-FS", manufactured by YUASASYSTEM Co., Ltd.), conduct a continuous folding test of folding 180 degrees 100,000 times. The two ends on the short side of the sample are fixed in the area 10 mm from the front end of the sample. The folding speed is 120 times per minute. The following shows a more detailed method of the folding test.

[0447] After the folding test, place the strip-shaped sample on a horizontal table, measure the angle at which the end of the sample floats from the table, and thus evaluate the flexural resistance in the slow axis direction. The results are shown in Table 1 or 2. Among them, when the sample breaks during the process, it is recorded as "broken".

[0448] <Fast axis direction>

[0449] Cut out a strip-shaped sample with a width of 30 mm in the flow direction and a length of 100 mm in the width direction from the central part in the width direction of the 200 mm × 300 mm large samples of Examples 1 to 10 and Comparative Example 6 prepared in 1-1. In the central part of the optical plastic films of Examples 1 to 10 and Comparative Example 6, the flow direction generally represents the average direction of the fast axis.

[0450] In addition, cut out a strip-shaped sample with a width of 30 mm in the fast axis direction and a length of 100 mm in the slow axis direction from the optical plastic films of Comparative Examples 1 to 5 prepared in "2" described later.

[0451] For these samples, the same measurements as above were carried out to evaluate the bending resistance in the fast axis direction.

[0452] <Details of the folding test>

[0453] As Figure 5 (A) shows, in the continuous folding test, first, the side portions 10C of the plastic film 10 and the side portions 10D facing the side portions 10C are respectively fixed by the fixing portions 60 arranged in parallel. The fixing portions 60 can slide and move in the horizontal direction.

[0454] Next, as Figure 5 (B) shows, the fixing portions 60 are moved closer to each other, thereby deforming the plastic film 10 by folding. Further, as Figure 5 (C) shows, the fixing portions 60 are moved to a position where the distance between the two opposite side portions of the plastic film 10 fixed by the fixing portions 60 is 10 mm, and then the fixing portions 60 are moved in the reverse direction, thereby eliminating the deformation of the plastic film 10.

[0455] By moving the fixing portions 60 as shown in Figure 5 (A) to (C), the plastic film 10 can be folded 180 degrees. In addition, the continuous folding test is carried out in such a way that the bent portion 10E of the plastic film 10 does not protrude from the lower end of the fixing portion 60, and the distance when the fixing portions 60 are closest is controlled to 10 mm, thereby enabling the distance between the two opposite side portions of the optical film 10 to be 10 mm.

[0456] 1 - 11. Pencil hardness

[0457] As samples for the pencil hardness test, 30 measurement samples of 40 mm × 50 mm of the examples and comparative examples prepared in 1 - 1 were prepared. The above samples were heated at 100 °C for 10 minutes. For the above samples after heating, a pencil hardness test was carried out. The pencil hardness test was carried out in a region of 30 mm × 40 mm after removing 5 mm from the edge of the above samples.

[0458] The pencil hardness test was carried out based on the pencil hardness test specified in JIS K5600 - 5 - 4:1999, and at the same time, the load, speed, and judgment conditions were changed according to the provisions of JIS. Specifically, the load was 100 g and the speed was 3 mm / s. After applying the load to the above samples after heating, before visually evaluating the damage, the above samples were heated at 100 °C for 10 minutes again. Then, the damage of the samples after heating was visually evaluated.

[0459] The judgment condition for passing was that there was no damage in more than 3 times out of 5 evaluations. For example, the judgment method was as follows: when there was no damage in more than 3 times out of 5 times at a hardness of 2B, the hardness of 2B was qualified, and then the test at a harder hardness was carried out.

[0460] The pencil hardness of the samples of the examples and comparative examples is shown in Table 1 or 2, and the number of evaluations without damage in 5 evaluations is shown. When the pencil hardness results of 30 samples are all different, the pencil hardness of the worst evaluation result is shown in Table 1 or 2.

[0461] When the number of evaluations without damage is 3 or more in 5 evaluations at the pencil hardness F, it is at the qualified level. When the number of evaluations without damage is 5 in 5 evaluations at the pencil hardness F, it is denoted as "AAA", when the number of evaluations without damage is 4 in 5 evaluations at the pencil hardness F, it is denoted as "AA", and when the number of evaluations without damage is 3 in 5 evaluations at the pencil hardness F, it is denoted as "A". When it does not reach the qualified level, it is denoted as "C".

