Polyester film with easily adhesive layer, optical laminate, polarizing plate, surface plate, image display panel, and image display device

Abstract

The present application relates to a polyester film with an easily adhesive layer, an optical laminate, a polarizing plate, a surface plate, an image display panel, and an image display device. Provided is a polyester film with a highly adhesive layer, which is capable of improving the adhesion of an optical laminate comprising a polyester film having high pencil hardness, a highly adhesive layer, and a functional layer in this order. A polyester film with an easily adhesive layer, which has an easily adhesive layer on a polyester film, and wherein the pencil hardness of the polyester film is B or more, and the average value of [delta] q / [delta] a on the surface of the easily adhesive layer is 1.60 or less. Delta a is an arithmetic mean value of the phase signals on the surface of the easy-to-adhere layer, and Delta q is a root-mean-square of the phase signals on the surface of the easy-to-adhere layer.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of March 1, 2023, an invention title of "Polyester Film with an Easy-Adhesion Layer, Optical Laminate Comprising the Above Polyester Film, and Polarizer, Front Panel, Image Display Panel, and Image Display Device Comprising the Above Optical Laminate", and an application number of 202380024064.2. Technical Field

[0002] The present invention relates to a polyester film with an easy-adhesion layer, an optical laminate comprising the above polyester film, and a polarizer, front panel, and image display device comprising the above optical laminate. Background Art

[0003] In image display devices such as liquid crystal display devices, organic EL display devices, micro LED display devices, mini LED display devices, display devices using quantum dots, and laser holographic display devices, various optical laminates are arranged for the purpose of improving the visibility of images and suppressing damage to the surface of the device. In addition, on the surface of display windows and painting covers, etc., optical laminates are sometimes arranged for the purpose of improving the visibility of articles and protecting the articles. Such optical laminates are mostly formed of a structure having a functional layer on a plastic film. And, as the plastic film of the optical laminate, a triacetyl cellulose film with small optical anisotropy is preferably used. In this specification, the "triacetyl cellulose film" is sometimes referred to as a "TAC film".

[0004] However, the TAC film has problems in terms of dimensional stability and mechanical strength, and these problems occur significantly especially in large-screen image display devices.

[0005] Therefore, as a substance to replace the TAC film, a polyester film such as a polyethylene terephthalate film has been proposed. In this specification, the "polyethylene terephthalate film" is sometimes referred to as a "PET film".

[0006] However, when the PET film is applied to an image display device that outputs polarized light such as a liquid crystal display device and an organic EL display device, due to the in-plane retardation of the PET film, a rainbow-like interference pattern called iridescence is generated, and there is a problem of reducing visibility.

[0007] As a countermeasure against iridescence, a means of making the in-plane retardation of the PET film extremely large has been proposed (for example, Patent Document 1).

[0008] The PET film with extremely large in-plane retardation in Patent Document 1 is obtained by uniaxially stretching the PET film. However, the uniaxially stretched film has problems such as being easily broken in the stretching direction.

[0009] As a countermeasure against rainbow spots, contrary to Patent Document 1, means for reducing the in-plane retardation of the PET film were considered.

[0010] Prior art documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-107198

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-32819

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-6530 Summary of the invention

[0015] Problems to be solved by the invention

[0016] A PET film with a small in-plane retardation can be obtained, for example, by reducing the draw ratio. However, the PET film with a reduced draw ratio has a problem of easy damage because the orientation in the thickness direction is inconsistent and the pencil hardness is reduced.

[0017] In addition, as PET films with a small in-plane retardation, the PET films of Patent Documents 2 and 3 can be cited. Compared with general biaxially stretched PET films, the PET films of Patent Documents 2 and 3 reduce the in-plane retardation by reducing the draw ratio difference between the MD direction as the flow direction and the TD direction as the width direction.

[0018] PET films that reduce the in-plane retardation without reducing the draw ratio as in Patent Documents 2 and 3 are likely to have an increased pencil hardness. The adhesion of the easy-adhesion layer of such a biaxially stretched PET film with a high pencil hardness is poor. Therefore, in an optical laminate having a functional layer formed on the easy-adhesion layer of a biaxially stretched PET film with a high pencil hardness, there is a problem that the interface between the PET film and the easy-adhesion layer is likely to peel off. The above problem can be solved by applying an easy-adhesion layer made of a material with excellent adhesion. However, in the above solution, the choice of materials for the easy-adhesion layer is limited, and there are limitations in product design, so it lacks practicality. In addition, when performing the optical design of the entire optical laminate, when there is an easy-adhesion layer of a specific material on the PET film, there are also limitations in the materials for the functional layer formed on the easy-adhesion layer.

[0019] An object of the present invention is to provide a polyester film with an easy-adhesion layer that can improve the adhesion of an optical laminate sequentially having a polyester film with a high pencil hardness, an easy-adhesion layer, and a functional layer. Another object of the present invention is to provide an optical laminate including the above polyester film, a polarizing plate including the above optical laminate, a surface plate, and an image display device.

[0020] Means for solving the problems

[0021] In order to solve the above problems, the present invention provides the following [1] to [5].

[0022] [1] A polyester film with an easy-bonding layer, which is a polyester film with an easy-bonding layer having an easy-bonding layer on the polyester film. Among them, the pencil hardness of the above polyester film is B or more, and the average value of δq / δa on the surface of the above easy-bonding layer is 1.60 or less.

[0023] <Calculation of the average value of δq / δa>

[0024] Use the phase mode of the atomic force microscope to measure a 10 μm × 10 μm area on the surface of the above easy-bonding layer. Through the above measurement, the distribution of the phase signal on the surface of the easy-bonding layer is obtained. The unit of the phase signal is [deg].

[0025] Let the arithmetic mean of the phase signals shown in the following formula 1 be δa. Let the root mean square of the phase signals shown in the following formula 2 be δq.

[0026] (In the following formula 1 and the following formula 2, on the reference surface representing the average value of the phase signal, the right-angled coordinate axes X-axis and Y-axis are arranged, the axis orthogonal to the reference surface is set as the Z-axis, and the curved surface of the phase signal is set as f(x, y). In the following formula 1 and the following formula 2, the size of the region for calculating δa and δq is set as Lx and Ly. In the following formula 1 and the following formula 2, Ar = Lx × Ly.)

[0027] Select 7 measurement and evaluation regions of 2 μm × 2 μm from within the 10 μm × 10 μm measurement region. Calculate δa, δq, and δq / δa for the above 7 measurement and evaluation regions respectively. Based on the 5 δq / δa values obtained by removing the maximum and minimum values from the above 7 δq / δa values, calculate the average value of δq / δa.

[0028] [Equation 1]

[0029]

[0030] [Equation 2]

[0031]

[0032] [2] An optical laminate, which has one or more functional layers on the above easy-bonding layer of the polyester film described in [1].

[0033] [3]A polarizing plate, which has: 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 is the optical laminate described in [2], and the optical laminate is disposed such that the surface on the functional layer side faces the side opposite to the polarizing element.

[0034] [4]A surface plate, which is a surface plate in which an optical laminate is bonded to a resin plate or a glass plate, wherein the optical laminate is the optical laminate described in [2], and the optical laminate is disposed such that the surface on the functional layer side faces the side opposite to the resin plate or the glass plate.

[0035] [5]An image display device, which has the optical laminate described in [2] disposed on a display element.

[0036] Effects of the Invention

[0037] The polyester film with an easy-bonding layer of the present invention does not use a specific material in the easy-bonding layer, and can improve the adhesion of an optical laminate sequentially having a polyester film with a high pencil hardness, an easy-bonding layer, and a functional layer. The optical laminate of the present invention can improve the adhesion of the optical laminate despite the high pencil hardness of the polyester film. The polarizing plate, surface plate, and image display device of the present invention have an optical laminate with good adhesion, and thus can suppress defects caused by poor adhesion of the optical laminate. Description of the Drawings

[0038] Figure 1 It is a cross-sectional view schematically illustrating an embodiment of the optical laminate of the present invention.

[0039] Figure 2 It is a schematic cross-sectional view of a device for measuring the erosion rate.

[0040] Figure 3 It is an image of the state in which the polyester film is worn by a test liquid containing pure water and spherical silica ejected from a spraying portion.

[0041] Figure 4 It is a diagram for explaining an example of a method for selecting a plurality of 10 μm × 10 μm measurement regions. Detailed Description

[0042] Hereinafter, the polyester film with an easy-bonding layer, optical laminate, polarizing plate, surface plate, and image display device of the present invention will be described.

[0043] It should be noted that the description of the numerical range of "AA to BB" in this specification means "AA or more and BB or less".

[0044] [Optical laminate]

[0045] The polyester film with an easy - adhesion layer of the present invention has an easy - adhesion layer on the polyester film. The pencil hardness of the above - mentioned polyester film is B or more, and the average value of δq / δa on the surface of the above - mentioned easy - adhesion layer is 1.60 or less.

[0046] [Calculation of the average value of δq / δa]

[0047] Use the phase mode of the atomic force microscope to measure a 10μm×10μm area on the surface of the above - mentioned easy - adhesion layer. Through the above measurement, the distribution of the phase signal on the surface of the easy - adhesion layer is obtained. The unit of the phase signal is [deg].

[0048] Let the arithmetic mean of the phase signals shown in the following formula 1 be δa. Let the root - mean - square of the phase signals shown in the following formula 2 be δq.

[0049] (In the following formula 1 and the following formula 2, on the reference surface representing the average value of the phase signal, set the right - angled coordinate axes X - axis and Y - axis, set the axis orthogonal to the reference surface as the Z - axis, and set the curved surface of the phase signal as f(x,y). In the following formula 1 and the following formula 2, set the size of the area for calculating δa and δq as Lx and Ly. In the following formula 1 and the following formula 2, Ar = Lx×Ly.)

[0050] Select 7 measurement and evaluation areas of 2μm×2μm from within the 10μm×10μm measurement area. Calculate δa, δq, and δq / δa for the above - mentioned 7 measurement and evaluation areas respectively. Based on the 5 δq / δa values obtained by removing the maximum and minimum values from the above - mentioned 7 δq / δa values, calculate the average value of δq / δa.

[0051] [Equation 3]

[0052]

[0053] [Equation 4]

[0054]

[0055] [Polyester film]

[0056] The pencil hardness of the polyester film needs to be B or more.

[0057] When the pencil hardness of the polyester film is less than B, it is easy to improve the adhesion between the polyester film and the easy - adhesion layer, and thus it is also possible to easily improve the adhesion of the optical laminate as a whole. However, when the pencil hardness of the polyester film is less than B, the surface of the functional layer of the optical laminate or the polyester film itself is easily damaged, so the quality of the optical laminate is likely to decrease.

[0058] The pencil hardness of the polyester film of the polyester film with an easy-bonding layer of the present invention is B or more. Therefore, it is possible to easily improve the abrasion resistance of the optical laminate having a functional layer formed on the easy-bonding layer. In addition, in the polyester film with an easy-bonding layer of the present invention, although the pencil hardness of the polyester film is B or more, the δq / δa of the surface of the easy-bonding layer also shows a specified value, so that the adhesion of the optical laminate can be improved.

[0059] The reason why it is considered difficult to improve the adhesion between the polyester film and the easy-bonding layer when the pencil hardness of the polyester film is B or more is that the polyester film with a high pencil hardness tends to have a high orientation, and it is difficult for the easy-bonding layer to penetrate into the highly oriented polyester film.

[0060] The pencil hardness of the polyester film is preferably HB or more, more preferably F or more.

[0061] If the pencil hardness of the polyester film is too high, the in-plane retardation of the polyester film tends to increase.

[0062] If the difference in the stretching ratio between the longitudinal direction and the transverse direction of the polyester film is reduced, the in-plane retardation of the polyester film can be reduced. However, when reducing the above stretching ratio difference by reducing the longitudinal and transverse stretching ratios, it is difficult to make the pencil hardness of the polyester film HB or more. In addition, when reducing the above stretching ratio difference at a stretching ratio with a pencil hardness exceeding 2H, the orientation in the XY plane of the polyester film becomes high, while the orientation in the Z-axis direction becomes low, so that it tends to be brittle in the film thickness direction. Therefore, the pencil hardness of the polyester film is preferably 2H or less.

[0063] In this specification, the pencil hardness is measured and determined according to the following steps (1) to (6).

[0064] (1) Cut the polyester film into a size of 5 cm × 10 cm to produce a sample.

[0065] (2) Heat the polyester film at 100 °C for 10 minutes. After heating, leave the polyester film to stand in an environment of 24 °C and a relative humidity of 40% or more and 60% or less for 30 minutes or more and 60 minutes or less. (Note: In the operation of (2), keep the polyester film clean and flat. For example, when heating, hold one end with a paper clip and hang it in the oven without applying a burden to the other end. And in the pencil hardness test of (3), conduct the test at a position not in contact with the paper clip.)

[0066] (3) Perform a pencil hardness test on the polyester film. The pencil hardness test is based on the scratch hardness (pencil method) of JIS K 5600-5-4:1999, and for the matters specifically described in (3) to (6), it is carried out with changes according to the provisions of JIS. In the pencil hardness test, first, a pencil with a specified hardness is brought into contact with the surface of the polyester film at an angle of 45°, and moved at a speed of 3.0 mm / sec under a load of 100 g, thereby applying a load to the polyester film.

[0067] (4) After applying the load to the polyester film, heat the sample again at 100 °C for 10 minutes.

[0068] (5) Immediately after reheating, visually evaluate the damage of the polyester film. The environment for visual evaluation is set at 24 °C and a relative humidity of 40% or more and 60% or less.

[0069] (6) Perform the operations of (1) to (5) above 5 times. Then, take the hardness of the hardest pencil among the pencils that are not damaged in 4 or more of the 5 times as the pencil hardness of the polyester film to be evaluated.

[0070] In the above method for measuring and determining the pencil hardness, when it is not damaged 4 times out of 5 times at hardness B and not damaged 3 times out of 5 times at hardness F, it is determined as hardness B.

[0071] When the polyester film has a slow axis and a fast axis, it is preferable that the pencil hardness is B or more in both the slow axis direction and the fast axis direction. The slow axis of the polyester film refers to the direction with the highest refractive index in the plane of the polyester film. The fast axis of the polyester film refers to the direction orthogonal to the above slow axis in the plane of the polyester film.

[0072] Preferably, for the polyester film, when the refractive index in the slow axis direction in the plane of the polyester film is defined as nx and the refractive index in the direction orthogonal to the slow axis in the same plane is defined as ny, nx and ny satisfy the following relationship.

[0073] nx - ny ≤ 0.0250

[0074] By making nx - ny 0.0250 or less, it is possible to easily suppress iridescence caused by in-plane phase difference. According to the design of the optical laminate, even when nx - ny is 0.0300 or less, it is possible to easily suppress iridescence.

[0075] In this specification, unless otherwise specifically mentioned, iridescence refers to the iridescence observed with the naked eye.

[0076] nx - ny is more preferably 0.0240 or less, and further preferably 0.0230 or less.

[0077] If nx - ny is too small, it is difficult to suppress blackening. Therefore, nx - ny is preferably 0.0050 or more, more preferably 0.0080 or more, still more preferably 0.0100 or more, still more preferably 0.0120 or more, and still more preferably 0.0130 or more.

[0078] In this specification, blackening refers to the phenomenon that the entire surface becomes dark when observing the light that has passed through a polarization element and a polyester film in sequence through a polarization element such as a polarized sunglasses.

[0079] Among the components shown in this specification, when upper limit options and lower limit options of multiple values are shown respectively, one selected from the upper limit options and one selected from the lower limit options can be combined as an embodiment of the numerical range.

[0080] For example, in the case of nx - ny, embodiments of numerical ranges such as 0.0050 or more and 0.0300 or less, 0.0050 or more and 0.0250 or less, 0.0050 or more and 0.0240 or less, 0.0050 or more and 0.0230 or less, 0.0080 or more and 0.0300 or less, 0.0080 or more and 0.0250 or less, 0.0080 or more and 0.0240 or less, 0.0080 or more and 0.0230 or less, 0.0100 or more and 0.0300 or less, 0.0100 or more and 0.0250 or less, 0.0100 or more and 0.0240 or less, 0.0100 or more and 0.0230 or less, 0.0120 or more and 0.0300 or less, 0.0120 or more and 0.0250 or less, 0.0120 or more and 0.0240 or less, 0.0120 or more and 0.0230 or less, 0.0130 or more and 0.0300 or less, 0.0130 or more and 0.0250 or less, 0.0130 or more and 0.0240 or less, 0.0130 or more and 0.0230 or less can be cited.

[0081] In this specification, unless otherwise specified, refractive indices such as nx and ny, in-plane retardation, and retardation in the thickness direction refer to values at a wavelength of 550 nm. In this specification, "in-plane retardation" is sometimes denoted as "Re", and "retardation in the thickness direction" is denoted as "Rth".

