TWI812749B - Substrate for surface protection film, method for producing same, surface protection film using same, and optical film with surface protection film - Google Patents

Abstract

The present invention provides a substrate for a surface protection film that has excellent flexibility or bending resistance and can well suppress light leakage, coloration, and rainbow-like unevenness during optical inspection. The base material for a surface protection film of the present invention is composed of a film containing a polymer alloy of a fluorene ring-containing polyester and an aromatic polycarbonate, has an in-plane phase difference Re (550) of 30 nm or less, and has a retardation rate until fracture in the MIT test. The number of bending times is more than 500 times. The manufacturing method of a base material for a surface protection film of the present invention includes: forming a film-forming material containing a polymer alloy, which is a polymer alloy of a fluorene ring-containing polyester and an aromatic polycarbonate, into a film shape; and The formed film is subjected to sequential biaxial stretching or simultaneous biaxial stretching.

Description

Base material for surface protection film, method for manufacturing the base material, surface protection film using the same, and optical film with surface protection film

Field of invention The present invention relates to a base material for a surface protection film, a method for manufacturing the base material, a surface protection film using the base material, and an optical film with a surface protection film.

Background of the invention An optical film (for example, a polarizing plate, a laminate including a polarizing plate) is peelable in order to protect the optical film (and ultimately the image display device) until the image display device to which the optical film is applied is actually used. A surface protection film is attached. In practice, a laminate of an optical film/surface protection film is bonded to a display unit to produce an image display device, and the image display device is subjected to an optical test (for example, a lighting test) in a state where the laminate is bonded. Peel off and remove the surface protective film at an appropriate time. The surface protection film typically has a resin film and an adhesive layer as a base material. With conventional surface protection films, light leakage, coloration, rainbow-like unevenness, etc. may occur during optical inspection, which may cause a decrease in optical inspection accuracy. As a result, even if there is no problem with the image display device itself, it may be judged as defective during the optical inspection before shipment. This causes a problem of reduced efficiency from manufacturing to shipment of the image display device. Furthermore, the surface protection film (substantially a base material) is required to have excellent flexibility in consideration of workability during lamination and peeling. existing technical documents patent documents

Patent Document 1: Japanese Patent Application Publication No. 2017-190406

Summary of the invention Invent the problem to be solved The present invention was made to solve the above-mentioned existing problems, and its main purpose is to provide a surface protection film that has excellent flexibility or bending resistance and can well suppress light leakage, coloration, and rainbow-like unevenness during optical inspection. Use base material. means to solve problems

The base material for a surface protection film according to an embodiment of the present invention is composed of a film containing a polymer alloy, which is a polymer alloy containing a fluorene ring-containing polyester and an aromatic polycarbonate. The surface of the base material for a surface protection film is The internal phase difference Re (550) is 30 nm or less, and the number of bends until fracture in the MIT test is more than 500 times. In one embodiment, the fluorene ring-containing polyester contains a dicarboxylic acid component (A) and a diol component (B) as copolymer components, and the dicarboxylic acid component (A) contains a fluorenedicarboxylic acid component (A1). The fluorene dicarboxylic acid component (A1) is at least one selected from the dicarboxylic acids represented by the following formulas (1a) and (1b): [Chemical Formula 1] In formula (1a) and formula (1b), R ¹ and R ² are each a substituent, k, m and n are each an integer from 0 to 4, and X ¹ and X ² are each a substituted or unsubstituted divalent hydrocarbon group. In one embodiment, the fluorene ring-containing polyester contains 50 mol% or more of the fluorene dicarboxylic acid component (A1) derived from the total amount of structural units derived from the dicarboxylic acid component (A). structural unit. In one embodiment, the diol component (B) includes a fluorene diol component (B1) represented by the following formula (2): [Chemical Formula 2] In formula (2), Z is an aromatic hydrocarbon ring, R ³ and R ⁴ are each a substituent, p is each an integer from 0 to 4, q and r are each an integer of 0 or more than 1, and R ⁵ is an alkane. base. In one embodiment, the surface protection film base material has a total light transmittance of 80% or more and a haze of 1.0% or less. According to another aspect of the present invention, there is provided a method for manufacturing the above-mentioned base material for surface protection film. The manufacturing method includes: forming a film-forming material containing a polymer alloy into a film shape; and subjecting the formed film to sequential biaxial stretching or simultaneous biaxial stretching, wherein the polymer alloy is a fluorene ring-containing polyester. Polymer alloy with aromatic polycarbonate. In one embodiment, in the above manufacturing method, the stretching speed in the sequential biaxial stretching or simultaneous biaxial stretching is 10%/second or less. According to yet another aspect of the present invention, a surface protection film is provided. The surface protection film includes the above-mentioned base material for surface protection film and an adhesive layer. According to yet another aspect of the present invention, an optical film with a surface protection film is provided. The optical film with a surface protection film includes: an optical film and the above-mentioned surface protection film; the surface protection film is peelably attached to the optical film. Invention effect