[0462] 2. Fabrication and preparation of the plastic film for optics

[0463] [Example 1]

[0464] 1 kg of PET (melting point: 258 °C, absorption center wavelength: 320 nm) and 0.1 kg of an ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one)) were melt-mixed at 280 °C using a kneader to produce pellets containing the ultraviolet absorber. The pellets and PET with a melting point of 258 °C were put into a single-screw extruder, melt-kneaded at 280 °C, and then extruded from a T-die and cast onto a casting drum with a surface temperature controlled at 25 °C to obtain a cast film. The amount of the ultraviolet absorber in the cast film was 1 part by mass relative to 100 parts by mass of PET.

[0465] After heating the obtained cast film with a roll set set at 95 °C, while heating with a radiation heater, the film was stretched 3.3 times in the flow direction in such a manner that the film temperature at the 130 mm position in the 400 mm stretching section was 99 °C and the film temperature at the 150 mm position was 100 °C, and then temporarily cooled to obtain a uniaxially stretched film. In the above stretching section, the starting point was stretching roll A and the ending point was stretching roll B, and stretching rolls A and B each had 2 nip rolls. It should be noted that when heating with the radiation heater, air at 80 °C and 5 m / s was blown from the back of the radiation heater to the film to generate turbulence, thereby disturbing the temperature uniformity of the film.

[0466] Next, corona discharge treatment was performed on both sides of the uniaxially stretched film in air to set the wetting tension of the base film to 55 mN / m. Next, the following slip layer coating liquid was coated online on the corona discharge treatment surfaces on both sides of the film to form a slip layer.

[0467] Next, the uniaxially stretched film is introduced into a tenter. After preheating with hot air at 95°C, it is stretched 4.5 times in the film width direction at a temperature of 105°C in the first stage and 135°C in the second stage. Here, when the stretching section in the width direction is divided into two parts, stretching is performed in two stages in such a way that the stretching amount of the film at the midpoint of the stretching section in the width direction is 80% of the stretching amount at the end of the stretching section in the width direction. The above "stretching amount" refers to the difference between the film width at the measurement location and the film width before stretching. For the film stretched in the width direction, wind containing turbulence at 55°C and 5 m / s is blown from both sides of the film for about 2 seconds, thereby cooling in a manner that disrupts the film temperature uniformity. Next, heat treatment is performed using hot air in the tenter. The temperature of the hot air is gradually increased from 180°C to 245°C. Then, a 1% relaxation treatment is performed in the width direction under the same temperature conditions, and then it is rapidly cooled to 100°C, and a 1% relaxation treatment is performed in the width direction. After that, winding is carried out to obtain a biaxially stretched polyester film as the optical plastic film of Example 1 with a width of more than 2100 mm.

[0468] <Slip layer coating liquid>

[0469] A coating liquid containing a polyester resin with a glass transition temperature of 18°C, a polyester resin with a glass transition temperature of 82°C, and silica particles with an average particle size of 100 nm.

[0470] [Example 2]

[0471] The film temperature at the 130 mm location of the cast film is changed to 97°C, the film temperature at the 150 mm location is changed to 98°C, and the temperature of the wind containing turbulence blown to the film stretched in the width direction is changed to 60°C. Otherwise, a biaxially stretched polyester film as the optical plastic film of Example 2 is obtained in the same manner as in Example 1.

[0472] [Example 3]

[0473] The film temperature at the 130 mm location of the cast film is changed to 98°C. Otherwise, a biaxially stretched polyester film as the optical plastic film of Example 3 is obtained in the same manner as in Example 2.

[0474] [Example 4]

[0475] The film temperature at the 130 mm location of the cast film is changed to 98°C, the film temperature at the 150 mm location is changed to 105°C, the stretching ratio in the flow direction is changed to 3.9 times, and the temperature of the wind containing turbulence blown to the film stretched in the width direction is changed to 60°C. Otherwise, a biaxially stretched polyester film as the optical plastic film of Example 4 is obtained in the same manner as in Example 1.

[0476] [Example 5]

[0477] Change the film temperature at the 130 mm position of the cast film to 98 °C, change the film temperature at the 150 mm position to 105 °C, change the draw ratio in the flow direction to 4.1 times, and change the temperature of the turbulent-flow-containing air blown to the film stretched in the width direction to 60 °C. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Example 5 in the same manner as in Example 1.