[0082] The nx - ny of the polyester film, as well as the in-plane retardation and the retardation in the thickness direction described later, can be measured or calculated, for example, using the product name "RETS-100" of Otsuka Electronics Co., Ltd. The nx - ny can be calculated as long as there is thickness information of the polyester film in addition to the measurement result of the in-plane retardation in the above "RETS-100". The retardation in the thickness direction can be calculated as long as there is thickness information and average refractive index information of the polyester film in addition to the measurement result of the in-plane retardation in the above "RETS-100" (for example, the average refractive index of polyethylene terephthalate is known to be 1.617, and this value is used for calculation in this specification).

[0083] The thickness of the polyester film can be measured as follows.

[0084] (1) For a polyester film having an easy - adhesion layer and a functional layer, etc., first, in order to enable cross - sectional observation, a sample with the cross - section of the polyester film exposed is made. A microtome is used when making the sample. As the microtome, a microtome manufactured by Leica Co., Ltd. can be cited. Then, by observing the cross - section with a scanning electron microscope, the thickness of the polyester film can be measured. As the scanning electron microscope, for example, "Model No.: S4800" manufactured by Hitachi, Ltd. can be cited.

[0085] (2) The thickness of a polyester film without an easy - adhesion layer and a functional layer, etc., can be measured using a film thickness gauge. As the film thickness gauge, the product name "Digimicro" of Nikon Corporation can be cited. For the product name "Digimicro" of Nikon Corporation, it is preferably used with "MS - 5C" + "MH - 15M" as the "stage" + "main body", and the "counter" is preferably "TC - 101A".

[0086] In this specification, unless otherwise specified, nx - ny, Re, and Rth refer to the average value of three measured values after removing the minimum and maximum values among five measured values.

[0087] In this specification, the five measurement sites are selected from any five locations without defects such as deformation, damage, and dirt.

[0088] In this specification, unless otherwise specified, the atmosphere for measuring various parameters is a temperature of 23°C ± 5°C and a relative humidity of 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 and 60 minutes or less before each measurement.

[0089] As various parameters, for example, nx - ny, Re, Rth, δa, δq, total light transmittance, and haze can be cited.

[0090] The polyester film preferably has other physical properties such as in - plane retardation and retardation in the thickness direction within the following ranges.

[0091] In this specification, the in-plane retardation and the retardation in the thickness direction refer to the retardation calculated by the following formula. "T" in the following formula refers to the thickness of the polyester film.

[0092] In-plane retardation (Re) = (nx - ny) × T [nm]

[0093] Retardation in the thickness direction (Rth) = ((nx + ny) / 2 - nz) × T [nm]

[0094] - In-plane retardation (Re) -

[0095] The in-plane retardation of the polyester film is preferably 1200 nm or less, more preferably 1148 nm or less, more preferably 1100 nm or less, more preferably 1000 nm or less, and more preferably 950 nm or less. By making the in-plane retardation 1200 nm or less, it is possible to easily suppress iridescence.

[0096] Iridescence can also be suppressed by adjusting the functional layer and the light source. In addition, there are applications where iridescence is not emphasized. Therefore, the in-plane retardation of the polyester film is not limited to 1200 nm or less and can also exceed 1200 nm.

[0097] The in-plane retardation of the polyester film is preferably 50 nm or more, more 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 450 nm or more, and more preferably 497 nm or more.

[0098] By making the in-plane retardation 50 nm or more, it is possible to easily suppress blackening. The reason is that a polyester film with an average in-plane retardation of less than 50 nm can hardly disturb linearly polarized light and allows the linearly polarized light to pass through directly, while a polyester film with an average in-plane retardation of 50 nm or more disturbs linearly polarized light. It should be noted that in order to easily improve the pencil hardness of the polyester film, the in-plane retardation is preferably 520 nm or more, more preferably 620 nm or more.

[0099] Examples of the preferred range of the in-plane phase difference include 50 nm or more and 1200 nm or less, 50 nm or more and 1148 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 1148 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 1148 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 1148 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 1148 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 1148 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 1148 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, 450 nm or more and 1200 nm or less, 450 nm or more and 1148 nm or less, 450 nm or more and 1100 nm or less, 450 nm or more and 1000 nm or less, 450 nm or more and 950 nm or less, 497 nm or more and 1200 nm or less, 497 nm or more and 1148 nm or less, 497 nm or more and 1100 nm or less, 497 nm or more and 1000 nm or less, 497 nm or more and 950 nm or less.

[0100] - Phase difference in the thickness direction (Rth)-

[0101] The phase difference in the thickness direction of the polyester film is preferably 2000 nm or more, more preferably 3000 nm or more, further preferably 4000 nm or more, and even more preferably 5000 nm or more.

[0102] By making the phase difference in the thickness direction of the polyester film 2000 nm or more, it is possible to easily suppress blackening when viewed obliquely as well as in the front direction.

[0103] In order to easily make Re / Rth fall within the range described below, the retardation in the thickness direction of the polyester film is preferably 15000 nm or less, more preferably 12000 nm or less, and still more preferably 9000 nm or less.

[0104] Examples of embodiments of the preferred range of the retardation in the thickness direction include 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.

[0105] -Re / Rth-

[0106] A small Re / Rth means that the stretching degree of the polyester film is close to uniform biaxiality. Therefore, by making Re / Rth 0.20 or less, it is possible to easily improve the pencil hardness of the polyester film. In addition, by making Re / Rth 0.20 or less, it is possible to easily suppress the generation of wrinkles in the polyester film under environmental changes and have an adverse effect on visibility. In order to easily exhibit the effects brought about by making Re / Rth fall within a specified range, the in-plane retardation of the polyester film is preferably within the above range. Re / Rth is more preferably 0.20 or less, still more preferably 0.17 or less, and still more preferably 0.15 or less.

[0107] If Re / Rth is too small, the orientation in the XY plane is high, while the orientation in the Z-axis direction decreases, and there is a tendency to become brittle in the film thickness direction. Therefore, if Re / Rth is too small, the polyester film may break when the polyester film is attached to the adherend or when the polyester film is peeled off from the adherend. Therefore, Re / Rth of the polyester film is preferably 0.01 or more, more preferably 0.03 or more, still more preferably 0.05 or more, and still more preferably 0.06 or more.

[0108] Examples of embodiments of the preferred range of Re / Rth include 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, 0.03 or more and 0.20 or less, 0.03 or more and 0.17 or less, 0.03 or more and 0.15 or less, 0.05 or more and 0.20 or less, 0.05 or more and 0.17 or less, 0.05 or more and 0.15 or less, 0.06 or more and 0.20 or less, 0.06 or more and 0.17 or less, 0.06 or more and 0.15 or less.

[0109] -Haze, total light transmittance-

[0110] The haze of the polyester film according to JIS K7136:2000 is preferably 3.0% or less, more preferably 2.0% or less, and further preferably 1.0% or less.

[0111] In addition, the total light transmittance of the polyester film according to JIS K7361-1:1997 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more.

[0112] -Ultraviolet transmittance-

[0113] The light transmittance of the polyester film at a wavelength of 380 nm is preferably 20% or less, more preferably 10% or less.

[0114] <Erosion rate>

[0115] The average of the erosion rate from the surface to a depth of 20 μm of the polyester film is defined as E 0-20 When it is, the E of the polyester film 0-20 is preferably 1.4 μm / g or more.

[0116] In this specification, E 0-20 is measured under the following measurement conditions.

[0117] <Measurement conditions>

[0118] A test solution prepared by mixing pure water, a dispersion, and spherical silica with an average particle size within ±8% based on 4.2 μm in a mass ratio of 968:2:30 is placed 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 above test solution in the above nozzle, and a specified amount of the above test solution is vertically sprayed from the ejection hole at the front end of the above nozzle onto the above polyester film so that the spherical silica in the above test solution collides with the above polyester film. The cross-sectional shape of the above nozzle is a square of 1 mm × 1 mm, and the distance between the above ejection hole and the above polyester film is 4 mm. In addition, the flow rates of the above test solution and the above compressed air supplied to the above nozzle, the pressure of the above compressed air, and the pressure of the above test solution in the above nozzle are set to specified values adjusted by calibration described later.

[0119] After spraying a specified amount of the above test solution, the spraying of the above test solution is temporarily stopped.

[0120] After temporarily stopping the spraying of the above test solution, the cross-sectional profile is measured at the portion of the above polyester film where the spherical silica in the above test solution collides.

[0121] The steps of ejecting a specified amount of the test liquid from the above ejection port, temporarily stopping the ejection of the test liquid after ejecting the specified 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 polyester film is calculated. The erosion rates of the polyester film in each cycle until the depth of the cross-sectional profile reaches 20 μm are averaged to calculate the above E 0-20 。

[0122] <Calibration>

[0123] 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 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 of 1 mm × 1 mm, and the distance between the above ejection hole and the above acrylic plate is 4 mm.

[0124] 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 position where the above spherical silica in the above test liquid collides with the above acrylic plate.

[0125] 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).

[0126] 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.

[0127] Hereinafter, reference Figure 2 is made to explain the measurement conditions of the erosion rate and the technical meaning of the erosion rate calculated according to the above measurement conditions. As Figure 2 such an erosion rate measurement device, for example, the part number "MSE-A203" of the MSE test device of Palmeso Co., Ltd. can be cited.

[0128] In the measurement conditions of the erosion rate of the present invention, first, pure water, a dispersant, and spherical silica having an average particle size within ±8% based on 4.2 μm are mixed at a mass ratio of 968:2:30, and the resulting test solution is stored in a container (11). Inside the container (11), the test solution is preferably stirred.

[0129] The dispersant only needs to be able to disperse the spherical silica and is not particularly limited. As the dispersant, for example, the product name “DEMOL N (Demol N)” of Wako Pure Chemical Industries, Ltd. can be cited.

[0130] In other words, “the average particle size is 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.

[0131] 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 (the so-called “median diameter”).

[0132] 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 frequency 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 “the particle size showing a frequency of 50 and located in the more positive direction than the particle size showing a frequency of 100 is defined as X” and “the particle size showing a frequency of 50 and located in the more negative direction than the particle size showing a frequency of 100 is defined 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”.

[0133] As the spherical silica having 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.

[0134] The test solution in the container is sent to the nozzle (51). The test solution can be sent to the nozzle through the test solution pipe (21), for example. A flowmeter (31) for measuring the flow rate of the test solution is preferably arranged between the container (11) and the nozzle (51). The flow rate of the test solution is the value adjusted by the above calibration.

[0135] It should be noted that Figure 2 in Figure 2 , the nozzle (51) is disposed within the housing (52) that constitutes the injection unit (50).

[0136] Compressed air is supplied into the nozzle (51). The compressed air is sent to the nozzle through, for example, a compressed-air pipe (22). Inside the nozzle, the position where the compressed air is introduced is preferably more upstream than the position where the test liquid is introduced. The upstream side refers to the side away from the injection holes of the nozzle.

[0137] Before the compressed air reaches the nozzle (51), a flowmeter (32) for measuring the flow rate of the compressed air and a pressure gauge (42) for measuring the pressure of the compressed air are preferably disposed. The compressed air can be supplied by an air compressor (not shown) or the like.

[0138] The flow rate and pressure of the compressed air are values adjusted through the above-described calibration.

[0139] When compressed air is supplied into the nozzle (51), the test liquid is accelerated while being mixed with the compressed air. Then, the accelerated test liquid is ejected from the injection holes at the front end of the nozzle (51) and perpendicularly impacts the polyester film (70). The polyester film is mainly worn by the spherical silica particles in the test liquid.

[0140] It should be noted that a pressure gauge (41) for measuring the pressure of the test liquid inside the nozzle (51) is preferably disposed inside the nozzle (51). The pressure gauge (41) is preferably more downstream than the position where the compressed air is introduced and the position where the test liquid is introduced.

[0141] The pressure of the test liquid inside the nozzle (51) is a value adjusted through the above-described calibration.

[0142] The test liquid ejected from the injection holes at the front end of the nozzle (51) is mixed with air and ejected in a mist form. Therefore, the impact pressure of the spherical silica particles on the polyester film can be reduced. Thus, the amount of wear of the polyester film caused by one spherical silica particle can be suppressed to a very small amount. Figure 3 It is an image of the state in which the polyester film (70) is worn by the test liquid containing pure water (A1) and spherical silica (A2) ejected from the injection unit (50). Figure 3 In Figure 3 , the symbol A3 represents air, and the symbol A4 represents the worn polyester film.

[0143] In addition, since the test liquid contains water with excellent cooling effect, deformation and deterioration of the polyester film caused by heat during the impact can be substantially eliminated. That is, abnormal wear of the polyester film can be substantially eliminated. In addition, water also has the function of cleaning the surface of the worn polyester film and achieving stable wear. In addition, water has the function of accelerating the spherical silica particles or controlling the fluid of the test liquid.

[0144] In addition, due to the collision of a large amount of spherical silica with the polyester film, the influence brought about by the subtle physical property differences of each spherical silica particle can be excluded.

[0145] 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 inside the nozzle are set to the 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 ejection hole and the polyester film is specified as 4 mm, thereby specifying the factors that affect the wear amount of the polyester film. It should be noted that the above distance is Figure 2 the distance indicated by "d" in

[0146] the vertical distance between the ejection hole, which is the front end of the nozzle, and the polyester film.

[0147] The polyester film (70) only needs to be installed on the specimen mounting table (81) of the measuring device (90). The plastic film (70) is preferably installed on the specimen mounting table (81) by a support (82) such as a stainless steel plate.

[0148] The test liquid sprayed onto the polyester film (70) is preferably recovered by the receiver (12) and returned to the container (11) through the return pipe (23). A reflux pump (24) is preferably arranged between the receiver (12) and the return pipe (23).

[0149] 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 polyester film that is collided by the spherical silica in the test liquid is measured.

[0150] The cross-sectional profile refers to the cross-sectional shape of the polyester film worn by the test liquid. The polyester film is mainly worn by the spherical silica particles in the test liquid.

[0151] The cross-sectional profile can be measured, for example, by a cross-sectional profile acquisition unit (60) such as a stylus type surface shape measuring device and a laser interferometry type surface shape measuring device. It should be noted that the cross-sectional profile acquisition unit (60) is usually arranged at a position far from the polyester film (70) when spraying the test liquid. Therefore, it is preferable that at least one of the polyester film (70) and the cross-sectional profile acquisition unit (60) is movable.

[0152] 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.

[0153] Furthermore, in the measurement conditions of the present invention, the three steps of ejecting a specified amount of the test liquid from the ejection port, temporarily stopping the ejection of the test liquid after ejecting the specified 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 operation is performed until the depth of the cross-sectional profile exceeds 20 μm.

[0154] By performing the above operations, the erosion rate of the polyester film in each cycle can be measured, and furthermore, the deviation of the erosion rate of the polyester film can be calculated.

[0155] The above cycle can also be continued 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 polyester film" is considered to be that the physical properties of the polyester film tend to change easily near the surface and become more stable towards the inside.

[0156] In this specification, the erosion rate of each cycle can be 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 depth (μm) of the cross-sectional profile of each cycle is the depth of the deepest position of the cross-sectional profile of each cycle.

[0157] The ejection amount of the test liquid in each cycle is "quantitative" in principle, but it can also vary slightly in each cycle.

[0158] The ejection amount of the test liquid in 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.

[0159] In the measurement conditions of the present invention, the erosion rate (μm / g) is calculated in each cycle until the depth of the cross-sectional profile reaches 20 μm. And the erosion rates of each cycle until the depth of the cross-sectional profile reaches 20 μm are averaged to calculate E 0-20 (average of the erosion rates from the surface to a depth of 20 μm of the polyester film).

[0160] The above cycle is implemented until the depth of the cross-sectional profile exceeds 20 μm, and the data of the cycles with the depth of the cross-sectional profile exceeding 20 μm are excluded from the data for calculating E 0-20 data.

[0161] Generally speaking, when the polyester film is soft, it is easily damaged, and when it is hard, it is not easily damaged. The present inventors studied using the values (Martens hardness, indentation hardness, elastic recovery work, etc.) obtained from the evaluation including the depth direction by PICODENRTOR as an index of pencil hardness. However, the above parameters such as Martens hardness, indentation hardness, and elastic recovery work sometimes cannot be used as an index of pencil hardness.

[0162] In addition, polyester films tend to have increased strength when stretched. Specifically, uniaxially stretched polyester films tend to have good pencil hardness compared to non-stretched polyester films, and biaxially stretched polyester films tend to have good pencil hardness compared to uniaxially stretched polyester films. However, even biaxially stretched polyester films sometimes have insufficient pencil hardness.

[0163] As an index of the pencil hardness of polyester films, the present inventors studied the erosion rate. As described above, polyester films are easily damaged when soft and not easily damaged when hard, so it is considered that good pencil hardness can be achieved when the erosion rate is small. However, the present inventors found that, conversely, by making the erosion rate (E 0-20 ) greater than or equal to 1.4 μm / g, the pencil hardness of the polyester film can be improved. In addition, the present inventors found that, regarding the erosion rate of polyester films, biaxially stretched polyester films show larger values than uniaxially stretched polyester films, and the pencil hardness of biaxially stretched polyester films can be judged by the erosion rate.

