JP7317475B2 - Substrate for surface protective film, surface protective film using the substrate, and polarizing plate with surface protective film and retardation layer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a substrate for a surface protective film, a surface protective film using the substrate, and a polarizing plate with a surface protective film and a retardation layer.

Until the image display device to which the optical film is applied is actually used, the optical film (for example, the polarizing plate, the laminate containing the polarizing plate) is used until the optical film (eventually, the image display device ), a surface protective film is releasably adhered to protect it. Practically, an image display device is produced by bonding a laminate of an optical film/surface protective film to a display cell, and the image display device is subjected to an optical test (e.g., a lighting test) while the laminate is bonded. ), and the surface protective film is peeled off at an appropriate time thereafter. A surface protective film typically has a resin film as a substrate and an adhesive layer. By the way, as an optical film, a polarizing plate with a retardation layer having a retardation layer on the viewing side is known. Such a retardation layer-attached polarizing plate can be typically used to improve visibility when viewed through polarized sunglasses. When such a polarizing plate with a retardation layer is subjected to optical inspection, light leakage, coloration, iridescent unevenness, etc. occur during the optical inspection according to the conventional surface protective film, which causes a decrease in the accuracy of the optical inspection. may be. As a result, even though the image display device itself has no problem, it may be determined to be defective in the optical inspection before shipment, and as a result, the efficiency from manufacture to shipment of the image display device decreases. There is a problem.

JP 2017-190406 A

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to prevent light leakage, coloration, and iridescent unevenness during optical inspection of a polarizing plate with a retardation layer having a retardation layer on the viewing side. An object of the present invention is to provide a base material for a surface protection film which can be well suppressed.

The substrate for a surface protective film of the present invention is a substrate for a surface protective film that is detachably attached to a polarizing plate with a retardation layer having a retardation layer on the viewing side. The in-plane retardation Reb (550) of the substrate and the in-plane retardation Rer (550) of the retardation layer of the retardation layer-attached polarizing plate satisfy the following relational expression (1), and the surface protective film is When attached to the retardation layer-attached polarizing plate, the slow axis of the substrate is configured to be substantially orthogonal to the slow axis of the retardation layer:
Rer(550)-20<Reb(550)<Rer(550)+20 (1).
Another substrate for a surface protective film of the present invention is a substrate for a surface protective film that is detachably attached to a polarizing plate with a retardation layer having a retardation layer on the viewing side. The in-plane retardation Reb (550) of the substrate and the in-plane retardation Rer (550) of the retardation layer of the polarizing plate with the retardation layer satisfy the following relational expression (2), and the surface protective film is When attached to the retardation layer-attached polarizing plate, the slow axis of the substrate is configured to be substantially parallel to the slow axis of the retardation layer:
280−Rer(550)−20<Reb(550)<280−Rer(550)+20 (2).
In one embodiment, the in-plane retardation Rer(550) of the retardation layer of the retardation layer-attached polarizing plate is 80 nm to 160 nm.
According to another aspect of the invention, a surface protection film is provided. This surface protection film includes the substrate for surface protection film and an adhesive layer.
According to still another aspect of the present invention, a polarizing plate with a surface protective film and a retardation layer is provided. This polarizing plate with a retardation layer with a surface protective film includes a polarizing plate with a retardation layer having a retardation layer on the viewing side, the surface protective film peelably bonded to the polarizing plate with a retardation layer, including.

According to an embodiment of the present invention, in the surface protective film to be bonded to the polarizing plate with a retardation layer having a retardation layer on the viewing side, the in-plane retardation of the substrate and the retardation layer of the polarizing plate with a retardation layer By optimizing the relationship between the in-plane retardation and optimizing the relationship between the slow axis direction of the substrate and the slow axis direction of the retardation layer, a retardation layer having a retardation layer on the viewing side It is possible to realize a substrate for a surface protective film that can satisfactorily suppress light leakage, coloration, and iridescent unevenness during optical inspection of a layered polarizing plate.

Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Substrate for Surface Protective Film The substrate for surface protective film according to the embodiment of the present invention is a substrate for a surface protective film that is detachably attached to a polarizing plate with a retardation layer having a retardation layer on the viewing side. The in-plane retardation Reb (550) of the substrate and the in-plane retardation Rer (550) of the retardation layer of the retardation layer-attached polarizing plate satisfy the following relational expression (1):
Rer(550)-20<Reb(550)<Rer(550)+20 (1).
Reb (550) and Rer (550) preferably satisfy the following relational expression (1a), more preferably satisfy the following relational expression (1b), and still more preferably satisfy the following relational expression (1c):
Rer(550)-10<Reb(550)<Rer(550)+10 (1a)
Rer(550)-5<Reb(550)<Rer(550)+5 (1b)
Rer(550)-3<Reb(550)<Rer(550)+3 (1c).
If Reb (550) and Rer (550) have such a relationship, synergy with the effect of optimizing the relationship between the slow axis direction of the substrate and the slow axis direction of the retardation layer will be described later. As a result, it is possible to satisfactorily suppress light leakage, coloration, and iridescent unevenness during optical inspection of a retardation layer-attached polarizing plate having a retardation layer on the viewing side. In this case, when the surface protective film containing the substrate is attached to the polarizing plate with the retardation layer, the slow axis of the substrate is configured to be substantially perpendicular to the slow axis of the retardation layer. ing. With such a configuration, due to the synergistic effect with the effect of optimizing the relationship between Reb (550) and Rer (550) as described above, polarized light with a retardation layer having a retardation layer on the viewing side Light leakage, coloration, and iridescent unevenness during optical inspection of a plate can be suppressed satisfactorily. In this specification, "Re(λ)" is a frontal phase difference measured with light having a wavelength of λnm at 23°C. Re(λ) is determined by the formula: Re=(nx−ny)×d, where d (nm) is the thickness of the layer (film). Therefore, “Re(550)” is the frontal phase difference measured at 23° C. with light having a wavelength of 550 nm. Here, “nx” is the refractive index in the direction in which the in-plane refractive index is maximized (i.e., slow axis direction), and “ny” is the in-plane direction perpendicular to the slow axis (i.e., fast axial direction). The suffix "b" represents a substrate for a surface protection film, and "r" represents a retardation layer of a polarizing plate with a retardation layer. Therefore, "Reb(λ)" represents the in-plane retardation of the substrate for surface protection film. Furthermore, in this specification, the expressions "substantially perpendicular", "substantially perpendicular" and "substantially perpendicular" include cases where the angle formed by two directions is 90° ± 10°, preferably It is 90°±7°, more preferably 90°±5°. The expressions "substantially parallel" and "substantially parallel" include cases where the angle formed by two directions is 0°±10°, preferably 0°±7°, more preferably 0°± 5°. Further, references herein to simply "perpendicular" or "perpendicular" or "parallel" are intended to include substantially perpendicular or perpendicular or substantially parallel states. It should be noted that when an angle is referred to in this specification, the angle includes both clockwise and counterclockwise rotations with respect to the reference direction.

In another embodiment, the in-plane retardation Reb (550) of the substrate and the in-plane retardation Rer (550) of the retardation layer of the retardation layer-attached polarizing plate satisfy the following relational expression (2):
280−Rer(550)−20<Reb(550)<280−Rer(550)+20 (2).
Reb (550) and Rer (550) preferably satisfy the following relational expression (2a), more preferably satisfy the following relational expression (2b), and still more preferably satisfy the following relational expression (2c):
280−Rer(550)−10<Reb(550)<280−Rer(550)+10 (2a)
280−Rer(550)−5<Reb(550)<280−Rer(550)+5 (2b)
280−Rer(550)−3<Reb(550)<280−Rer(550)+3 (2c).
If Reb (550) and Rer (550) have such a relationship, synergy with the effect of optimizing the relationship between the slow axis direction of the substrate and the slow axis direction of the retardation layer will be described later. As a result, it is possible to satisfactorily suppress light leakage, coloration, and iridescent unevenness during optical inspection of a retardation layer-attached polarizing plate having a retardation layer on the viewing side. In this case, when the surface protective film containing the substrate is attached to the polarizing plate with the retardation layer, the slow axis of the substrate is substantially parallel to the slow axis of the retardation layer. It is With such a configuration, due to the synergistic effect with the effect of optimizing the relationship between Reb (550) and Rer (550) as described above, polarized light with a retardation layer having a retardation layer on the viewing side Light leakage, coloration, and iridescent unevenness during optical inspection of a plate can be suppressed satisfactorily.

As described above, the in-plane retardation Reb (550) of the surface protection film substrate can be set based on the in-plane retardation Rer (550) of the retardation layer of the retardation layer-attached polarizing plate. The in-plane retardation Rer(550) of the reference retardation layer is preferably 80 nm to 160 nm, more preferably 90 nm to 150 nm, still more preferably 100 nm to 140 nm. If Rer(550) is within such a range, circularly polarized light can be emitted from the polarizing plate with a retardation layer. By setting the in-plane retardation Reb (550) of the substrate based on Rer (550) so as to satisfy the above relationship, the circularly polarized light can be favorably converted into linearly polarized light. As a result, in optical inspection (especially when inspecting using a camera with a polarizing filter attached), by adjusting the polarization direction of the linearly polarized light and the absorption axis direction of the polarizing filter, light leakage, coloring and Rainbow unevenness can be suppressed remarkably.