[0478] [Example 6]

[0479] Change the film temperature at the 130 mm position of the cast film to 98 °C, change the film temperature at the 150 mm position to 110 °C, change the draw ratio in the flow direction to 3.5 times, change the temperature of the air blown from the back of the radiation heater during stretching in the flow direction to 90 °C, and change the temperature of the turbulent-flow-containing air blown to the film stretched in the width direction to 45 °C. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Example 6 in the same manner as in Example 1.

[0480] [Example 7]

[0481] Change the film temperature at the 130 mm position of the cast film to 95 °C, change the film temperature at the 150 mm position to 99 °C, change the draw ratio in the flow direction to 3.1 times, change the draw ratio in the width direction to 3.8 times, and change the temperature of the turbulent-flow-containing air blown to the film stretched in the width direction to 45 °C. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Example 7 in the same manner as in Example 1.

[0482] [Example 8]

[0483] Change the film temperature at the 130 mm position of the cast film to 98 °C, change the draw ratio in the flow direction to 3.9 times, and change the temperature of the turbulent-flow-containing air blown to the film stretched in the width direction to 55 °C. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Example 8 in the same manner as in Example 1.

[0484] [Example 9]

[0485] Change the film temperature at the 130 mm position of the cast film to 95 °C, change the film temperature at the 150 mm position to 98 °C, change the draw ratio in the flow direction to 4.1 times, and change the temperature of the turbulent-flow-containing air blown to the film stretched in the width direction to 60 °C. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Example 9 in the same manner as in Example 1.

[0486] [Example 10]

[0487] Change the film temperature at the 130 mm position of the cast film to 102 °C, change the film temperature at the 150 mm position to 110 °C, change the draw ratio in the flow direction to 3.0 times, change the draw ratio in the width direction to 3.2 times, and change the temperature of the turbulent-flow-containing air blown onto the film stretched in the width direction to 40 °C. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Example 10 in the same manner as in Example 1.

[0488] [Comparative Examples 1 - 5]

[0489] Prepare the following plastic films as optical plastic films for comparative examples.

[0490] [Comparative Example 1]

[0491] Triacetyl cellulose film (manufactured by Fujifilm Corporation, part number: TD40, thickness: 40 μm)

[0492] [Comparative Example 2]

[0493] Biaxially stretched polyester film (manufactured by Toyobo Co., Ltd., trade name: Cosmoshine A4300, thickness: 38 μm)

[0494] [Comparative Example 3]

[0495] Biaxially stretched polyester film (manufactured by Toray Industries, Inc., trade name: Lumiror 50U403, thickness: 50 μm)

[0496] [Comparative Example 4]

[0497] Biaxially stretched polyester film (manufactured by Mitsubishi Chemical Corporation, trade name: DIAFOIL T600, thickness: 23 μm)

[0498] [Comparative Example 5]

[0499] Uniaxially stretched polyester film (manufactured by Toyobo Co., Ltd., trade name: Cosmoshine TA048, thickness: 80 μm)

[0500] [Comparative Example 6]

[0501] Change the film temperature at the 130 mm position of the cast film to 102 °C, change the film temperature at the 150 mm position to 110 °C, change the draw ratio in the flow direction to 3.0 times, change the draw ratio in the width direction to 3.2 times, and change the temperature of the turbulent-flow-containing air blown onto the film stretched in the width direction to 65 °C. At the same time, change the air supply during stretching in the flow direction so that air is not supplied from the back of the radiation heater. Otherwise, obtain a biaxially stretched polyester film as an optical plastic film of Comparative Example 6 in the same manner as in Example 1.

[0502] 3. Fabrication of the optical laminate

[0503] On the plastic films for optical use in Examples 1 to 10 and Comparative Examples 1 to 6, a coating liquid for forming a hard coat having the following formulation was applied, dried, and irradiated with ultraviolet rays to form a hard coat with a thickness of 5 μm. Subsequently, a coating liquid for forming a low refractive index layer having the following formulation was applied on the hard coat, dried, and irradiated with ultraviolet rays to form a low refractive index layer with a thickness of 100 nm and a refractive index of 1.30, thereby obtaining the optical laminates of Examples 1 to 10 and Comparative Examples 1 to 6.