[0164] The reason why the erosion rate of polyester films is related to pencil hardness can be considered as follows.

[0165] As described above, in the measurement conditions of the present invention, the test liquid 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 polyester film is suppressed to a low level. Thus, it is considered that when the polyester film is soft, the stress during the collision of the spherical silica with the polyester film is easily dispersed, so the polyester film is not easily worn and the erosion rate decreases. On the other hand, when the polyester film is hard, since the stress during the collision of the spherical silica with the polyester film is difficult to be dispersed, it is considered that the polyester film is easily worn and the erosion rate increases.

[0166] In addition, the difference in the erosion rate in biaxially stretched polyester films is considered to be caused by differences in the elongation of molecular chains and differences in the degree of molecular orientation, etc. For example, in principle, molecules in biaxially stretched polyester films 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 polyester film becomes locally soft and the erosion rate decreases. In addition, it is considered that even biaxially stretched polyester films with the same in-plane phase difference will show different erosion rates due to different local molecular orientations.

[0167] To improve the pencil hardness of polyester films, E 0-20 is preferably 1.4 μm / g or more, more preferably 1.5 μm / g or more, more preferably 1.6 μm / g or more, more preferably 1.78 μm / g or more, more preferably 1.8 μm / g or more, more preferably 1.9 μm / g or more, more preferably 2.0 μm / g or more.

[0168] In order to make the polyester film not easily break, E 0-20 is preferably 3.0 μm / g or less, more preferably 2.5 μm / g or less, still more preferably 2.2 μm / g or less, and even more preferably 2.07 μm / g or less.

[0169] The E of the polyester film 0-20 Preferred ranges of embodiments may include 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, 1.4 μm / g or more and 2.07 μm / g or less, 1.5 μm / g or more and 3.0 μm / g or less, 1.5 μm / g or more and 2.5 μm / g or less, 1.5 μm / g or more and 2.2 μm / g or less, 1.5 μm / g or more and 2.07 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, 1.6 μm / g or more and 2.07 μm / g or less, 1.78 μm / g or more and 3.0 μm / g or less, 1.78 μm / g or more and 2.5 μm / g or less, 1.78 μm / g or more and 2.2 μm / g or less, 1.78 μm / g or more and 2.07 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, 1.8 μm / g or more and 2.07 μm / g or less.

[0170] Before measuring the above erosion rate, the above correction is performed.

[0171] The correction can be performed as follows.

[0172] <Correction>

[0173] 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 to accelerate the above test liquid in the above nozzle, and an arbitrary amount of the above test liquid is vertically sprayed from the spray 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 side length of 1 mm × 1 mm, and the distance between the above spray hole and the above acrylic plate is 4 mm.

[0174] 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.

[0175] 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).

[0176] The erosion rate of the above acrylic plate is qualified 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, adjust and calibrate 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.

[0177] The test liquid used in the calibration is the same as the test liquid used in the measurement conditions implemented later.

[0178] In addition, the measuring device used in the calibration is the same as the measuring device used in the measurement conditions implemented later.

[0179] 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 sample in the calibration, while a polyester film is used as a sample in the measurement conditions.

[0180] The acrylic plate with a thickness of 2 mm as the standard sample is preferably a polymethyl methacrylate plate (PMMA plate). In addition, for the acrylic plate with a thickness of 2 mm as the standard sample, it is preferred 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.

[0181] <Measurement Condition A>

[0182] Pure water, a dispersant, and spherical silica with an average particle size within ±8% of 4.2 μm were mixed at a mass ratio of 968:2:30, and the mixed test solution was stored in a container. The test solution in the container was sent to a nozzle. Compressed air was supplied into the nozzle to accelerate the test solution in the nozzle, and a specified amount of the test solution was vertically sprayed from the ejection holes at the front end of the nozzle onto the acrylic plate, causing the spherical silica in the test solution to collide with the acrylic. The cross-sectional shape of the nozzle was a 1 mm × 1 mm square, and the distance between the ejection holes and the acrylic was 4 mm. Additionally, regarding the flow rates of the test solution and the compressed air supplied to the nozzle, the pressure of the compressed air, and the pressure of the test solution in the nozzle, the flow rate of the test solution was 100 ml / min or more and 150 ml / min or less, the flow rate of the compressed air was 4.96 L / min or more and 7.44 L / min or less, the pressure of the compressed air was 0.184 MPa or more and 0.277 MPa or less, and the pressure of the test solution in the nozzle was 0.169 MPa or more and 0.254 MPa or less.

[0183] After spraying 4 g of the test solution, the spraying of the test solution was temporarily stopped.

[0184] After temporarily stopping the spraying of the test solution, the cross-sectional profile was measured at the part of the acrylic plate where the spherical silica in the test solution collided.

[0185] Then, the erosion rate AcE (unit: "μm / g") of the acrylic plate was calculated by dividing the depth (μm) of the cross-sectional profile by the spraying amount of 4 g of the test solution.

[0186] In calibration, the qualified condition was that the erosion rate of the acrylic plate was within the range of ±5% based on 1.88 (μm / g). The operations of adjusting the flow rates of the test solution and the compressed air, the pressure of the compressed air, and the pressure of the test solution in the nozzle were carried out in such a way that the erosion rate of the acrylic plate was within the above range.

[0187] It should be noted that, in other words, "the erosion rate is within the range of ±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.

[0188] <σ 0-20 / E 0-20 >

[0189] For the polyester film, the deviation of the erosion rate calculated from the erosion rate from the surface to a depth of 20 μm of the polyester film was defined as σ 0-20 When, σ 0-20 / E 0-20Preferably 0.100 or less.

[0190] 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.

[0191] σ 0-20 / E 0-20 represents the coefficient of variation of the erosion rate, and σ 0-20 / E 0-20 being small means that the erosion rate is not likely to vary in the thickness direction of the polyester film. By making σ 0-20 / E 0-20 0.100 or less, the erosion rate in the thickness direction is stable, and it is possible to easily further improve the pencil hardness.

[0192] σ 0-20 / E 0-20 The upper limit of is more preferably 0.080 or less, further preferably 0.077 or less, further preferably 0.070 or less, further preferably 0.060 or less, and further preferably 0.055 or less.

[0193] σ 0-20 / E 0-20 The lower limit of has no particular limitation, and is usually 0.020 or more, preferably 0.035 or more, and more preferably 0.040 or more. In addition, when the value of σ 0-20 / E 0-20 is low, the polyester film may be weak in tensile strength. A polyester film with weak tensile strength tends to have poor solvent resistance, be easily broken, and have low stability to heat and humidity. Therefore, σ 0-20 / E 0-20 is preferably 0.020 or more.

[0194] σ 0-20 / E 0-20 Examples of the preferred range embodiments of are 0.020 or more and 0.100 or less, 0.020 or more and 0.080 or less, 0.020 or more and 0.077 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 0.077 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, 0.040 or more and 0.100 or less, 0.040 or more and 0.080 or less, 0.040 or more and 0.077 or less, 0.040 or more and 0.070 or less, 0.040 or more and 0.060 or less, 0.040 or more and 0.055 or less.

[0195] - Thickness -

[0196] To improve the mechanical strength, the thickness of the polyester film is preferably 10 μm or more, more preferably 21 μm or more, further preferably 25 μm or more, and even more preferably 30 μm or more. Further, by making the thickness of the polyester film 10 μm or more, when stress is generated due to contact of other members with the side of the optical laminate opposite to the functional layer, it becomes difficult for the above stress to be transmitted to the interface between the polyester film and the easily adhesive layer.

[0197] To reduce the in-plane retardation and to improve the bending resistance, the thickness of the polyester film is preferably 75 μm or less, more preferably 60 μm or less, further preferably 55 μm or less, and even more preferably 50 μm or less.

[0198] Examples of the preferred range of the thickness of the polyester 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, 21 μm or more and 75 μm or less, 21 μm or more and 60 μm or less, 21 μm or more and 55 μm or less, 21 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.

[0199] 《Raw Materials》

[0200] Examples of the polyester constituting the polyester film include: homopolymers obtained by polycondensation of dicarboxylic acids and diols; copolymers obtained by polycondensation of one or more dicarboxylic acids and two or more diols; copolymers obtained by polycondensation of two or more dicarboxylic acids and one or more diols; and blend resins formed by mixing one or more homopolymers and one or more copolymers.

[0201] The polyester film may contain additives such as ultraviolet absorbers, slip particles such as inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light-resistant agents, flame retardants, heat stabilizers, antioxidants, anti-gelation agents, and surfactants within a range that does not hinder the effects of the present invention.

[0202] The raw materials of the polyester film can be newly synthesized raw materials, natural source raw materials, or recycled raw materials.

[0203] Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecanedicarboxylic acid, etc.

[0204] Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, etc.

[0205] In the polyester, polyethylene terephthalate is preferred for improving mechanical strength. That is, the polyester film preferably contains polyethylene terephthalate.

[0206] Examples of the polymerization method of polyethylene terephthalate include: a direct polymerization method in which terephthalic acid directly reacts with ethylene glycol and, if necessary, other dicarboxylic acid components and diol components; a transesterification method in which dimethyl terephthalate reacts with ethylene glycol; etc. In the transesterification method, the dimethyl terephthalate may contain methyl esters of other dicarboxylic acids as needed. In the transesterification method, ethylene glycol may contain other diol components as needed.

[0207] The intrinsic viscosity of polyethylene terephthalate is preferably 0.45 or more and 0.70 or less. If the intrinsic viscosity is less than 0.45, the tear resistance may sometimes decrease. If the intrinsic viscosity is greater than 0.70, the filter pressure rise increases, and thus the filtration accuracy may sometimes decrease.

[0208] 《Layer Structure》

[0209] The polyester film may have a single-layer structure or a multilayer structure.

[0210] The single-layer structure is easy to control stretching. Therefore, the single-layer structure can easily improve the pencil hardness of the polyester film by not reducing the stretching ratios in the flow direction and the width direction and making the stretching ratios in both directions close. Therefore, from the aspect of easily improving the pencil hardness of the polyester film, the single-layer structure that is easy to control stretching is preferred. In addition, in order to control the erosion rate, it is important to evenly elongate the molecules in the plane of the polyester film. Therefore, from the aspect of easily controlling the erosion rate, the single-layer structure is preferred.

[0211] On the other hand, from the aspect of easily imparting the effects resulting from changing the composition of each layer, a polyester film with a multilayer structure is preferred. For example, by coextrusion, a laminated polyester film composed of at least three layers or more is produced. If polyesters with a low oligomer content are used for the surface layers on both sides, the amount of oligomer precipitation after heat treatment can be easily suppressed.

[0212] -Stretching-

[0213] To improve the pencil hardness of the polyester film, it is preferred not to reduce the stretching ratios in the flow direction and the width direction, and to make the stretching ratios in the two directions close to each other.

[0214] Therefore, the polyester film is preferably a stretched film, and more preferably a biaxially stretched film.

[0215] -Stepwise biaxial stretching-

[0216] In stepwise biaxial stretching, the cast film is stretched in the flow direction first, and then in the width direction of the film.

[0217] The stretching in the flow direction is usually carried out using the circumferential speed difference of a pair of stretching rolls. The stretching in the flow direction can be carried out in one stage, or can be carried out in multiple stages using multiple pairs of stretching rolls. To suppress excessive deviation of optical properties such as in-plane phase difference, it is preferred to make the plurality of 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. To suppress excessive deviation of optical properties such as in-plane phase difference, 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.

[0218] To suppress excessive deviation of physical properties such as in-plane phase difference, 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.

[0219] Regarding the stretching temperature, by quickly heating the film etc. to shorten the stretching interval at low temperature, there is a tendency for the average value of the in-plane phase difference to become smaller. On the other hand, by slowly heating the film etc. to extend the stretching interval at low temperature, there is a tendency for the orientation to increase and the average value of the in-plane phase difference to become larger.

[0220] In addition, in the stretching in the flow direction, if the stretching time is shortened, there is a tendency for the erosion rate to decrease, and if the stretching time is extended, there is a tendency for the erosion rate to increase. The reason is considered that if the stretching time is short, the molecules in the plane of the polyester film are difficult to elongate evenly, and if the stretching time is long, the molecules in the plane of the polyester film are easy to elongate evenly. That is, to make E 0-20is 1.4 μm / g or more, and it is preferable to extend the stretching time. Furthermore, by extending the stretching time while appropriately increasing the stretching ratio to the extent that no deviation in physical properties occurs, it is easier to make E 0-20 is 1.4 μm / g or more.

[0221] A layer having functions such as slipperiness and antistatic properties can be formed on the film stretched in the flow direction by in-line coating or off-line coating. In this specification, the layer formed by in-line coating or off-line coating is not counted as the number of layers constituting the polyester film.

[0222] Regarding the stretching in the width direction, generally, the tenter frame method is used, and while holding both ends of the film with clamps, the film is conveyed and stretched 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 physical 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 6 times or less, and further preferably 4 times or more and 5 times or less. In addition, compared with the stretching ratio in the flow direction, it is more preferable to increase the stretching ratio in the width direction.

[0223] 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, when the stretching section in the width direction is divided into two parts, the temperature difference between the upstream and the downstream is preferably 20°C or more, more preferably 30°C or more, further preferably 35°C or more, and even more preferably 40°C or more. In addition, 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.

[0224] For the polyester 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 above the stretching temperature and less than the melting point in the 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 physical 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.

[0225] After heat-treating the polyester film, it is slowly cooled to room temperature and then wound up. Additionally, if necessary, relaxation treatment or the like can be combined during heat treatment or slow cooling. In order to suppress excessive deviation of physical properties such as in-plane retardation, the relaxation rate during 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 even more preferably 1% or more and 2% or less. Also, in order to suppress excessive deviation of physical 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 even more preferably 0.5% or more and 1.0% or less. In order to easily 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 even more preferably 100°C or more and 120°C or less.

[0226] When manufacturing the stretched polyester film, the conveyance speed is approximately 100 m / s or more and 300 m / s or less.

[0227] - Simultaneous biaxial stretching -

[0228] In simultaneous biaxial stretching, the cast film is introduced into a synchronous twin-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 perform relaxation treatment at an arbitrary location is preferred.

[0229] The stretching ratio in simultaneous biaxial stretching is usually 6 times or more and 50 times or less in terms of area ratio. In order to suppress excessive deviation of physical properties such as in-plane retardation, the area ratio 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 even more preferably 10 times or more and 15 times or less. In simultaneous biaxial stretching, it is preferred to adjust to the above-mentioned area ratio within the range where the stretching ratio in the flow direction and the stretching ratio in the width direction are 2 times or more and 15 times or less.

[0230] In addition, in the case of simultaneous biaxial stretching, in order to suppress the in-plane orientation difference, it is preferred that the stretching ratio in the flow direction and the stretching ratio in the width direction are substantially the same, and the stretching speeds in the flow direction and the width direction are also substantially the same.

[0231] In order to suppress excessive deviation of physical properties such as in-plane phase difference, the stretching temperature in synchronous biaxial stretching is preferably not less than the glass transition temperature of the resin and not more than the glass transition temperature + 120°C. In the case of PET, it is preferably not less than 80°C and not more than 160°C, more preferably not less than 90°C and not more than 150°C, and further preferably not less than 100°C and not more than 140°C.

[0232] 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 not less than 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 of the heat treatment after sequential biaxial stretching.

[0233] <Easy adhesion layer>

[0234] The polyester film with an easy adhesion layer of the present invention needs to have an easy adhesion layer. In addition, for the polyester film with an easy adhesion layer of the present invention, the average value of δq / δa on the surface of the easy adhesion layer needs to be 1.60 or less.

[0235] -Calculation of the average value of -δq / δa-

[0236] Use the phase mode of the atomic force microscope to measure a 10 μm × 10 μm area on the surface of the above easy adhesion layer. Through the above measurement, the distribution of the phase signal on the surface of the easy adhesion layer is obtained. The unit of the phase signal is [deg].

[0237] Let the arithmetic mean of the phase signals shown in the following formula 1 be δa. Let the root mean square of the phase signals shown in the following formula 2 be δq.

[0238] (In the following formula 1 and formula 2, on the reference surface representing the average value of the phase signal, the right-angled coordinate axes X-axis and Y-axis are arranged, the axis orthogonal to the reference surface is set as the Z-axis, and the curved surface of the phase signal is set as f(x, y). In the following formula 1 and formula 2, the sizes of the regions for calculating δa and δq are set as Lx and Ly. In the following formula 1 and formula 2, Ar = Lx × Ly.)

[0239] Select 7 measurement and evaluation regions of 2 μm × 2 μm from the 10 μm × 10 μm measurement region. Calculate δa, δq, and δq / δa for the above 7 measurement and evaluation regions respectively. Based on the 5 δq / δa values obtained by removing the maximum and minimum values from the above 7 δq / δa values, calculate the average value of δq / δa.

[0240] The above 7 measurement and evaluation regions may be partially repeated. However, the repetition ratio of any measurement and evaluation region to the other 6 measurement and evaluation regions is preferably 25% or less, more preferably 12% or less, and further preferably 5% or less based on the area of the measurement and evaluation region.