As described above, the surface protective film substrate has a predetermined in-plane retardation and a slow axis. Therefore, the substrate for a surface protection film typically exhibits a relationship of nx>ny in refractive index characteristics. The surface protective film substrate exhibits any appropriate refractive index characteristics as long as it has a relationship of nx>ny. Preferably, the refractive index characteristics of the substrate for surface protection film exhibit a relationship of nx>ny≧nz. Here, "ny=nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, it is possible that ny<nz to the extent that the effects of the present invention are not impaired. The Nz coefficient of the base material for surface protection film is preferably 0.9 to 2, more preferably 0.9 to 1.5, still more preferably 0.9 to 1.2. The "Nz coefficient" is obtained by Nz=Rth(λ)/Re(λ). “Rth(λ)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of λ nm. Rth(λ) is determined by the formula: Rth=(nx−nz)×d, where d (nm) is the thickness of the layer (film). Therefore, "Rth(550)" is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Here, "nz" is the refractive index in the thickness direction.

The surface protection film substrate may exhibit reverse wavelength dispersion characteristics in which the in-plane retardation increases according to the wavelength of the measurement light, or positive wavelength dispersion in which the in-plane retardation decreases according to the wavelength of the measurement light. It may exhibit a flat wavelength dispersion characteristic in which the in-plane retardation hardly changes even with the wavelength of the measurement light. Preferably, the wavelength dispersion characteristics of the surface protection film substrate are the same as the wavelength dispersion characteristics of the retardation layer of the retardation layer-attached polarizing plate. For example, when the retardation layer exhibits reverse dispersion wavelength dispersion characteristics, it is preferable that the surface protection film substrate also exhibits reverse dispersion wavelength dispersion characteristics. With such a configuration, since a neutral hue is achieved in optical inspection, it is possible to further improve the accuracy of optical inspection. For example, the difference between Re (450) / Re (550) of the surface protective film substrate and Re (450) / Re (550) of the retardation layer is preferably 0.03 or less, more preferably 0 0.01 or less.

The total light transmittance of the surface protection film substrate is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more, and particularly preferably 95% or more. Furthermore, the haze of the surface protection film substrate is preferably 1.0% or less, more preferably 0.7% or less, still more preferably 0.5% or less, and particularly preferably 0.3%. % or less. If the total light transmittance or haze is in such a range, excellent visibility is ensured when the surface protective film using the substrate for a surface protective film of the present invention is subjected to optical inspection of an image display device. be able to. As a result, the accuracy of optical inspection of the image display device can be significantly improved.

The substrate for a surface protective film preferably has a number of times of bending before breaking in the MIT test of 500 times or more, more preferably 700 times or more, still more preferably 900 times or more, and particularly preferably 1100 times or more. be. That is, the substrate for surface protective film can preferably have excellent flexibility or bending resistance. With such a structure, it is possible to obtain a surface protective film that is excellent in operability during lamination and peeling, and in which cracking is suppressed. Note that the MIT test can be performed in compliance with JIS P 8115.

The surface protective film substrate preferably has a water absorption rate of 5% or less, more preferably 4% or less, and still more preferably 2% or less. In addition, the surface protective film substrate preferably has a moisture permeability of 400 g/m ² ·24 h or less, more preferably 160 g/m ^{2 ·} after being left in an environment of 40°C and 92% RH for 24 hours. It is 24 hours or less, more preferably 130 g/m ² ·24 hours or less, and particularly preferably 90 g/m ² ·24 hours or less. If the water absorption rate or moisture permeability is within such a range, it is possible to suppress floating in a humidified environment. As a result, quality stability during long-distance transportation (for example, export) can be ensured. Incidentally, the water absorption can be measured according to JIS K 7209. Moisture permeability can be measured according to JIS Z 0208 (temperature and humidity conditions: 40°C, 90% RH).

The surface protection film substrate preferably has a glass transition temperature (Tg) of 145° C. or higher, more preferably 160° C. or higher. If the Tg is within such a range, the pressure-sensitive adhesive layer can be formed by directly coating the substrate for the surface protective film when producing the surface protective film. In other words, it is not necessary to transfer the pressure-sensitive adhesive layer formed on the predetermined film to the substrate for the surface protective film. Therefore, the surface protective film can be produced with extremely high production efficiency. On the other hand, the upper limit of Tg of the substrate for surface protection film can be, for example, 200°C.