[0504] <Coating liquid for forming a hard coat>

[0505] · 25.1 parts by mass of an ultraviolet curable compound

[0506] (Acrylic polymer, manufactured by Dainippon Fine Chemical Co., Ltd., trade name 8KX - 077)

[0507] · 25.4 parts by mass of an ultraviolet curable compound

[0508] (Polyfunctional acrylate, manufactured by Nippon Kayaku Co., Ltd., trade name PET - 30)

[0509] · 1.0 part by mass of a photoinitiator

[0510] (IGM Resins B.V., trade name “Omnirad 184”)

[0511] · 0.30 part by mass of a silicone - based leveling agent

[0512] (Manufactured by Momentive Performance Materials Inc., trade name TSF4460)

[0513] · 37.4 parts by mass of a diluting solvent

[0514] (A mixed solvent of toluene, IPA, and PMA with a mass ratio of 47:33:20)

[0515] <Coating liquid for forming a low refractive index layer>

[0516] · 0.6 part by mass of an ultraviolet curable compound

[0517] (An alkoxylated pentaerythritol acrylate having 3 to 4 functional groups, manufactured by Shin - Nakamura Chemical Co., Ltd., trade name “NK ESTER ATM - 4PL”)

[0518] · 0.1 part by mass of a photoinitiator

[0519] (IGM Resins B.V., trade name "Omnirad 127")

[0520] · 1.88 parts by mass of hollow silica

[0521] (average particle size 60 nm)

[0522] · 0.3 parts by mass of solid silica

[0523] (average particle size 12 nm)

[0524] · 1.16 parts by mass of fluorine-based antifouling agent

[0525] (manufactured by DIC Corporation, trade name "MEGAFACE F-568")

[0526] · 92.7 parts by mass of diluting solvent (mixed solvent of methyl isobutyl ketone and propylene glycol monomethyl ether acetate with a mass ratio of 90:10)

[0527]

[0528] In Tables 1 and 2, Ratio 1 to Ratio 5 refer to the following ratios.

[0529] Ratio 1: Ratio of small samples with an average in-plane retardation of 50 nm or more and 1200 nm or less

[0530] Ratio 2: Ratio of small samples with a standard deviation σ of the slow axis angle of 0.8 degrees or more

[0531] Ratio 3: Ratio of small samples with a retardation in the thickness direction of 2000 nm or more

[0532] Ratio 4: Ratio of small samples with a ratio of the average in-plane retardation to the retardation in the thickness direction of 0.20 or less

[0533] Ratio 5: E 0-20 Ratio of small samples of 1.4 μm / g or more

[0534] In addition, in Tables 1 to 3, S1 represents Sample 1, S2 represents Sample 2, S3 represents Sample 3, and S4 represents Sample 4.

[0535]

[0536] [Table 3]

[0537] Table 3

[0538]

[0539] From the results in Tables 1 to 3, it can be confirmed that the plastic films for optics in the examples can suppress iridescence when observed with the naked eye and black screens when observed with polarized sunglasses without increasing the in-plane retardation and without requiring axis alignment. In addition, it was confirmed that: regardless of the bending direction, the plastic films for optics in the examples can suppress residual bending marks or fractures after the bending test.

[0540] In addition, it can be confirmed that: since the erosion rate of the plastic films for optics in the examples satisfies Condition 5, the pencil hardness is good. In particular, it can be confirmed that: for the plastic films for optics in Examples 1 to 3, Sample 2 of Example 4, Samples 1 to 2 of Example 5, and Examples 8 to 9, since the proportion of small samples satisfying the erosion rate of Condition 5 is 90% or more and the σ of the angle of the slow axis of Condition 2 is not too large, the pencil hardness is extremely good. It is considered that the erosion rate of Condition 5 mainly improves the strength in the thickness direction. Therefore, it is considered that the plastic films for optics in the examples satisfying the erosion rate of Condition 5 can improve the pencil hardness. Among them, when the proportion of small samples satisfying the erosion rate of Condition 5 is 90% or more, the pencil hardness can be easily further improved. In addition, in the examples, for the plastic films for optics in Examples 1 to 5 and 8 to 9, since the σ of the angle of the slow axis of Condition 2 is not too large, the in-plane orientation is good. That is, for the plastic films for optics in Examples 1 to 5 and 8 to 9 with good in-plane orientation, since the in-plane physical property deviation is small, it is considered that the reduction of the pencil hardness starting from the part with weak local strength can be easily suppressed. Thus, it is considered that in the examples, for the plastic films for optics in Examples 1 to 3, Sample 2 of Example 4, Samples 1 to 2 of Example 5, and Examples 8 to 9, the pencil hardness can be extremely good.