[0241] [Equation 5]

[0242]

[0243] [Number 6]

[0244]

[0245] In the case of not having an easy - adhesion layer, even if a functional layer is formed on a polyester film, the adhesion of the optical laminate having the polyester film and the functional layer cannot be improved.

[0246] In addition, even if an easy - adhesion layer is formed on a polyester film, when the average value of δq / δa on the surface of the easy - adhesion layer exceeds 1.60, the adhesion of the optical laminate having a polyester film, an easy - adhesion layer, and a functional layer in this order cannot be improved.

[0247] Hereinafter, the technical meaning of the average value of δq / δa on the surface of the easy - adhesion layer will be described.

[0248] δa and δq are parameters related to the phase signal when measuring a specified region on the surface of the easy - adhesion layer using the phase mode of an atomic force microscope. The unit of the phase signal is [deg]. The above - mentioned phase signal represents the viscoelasticity of the surface of the easy - adhesion layer. An atomic force microscope is a device for measuring the physical properties of a surface by scanning the surface of a sample with a minute probe mounted on a leaf spring. In the phase mode, by vibrating the probe while measuring, the change in the in - plane vibration phase can be mapped. Therefore, in the phase mode, the contrast caused by the viscoelasticity difference of the surface components can be mapped.

[0249] δa is the arithmetic mean of the phase signals in the specified region. On the other hand, δq is the root - mean - square of the phase signals in the specified region. The root - mean - square emphasizes the values deviated from the arithmetic mean. Therefore, even if the value of δa as the arithmetic mean is the same, when the deviation of the phase signals in the specified region is large, the average value of δq as the root - mean - square becomes large. Similarly, even if the value of δa as the arithmetic mean is the same, when the deviation of the phase signals in the specified region is large, the average value of δq / δa also becomes large. On the contrary, even if the value of δa as the arithmetic mean is the same, when the deviation of the phase signals in the specified region is small, the average value of δq / δa also becomes small. That is, for an easy - adhesion layer with a small arithmetic mean of δq / δa, the phase signals in the specified region are concentrated near the arithmetic mean of the phase signals, indicating that the deviation of the phase signals in the specified region is small. Since the phase signal represents the viscoelasticity of the surface of the easy - adhesion layer, an easy - adhesion layer with a small average value of δq / δa indicates that the change in viscoelasticity in the specified region is small.

[0250] It should be noted that the phase signal represents the relative change amount within the same image. Therefore, generally, δa and δq of different samples cannot be compared. In the present invention, attention is focused on the ratio δq / δa of δa to δq. As described above, δq / δa is a parameter representing the deviation of the phase within the sample and is a dimensionless parameter. Therefore, it can be said that δq / δa is appropriate as a parameter for comparing the phase deviation between samples.

[0251] As described above, an easily adherable layer with a small average value of δq / δa indicates a small change in viscoelasticity in a specified region. Moreover, a polyester film having an easily adherable layer with a small average value of δq / δa can improve the adhesion of an optical laminate having a functional layer formed on the easily adherable layer. It is considered that the adhesion of the optical laminate becomes good for the following reasons.

[0252] When another member comes into contact with the functional layer of the optical laminate, a specified stress is generated. The stress is transmitted through the functional layer and the easily adherable layer to the interface between the polyester film and the easily adherable layer. The stress transmission mode varies depending on the viscoelastic value of the easily adherable layer. Therefore, when the change in the in-plane viscoelasticity of the easily adherable layer is large, the magnitude of the stress transmitted to the interface between the polyester film and the easily adherable layer varies depending on the in-plane position. Therefore, when the average value of δq / δa of the easily adherable layer is large, it is easy to apply a large stress to a specified part in the plane, and interface peeling of the optical laminate is likely to occur. On the other hand, it is considered that when the average value of δq / δa of the easily adherable layer is small, the stress is dispersed in the plane, so that interface peeling of the optical laminate can be suppressed and the adhesion can be improved.

[0253] The reason why the viscoelasticity of the easily adherable layer varies depending on the position can be considered the compatibility of the components constituting the easily adherable layer, etc.

[0254] The average value of δq / δa is preferably 1.57 or less, more preferably 1.54 or less, more preferably 1.536 or less, more preferably 1.50 or less, more preferably 1.45 or less, more preferably 1.40 or less.

[0255] The smaller the average value of δq / δa, the closer the viscoelasticity of the surface of the easily adherable layer is to being homogeneous. When the viscoelasticity of the surface of the easily adherable layer is too homogeneous, the components of the functional layer are difficult to penetrate into the easily adherable layer, and sometimes it is difficult to improve the adhesion between the easily adherable layer and the functional layer. Therefore, the average value of δq / δa is preferably 1.125 or more, more preferably 1.20 or more, more preferably 1.25 or more, more preferably 1.30 or more, more preferably 1.326 or more.

[0256] Examples of the preferred range of the average value of δq / δa include 1.125 or more and 1.60 or less, 1.125 or more and 1.57 or less, 1.125 or more and 1.54 or less, 1.125 or more and 1.536 or less, 1.125 or more and 1.50 or less, 1.125 or more and 1.45 or less, 1.125 or more and 1.40 or less, 1.20 or more and 1.60 or less, 1.20 or more and 1.57 or less, 1.20 or more and 1.54 or less, 1.20 or more and 1.536 or less, 1.20 or more and 1.50 or less, 1.20 or more and 1.45 or less, 1.20 or more and 1.40 or less, 1.25 or more and 1.60 or less, 1.25 or more and 1.57 or less, 1.25 or more and 1.54 or less, 1.25 or more and 1.536 or less, 1.25 or more and 1.50 or less, 1.25 or more and 1.45 or less, 1.25 or more and 1.40 or less, 1.30 or more and 1.60 or less, 1.30 or more and 1.57 or less, 1.30 or more and 1.54 or less, 1.30 or more and 1.536 or less, 1.30 or more and 1.50 or less, 1.30 or more and 1.45 or less, 1.30 or more and 1.40 or less, 1.326 or more and 1.60 or less, 1.326 or more and 1.57 or less, 1.326 or more and 1.54 or less, 1.326 or more and 1.536 or less, 1.326 or more and 1.50 or less, 1.326 or more and 1.45 or less, 1.326 or more and 1.40 or less.

[0257] The average value of δq / δa on the surface of the easily adherable layer is the value in a specified 10 μm × 10 μm area.

[0258] In the total area of the surface of the easily adherable layer, the proportion of the area where the average value of δq / δa is 1.60 or less is preferably 80% or more, more preferably 90% or more, further preferably 95% or more, still further preferably 98% or more, and most preferably 100%.

[0259] When the polyester film with the easily adherable layer is in a sheet form, in 10 specific 10 μm × 10 μm areas in the following (1) to (4), the number of parts where the average value of δq / δa is 1.60 or less is preferably 8 or more, more preferably 9 or more, and further preferably 10. In addition, among the above 10 parts, the number of parts where the coefficient of variation of δq / δa is 0.040 or less is preferably 8 or more, more preferably 9 or more, and further preferably 10.

[0260] (1) Draw the circumscribed circle B1 circumscribing the sheet S.

[0261] (2) With the center of the circumscribed circle B1 as the center, draw the inscribed circle B2 inscribed in the sheet.

[0262] (3) With the center of the circumscribed circle B1 as the center, draw a circle B3 with a diameter that is 1 / 2 of the diameter of the inscribed circle B2.

[0263] (4) On the circumference of the circle B3, select 10 regions of 10 μm × 10 μm at equal intervals. Figure 4 The symbols C1 and C6 correspond to a part of the 10 regions of 10 μm × 10 μm.

[0264] When the polyester film with an easy - adhesion layer is in a roll form, cut out a sheet from the roll and measure the average value of δq / δa and the coefficient of variation of δq / δa for the cut - out sheet. In addition, for the cut - out sheet, in the 10 regions of 10 μm × 10 μm specified in the above (1) to (4), preferably 8 or more, more preferably 9 or more, and further preferably 10 of the parts where the average value of δq / δa is 1.60 or less. Also, among the above 10 parts, preferably 8 or more, more preferably 9 or more, and further preferably 10 of the parts where the coefficient of variation of δq / δa is 0.040 or less.

[0265] The physical properties of the roll - shaped polyester film with an easy - adhesion layer in the flow direction are substantially the same. Therefore, when the sheet cut out from an arbitrary position A in the width direction satisfies the average value of δq / δa of the present invention, it can be assumed that at any position A, the whole in the flow direction of the roll satisfies the above - mentioned average value. The same applies to the coefficient of variation of δq / δa. For the sake of caution, it is also possible to cut out sheets from two parts, the core - side of the roll and the surface - side of the roll, at an arbitrary position A, and measure the cut - out sheets respectively. It should be noted that in the case of the core - side of the roll, it is preferable to sample from a part far from the core. This is because the part close to the core may have defects such as roll marks. When the thickness of the polyester film is 40 μm or more, the part far from the core is preferably a part 10 m or more and 20 m or less away from the core, and when the thickness of the polyester film is less than 40 μm, it is preferably a part more than 20 m and 40 m or less away from the core.

[0266] The physical properties of the roll - shaped polyester film with an easy - adhesion layer in the width direction sometimes vary. Therefore, it is preferable to divide the roll into 5 equal parts in the width direction, cut out sheets from each of the 5 equal - divided regions, and measure the average value of δq / δa for the cut - out sheets.

[0267] In the present invention, δa can be calculated by Equation 1 above. Equation 1 adopts the formula for arithmetic mean height in ISO 25178-2:2012. In other words, in the formula for arithmetic mean height in ISO 25178-2:2012, elevation is used as the data for the Z-axis, but in Equation 1, phase signal [deg] is used instead of elevation as the data for the Z-axis. That is, the difference between δa and the arithmetic mean height in ISO 25178-2:2012 is that the former uses phase signal [deg] as the data for the Z-axis, while the latter uses elevation [μm] as the data for the Z-axis.

[0268] In the present invention, δq can be calculated by Equation 2 above. Equation 2 adopts the formula for root mean square height in ISO 25178-2:2012. In other words, in the formula for root mean square height in ISO 25178-2:2012, elevation is used as the data for the Z-axis, but in Equation 2, phase signal [deg] is used instead of elevation as the data for the Z-axis. That is, the difference between δq and the root mean square height in ISO 25178-2:2012 is that the former uses phase signal [deg] as the data for the Z-axis, while the latter uses elevation [μm] as the data for the Z-axis.

[0269] The average value of δq / δa can be calculated according to the following steps A1 to A4.

[0270] (A1) Use the phase mode of an atomic force microscope to measure a 10 μm × 10 μm area on the surface of the easily adherable layer. (When measuring using the product name "SPM-9600" manufactured by Shimadzu Corporation, it is preferable to adjust the P gain, I gain, and offset.)

[0271] (A2) Select seven 2 μm × 2 μm measurement and evaluation areas from within the 10 μm × 10 μm measurement area.

[0272] (A3) Within the seven selected measurement and evaluation areas, calculate δa, δq, and δq / δa.

[0273] (A4) Based on the five δq / δa values obtained by removing the maximum and minimum values from the seven δq / δa values, calculate the average value of δq / δa.

[0274] In the above A1, examples of the atomic force microscope include the product name "SPM-9600" manufactured by Shimadzu Corporation.

[0275] In the above A2, the selected 2 μm × 2 μm area is selected from the area where the maximum height of the amplitude measured by an atomic force microscope is 90 nm or less. The maximum height is the maximum height Sz of ISO 25178-2:2012. By selecting a 2 μm × 2 μm area from the area where Sz is 90 nm or less, the influence of foreign matters and defects can be easily excluded. The seven measurement and evaluation areas are preferably selected in a non-overlapping manner with each other, but they can also overlap with each other. It should be noted that when the measurement and evaluation areas overlap, the overlapping ratio of any measurement and evaluation area with the other six measurement and evaluation areas is preferably 25% or less, more preferably 12% or less, and further preferably 5% or less based on the area of the measurement and evaluation area.

[0276] In addition, in the above A2, in order to more easily exclude the influence of foreign matters and defects, the selected 2 μm × 2 μm measurement and evaluation area is preferably selected from the area where the arithmetic mean height of the amplitude measured by an atomic force microscope is 10 nm or less. The arithmetic mean height is the arithmetic mean height Sa of ISO 25178-2:2012.

[0277] The easy-to-bond layer preferably has a coefficient of variation of δq / δa calculated based on the above five δq / δa values of 0.040 or less.

[0278] By making the coefficient of variation of δq / δa 0.040 or less, the stress can be more easily dispersed in the plane, and the adhesion can be more easily improved. The coefficient of variation of δq / δa is more preferably 0.039 or less, more preferably 0.037 or less, and more preferably 0.035 or less.

[0279] When the coefficient of variation of δq / δa is too small, it is sometimes difficult for the components of the functional layer to penetrate into the easy-to-bond layer, and it is difficult to improve the adhesion between the easy-to-bond layer and the functional layer. Therefore, the coefficient of variation of δq / δa is preferably 0.009 or more, more preferably 0.010 or more, more preferably 0.015 or more, and more preferably 0.018 or more.

[0280] Examples of the implementation modes of the preferred range of δq / δa include 0.009 or more and 0.040 or less, 0.009 or more and 0.039 or less, 0.009 or more and 0.037 or less, 0.009 or more and 0.035 or less, 0.010 or more and 0.040 or less, 0.010 or more and 0.039 or less, 0.010 or more and 0.037 or less, 0.010 or more and 0.035 or less, 0.015 or more and 0.040 or less, 0.015 or more and 0.039 or less, 0.015 or more and 0.037 or less, 0.015 or more and 0.035 or less, 0.018 or more and 0.040 or less, 0.018 or more and 0.039 or less, 0.018 or more and 0.037 or less, 0.018 or more and 0.035 or less.

[0281] Among the total surface area of the surface of the easy - adhesion layer, the proportion of the area where the coefficient of variation of δq / δa is 0.040 or less is preferably 80% or more, more preferably 90% or more, further preferably 95% or more, still further preferably 98% or more, and most preferably 100%.

[0282] The resin constituting the easy - adhesion layer is not particularly limited, and examples thereof include thermoplastic resins such as polyester resins, polyurethane resins, and acrylic resins, and thermosetting resins. Thermoplastic resins are preferred. Further, among thermoplastic resins, either a polyester resin or a polyurethane resin that can easily reduce the refractive index difference between the polyester film and the easy - adhesion layer and the refractive index difference between the easy - adhesion layer and the uneven layer is preferred, and a resin containing both a polyester component and a polyurethane component is more preferred.

[0283] The polyurethane component can easily improve the adhesion, but it is difficult to enhance the film strength. Therefore, a resin containing both a polyester component and a polyurethane component is preferred. However, when the polyurethane component is excessive relative to the polyester component, phase separation is likely to occur, and thus the average value of δq / δa and the coefficient of variation of δq / δa are likely to increase. In addition, since the polyurethane component is soft, when the polyurethane component is excessive, due to the difference in the in - plane cross - link density, the average value of δq / δa and the coefficient of variation of δq / δa are likely to increase. Therefore, in the resin containing both a polyester component and a polyurethane component, the mass ratio of the polyester component to the polyurethane component is preferably 95:5 to 60:40, more preferably 90:10 to 60:40.

[0284] The number - average molecular weight of the resin constituting the easy - adhesion layer is preferably 10,000 or more, more preferably 15,000 or more. The number - average molecular weight of this resin is preferably 100,000 or less, more preferably 60,000 or less. By making the number - average molecular weight of the resin constituting the easy - adhesion layer within the above range, cohesive failure of the easy - adhesion layer can be easily suppressed.

[0285] The glass transition temperature of the resin constituting the easy - adhesion layer is preferably 30°C or more, more preferably 50°C or more, further preferably 70°C or more. The glass transition temperature of this resin is preferably 120°C or less, more preferably 110°C or less, further preferably 90°C or less.

[0286] By making the glass transition temperature of the resin constituting the easy - adhesion layer 30°C or more, it is possible to easily suppress the easy - adhesion layer from flowing due to heat during the process and generating internal stress, and thus it is possible to easily make the average value of δq / δa and the coefficient of variation of δq / δa within the above range. Examples of the heat during the process include the heat in the drying process of the coating liquid for the functional layer and the heat caused by heating when laminating the optical laminate to the polarizing element.

[0287] By making the glass transition temperature of the resin constituting the easily adherable layer 120°C or lower, it is possible to easily suppress the stress caused by the difference in the thermal behavior between the easily adherable layer and the polyester film due to heat during the process, and thus it is possible to suppress the generation of cracks and the like in the easily adherable layer due to the above stress. Therefore, by making the glass transition temperature of the resin constituting the easily adherable layer 120°C or lower, it is possible to easily make the average value of δq / δa and the coefficient of variation of δq / δa within the above ranges.