The elastic modulus of the substrate for surface protective film is preferably 50 MPa to 350 MPa at a tensile speed of 100 mm/min. If the elastic modulus is within such a range, a surface protective film having excellent transportability and operability can be obtained. According to the embodiments of the present invention, both excellent elastic modulus (strength) and excellent flexibility or bending resistance (softness) as described above can be achieved. The elastic modulus is measured according to JIS K 7127:1999.

The tensile elongation of the substrate for surface protection film is preferably 70% to 200%. If the tensile elongation is within such a range, it has the advantage of being less likely to break during transportation. The tensile elongation is measured according to JIS K 6781.

The surface protection film base material may be in the shape of a sheet or in the shape of an elongated sheet. When the surface protective film base material is elongated, its slow axis may be in a direction having a predetermined angle with respect to the elongated direction. With such a configuration, the polarizing plate with the retardation layer and the surface protection film can be bonded together by so-called roll-to-roll. The predetermined angle is such that the slow axis of the retardation layer and the slow axis of the substrate for the surface protective film are substantially orthogonal or parallel when the polarizing plate with the retardation layer and the surface protective film are bonded together. The angle is such that

The surface protective film substrate can be made of any suitable material as long as it has the desired properties as described above. A substrate for a surface protection film can typically be composed of a resin film. Examples of resins constituting the film include polyarylates, polyamides, polyimides, polyesters, polyaryletherketones, polyamideimides, polyesterimides, polyvinyl alcohols, polyfumarates, polyethersulfones, polysulfones, cycloolefin resins (e.g. , norbornene-based resins), polycarbonates, polyester carbonates, cellulose resins (eg, triacetylcellulose), acrylic resins and polyurethanes. These resins may be used alone or in combination.

The substrate for surface protection film is obtained, for example, by stretching a film formed from the above resin. Any appropriate molding method can be adopted as a method of forming a film from a resin. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (e.g., casting method), calendar molding method, and heat press. law, etc. Extrusion or cast coating methods are preferred. This is because the smoothness of the resulting film can be enhanced and good optical uniformity can be obtained. Molding conditions can be appropriately set according to the composition and type of the resin to be used, properties desired for the substrate for the surface protection film, and the like.

Any suitable drawing method and drawing conditions (eg, drawing temperature, draw ratio, drawing direction) may be employed for the above-mentioned drawing. Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinking, and fixed-end shrinking can be used singly or simultaneously or sequentially. As for the stretching direction, the stretching can be performed in various directions and dimensions such as the length direction, the width direction, the thickness direction, the oblique direction, and the like.

By appropriately selecting the stretching method and stretching conditions, it is possible to obtain a substrate for a surface protective film having the desired optical properties (eg, refractive index properties, in-plane retardation, Nz coefficient).

In one embodiment, the surface protection film substrate is produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. As a specific example of fixed-end uniaxial stretching, there is a method in which the resin film is stretched in the width direction (horizontal direction) while running in the longitudinal direction. The draw ratio is preferably 1.1 times to 3.5 times.

In another embodiment, the surface protective film substrate can be produced by continuously obliquely stretching a long resin film in a direction at a predetermined angle with respect to the longitudinal direction. By adopting oblique stretching, a long stretched film having a slow axis in a direction at a predetermined angle with respect to the longitudinal direction of the film can be obtained. Toe roll is possible, and the manufacturing process can be simplified. In addition, the said predetermined angle is as above-mentioned.

A stretching machine used for diagonal stretching includes, for example, a tenter-type stretching machine capable of applying a feeding force, a pulling force, or a taking-up force at different speeds in the horizontal and/or vertical direction. The tenter-type stretching machine includes a horizontal uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, but any suitable stretching machine can be used as long as it can continuously obliquely stretch a long resin film.

By appropriately controlling the left and right speeds in the stretching machine, the surface protection film substrate (substantially , a long retardation film) can be obtained.

As a method of diagonal stretching, for example, JP-A-50-83482, JP-A-2-113920, JP-A-3-182701, JP-A-2000-9912, JP-A-2002-86554, A method described in JP-A-2002-22944 and the like can be mentioned.

The stretching temperature of the film may vary depending on the in-plane retardation value and thickness desired for the base material for the surface protective film, the type of resin used, the thickness of the film used, the stretching ratio, and the like. Specifically, the stretching temperature is preferably Tg+5°C to Tg+30°C, more preferably Tg+10°C to Tg+30°C. By stretching at such a temperature, it is possible to obtain a substrate for a surface protection film having suitable properties in the present invention.

A commercially available resin film may be used as it is for the substrate for the surface protection film, or it may be formed by subjecting a commercially available resin film to the stretching treatment as described above.