[0541] It should be noted that although not recorded in the table, the plastic films in Examples 1 to 10 satisfy Condition 6 described in the main text of the specification. Thus, it can be said that the plastic films in Examples 1 to 10 are plastic films with excellent film quality homogeneity in the thickness direction and good coating adaptability.

[0542] Symbol Explanation

[0543] 10: Plastic film for optics

[0544] 10a: Sheet-like plastic film

[0545] 10b: Rolled plastic film

[0546] 20: Display element

[0547] 30: Polarizer

[0548] 31: Polarizing element

[0549] 32: First transparent protective plate

[0550] 33: Second transparent protective plate

[0551] 40: Optical laminate

[0552] 41: Hard coat

[0553] 42: Anti-reflection layer

[0554] 100: Image display device

[0555] 110: Container

[0556] 120: Receiver

[0557] 210: Test liquid pipe

[0558] 220: Compressed air pipe

[0559] 230: Return pipe

[0560] 310, 320: Flow meter

[0561] 410, 420: Pressure gauge

[0562] 500: Injection part

[0563] 510: Nozzle

[0564] 520: Housing

[0565] 600: Cross-sectional profile acquisition part

[0566] 810: Specimen mounting table

[0567] 820: Support

[0568] 900: Erosion rate measurement device

[0569] A1: Water

[0570] A2: Spherical silica

[0571] A3: Air

[0572] A4: Worn plastic film.

Claims

1. A plastic film for optics, which satisfies the following Condition 1 and Condition 2, <Condition 1> Cut a large sample with a size of 200 mm × 300 mm from the plastic film; divide the large sample into 30 small samples of 40 mm × 50 mm; subdivide the area of 30 mm × 40 mm after removing 5 mm from the edge of each small sample into more than 47,000 regions, and then measure the in-plane retardation of each subdivided region; among the 30 small samples, the proportion of small samples in which the average value of the in-plane retardation of each measurement region shows 300 nm or more and 950 nm or less is 50% or more; <Condition 2> For the 30 small samples, in the same manner as in Condition 1, measure the angle of the slow axis of each region after subdivision of each small sample; among the 30 small samples, the proportion of small samples in which the standard deviation σ calculated from the angles of the slow axes of each measurement region shows 0.8 degrees or more and 15.0 degrees or less is 50% or more.

2. The plastic film for optics according to claim 1, wherein in Condition 1, among the 30 small samples, the proportion of small samples in which the average value of the in-plane retardation of each measurement region shows 300 nm or more and 950 nm or less is 100%, in Condition 2, among the 30 small samples, the proportion of small samples in which the standard deviation σ calculated from the angles of the slow axes of each measurement region shows 0.8 degrees or more and 20.0 degrees or less is 100%.

3. The plastic film for optics according to claim 1 or 2, which further satisfies the following Condition 3, <Condition 3> For the 30 small samples, measure the retardation in the thickness direction at the center of the 30 mm × 40 mm region respectively; among the 30 small samples, the proportion of small samples in which the retardation in the thickness direction shows 2000 nm or more is 50% or more.

4. The plastic film for optics according to claim 3, which further satisfies the following Condition 4, <Condition 4> Among the 30 small samples, the proportion of small samples in which the average value of the in-plane retardation shows 0.20 or less with respect to the retardation in the thickness direction is 50% or more.

5. An optical laminate having a functional layer on the plastic film for optics according to any one of claims 1 to 4.

6. The optical laminate according to claim 5, which includes an antireflection layer as the functional layer.

7. A polarizing plate, which is a polarizing plate having a polarizing element, a first transparent protective plate disposed on one side of the polarizing element, and a second transparent protective plate disposed on the other side of the polarizing element, wherein, At least one of the first transparent protection plate and the second transparent protection plate includes the plastic film for optics according to any one of claims 1 to 4.

8. An image display device, which is an image display device having a display element and a plastic film disposed on the light-emitting surface side of the display element, wherein, The plastic film is the plastic film for optics according to any one of claims 1 to 4.

9. The image display device according to claim 8, which has a polarization element between the display element and the plastic film.

Images