[0288] The easily adherable layer may contain additives such as a refractive index modifier, a dye, a pigment, a leveling agent, an ultraviolet absorber, an antioxidant, and a light stabilizer within a range that does not hinder the effects of the present invention; a crosslinking agent for adjusting hardness or viscosity. As the above crosslinking agent, non-yellowing XDI-based, IPDI-based, HDI-based isocyanates, radiation-curable polyfunctional monomers, etc. can be cited.

[0289] The easily adherable layer can be formed by an in-line coating method in which coating is performed during the production of the polyester film, or by an off-line coating method in which coating is performed after the production of the polyester film.

[0290] In the in-line coating method and the off-line coating method, it is preferable to use a coating liquid for the easily adherable layer containing the components constituting the easily adherable layer. For example, by coating the coating liquid for the easily adherable layer on the polyester film by a general coating method and drying it, the easily adherable layer can be formed. At this time, it is preferable that the drying time is 120 seconds or less, more preferably 90 seconds or less. By making the drying time 120 seconds or less, it is possible to suppress the phase separation of the components constituting the easily adherable layer, and it is easy to make the average value of δq / δa and the coefficient of variation of δq / δa within the above ranges. If the drying time is too short, the surface of the coating film may be rough and the optical properties may be reduced. Therefore, the drying time is preferably 15 seconds or more, more preferably 20 seconds or more. The drying time can be adjusted according to the drying temperature and the drying wind speed.

[0291] The direction of the drying wind is preferably opposite to the conveyance direction of the polyester film. By making the direction of the drying wind and the conveyance direction of the polyester film in the above relationship, it is possible to significantly shorten the drying time of the coating liquid for the easily adherable layer without excessively increasing the drying temperature.

[0292] The drying temperature of the coating liquid for the easily adherable layer is preferably 50°C or higher and 200°C or lower, more preferably 60°C or higher and 150°C or lower. By making the drying temperature 50°C or higher, it is possible to easily shorten the drying time of the coating liquid for the easily adherable layer, and thus it is possible to easily suppress the phase separation of the components constituting the easily adherable layer. By making the drying temperature 200°C or lower, it is possible to easily suppress the thermal decomposition of the components constituting the easily adherable layer.

[0293] In order to dissolve or disperse the components constituting the easily adherable layer or adjust the viscosity, the coating liquid for the easily adherable layer preferably contains a solvent.

[0294] Solvents may include, for example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; ethers such as dioxane, tetrahydrofuran; aliphatic hydrocarbons such as hexane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as toluene, xylene; halogenated carbons such as dichloromethane, dichloroethane; esters such as methyl acetate, ethyl acetate, butyl acetate; alcohols such as isopropyl alcohol, butanol, cyclohexanol; cellosolves such as methyl cellosolve, ethyl cellosolve; glycol ethers such as propylene glycol monomethyl ether acetate; cellosolve acetates; sulfoxides such as dimethyl sulfoxide; amides such as dimethylformamide, dimethylacetamide, etc., and may also be mixtures thereof.

[0295] If the drying time of the solvent in the coating liquid for the easy-bonding layer is too long, the components constituting the easy-bonding layer are likely to undergo phase separation. Therefore, the solvent in the coating liquid for the easy-bonding layer preferably contains a solvent with a fast evaporation rate.

[0296] On the other hand, if the drying time of the solvent in the coating liquid for the easy-bonding layer is too short, the surface of the coating film is likely to become rough. Therefore, the solvent in the coating liquid for the easy-bonding layer preferably uses a mixture of a solvent with an extremely fast evaporation rate and a solvent with a moderately fast evaporation rate.

[0297] In this specification, a solvent with an extremely fast evaporation rate means a solvent with an evaporation rate of 280 or more when the evaporation rate of butyl acetate is set to 100. In addition, in this specification, a solvent with a moderately fast evaporation rate means a solvent with an evaporation rate of 150 or more and less than 280 when the evaporation rate of butyl acetate is set to 100.

[0298] The evaporation rate of the solvent with an extremely fast evaporation rate is preferably 320 or more and 430 or less, more preferably 340 or more and 400 or less. As a solvent with an extremely fast evaporation rate, for example, methyl ethyl ketone with an evaporation rate of 370 and n-heptane with an evaporation rate of 362 can be cited.

[0299] The evaporation rate of the solvent with a moderately fast evaporation rate is preferably 170 or more and 250 or less, more preferably 180 or more and 220 or less. As a solvent with a moderately fast evaporation rate, for example, toluene with an evaporation rate of 200 and propyl acetate with an evaporation rate of 214 can be cited.

[0300] In the solvent of the coating liquid for the easy-bonding layer, the mass ratio of the solvent with an extremely fast evaporation rate to the solvent with a moderately fast evaporation rate is preferably 50:50 to 90:10, more preferably 70:30 to 85:15.

[0301] To easily suppress phase separation, the lower limit of the solid content concentration of the coating liquid for the easy-bonding layer is preferably 2% by mass or more, more preferably 4% by mass or more. In addition, the content of the solvent in the coating liquid for the easy-bonding layer preferably has an upper limit of 30% by mass or less, more preferably 10% by mass or less, based on the solid content concentration.

[0302] The dry coating amount of the easily adherable layer is preferably 0.05 g / m 2 or more and 0.75 g / m 2 or less. The thickness of the easily adherable layer is not particularly limited, preferably 10 nm or more and 600 nm or less, more preferably 20 nm or more and 300 nm or less, and further preferably 50 nm or more and 200 nm or less. In order to suppress interference fringes, it is preferable that the thickness of the easily adherable layer is thin.

[0303] In this specification, the thickness of the easily adherable layer, the functional layer, etc. can be calculated as follows: Select any 20 parts from the cross-sectional photograph obtained by a scanning transmission electron microscope (STEM), and calculate from the average value at 20 places. Among them, the 20 parts are selected in a non-concentrated manner according to the location. The acceleration voltage and magnification of the STEM can be set according to the layer to be measured.

[0304] <Dimensions, shape, etc.>

[0305] The polyester film with an easily adherable layer can be in the form of a single leaf cut into a specified size, or in the form of a roll 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 2 inches or more and 500 inches or less. "Maximum diameter" refers to the maximum length when connecting any two points of the polyester film. For example, when the polyester film is rectangular, the diagonal of the rectangle is the maximum diameter. When the polyester film is circular, the diameter of the circle is the maximum diameter.

[0306] The width and length of the roll are not particularly limited. Generally, the width is 500 mm or more and 8000 mm or less, and the length is 100 m or more and 10000 m or less. The polyester film in the form of a roll can be cut into single-leaf form for use according to the size of an image display device, etc. When cutting, it is preferable to exclude the roll end where the physical properties are unstable.

[0307] 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. More specifically, when the polyester film is quadrilateral, the aspect ratio is not particularly limited as long as it is suitable for the display screen. For example, it can be cited as horizontal: vertical = 1:1, 4:3, 16:10, 16:9, 2:1, 5:4, 11:8, etc.

[0308] [Optical laminate]

[0309] The optical laminate of the present invention has one or more functional layers on the easily adherable layer of the polyester film of the present invention.

[0310] Figure 1 It is a cross-sectional view showing an embodiment of the optical laminate 1000 of the present invention. Figure 1The optical laminate 1000 successively has a polyester film 100, an easy-bonding layer 200, and a functional layer 300.

[0311] <Functional layer>

[0312] The functional layer may have a single-layer structure or a multi-layer structure. Examples of the layers constituting the functional layer include a hard coat layer, an antiglare layer, an antireflection layer, a selective wavelength absorption layer, an antifouling layer, and an antistatic layer. The functional layer may also have multiple functions in one layer.

[0313] Examples of the antireflection layer in the functional layer include a single-layer structure and a multi-layer structure. As a single-layer antireflection layer, a single layer of a low refractive index layer can be cited. The multi-layer antireflection layer can be cited as a two-layer structure of a high refractive index layer and a low refractive index layer, and can also be cited as a structure of three or more layers.

[0314] Examples of the functional layer formed on the easy-bonding layer include the following B1 to B7.

[0315] B1: Single-layer structure of a hard coat layer

[0316] B2: Single-layer structure of an antiglare layer

[0317] B3: Multi-layer structure successively having a hard coat layer and an antireflection layer

[0318] B4: Multi-layer structure successively having an antiglare layer and an antireflection layer

[0319] B5: Multi-layer structure successively having a hard coat layer and an antifouling layer

[0320] B6: Multi-layer structure successively having an antiglare layer and an antifouling layer

[0321] B7: Multi-layer structure successively having a hard coat layer, an antireflection layer, and an antifouling layer

[0322] Among one or more functional layers, the functional layer in contact with the easy-bonding layer preferably contains a cured product of an ionizing radiation curable resin composition. The functional layer in contact with the easy-bonding layer is preferably a hard coat layer or an antiglare layer.

[0323] When the functional layer in contact with the easy-bonding layer contains a cured product of an ionizing radiation curable resin composition, the adhesion of the optical laminate is likely to decrease. However, in the optical laminate of the present invention, since the average value of δq / δa on the surface of the easy-bonding layer is a specified value, even if the functional layer in contact with the easy-bonding layer contains a cured product of an ionizing radiation curable resin composition, the adhesion of the optical laminate can be easily improved.

[0324] In addition, by making the functional layer in contact with the easy-bonding layer contain a cured product of an ionizing radiation curable resin composition, the pencil hardness of the optical laminate can be easily increased.

[0325] The functional layer in contact with the easy - adhesion layer in one or more functional layers preferably contains a cured product of an ionizing radiation - curable resin composition and has a thickness of 0.5 μm or more. With the above - mentioned configuration, the pencil hardness of the optical laminate can be easily improved. The thickness of the functional layer in contact with the easy - adhesion layer is more preferably 1.0 μm or more, further preferably 2.0 μm or more, and the upper limit is preferably 20.0 μm or less, more preferably 10.0 μm or less, more preferably 7.0 μm or less, more preferably 5.0 μm or less. The functional layer in contact with the easy - adhesion layer is preferably a hard coat layer or an antiglare layer.

[0326] Examples of the preferred range of the thickness of the functional layer in contact with the easy - adhesion layer include 0.5 μm or more and 20.0 μm or less, 0.5 μm or more and 10.0 μm or less, 0.5 μm or more and 7.0 μm or less, 0.5 μm or more and 5.0 μm or less, 1.0 μm or more and 20.0 μm or less, 1.0 μm or more and 10.0 μm or less, 1.0 μm or more and 7.0 μm or less, 1.0 μm or more and 5.0 μm or less, 2.0 μm or more and 20.0 μm or less, 2.0 μm or more and 10.0 μm or less, 2.0 μm or more and 7.0 μm or less, 2.0 μm or more and 5.0 μm or less.

[0327] The contact angle of the surface of the side of the optical laminate having the functional layer with respect to pure water is preferably 80 degrees or more, more preferably 85 degrees or more, more preferably 90 degrees or more, more preferably 95 degrees or more, more preferably 100 degrees or more. By making the contact angle 80 degrees or more, the slidability when other members come into contact with the surface of the optical laminate becomes good, so stress is not easily generated. Therefore, the adhesion of the optical laminate can be easily improved. That is, by laminating a functional layer with an adjusted contact angle on the easy - adhesion layer of the polyester film with an easy - adhesion layer of the present invention where the average value of δq / δa is in a specified range, the adhesion of the optical laminate can be easily made better.

[0328] If the contact angle of pure water is too large, the functional layer on the surface side of the optical laminate will contain a large amount of antifouling agent. Therefore, physical properties such as the surface hardness of the optical laminate may decrease. Therefore, the contact angle is preferably 130 degrees or less, more preferably 120 degrees or less. In this specification, the contact angle refers to the static contact angle measured by the θ / 2 method.

[0329] General pure water can be used for pure water. The resistivity value of pure water is usually 0.1 MΩ·cm or more and 15 MΩ·cm or less.

[0330] Examples of the preferred range of the contact angle described above include 80 degrees or more and 130 degrees or less, 80 degrees or more and 120 degrees or less, 85 degrees or more and 130 degrees or less, 85 degrees or more and 120 degrees or less, 90 degrees or more and 130 degrees or less, 90 degrees or more and 120 degrees or less, 95 degrees or more and 130 degrees or less, 95 degrees or more and 120 degrees or less, 100 degrees or more and 130 degrees or less, 100 degrees or more and 120 degrees or less.

[0331] The functional layer contains, for example, a binder resin and additives as required.

[0332] The thickness of the functional layer can be appropriately selected according to the function to be imparted.

[0333] The functional layer preferably contains a cured product of a curable resin composition as the binder resin. Examples of the cured product of the curable resin composition include a cured product of a thermosetting resin composition and a cured product of an ionizing radiation-curable resin composition. To improve the pencil hardness, a cured product of an ionizing radiation-curable resin composition is preferred.

[0334] The proportion of the cured product of the curable resin composition relative to all the binder resins in the functional layer is preferably 60% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and even more preferably 100%.

[0335] The thermosetting resin composition is a composition containing at least a thermosetting resin and is a resin composition that cures by heating.

[0336] Examples of the thermosetting resin include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, unsaturated polyester resins, silicone resins, etc. In the thermosetting resin composition, a curing agent can be added to these curable resins as required.

[0337] The ionizing radiation-curable resin composition is a composition containing a compound having an ionizing radiation-curable functional group. In this specification, the "compound having an ionizing radiation-curable functional group" is sometimes referred to as an "ionizing radiation-curable compound".

[0338] Ionizing radiation refers to ionizing radiation in electromagnetic waves or charged particle beams that has energy quanta capable of polymerizing or crosslinking molecules. Usually, ultraviolet rays or electron beams are used. In addition to these, electromagnetic waves such as X-rays and γ-rays, and charged particle beams such as α-rays and ion beams can also be used.

[0339] Examples of the ionizing radiation curable functional group include ethylenically unsaturated bond groups such as (meth)acryloyl group, vinyl group, allyl group, and epoxy group, oxetanyl group, etc. As the ionizing radiation curable compound, a compound having an ethylenically unsaturated bond group is preferred, and a compound having two or more ethylenically unsaturated bond groups is more preferred. Among them, a polyfunctional (meth)acrylate compound having two or more ethylenically unsaturated bond groups is further preferred.

[0340] As the polyfunctional (meth)acrylate compound, either a monomer or an oligomer can be used, and an oligomer is preferably included. That is, the functional layer preferably contains a cured product of a polyfunctional (meth)acrylate oligomer as a binder resin. Particularly preferably, the functional layer in contact with the easy-bonding layer contains a cured product of a polyfunctional (meth)acrylate oligomer as a binder resin. The cured product of the polyfunctional (meth)acrylate oligomer can improve the surface hardness of the optical laminate while suppressing excessive curing shrinkage of the functional layer. Therefore, it is possible to easily improve the pencil hardness of the optical laminate while improving the adhesion of the optical laminate.

[0341] In order to easily further improve the balance between the pencil hardness and the adhesion of the optical laminate, as the polyfunctional (meth)acrylate compound, it is more preferably composed of an oligomer and a monomer. That is, the functional layer preferably contains a cured product of a polyfunctional (meth)acrylate oligomer and a cured product of a polyfunctional (meth)acrylate monomer as a binder resin. Particularly preferably, the functional layer in contact with the easy-bonding layer contains a cured product of a polyfunctional (meth)acrylate oligomer and a cured product of a polyfunctional (meth)acrylate monomer as a binder resin.

[0342] When an oligomer and a monomer are used as the polyfunctional (meth)acrylate compound, the mass ratio of the oligomer to the monomer is preferably 5:95 to 95:5, more preferably 50:50 to 85:15, and further preferably 60:40 to 80:20.

[0343] Examples of the polyfunctional (meth)acrylate oligomer include (meth)acrylate polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, etc.

[0344] Urethane (meth)acrylate is obtained, for example, by the reaction of a polyol and an organic diisocyanate with a hydroxy (meth)acrylate.

[0345] The lower limit of the weight average molecular weight of the polyfunctional (meth)acrylate oligomer is preferably 500 or more, more preferably 1000 or more, and the upper limit is preferably 5000 or less, more preferably 3000 or less.

[0346] By making the weight-average molecular weight of the oligomer 500 or more, it is possible to easily suppress excessive curing shrinkage of the functional layer. Further, by making the weight-average molecular weight of the oligomer 5000 or less, it is possible to easily suppress a decrease in pencil hardness.

[0347] As an embodiment of the range of the weight-average molecular weight of the polyfunctional (meth)acrylate oligomer, examples include 500 or more and 5000 or less, 500 or more and 3000 or less, 1000 or more and 5000 or less, and 1000 or more and 3000 or less.

[0348] In this specification, the weight-average molecular weight and the number-average molecular weight refer to polystyrene conversion values measured by gel permeation chromatography.

[0349] In the polyfunctional (meth)acrylate compound, as the bifunctional (meth)acrylate monomer, examples include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxy diacrylate, bisphenol A tetrapropoxy diacrylate, 1,6-hexanediol diacrylate, and the like.

[0350] As the trifunctional or higher (meth)acrylate monomer, examples include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, isocyanuric acid-modified tri(meth)acrylate, and the like.