The thickness of the substrate for surface protective film is typically 10 μm to 100 μm, preferably 20 μm to 70 μm.

B. Surface Protection Film The substrate for surface protection film described in the above section A can be suitably used as a surface protection film. Accordingly, embodiments of the present invention also include surface protection films. A surface protection film according to an embodiment of the present invention includes the substrate for surface protection film described in section A above and a pressure-sensitive adhesive layer.

Any appropriate pressure-sensitive adhesive may be employed as the pressure-sensitive adhesive that forms the pressure-sensitive adhesive layer. Examples of base resins for adhesives include acrylic resins, styrene resins, silicone resins, urethane resins, and rubber resins. Such base resins are described, for example, in JP-A-2015-120337 or JP-A-2011-201983. The descriptions of these publications are incorporated herein by reference. Acrylic resins are preferred from the viewpoints of chemical resistance, adhesiveness for preventing infiltration of the treatment liquid during immersion, flexibility to the adherend, and the like. Cross-linking agents that can be contained in the adhesive include, for example, isocyanate compounds, epoxy compounds, and aziridine compounds. The adhesive may contain, for example, a silane coupling agent. The formulation of the pressure-sensitive adhesive can be appropriately set according to the purpose and desired properties.

The storage modulus of the adhesive layer is preferably 1.0×10 ⁴ Pa to 1.0×10 ⁷ Pa, more preferably 2.0×10 ⁴ Pa to 5.0×10 ⁶ Pa. If the storage elastic modulus of the pressure-sensitive adhesive layer is within such a range, blocking during roll formation can be suppressed. The storage modulus can be determined, for example, by dynamic viscoelasticity measurement at a temperature of 23° C. and an angular velocity of 0.1 rad/s.

The thickness of the adhesive layer is preferably 1 μm to 60 μm, more preferably 3 μm to 30 μm. If the thickness is too thin, the adhesiveness will be insufficient, and air bubbles and the like may enter the adhesive interface. If the thickness is too thick, problems such as protrusion of the adhesive tend to occur.

Practically, until the surface protective film is actually used (that is, pasted onto an optical film or an image display device), the separator is temporarily adhered to the surface of the pressure-sensitive adhesive layer in a releasable manner. By providing the separator, it is possible to protect the pressure-sensitive adhesive layer and wind the surface protection film into a roll. Examples of separators include plastic (e.g., polyethylene terephthalate (PET), polyethylene, polypropylene) films surface-coated with release agents such as silicone-based release agents, fluorine-based release agents, and long-chain alkyl acrylate-based release agents, non-woven fabrics, or paper and the like. Any appropriate thickness can be adopted as the thickness of the separator depending on the purpose. The thickness of the separator is, for example, 10 μm to 100 μm.

C. Optical film with surface protective film The surface protective film according to the above item B is used until the polarizing plate with a retardation layer (ultimately, an image display device) having a retardation layer on the viewing side is actually used. , is used to protect the polarizing plate with the retardation layer. Therefore, the embodiment of the present invention also includes a polarizing plate with a surface protective film and a retardation layer. A polarizing plate with a retardation layer with a surface protective film according to an embodiment of the present invention includes a polarizing plate with a retardation layer having a retardation layer on the viewing side, and a polarizing plate with a retardation layer on the viewing side (retardation layer side) of the polarizing plate with the retardation layer. and the surface protective film according to the above item B, which is releasably attached to the surface protection film.

A polarizing plate with a retardation layer includes a retardation layer and a polarizer in order from the viewing side. A protective film may be placed on one or both sides of the polarizer. A polarizing plate with a retardation layer can typically be arranged on the viewing side of an image display device. Such a retardation layer-attached polarizing plate can be used, for example, in an image display device viewed through polarized sunglasses.

The in-plane retardation Rer(550) of the retardation layer is, as described above, preferably 80 nm to 160 nm, more preferably 90 nm to 150 nm, still more preferably 100 nm to 140 nm. The retardation layer typically exhibits a refractive index characteristic of nx>ny and has a slow axis. The angle between the slow axis of the retardation layer and the absorption axis of the polarizer is preferably 35° to 55° or 125° to 145°, more preferably 38° to 52° or 128° to 142°. , more preferably 42° to 48° or 132° to 138°, particularly preferably about 45° or about 135°. When the angle is within such a range, the retardation layer has the in-plane retardation as described above, so that very excellent visibility can be realized when viewed through polarized sunglasses.

The retardation layer may exhibit a reverse wavelength dispersion characteristic in which the in-plane retardation increases according to the wavelength of the measurement light, or exhibits a positive wavelength dispersion characteristic in which the in-plane retardation decreases according to the wavelength of the measurement light. Alternatively, it may exhibit a flat wavelength dispersion characteristic in which the in-plane retardation hardly changes even with the wavelength of the measurement light. Preferably, as described above, the wavelength dispersion property of the retardation layer is the same as the wavelength dispersion property of the surface protection film substrate. With such a configuration, since a neutral hue is achieved in optical inspection, it is possible to further improve the accuracy of optical inspection.

The materials constituting the retardation layer, the manufacturing method, and the like are as described in section A regarding the base material for the surface protective film. As for the polarizer and the protective film, any appropriate configuration can be adopted, so detailed description thereof is omitted.

The polarizing plate with a retardation layer may be sheet-shaped or elongated. When the retardation layer-attached polarizing plate is elongated, the slow axis of the retardation layer may be in a direction that defines the above angle (for example, about 45°) with respect to the elongated direction. With such a configuration, the retardation layer (retardation film) and the polarizer (or polarizing plate) can be bonded together by roll-to-roll. Since the absorption axis of the polarizer is typically expressed in the longitudinal direction, by setting the slow axis of the retardation layer in a direction that defines the above angle (for example, about 45 °) with respect to the absorption axis, A polarizing plate with a retardation layer having excellent visibility when viewed through polarized sunglasses can be produced by roll-to-roll. Furthermore, such a long retardation layer-attached polarizing plate can be directly and continuously attached to a display cell being conveyed (so-called roll-to-panel), so that the manufacturing efficiency of the image display device can be significantly improved. can be improved to

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measuring method of each property in the examples is as follows. "Parts" and "%" in the examples are by weight unless otherwise specified.

(1) In-plane retardation Re(450) and Re(550)
The surface protection film substrates obtained in Examples and Comparative Examples and the retardation layers of the retardation layer-attached polarizing plates used in Examples and Comparative Examples were cut into 4 cm long and 4 cm wide pieces, and used as measurement samples. Re(450) and Re(550) of the measurement sample were measured using a product name "Axoscan" manufactured by Axometrics. Furthermore, Re(450)/Re(550) was calculated as an index of wavelength dispersion characteristics. The measurement wavelengths were 450 nm and 550 nm, and the measurement temperature was 23°C.
(2) Light Leakage The substrates for surface protection films obtained in Examples and Comparative Examples were placed on the surface of the retardation layer of a polarizing plate with a retardation layer having the retardation layer on the viewing side. Further, a normal polarizing plate was placed on the opposite side of the polarizing plate with the retardation layer from the substrate for the surface protective film so as to form a crossed Nicols state. In this way, a test sample having a configuration of substrate for surface protection film/retardation layer/viewing side polarizing plate/lower side polarizing plate was obtained. Light from a fluorescent lamp was irradiated from below the lower polarizing plate, and the presence or absence of light leakage was visually observed. Evaluation was made according to the following criteria.
○: No light leakage was observed
△: Light leakage was slightly observed
x: Significant light leakage was observed Further, the presence or absence of iridescent unevenness was visually observed and evaluated according to the following criteria.
○: Rainbow unevenness was not observed
△: Rainbow unevenness was slightly observed
x: Remarkable rainbow unevenness was observed. As the polarizing plate with a retardation layer, the product name "NZD-MCDGRTTKHC10" manufactured by Nitto Denko Corporation was used. Re(550) of the retardation layer of this retardation layer-attached polarizing plate was 100 nm, and Re(450)/Re(550) was 1.01. Furthermore, the slow axis direction of the retardation layer was 45° when the absorption axis direction of the polarizer was 0°.

<Example 1>
A commercially available polycarbonate resin film (manufactured by Mitsubishi Chemical Corporation, trade name “DURABIO T7450A”, isosorbide structural unit 62 mol%, tricyclodecanedimethanol structural unit 38 mol%)) was vacuum-dried at 105 ° C. for 5 hours, and then Using a film forming apparatus equipped with a screw extruder (Toshiba Machine Co., Ltd., cylinder temperature 230 ° C.), a T-die (width 1700 mm, temperature 230 ° C.), a cast roll (temperature 120 ° C.) and a winder, the thickness was 75 μm. A film of This film was diagonally stretched 1.96 times in the diagonal direction. The stretching direction was 135° and the stretching temperature was 139 (Tg+10)°C. Thus, a substrate for a surface protective film (thickness: 40 µm) was obtained. Re(550) of the obtained substrate for surface protection film was 100 nm, Rth(550) was 118 nm, and Re(450)/Re(550) was 1.02. The obtained base material for a surface protection film was subjected to the evaluation of light leakage and iridescent unevenness. Table 1 shows the results. In the preparation of the measurement sample, the slow axis direction of the base material for the surface protective film is 135° when the absorption axis direction of the polarizer of the polarizing plate with a retardation layer is 0°. It was arranged on the surface of the retardation layer of the polarizing plate with the retardation layer. That is, the surface protective film base material was arranged such that the slow axis direction of the surface protective film base material was perpendicular to the slow axis direction of the retardation layer of the retardation layer-attached polarizing plate.