[0351] A part of the molecular skeleton of the above (meth)acrylate monomer can be modified. For example, (meth)acrylate monomers modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cycloalkyl, aromatic, bisphenol, etc. can also be used.

[0352] For the purpose of adjusting the viscosity of the coating liquid for the functional layer, etc., as the radiation-curable compound, a monofunctional (meth)acrylate can also be added.

[0353] As the monofunctional (meth)acrylate, examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isobornyl (meth)acrylate.

[0354] The above radiation-curable compounds can be used alone or in combination of two or more.

[0355] In addition to the radiation-curable compound, a polymer may be added to the coating liquid for the functional layer to adjust the viscosity. Examples of the polymer include those having a weight-average molecular weight of more than 5,000 and 200,000 or less.

[0356] When the radiation-curable compound is an ultraviolet-curable compound, the radiation-curable resin composition preferably contains additives such as a photoinitiator and a photopolymerization accelerator.

[0357] Examples of the photoinitiator include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzoin dimethyl ether, benzoyl benzoate, α-acyl oxime ester, anthraquinone, halogenated ketone, thioxanthone, and the like. Among these, α-hydroxyalkylphenone, which is less likely to cause yellowing, is preferred.

[0358] The photopolymerization accelerator can reduce the polymerization inhibition caused by air during curing and increase the curing speed. Examples thereof include one or more selected from isopentyl p-dimethylaminobenzoate, ethyl p-dimethylaminobenzoate, and the like.

[0359] The functional layer may contain additives as needed.

[0360] The additives can be appropriately selected from general materials according to the functions imparted to the functional layer. For example, when imparting antiglare properties to the functional layer, it is preferable to contain organic particles and / or inorganic particles as additives. When imparting antireflection properties to the functional layer, as additives, it is preferable to contain refractive index adjusting materials such as a high refractive index material and a low refractive index material. When imparting antifouling properties to the functional layer, it is preferable to contain an antifouling agent as an additive.

[0361] Furthermore, examples of the additives also include antistatic agents, leveling agents, ultraviolet absorbers, dyes, pigments, conductive particles, flocculants, defoaming agents, antioxidants, and light stabilizers.

[0362] <Physical Properties>

[0363] The total light transmittance of the optical laminate according to JIS K7361-1:1997 is preferably 50% or more, more preferably 80% or more, and further preferably 90% or more.

[0364] The total light transmittance and the haze described below are measured with the light incident surface being the polyester film side. The total light transmittance and the haze described below can be measured, for example, using a haze meter (model number: HM-150) manufactured by Murakami Color Research Institute.

[0365] In the optical laminate, the lower limit of the haze according to JIS K7136:2000 is preferably 0.3% or more, more preferably 0.4% or more, and further preferably 0.5% or more, and the upper limit is preferably 10% or less, more preferably 7% or less, and further preferably 5% or less.

[0366] <Dimensions, shape, etc.>

[0367] The optical laminate may 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 into a roll. The size of the single leaf is not particularly limited, and the maximum diameter is about 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.

[0368] The width and length of the roll are not particularly limited. Generally, the width is 500 mm or more and 8000 mm or less, and the length is 100 m or more and 10000 m or less. The optical laminate in the form of a roll 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.

[0369] 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. More specifically, when the optical laminate is quadrilateral, the aspect ratio is not particularly limited as long as it is suitable for the display screen. For example, examples include horizontal:vertical = 1:1, 4:3, 16:10, 16:9, 2:1, 5:4, 11:8, etc.

[0370] [Polarizer]

[0371] 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 is the optical laminate of the present invention, and the optical laminate is disposed such that the surface facing the functional layer side faces the side opposite to the polarizing element.

[0372] [Polarizing element]

[0373] As the polarization element, for example, a sheet-type polarization element such as a polyvinyl alcohol film, a polyvinyl formal film, a polyvinyl acetal film, or a saponified ethylene-vinyl acetate copolymer film that is dyed with iodine or the like and stretched; a wire grid-type polarization element composed of a large number of parallel metal wires; a coated-type polarization element coated with a lyotropic liquid crystal or a dichroic host-guest material; a multilayer thin film-type polarization element, etc. These polarization elements may be reflective polarization elements having a function of reflecting non-transmitting polarization components.

[0374] <Transparent protective plate>

[0375] A first transparent protective plate is disposed on one side of the polarization element, and a second transparent protective plate is disposed on the other side. At least one of the first transparent protective plate and the second transparent protective plate is the optical laminate of the present invention described above.

[0376] As the first transparent protective plate and the second transparent protective plate other than the optical laminate, plastic films and glass, etc. can be cited. As the plastic film, a polyester film, a polycarbonate film, a cycloolefin polymer film, and an acrylic film can be cited, and their stretched films are preferred in order to improve mechanical strength. Glass can include soda-lime glass, nitrided glass, soda-lime glass, borosilicate glass, and lead glass, etc. In addition, the glass of the transparent protective plate for protecting the polarization element is preferably shared with other components of the image display device. For example, it is preferable to share the glass substrate of the liquid crystal display element with the transparent protective plate for protecting the polarization element.

[0377] It should be noted that the polarization element and the transparent protective plate are preferably adhered by an adhesive. As the adhesive, a general adhesive can be used, and a PVA-based adhesive is preferred.

[0378] The polarizing plate of the present invention may have both the first transparent protective plate and the second transparent protective plate as the optical laminate of the present invention described above, but it is preferable that one of the first transparent protective plate and the second transparent protective plate is the optical laminate of the present invention described above. In addition, when the polarizing plate of the present invention is used as the polarizing plate disposed on the light-emitting surface side of the display element, it is preferable that the transparent protective plate on the light-emitting surface side of the polarization element is the optical laminate of the present invention described above. On the other hand, when the polarizing plate of the present invention is used as the polarizing plate disposed on the side opposite to the light-emitting surface of the display element, it is preferable that the transparent protective plate on the side opposite to the light-emitting surface of the polarization element is the optical laminate of the present invention described above.

[0379] [Surface plate]

[0380] The surface plate of the present invention is a surface plate in which an optical laminate is adhered to a resin plate or a glass plate, wherein the optical laminate is the optical laminate of the present invention described above, and the optical laminate is disposed such that the surface on the functional layer side faces the side opposite to the resin plate or the glass plate.

[0381] The front panel of the present invention can be used, for example, as a front panel for an image display device. In addition, the front panel of the present invention can be used as a front panel for protecting articles such as clocks and paintings. Furthermore, the front panel of the present invention can be used as a member for display windows and display cabinets.

[0382] The front panel for an image display device is preferably arranged such that the surface on the side where the optical laminate is adhered faces the front side. In other words, the front panel for an image display device is preferably arranged such that the surface on the side where the optical laminate is adhered faces the side opposite to the display element.

[0383] The front panel for protecting an article is preferably arranged such that the surface on the side where the optical laminate is adhered faces the side opposite to the article.

[0384] As the resin plate or glass plate, a resin plate or glass plate generally used as a front panel can be used.

[0385] To improve the strength, the thickness of the resin plate or glass plate is preferably 10 μm or more. The upper limit of the thickness of the resin plate or glass plate is generally 5000 μm or less. In recent years, due to the popularity of the thinning of image display devices, it is preferably 1000 μm or less, more preferably 500 μm or less, and further preferably 100 μm or less.

[0386] As embodiments of the thickness range of the resin plate or glass plate, 10 μm or more and 5000 μm or less, 10 μm or more and 1000 μm or less, 10 μm or more and 500 μm or less, 10 μm or more and 100 μm or less can be cited.

[0387] [Image display panel]

[0388] In the image display panel of the present invention, the above-described optical laminate of the present invention is arranged on the display element.

[0389] In the image display panel, the optical laminate is preferably arranged such that the surface on the functional layer side faces the side opposite to the display element. In addition, the optical laminate is preferably arranged on the outermost surface of the image display panel.

[0390] As the display element, EL display elements such as liquid crystal display elements, organic EL display elements, and inorganic EL display elements, plasma display elements, etc. can be cited. Furthermore, LED display elements such as small LED display elements and micro LED display elements can be cited. In addition, a laser holographic display element can also be cited. These display elements can also have a touch panel function inside the display element.

[0391] As display modes of liquid crystal for a liquid crystal display element, an IPS mode, a VA mode, a multi-domain mode, an OCB mode, an STN mode, a TSTN mode, a ferroelectric liquid crystal mode, etc. can be cited. When the display element is a liquid crystal display element, a backlight is required. The backlight is disposed on the side opposite to the side having the optical laminate of the liquid crystal display element. As the backlight, a backlight using quantum dots, a backlight using white light emitting diodes can be cited.

[0392] The image display panel can be a foldable image display panel or a rollable image display panel. In addition, the image display panel can be an image display panel with a touch panel.

[0393] The size of the image display panel is not particularly limited, and the maximum diameter is about 2 inches or more and 500 inches or less. The maximum diameter refers to the maximum length when connecting any two points in the plane of the image display panel.

[0394] [Image Display Device]

[0395] The image display device of the present invention includes the above-mentioned image display panel of the present invention.

[0396] In the image display device, the optical laminate is preferably disposed such that the surface on the functional layer side faces the side opposite to the display element. In addition, the optical laminate is preferably disposed on the outermost surface of the image display device.

[0397] The image display device of the present invention preferably further includes a drive control unit electrically connected to the above-mentioned image display panel, and a housing that houses the above-mentioned image display panel and the above-mentioned drive control unit, etc.

[0398] When the display element is a liquid crystal display element, the image display device of the present invention requires a backlight. The backlight is disposed on the side opposite to the light-emitting surface side of the liquid crystal display element.

[0399] The size of the image display device is not particularly limited, and the maximum diameter of the effective display area is about 2 inches or more and 500 inches or less.

[0400] The effective display area of the image display device refers to the area where an image can be displayed. For example, when the image display device has a housing that surrounds the display element, the area inside the housing becomes the effective display area.

[0401] The maximum diameter of the effective display area refers to the maximum length when connecting any two points within the effective display area. For example, when the effective display area is rectangular, the diagonal of the rectangle becomes the maximum diameter. When the effective display area is circular, the diameter of the circle is the maximum diameter.

[0402] Examples

[0403] Hereinafter, examples and comparative examples are given to specifically illustrate the present invention. The present invention is not limited to the embodiments described herein.

[0404] 1. Evaluation and measurement

[0405] The polyester films with an easy-to-bond layer and the optical laminates obtained in the examples and comparative examples were subjected to the following measurements and evaluations. The results are shown in Table 1 or 2. It should be noted that unless otherwise specified, the atmosphere for each measurement and evaluation is a temperature of 23 ± 5°C and a relative humidity of 40% or more and 65% or less. Samples for measurement and evaluation were defect-free, clean, and flat. In addition, unless otherwise specified, before each measurement and evaluation, the target sample was exposed to the above atmosphere for 30 minutes or more and 60 minutes or less.

[0406] 1-1. Pencil hardness

[0407] Regarding the polyester films with an easy-to-bond layer in the examples and comparative examples, the pencil hardness of the polyester films was measured. The measurement method of the pencil hardness was carried out according to the steps of (1) to (6) in the text of the specification. The measurement of the pencil hardness was carried out before forming the easy-to-bond layer. For a commercially available polyester film with an easy-to-bond layer formed on one side in advance, the pencil hardness of the surface where the easy-to-bond layer was not formed was measured. The measurement of the pencil hardness was carried out for both the slow axis and the fast axis.

[0408] 1-2. Calculation of the average value of δq / δa

[0409] Samples of 5 mm × 5 mm were cut out from the polyester films with an easy-to-bond layer in the examples and comparative examples. Then, regarding the above samples, the 10 μm × 10 μm region of the surface of the adhesive layer was measured using the phase mode of an atomic force microscope. The measurement device and measurement conditions are as described above. Seven 2 μm × 2 μm measurement and evaluation regions were selected from the 10 μm × 10 μm measurement region. The above seven regions were selected from the region where the maximum height of the amplitude measured by the atomic force microscope was 90 nm or less and the arithmetic average height of the amplitude was 10 nm or less. The δa, δq, and δq / δa of the above seven measurement and evaluation regions were calculated respectively. Based on the δa and δq of the five measurement and evaluation regions after removing the maximum and minimum values from the δq / δa of the above seven regions, the average value and the coefficient of variation of δq / δa were calculated. It should be noted that in the following measurement device, if a 2 μm × 2 μm measurement and evaluation region is selected on the screen, the δa and δq of the selected measurement and evaluation region are automatically displayed (where, for the setting of the following measurement device, in the display screen of the following measurement device, the item corresponding to δa is displayed as "Ra", and the item corresponding to δq is displayed as "Rq").

[0410] <Measurement device>

[0411] The product name "SPM-9600" of Shimadzu Corporation

[0412] <Analysis software>

[0413] SPM manager

[0414] <AFM analysis conditions>

[0415] Tilt correction: Line fitting

[0416] <The cantilever used>

[0417] The part number "NCHR" of NanoWorld Corporation

[0418] (Resonance frequency: 320 kHz, spring constant 42 N / m)

[0419] <Measurement mode>

[0420] Phase (In the "Phase Mode" of the above measurement device, not only the phase but also the amplitude is measured.)

[0421] <Measurement conditions>

[0422] ―Amplitude · Phase―

[0423] · Sensitivity: ×2

[0424] · Phase offset: 95.00 deg

[0425] -XY control-

[0426] · Scan range: 10.0000 μm

[0427] · Scan speed: 1.00 Hz

[0428] · Number of pixels: 512 × 512

[0429] · Bias X: 0.0000 μm

[0430] · Bias Y: 0.0000 μm

[0431] · Scan angle: 0.0000 deg

[0432] -Z control-

[0433] · Operating point: 0.228 V

[0434] · P gain: 0.001

[0435] · I gain: 15000.000

[0436] · Bias Z: 0.0630 μm

[0437] 1-3. Adhesion

[0438] The cutting edge of a cutter was inserted from the surface on the hard coat side of the optical laminates of the examples and comparative examples, thereby forming 100 checkerboard-shaped incisions (number of cuts: 11 cutting lines in the longitudinal and transverse directions, cutting interval: 1 mm). The cutting edge of the cutter used the product number "BA-52P" of NT Corporation. Next, a tape (product name "Cellotape (registered trademark)" of Mitsubang Co., Ltd.) was pasted on the surface of the optical laminate where the checkerboard pattern was formed, and then the tape was peeled off. Thus, a peel test was conducted according to the cross-cut method specified in JIS K5600-5-6:1999. The adhesion of the optical laminates of the examples and comparative examples was evaluated according to the following evaluation criteria.

[0439] <Evaluation Criteria>

[0440] A: The number of peeled grids is 0, and there is no case where a part of the grid is missing.

[0441] B: The number of peeled grids is 0, but there is a part where a part of the grid is missing along the incision, etc., resulting in a part of the grid being missing.

[0442] C: The number of peeled grids is 1 or more.

[0443] 1-4. Total light transmittance (Tt) and haze (Hz)

[0444] Using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute), the total light transmittance of JIS K7361-1:1997 and the haze of JIS K7136:2000 were measured for the optical laminates of the examples and comparative examples. The light incident surface was the polyester film side.

[0445] 1-5. Measurement of erosion rate

[0446] Using an erosion rate measurement device (MSE test device of Palmeso Co., Ltd., part number "MSE-A203", the cross-sectional shape of the nozzle was a square of 1 mm × 1 mm, and the measurement method of the cross-sectional profile: stylus type), the erosion rate of the polyester film with an easy-bonding layer of the examples and comparative examples was measured, and E 0-20 and σ 0-20 / E 0-20 . Each polyester film was measured 3 times, and the average value of the 3 times was used as the E 0-20 and σ 0-20 / E 0-20。The measurement area of the erosion rate is 1 mm × 1 mm. The measurement of the erosion rate is carried out before forming the easy-to-bond layer. For a commercially available polyester film with an easy-to-bond layer formed on one side in advance, the pencil hardness of the side without the easy-to-bond layer is measured.

[0447] The measurement of the erosion rate of each sample is carried out after the following calibration using a standard acrylic plate. In addition, the test solution is prepared before calibration, and dispersion operation is carried out in advance before calibration. In addition, the AcE (average of the erosion rate of the acrylic plate measured under measurement condition A) in the main text of the specification of the above standard acrylic plate is in the range of 1.786 μm / g or more and 1.974 μm / g or less.

[0448] (0-1) Preparation of test solution

[0449] In a beaker, a test solution is prepared by mixing pure water, a dispersant (trade name “DEMOL N” of Wako Pure Chemical Industries, Ltd.), and spherical silica with an average particle diameter (median particle diameter) of 3.94 μm (designated model “MSE-BS-5-3” of Palmeso Co., Ltd., full width at half maximum of particle size distribution: 4.2 μm) in a mass ratio of 968:2:30, and mixed with a glass rod. After filling the prepared test solution and a stir bar into a container (tank), cover the tank and install a clamp. Then, place the tank in the measuring device. In this example, as the designated model “MSE-BS-5-3” of Palmeso Co., Ltd., the part number “BS5-3” of Potters-Ballotini Co., Ltd. is used.

[0450] (0-2) Dispersion operation

[0451] After placing the tank containing the test solution in the measuring device, set a dummy sample on the sample mounting table. Then, press the buttons “Erosion force setting” and “Execute” on the operation panel of the main body of the measuring device in sequence. Then, input specified values for the flow rates of the test solution and compressed air, the pressure of the compressed air, and the pressure of the test solution in the nozzle, and project the test solution onto the dummy sample. After stopping the projection, press the buttons “Return”, “Complete”, and “Confirm” on the operation panel in sequence.

[0452] (1) Calibration

[0453] Fix an acrylic plate with a thickness of 4 mm as a calibration sample to the sample mounting table of the measuring device by double-sided tape (“KAPTON double-stick tape” of Nitto Denko America Inc., part number: P-223 1-6299-01). The acrylic plate is a PMMA plate.

[0454] Next, the specimen mounting table with the acrylic plate fixed thereon is set in the measuring device.

[0455] Next, unlock the thickness gauge and adjust the height of the specimen mounting table with a height gauge. The distance between the injection hole of the measuring device and the acrylic plate is adjusted to 4 mm.

[0456] Next, after pressing the button "To the processing condition input screen" on the operation panel of the main body of the measuring device, set it to "Number of steps: 1, Specified injection amount g × 1 time". The injection amount is 4 g.

[0457] Next, sequentially press the buttons "Setting completed", "Operation start", and "Yes" on this operation panel. The flow rates of the test liquid and compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle are maintained at the values input in "(0 - 2) dispersion operation".

[0458] Next, click "Online" on the operation screen of the data processing PC to cancel the online state and change it to the offline state.

[0459] Next, click "Lower" on this operation screen to lower the stylus of the stylus type height difference gauge of the cross-sectional profile acquisition unit.

[0460] Next, confirm that the thickness gauge is unlocked and rotate the thickness gauge upward. At this time, adjust the red arrow of the monitor to the center. Through the above adjustment, the stylus of the stylus type height difference gauge contacts the surface of the calibration sample, and the 0 point of the z-axis in the height direction can be adjusted.

[0461] Next, switch the lock of the thickness gauge from unlocked (disconnected) to locked.

[0462] Next, click "Raise" to raise the stylus of the stylus type height difference gauge of the cross-sectional profile acquisition unit.

[0463] Next, click "Offline" on the operation screen of the data processing PC to cancel the offline state and change it to the online state.

[0464] Next, close the cover of the main body of the measuring device and press the button "Confirm" on the operation panel of the main body of the measuring device to inject 4 g of the test liquid.

[0465] After stopping the injection of the test liquid, click "Proceed" to calculate the erosion rate. If the erosion rate is within the range of ±5% based on 1.88 (μm / g), the calibration is completed. In the case where the erosion rate deviates from the above range, adjust the flow rate of the test liquid, the flow rate of the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle, and repeat the calibration until the erosion rate reaches the above range.

[0466] (2) Measurement of the erosion rate of each sample

[0467] (2-1) Installation of the sample

[0468] Fabricate a laminate by attaching the sample (plastic films of the examples and comparative examples) to a stainless steel plate, and fix the laminate to the specimen mounting stage with a double-sided tape ("KAPTON double-stick tape" of Nitto Denko America Inc., part number: P-2231-6299-01). The above sample has a size of 1 cm × 1 cm.

[0469] Next, set the specimen mounting stage on the measuring device. Then, unlock the thickness gauge and adjust the height of the specimen mounting stage using a height gauge. The distance between the ejection hole of the measuring device and the plastic film is adjusted to 4 mm.

[0470] Next, after pressing the button "To the processing condition input screen" on the operation panel of the measuring device main body, input the number of steps, and input the ejection amount of the test liquid (g / time) for each step. The ejection amount for each step is in the range of 0.5 g or more and 3.0 g or less. The flow rates of the test liquid and compressed air, the pressure of the compressed air, and the pressure of the test liquid inside the nozzle are maintained at the qualified conditions in "(1) Calibration".

[0471] Next, press the buttons "Setting completed", "Operation start", and "Yes" on this operation panel in sequence.

[0472] Next, click "Online" on the operation screen of the data processing PC to cancel the online state and change it to the offline state.

[0473] Next, click "Down" on this operation screen to lower the stylus of the stylus type height difference gauge of the cross-sectional profile acquisition unit.

[0474] Next, confirm that the thickness gauge is unlocked and rotate the thickness gauge upward. At this time, adjust the red arrow on the monitor to the center. Through the above adjustment, the stylus of the stylus type height difference gauge contacts the surface of the calibration sample, and the 0 point of the z-axis in the height direction can be adjusted.

[0475] Next, switch the lock of the thickness gauge from unlocked (off) to on.

[0476] Next, click "Up" to raise the stylus of the stylus type height difference gauge of the cross-sectional profile acquisition unit.

[0477] Next, click "Offline" on the operation screen of the data processing PC to cancel the offline state and change it to the online state.

[0478] (2-2) Start of measurement

[0479] Close the cover of the measuring device main body, press the "Confirm" button on the operation panel of the measuring device main body, take the injection of the test liquid and the measurement of the cross-sectional profile as one cycle, and perform this measurement until the depth of the cross-sectional profile exceeds 20 μm. Specifically, perform it until the depth of the cross-sectional profile is 25 μm or more and 30 μm or less.

[0480] After the measurement, start "MseCalc" of the attached software and click "Analysis Method". Then, click "Average Value Analysis". Then, click "Add" on the screen of the average value analysis twice to make "A-1" and "A-2" appear in the column of the analysis name. Double-click the "Reference" column of "A-1" to make the "〇" appear in the reference column.

[0481] Next, click "A-1" on the average value analysis screen to activate it and operate the position of the X-axis position bar. The position of the above position bar is determined by the un-worn part of the plastic film within the cross-sectional profile screen.

[0482] Next, click "A-2" on the average value analysis screen to activate it and operate the position of the X-axis position bar. The position of the above position bar is determined as the deepest part where the plastic film is worn within the cross-sectional profile screen.

[0483] Next, click "File List" of the above attached software. Then, in the "Calibration" column of the file list screen, select "BS5-3".

[0484] Next, perform csv output of the cross-sectional profile and erosion rate data of each step, and calculate the erosion rate E 0-20 . Specifically, in the csv output data, average the "Erosion Rate (Calibrated)" with a depth of 0 μm or more and 20 μm or less to calculate the erosion rate E 0-20 .

[0485] 1-6. Iris spots

[0486] Regarding the polyester films with an easy-bonding layer in the examples and comparative examples, evaluate the iris spots in the following order of (1) to (3).

[0487] (1) Prepare samples by cutting the polyester films with an easy-bonding layer in the examples and comparative examples into A4 size.

[0488] (2) Attach the sample produced in (1) to the viewing-side polarizer of the image display device configured as follows. By means of the water present at the interface between the viewing-side polarizer and the sample, the optical effects of the surface irregularities of the polarization element protective film of the viewing-side polarizer can be suppressed. The sample is arranged such that the direction of the long side of the sample and the absorption axis direction of the polarization element of the viewing-side polarizer are within a specified angular range. The specified angular range is three angles: 0 ± 5 degrees, 45 ± 5 degrees, and 90 ± 5 degrees. The absorption axis direction of the polarization element of the viewing-side polarizer can be confirmed as follows.

[0489] <Method for Confirming the Absorption Axis Direction of the Polarization Element of the Viewing-Side Polarizer>

[0490] Overlay a polarizing film marked with the direction of the absorption axis on the image display device configured as follows. Slowly rotate the above polarizing film and stop at the position where it becomes completely black. At this position, the direction orthogonal to the mark on the polarizing film is the absorption axis direction of the polarization element of the viewing-side polarizer.

[0491] (3) In a darkroom environment, turn on the image display device, and 10 evaluators observe it with the naked eye from various angles and evaluate the presence or absence of rainbow spots according to the following criteria. The distance between the observer and the image display device is 0.3 - 1.0 m. The image display device is turned on under the conditions of a color temperature of 6500K, white display, and a brightness of 250 cd / m 2 .

[0492] <Configuration of the Image Display Device>

[0493] · Backlight: White LED

[0494] · Light-source-side polarizer: Having a TAC film as the protective film on both sides of the polarization element composed of PVA and iodine. It is arranged such that the absorption axis direction of the polarization element is perpendicular to the horizontal direction of the screen.

[0495] · Image display unit: Liquid crystal unit

[0496] · Viewing-side polarizer: A polarizer using a TAC film as the polarization element protective film on both sides of the polarization element composed of PVA and iodine. It is arranged such that the absorption axis direction of the polarization element is perpendicular to the parallel direction of the screen. An anti-glare layer is laminated on the polarization element protective film on the viewing side.

[0497] · Size: 20 inches diagonally

[0498] <Evaluation Criteria>

[0499] AA: Seven or more and ten or fewer people answer that rainbow spots cannot be observed in all three angular ranges.

[0500] A: Six people answered that the rainbow spot could not be observed in all three angular ranges.

[0501] B + : Five people answered that the rainbow spot could not be observed in all three angular ranges.

[0502] B: Two or more and four or less people answered that the rainbow spot could not be observed in all three angular ranges.

[0503] C: One or less people answered that the rainbow spot could not be observed in all three angular ranges.

[0504] 2. Preparation of the coating liquid for the easy-bonding layer

[0505] 2-1. Coating liquid A for the easy-bonding layer

[0506] Mix the following materials and carry out a transesterification reaction at 200 °C for 2 hours to obtain Compound 1.

[0507] · 106 parts by mass of dimethyl terephthalate

[0508] · 25 parts by mass of ethylene glycol

[0509] · 25 parts by mass of 1,4-butanediol

[0510] · 0.1 part by mass of zinc acetate

[0511] · 0.1 part by mass of antimony trioxide

[0512] Then, add 4.0 parts by mass of fumaric acid to Compound 1 and carry out an esterification reaction at 230 °C for 2 hours. Then, carry out a polycondensation reaction at 250 °C under reduced pressure (3 - 6 mmHg) for 1 hour to obtain Compound 2.

[0513] Add 230 parts by mass of methyl ethyl ketone and 120 parts by mass of isopropyl alcohol to Compound 2. Stir while heating at 70 °C to dissolve Compound 2 and obtain Resin Solution 3.

[0514] Add 25 parts by mass of m-xylylene diisocyanate to Resin Solution 3 and stir for 3 hours. Then, raise the temperature of the reaction vessel to 100 °C to remove methyl ethyl ketone and isopropyl alcohol and obtain the resin for easy bonding 4.

[0515] Dissolve the resin for easy bonding 4 in a mixed solvent prepared by mixing methyl ethyl ketone and toluene in a mass ratio of 8:2 to obtain a coating liquid A for the easy-bonding layer with a solid content of 5 mass%. The mass ratio of the polyester component to the polyurethane component of the resin in the coating liquid A for the easy-bonding layer is 8:2.

[0516] 2-2. Coating liquid B for the easy-bonding layer

[0517] Mix the following materials and conduct a transesterification reaction at 200 °C for 2 hours to obtain Compound 5.

[0518] · 106 parts by mass of dimethyl terephthalate

[0519] · 28 parts by mass of ethylene glycol

[0520] · 30 parts by mass of 1,4-butanediol

[0521] · 0.1 part by mass of zinc acetate

[0522] · 0.1 part by mass of antimony trioxide

[0523] Next, add 4.0 parts by mass of fumaric acid to Compound 5 and conduct an esterification reaction at 230 °C for 2 hours. Then, conduct a polycondensation reaction at 250 °C under reduced pressure (3 - 6 mmHg) for 1 hour to obtain Compound 6.

[0524] Add 230 parts by mass of methyl ethyl ketone and 120 parts by mass of isopropyl alcohol to Compound 6. Heat and stir at 70 °C to dissolve Compound 6 and obtain Resin Solution 7.

[0525] Add 45 parts by mass of m-xylylene diisocyanate to Resin Solution 7 and stir for 3 hours. Then, raise the temperature of the reaction vessel to 100 °C to remove methyl ethyl ketone and isopropyl alcohol, obtaining Adhesion-Promoting Resin 8.

[0526] Dissolve Adhesion-Promoting Resin 8 in a mixed solvent composed of methyl ethyl ketone and toluene in a mass ratio of 8:2 to obtain Coating Liquid B for Adhesion-Promoting Layer with a solid content of 5 mass%. The mass ratio of the polyester component to the polyurethane component of the resin in Coating Liquid B for Adhesion-Promoting Layer is 7:3.

[0527] 2 - 3. Coating Liquid C for Adhesion-Promoting Layer

[0528] Mix the following materials to obtain Coating Liquid C for Adhesion-Promoting Layer.

[0529] · 12 parts by mass of the first urethane-based resin

[0530] (Dainippon Ink and Chemicals, Inc., trade name: HYDRAN AP-20, glass transition temperature: 27 °C, flow start temperature 90 °C)

[0531] · 3 parts by mass of the second urethane-based resin

[0532] (Dainippon Ink and Chemicals, Inc., trade name: HYDRAN AP-30, glass transition temperature 61 °C, flow start temperature 105 °C)

[0533] · 2 parts by mass of curing agent

[0534] (Sumitomo Chemical Co., Ltd., trade name: Sumimal M30W, main component: hydroxymethylated melamine)

[0535] · 85 parts by mass of water

[0536] 2 - 4. Coating liquid D for easy - adhesion layer

[0537] Mix the following materials and carry out transesterification reaction at 160 - 220 °C by a conventional method to obtain Compound 9.

[0538] · 34.5 parts by mass of dimethyl terephthalate

[0539] · 21.1 parts by mass of 1,4 - butanediol

[0540] · 27 parts by mass of ethylene glycol

[0541] · 0.05 parts by mass of tetra - n - butyl titanate

[0542] Then, add 1.4 parts by mass of fumaric acid and 16 parts by mass of sebacic acid to Compound 9 and carry out esterification reaction at 200 - 220 °C to obtain copolyester resin 10.

[0543] Add 75 parts by mass of copolyester resin 10 to a mixed solvent of 56 parts by mass of methyl ethyl ketone and 19 parts by mass of isopropyl alcohol, and stir at 65 °C to dissolve copolyester resin 10 to obtain resin solution 11.

[0544] Add 15 parts by mass of maleic anhydride to resin solution 11 to obtain resin solution 12. Prepare resin solution 13 by dissolving 10 parts by mass of styrene and 1.5 parts by mass of azobisisobutyronitrile in 12 parts by mass of methyl ethyl ketone. For resin solution 12, dropwise add resin solution 13 at 0.1 ml / min and continuously stir for 2 hours. Add 5 parts by mass of methanol, further add 300 parts by mass of water and 15 parts by mass of triethylamine, and stir for 1 hour. Then, raise the temperature of the reaction vessel to 100 °C and distill off methyl ethyl ketone, isopropyl alcohol and excess triethylamine to obtain easy - adhesion resin 14.

[0545] Dissolve easy - adhesion resin 14 in a mixed solvent prepared by mixing methyl ethyl ketone and toluene in a mass ratio of 8:2 to obtain coating liquid D for easy - adhesion layer with a solid content of 5%. The mass ratio of the polyester component to the polyurethane component of the resin in coating liquid D for easy - adhesion layer is 5:5.

[0546] 2 - 5. Coating liquid E for easy - adhesion layer

[0547] Change the compounding amounts of dimethyl terephthalate, ethylene glycol, 1,4-butanediol, and m-xylylene diisocyanate to the following amounts, and obtain coating liquid E for the easy-bonding layer in the same manner as coating liquid A for the easy-bonding layer. The mass ratio of the polyester component to the polyurethane component of the resin in coating liquid E for the easy-bonding layer is 2:8.

[0548] · 106 parts by mass of dimethyl terephthalate

[0549] · 25 parts by mass of ethylene glycol

[0550] · 25 parts by mass of 1,4-butanediol

[0551] · 0.1 part by mass of m-xylylene diisocyanate

[0552] 2-6. Coating liquid F for the easy-bonding layer

[0553] Change the compounding amounts of dimethyl terephthalate, ethylene glycol, 1,4-butanediol, and m-xylylene diisocyanate to the following amounts, and obtain coating liquid F for the easy-bonding layer in the same manner as coating liquid A for the easy-bonding layer. The mass ratio of the polyester component to the polyurethane component of the resin in coating liquid F for the easy-bonding layer is 88:12.

[0554] · 100 parts by mass of dimethyl terephthalate

[0555] · 21.5 parts by mass of ethylene glycol

[0556] · 21.5 parts by mass of 1,4-butanediol

[0557] · 13 parts by mass of m-xylylene diisocyanate

[0558] 2-7. Coating liquid G for the easy-bonding layer

[0559] Change the compounding amounts of dimethyl terephthalate, ethylene glycol, 1,4-butanediol, and m-xylylene diisocyanate to the following amounts, and obtain coating liquid G for the easy-bonding layer in the same manner as coating liquid A for the easy-bonding layer. The mass ratio of the polyester component to the polyurethane component of the resin in coating liquid G for the easy-bonding layer is 83:17.