<Example 2>
A substrate for a surface protective film (thickness: 40 µm) was obtained in the same manner as in Example 1 except that the stretching direction was 45° and the stretching temperature was 133.7 (Tg + 4.7)°C. Re(550) of the obtained substrate for surface protection film was 180 nm, Rth(550) was 201.6 nm, and Re(450)/Re(550) was 1.02. The obtained base material for a surface protection film was subjected to the evaluation of light leakage and iridescent unevenness. Table 1 shows the results. In the preparation of the measurement sample, the slow axis direction of the base material for the surface protective film is 45° when the absorption axis direction of the polarizer of the polarizing plate with a retardation layer is 0°. It was arranged on the surface of the retardation layer of the polarizing plate with the retardation layer. That is, the surface protective film substrate was arranged such that the slow axis direction of the surface protective film substrate was parallel to the slow axis direction of the retardation layer of the retardation layer-attached polarizing plate.

<Example 3>
A substrate for a surface protective film (thickness: 80 μm) was obtained in the same manner as in Example 1 except that a commercially available retardation film (manufactured by Nippon Zeon Co., Ltd., trade name “ZD12-099063-C1300UHC”) was used as it was. The Re (550) of the surface protective film substrate was 100 nm, the Rth (550) was 110 nm, and the Re (450)/Re (550) was 1.01. The base material was subjected to the evaluation of light leakage and iridescent unevenness, and the results are shown in Table 1. In the preparation of the measurement sample, the slow axis direction of the base material for the surface protective film was the same as that of the polarizing plate with a retardation layer. When the absorption axis direction of the polarizer is 0 °, it is arranged on the surface of the retardation layer of the polarizing plate with the retardation layer so that the slow axis direction of the base material for the surface protective film is A base material for a surface protective film was arranged so as to be parallel to the slow axis direction of the retardation layer of the retardation layer-attached polarizing plate.

<Example 4>
Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and reflux condensers controlled at 100°C. Bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane 29.60 parts by weight (0.046 mol), isosorbide 29.21 parts by weight (0.200 mol), spiroglycol 42.28 parts by weight (0 .139 mol), 63.77 parts by mass (0.298 mol) of diphenyl carbonate, and 1.19×10 ⁻² parts by mass (6.78×10 −5 mol) of calcium acetate monohydrate as a catalyst were charged. After the interior of the reactor was replaced with nitrogen under reduced pressure, heating was performed with a heating medium, and stirring was started when the internal temperature reached 100°C. After 40 minutes from the start of heating, the internal temperature was allowed to reach 220°C, and the pressure was reduced at the same time as controlling to maintain this temperature. Phenol vapor produced as a by-product of the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and recovered. After nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and the internal temperature was brought to 240° C. and the pressure to 0.2 kPa in 50 minutes. After that, polymerization was allowed to proceed until a predetermined stirring power was obtained. When a predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, the polyester carbonate produced was extruded into water, and strands were cut to obtain pellets.

After vacuum drying the resin polymerized by the above method at 120 ° C. for 5 hours, a single screw extruder (manufactured by Toshiba Machine Co., cylinder temperature 260 ° C.), T die (width 1700 mm, temperature 260 ° C.), cast roll (temperature 120° C.) and a film-forming apparatus equipped with a winder to prepare a film having a thickness of 130 μm. This film was diagonally stretched by 1.96 times. The stretching direction was 135° and the stretching temperature was 145 (Tg+5)°C. Thus, a substrate for a surface protection film (thickness: 58 µm) was obtained. Re(550) of the obtained substrate for surface protection film was 100 nm, Rth(550) was 112 nm, and Re(450)/Re(550) was 0.855. The obtained base material for a surface protection film was subjected to the evaluation of light leakage and iridescent unevenness. Table 1 shows the results. In the preparation of the measurement sample, the slow axis direction of the base material for the surface protective film is 135° when the absorption axis direction of the polarizer of the polarizing plate with a retardation layer is 0°. It was arranged on the surface of the retardation layer of the polarizing plate with the retardation layer. That is, the surface protective film base material was arranged such that the slow axis direction of the surface protective film base material was perpendicular to the slow axis direction of the retardation layer of the retardation layer-attached polarizing plate.