[0560] · 100 parts by mass of dimethyl terephthalate

[0561] · 23 parts by mass of ethylene glycol

[0562] · 23 parts by mass of 1,4-butanediol

[0563] · 20 parts by mass of m-xylylene diisocyanate

[0564] 3. Fabrication and preparation of the PET film, and measurement or calculation of in-plane retardation, etc. of the PET film

[0565] As the polyester films of the examples and comparative examples, the following PET films 1 to 6 were produced, and the following PET films 7 to 9 were prepared.

[0566] In addition, using the product name “RETS-100” of Otsuka Electronics Co., Ltd., the in-plane retardation (Re) of each PET film was measured. Then, the measured value of the in-plane retardation of each PET film was divided by the thickness of each PET film to calculate nx−ny of each PET film. The thickness of each PET film was measured using the product name “Digimicro” of Nikon Corporation (the stage + main body used “MS-5C+MH-15M”, and the counter used “TC-101A”).

[0567] 3-1. PET Film 1

[0568] 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, extruded from a T-die, and cast onto a casting drum with the surface temperature controlled to obtain a cast film. The amount of the ultraviolet absorber in the cast film was 3 parts by mass relative to 100 parts by mass of PET. (Control of the surface temperature of the casting drum: The part where the resin extruded from the T-die adhered was 45°C. The part of the resin peeling point was 23°C. From the part where the resin adhered to the resin peeling point, the temperature was adjusted to decrease slowly.)

[0569] The obtained cast film was heated with a roll set at 119°C, and while heating the film from both the front and back sides with a radiation heater so that the film temperature at the 180-mm point in the 480-mm stretching section (starting from stretching roll A and ending at stretching roll B. Stretching rolls A and B each had two nip rolls) was 138°C, the film was stretched 5.1 times in the flow direction and then temporarily cooled. The time for the cast film to pass through the stretching section in the flow direction was 0.194 seconds.

[0570] Next, the uniaxially stretched film is introduced into a tenter. After preheating with a roller group set at 119°C, it is heat-treated in the first stage with hot air at 105°C and in the second stage with hot air at 140°C, while being stretched 4.9 times in the film width direction. Here, when the stretching interval in the width direction is divided into two parts, stretching is carried out in two stages in such a way that the stretching amount of the film at the midpoint of the stretching interval in the width direction (film width at the measurement location - film width before stretching) is 80% of the stretching amount at the end of the stretching interval in the width direction. For the film stretched in the width direction, it is directly heat-treated in the tenter in stages with hot air at a heat treatment temperature of 245°C starting from 180°C. Then, a 1% relaxation treatment is carried out in the width direction under the same temperature conditions. Furthermore, after rapid cooling to 100°C, a 1% relaxation treatment is carried out in the width direction, and then it is wound up to obtain a biaxially stretched PET film 1 with a thickness of 40 μm.

[0571] 3-2. PET Film 2

[0572] A biaxially stretched PET film 2 is obtained in the same manner as PET film 1. The manufacturing conditions of PET film 2 are the same as those of PET film 1, but due to batch deviations, its physical properties are slightly different from those of PET film 1.

[0573] 3-3. PET Film 3

[0574] The time for the cast film to pass through the stretching interval in the flow direction is changed to 0.179 seconds, and the relaxation treatment after heat treatment and the relaxation treatment after rapid cooling are not carried out. Otherwise, a biaxially stretched PET film 3 is obtained in the same manner as PET film 1.

[0575] 3-4. PET Film 4

[0576] The time for the cast film to pass through the stretching interval in the flow direction is changed to 0.185 seconds, and the relaxation treatment after rapid cooling is not carried out. Otherwise, a biaxially stretched PET film 4 is obtained in the same manner as PET film 1.

[0577] 3-5. PET Film 5

[0578] A biaxially stretched PET film 5 is obtained in the same manner as PET film 1. The manufacturing conditions of PET film 5 are the same as those of PET film 1, but due to batch deviations, its physical properties are slightly different from those of PET film 1.

[0579] 3-6. PET Film 6

[0580] The time for the cast film to pass through the stretching interval in the flow direction is changed to 0.185 seconds, and the relaxation treatment after rapid cooling is not carried out. Otherwise, a biaxially stretched PET film 6 is obtained in the same manner as PET film 1. The manufacturing conditions of PET film 6 are the same as those of PET film 4, but due to batch deviations, its physical properties are slightly different from those of PET film 4.

[0581] 3-7. PET film 7

[0582] As the PET film 7, a commercially available biaxially stretched PET film (trade name “Cosmoshine A4160” manufactured by Toyobo Co., Ltd., thickness 38 μm, with an easy-adhesion layer on one side) was prepared.

[0583] 3-8. PET film 8

[0584] As the PET film 8, a commercially available biaxially stretched PET film (trade name “Cosmoshine A4160” manufactured by Toyobo Co., Ltd., thickness 38 μm, with an easy-adhesion layer on one side) was prepared.

[0585] 3-9. PET film 9

[0586] Polyethylene terephthalate was melted at 290 °C, extruded into a sheet through a film-forming die, and made to adhere to a rotating quenching drum cooled by water cooling for cooling to produce an unstretched film. The unstretched film was preheated at 160 °C for 150 seconds using a biaxial stretching test apparatus (manufactured by Toyo Seiki Co., Ltd.), and then uniaxially stretched 5.2 times with fixed ends at 160 °C to produce a PET film having birefringence in the plane. The refractive index of this PET film at a wavelength of 550 nm was nx = 1.701, ny = 1.6015, and Δn = 0.0995.

[0587] The film thickness of this PET film was adjusted to obtain a uniaxially stretched PET film having an in-plane retardation of 5174 nm, namely PET film 9.

[0588] 4. Production of a polyester film with an easy-adhesion layer and an optical laminate

[0589] [Example 1]

[0590] The above-described coating liquid A for the easy-adhesion layer was coated on PET film 1 and dried at 90 °C for 60 seconds to form an easy-adhesion layer with a thickness of 100 nm, obtaining a polyester film with an easy-adhesion layer of Example 1.

[0591] Next, a coating liquid for a hard coat having the following formulation was coated on the easy-adhesion layer, dried at 80 °C for 60 seconds, and irradiated with ultraviolet rays at 200 mJ / cm 2 for curing to form a hard coat with a dry thickness of 8 μm, obtaining an optical laminate of Example 1.

[0592] <Coating liquid for hard coat>

[0593] · 12 parts by mass of a polyfunctional acrylate monomer

[0594] (manufactured by Nippon Kayaku Co., Ltd., trade name: PET-30)

[0595] · 28 parts by mass of a polyfunctional acrylate oligomer

[0596] (Mitsubishi Chemical Corporation, trade name: Violet UV-1700B

[0597] · 48 parts by mass of toluene

[0598] · 12 parts by mass of methyl ethyl ketone

[0599] [Example 2]

[0600] The PET film 1 was changed to PET film 2, and the coating liquid A for the easy-bonding layer was changed to the coating liquid B for the easy-bonding layer. Otherwise, the optical laminate of Example 2 was obtained in the same manner as in Example 1.

[0601] [Example 3]

[0602] The PET film 1 was changed to PET film 3. Otherwise, the optical laminate of Example 3 was obtained in the same manner as in Example 1.

[0603] [Example 4]

[0604] The PET film 1 was changed to PET film 4. Otherwise, the optical laminate of Example 4 was obtained in the same manner as in Example 1.

[0605] [Example 5]

[0606] The coating liquid A for the easy-bonding layer was changed to the coating liquid F for the easy-bonding layer. Otherwise, the optical laminate of Example 5 was obtained in the same manner as in Example 1.

[0607] [Example 6]

[0608] The coating liquid A for the easy-bonding layer was changed to the coating liquid G for the easy-bonding layer. Otherwise, the optical laminate of Example 6 was obtained in the same manner as in Example 1.

[0609] [Comparative Example 1]

[0610] The PET film 1 was changed to PET film 5, the coating liquid A for the easy-bonding layer was changed to the coating liquid C for the easy-bonding layer, and the drying conditions of the easy-bonding layer were changed to 90 °C for 120 seconds. Otherwise, the optical laminate of Comparative Example 1 was obtained in the same manner as in Example 1.

[0611] [Comparative Example 2]

[0612] The PET film 1 was changed to PET film 6, and the coating liquid A for the easy-bonding layer was changed to the coating liquid E for the easy-bonding layer. Otherwise, the optical laminate of Comparative Example 2 was obtained in the same manner as in Example 1.

[0613] [Comparative Example 3]

[0614] The PET film 1 was changed to the PET film 7, and the optical laminate of Comparative Example 3 was obtained in the same manner as in Example 1 except for this. It should be noted that the easy - adhesion layer and the hard coat were formed on the surface opposite to the pre - formed easy - adhesion layer.

[0615] [Comparative Example 4]

[0616] The PET film 1 was changed to the PET film 8, and the coating liquid A for the easy - adhesion layer was changed to the coating liquid D for the easy - adhesion layer. The optical laminate of Comparative Example 4 was obtained in the same manner as in Example 1 except for this. It should be noted that the easy - adhesion layer and the hard coat were formed on the surface opposite to the pre - formed easy - adhesion layer.

[0617] [Comparative Example 5]

[0618] The PET film 1 was changed to the PET film 9, and the coating liquid A for the easy - adhesion layer was changed to the coating liquid E for the easy - adhesion layer. The optical laminate of Comparative Example 5 was obtained in the same manner as in Example 1 except for this.

[0619] [Comparative Example 6]

[0620] The drying conditions of the easy - adhesion layer were changed to 25 °C for 180 seconds, and the optical laminate of Comparative Example 6 was obtained in the same manner as in Example 1 except for this. It should be noted that in Comparative Example 6, since the drying of the easy - adhesion layer was slow, unevenness occurred in the film thickness of the easy - adhesion layer. In the above - mentioned measurement of 1 - 2, by using the part with less unevenness for evaluation, extreme uneven shapes were not included in the 7 measurement regions.

[0621] [Table 1]

[0622] Table 1

[0623]

[0624] [Table 2]

[0625] Table 2

[0626]

[0627] From the results in Tables 1 to 2, it was confirmed that by using the polyester films with an easy - adhesion layer of Examples 1 to 6, the adhesion of the optical laminate having in sequence a polyester film with high pencil hardness, an easy - adhesion layer, and a functional layer can be improved. The average value of δq / δa of the polyester film with an easy - adhesion layer of Example 2 is greater than that of other examples, so the adhesion is poor compared to other examples. The reason why the average value of δq / δa of Example 2 is greater than that of other examples is that the proportion of the polyurethane component in the easy - adhesion layer is more than that of other examples. The average value of δq / δa of the polyester film with an easy - adhesion layer of Example 5 is quite small, so the adhesion is poor compared to other examples. It is considered that in Example 5, since the component of the easy - adhesion layer is close to pure polyester, the viscoelasticity of the easy - adhesion layer is close to homogeneous, thus the average value of δq / δa becomes smaller.

[0628] From the results in Tables 1 to 2, it was confirmed that when using the polyester films with an easy - adhesion layer of Comparative Examples 1 to 2 and 6, the adhesion of the optical laminate having in sequence a polyester film with high pencil hardness, an easy - adhesion layer, and a functional layer cannot be improved. The reason is that the pencil hardness of the polyester films of Comparative Examples 1 to 2 and 6 with an easy - adhesion layer is B or more, and the average value of δq / δa exceeds 1.60. The reason why the average value of δq / δa of Comparative Example 1 exceeds 1.60 is that the coating liquid for the easy - adhesion layer is aqueous, so drying takes time, and the resin component of the easy - adhesion layer is polyurethane. The reason why the average value of δq / δa of Comparative Example 2 exceeds 1.60 is considered to be that although the resin component of the coating liquid for the easy - adhesion layer contains a polyurethane component and a polyester component, the proportion of the polyurethane component is high. The reason why the average value of δq / δa of Comparative Example 6 exceeds 1.60 is because the drying of the coating liquid for the easy - adhesion layer takes time.

[0629] Although the adhesion of the polyester films with an easy - adhesion layer of Comparative Examples 3 to 5 is good, the pencil hardness of the polyester film is less than B, so the surface of the functional layer of the optical laminate or the polyester film itself is easily damaged.

[0630] Although not described in Table 1, the contact angles of the surfaces of the optical laminates of Examples 1 to 4 on the side with the hard coat with respect to pure water are all 90 degrees.

[0631] In addition, from the results in Tables 1 to 2, it was confirmed that PET films 1 to 6 with an average erosion rate (E 0-20 ) of 1.4 μm / g or more are likely to have a pencil hardness of B or more.

[0632] Explanation of reference numerals

[0633] 100: Polyester film

[0634] 200: Easy - adhesion layer

[0635] 300: Functional layer

[0636] 1000: Optical laminate

[0637] 11: Container

[0638] 12: Receiver

[0639] 21: Pipe for test liquid

[0640] 22: Pipe for compressed air

[0641] 23: Return pipe

[0642] 24: Recirculation pump

[0643] 31, 32: Flowmeter

[0644] 41, 42: Pressure gauge

[0645] 50: Injection part

[0646] 51: Nozzle

[0647] 52: Housing

[0648] 60: Cross-sectional profile acquisition part

[0649] 70: Polyester film

[0650] 81: Specimen mounting table

[0651] 82: Support

[0652] 90: Erosion rate measurement device

[0653] A1: Water

[0654] A2: Spherical silica

[0655] A3: Air

[0656] A4: Worn polyester film.

Claims

1. A polyester film with an easy - adhesion layer, which is a polyester film with an easy - adhesion layer having an easy - adhesion layer on the polyester film, wherein, the pencil hardness of the polyester film is B or above, and the average value of δq / δa on the surface of the easy - adhesion layer is 1.60 or below, <Calculation of the average value of δq / δa> Use the phase mode of an atomic force microscope to measure a 10μm×10μm area on the surface of the easy - adhesion layer; through this measurement, obtain the distribution of the phase signal on the surface of the easy - adhesion layer; the unit of the phase signal is deg; Let the arithmetic mean of the phase signal shown in the following formula 1 be δa; let the root - mean - square of the phase signal shown in the following formula 2 be δq; In the following formula 1 and the following formula 2, on the reference surface representing the average value of the phase signal, configure the right - angled coordinate axes X - axis and Y - axis, set the axis orthogonal to the reference surface as the Z - axis, and set the curved surface of the phase signal as f(x,y); in the following formula 1 and the following formula 2, set the sizes of the regions for calculating δa and δq as Lx and Ly; in the following formula 1 and the following formula 2, Ar = Lx×Ly; Select 7 measurement and evaluation regions of 2μm×2μm from within the 10μm×10μm measurement region; calculate δa, δq, and δq / δa for each of the 7 measurement and evaluation regions; based on the 5 δq / δa values obtained by removing the maximum and minimum values from the 7 δq / δa values, calculate the average value of δq / δa, [Equation 1] [Equation 2] 2. The polyester film with an easy - adhesion layer according to claim 1, wherein, the coefficient of variation of δq / δa calculated based on the 5 δq / δa values is 0.040 or below.

3. The polyester film with an easy - adhesion layer according to claim 1 or 2, wherein, when defining the refractive index in the slow - axis direction in the plane of the polyester film as nx and the refractive index in the direction orthogonal to the slow - axis in the same plane as ny, nx and ny satisfy the following relationship, nx - ny ≤ 0.0250.

4. The polyester film with an easy - adhesion layer according to any one of claims 1 to 3, wherein, the thickness of the polyester film is 10μm or above and 75μm or below.

5. The polyester film with an easy - adhesion layer according to any one of claims 1 to 4, wherein, Define the average of the erosion rate from the surface to a depth of 20 μm of the polyester film as E 0-20 At this time, the E of the polyester film 0-20 is 1.4 μm / g or more.

6. An optical laminate having one or more functional layers on the easy - adhesion layer of the polyester film according to any one of claims 1 to 5.

7. The optical laminate according to claim 6, wherein, the functional layer in contact with the easy - adhesion layer among the one or more functional layers contains a cured product of an ionizing radiation - curable resin composition.

8. The optical laminate according to claim 6 or 7, wherein, the contact angle of the surface of the optical laminate having the functional layer with respect to pure water is 80 degrees or above.

9. 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 protection plate and the second transparent protection plate is the optical laminate according to any one of claims 6 to 8, and the optical laminate is arranged such that the surface on the functional layer side faces the side opposite to the polarizing element.

10. A surface plate, which is a surface plate having an optical laminate laminated on a resin plate or a glass plate, wherein, the optical laminate is the optical laminate according to any one of claims 6 to 8, and the optical laminate is arranged such that the surface on the functional layer side faces the side opposite to the resin plate or the glass plate.

11. An image display panel, on which the optical laminate according to any one of claims 6 to 8 is arranged.

12. An image display device, which includes the image display panel according to claim 11.

Images