<Comparative Example 1>
A commercially available polycarbonate resin containing a structural unit derived from a dihydroxy compound (manufactured by Mitsubishi Chemical Corporation, trade name DURABIO T7450A, isosorbide structural unit 62 mol%, tricyclodecanedimethanol structural unit 38 mol%) was heated at 105°C for 5 hours. After vacuum drying for a period of time, a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., screw diameter 25 mm, cylinder set temperature: 230 ° C.), T die (width 1700 mm, set temperature: 230 ° C.), chill roll (set temperature: 120 ° C.) A polycarbonate resin film having a thickness of 40 μm was produced using a film forming apparatus equipped with a winder and used as a base material for a surface protective film. Re(550) of the obtained substrate for surface protection film was 5.6 nm, Rth(550) was 11.5 nm, and Re(450)/Re(550) was 1.02. The obtained base material for a surface protection film was subjected to the evaluation of light leakage and iridescent unevenness. Table 1 shows the results. In the preparation of the measurement sample, the slow axis direction of the substrate for the surface protective film is 1.6° when the absorption axis direction of the polarizer of the polarizing plate with a retardation layer is 0°. , was placed on the surface of the retardation layer of the polarizing plate with the retardation layer.

<Comparative Example 2>
A commercially available ultra-high retardation polyethylene terephthalate film (manufactured by Mitsubishi Chemical Corporation, trade name "Diafoil MRF38CK") was used as it was to form a base material for a surface protection film (thickness: 38 µm). Re(550) of the substrate for surface protection film was 2950 nm, Rth(550) was 8989.4 nm, and Re(450)/Re(550) was 1.06. The obtained base material for a surface protection film was subjected to the evaluation of light leakage and iridescent unevenness. Table 1 shows the results. In the preparation of the measurement sample, the slow axis direction of the base material for the surface protective film is 1.3° when the absorption axis direction of the polarizer of the polarizing plate with a retardation layer is 0°. , was placed on the surface of the retardation layer of the polarizing plate with the retardation layer.

<Evaluation>
As is clear from Table 1, the substrates for surface protective films of the examples of the present invention are found to suppress light leakage and iridescent unevenness. In addition, it was confirmed that the same results as those of rainbow unevenness and light leakage were obtained for coloring.

The substrate for surface protective film of the present invention is suitably used for a surface protective film. The surface protection film of the present invention is used to protect the optical film (finally, the image display device) until it is actually used. By using the substrate for surface protective film and the surface protective film of the present invention, the accuracy of optical inspection of image display devices can be significantly improved.

Claims (5)

A substrate of a surface protective film that is detachably bonded to the retardation layer side of a polarizing plate with a retardation layer having a polarizer and a retardation layer on the viewing side of the polarizer,
The surface protective film includes the substrate and an adhesive layer, and is laminated to the retardation layer-attached polarizing plate via the adhesive layer,
The in-plane retardation Reb (550) of the substrate and the in-plane retardation Rer (550) of the retardation layer of the polarizing plate with the retardation layer satisfy the following relational expression (1),
When the surface protective film is attached to the retardation layer-attached polarizing plate, the slow axis of the substrate forms an angle of 85° to 95° with respect to the slow axis of the retardation layer. Substrate for surface protection film:
Rer(550)-20<Reb(550)<Rer(550)+20 (1). A substrate of a surface protective film that is detachably bonded to the retardation layer side of a polarizing plate with a retardation layer having a polarizer and a retardation layer on the viewing side of the polarizer,
The surface protective film includes the substrate and an adhesive layer, and is laminated to the retardation layer-attached polarizing plate via the adhesive layer,
The in-plane retardation Reb (550) of the substrate and the in-plane retardation Rer (550) of the retardation layer of the retardation layer-attached polarizing plate satisfy the following relational expression (2),
When the surface protective film is attached to the retardation layer-attached polarizing plate, the slow axis of the substrate forms an angle of −5° to 5° with respect to the slow axis of the retardation layer. A base material for a surface protection film, which consists of:
280−Rer(550)−20<Reb(550)<280−Rer(550)+20 (2). 3. The substrate for a surface protective film according to claim 1, wherein the in-plane retardation Rer(550) of the retardation layer of the retardation layer-attached polarizing plate is 80 nm to 160 nm. A surface protective film comprising the substrate and the pressure-sensitive adhesive layer, wherein the substrate is the substrate for a surface protective film according to any one of claims 1 to 3. 5. A polarizing plate with a retardation layer having a polarizer and a retardation layer on the viewing side of the polarizer, and a polarizing plate with a retardation layer attached to the retardation layer side of the polarizing plate with the retardation layer so as to be peelable according to claim 4. and an optical film with a surface protective film.