According to an embodiment of the present invention, by stretching a film containing a polymer alloy of a fluorene ring-containing polyester and an aromatic polycarbonate under predetermined stretching conditions (representatively a stretching speed), both aspects can be achieved. Base material for surface protection films with very small in-plane phase difference and excellent flexibility or bending resistance.

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

A.Substrate for surface protection film The base material for a surface protection film according to an embodiment of the present invention is composed of a film containing a polymer alloy that is a polymer alloy of a fluorene ring-containing polyester and an aromatic polycarbonate. The polymer alloy may be a polymer blend or a copolymer. Polymer blends are preferred. Although fluorene ring-containing polyester and aromatic polycarbonate are different types of polymers, once mixed, they will be in a completely miscible state or a stable micro-phase separation state, and can easily form a blended polymer without using a solubilizer. . As a mixing method of the fluorene ring-containing polyester and the aromatic polycarbonate, any appropriate method can be adopted. Specific examples of the mixing method include a method of dissolving the fluorene ring-containing polyester and the aromatic polycarbonate in a solvent, and melt-mixing the fluorene ring-containing polyester and the aromatic polycarbonate using a mixer or an extruder. Methods. Melt mixing is preferred. This is because it can prevent the optical properties (for example, phase difference, wavelength dispersion properties, etc.) from deteriorating due to residual solvent after the base material for surface protection films is produced.

The fluorene ring-containing polyester contains a dicarboxylic acid component (A) and a diol component (B) as copolymer components. The dicarboxylic acid component (A) contains a fluorenedicarboxylic acid component (A1). Examples of the fluorenedicarboxylic acid component include dicarboxylic acids represented by the following formulas (1a) and (1b). These dicarboxylic acids may be used alone or in combination. [Chemical formula 3] In formula (1a) and formula (1b), R ¹ and R ² are each a substituent, k, m and n are each an integer from 0 to 4, and X ¹ and X ² are each a substituted or unsubstituted divalent hydrocarbon group.

In the formula (1a), examples of the substituent R ¹ include a cyano group, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom), a hydrocarbon group [for example, an alkyl group, an aryl group (for example, a phenyl group, etc.) C _6-10 aryl)] and other non-reactive substituents. Examples of the alkyl group include C _1-12 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, and tert-butyl. A C _1-8 alkyl group is preferred, and a C _1-4 alkyl group (for example, methyl) is more preferred. Each substituent ^R1 may be the same or different. Furthermore, when the substitution number k of the substituent R ¹ is 2 or more, two or more groups R ¹ in the same benzene ring in the fluorene ring may be the same or different. In addition, examples of the bonding positions (substitution positions) of the substituent R ¹ in the two benzene rings constituting the fluorene ring include the 2-position, 7-position, 2- and 7-position of the fluorene ring.

The substitution number k of the substituent R ¹ is, for example, an integer from 0 to 2, preferably 0 or 1, and more preferably 0. In addition, the substitution numbers k of the two benzene rings constituting the fluorene ring may be the same or different.

In the formula (1b), the substituent R ² and the substitution number m are each the same as the substituent R ¹ and the substitution number k in the formula (1a).

In formula (1b), the repeating number n of methylene groups is, for example, an integer of 0 to 3, preferably an integer of 0 to 2, and more preferably 0 or 1.

In the formulas (1a) and (1b), examples of the hydrocarbon group represented by X ¹ and X ² include a linear or branched alkylene group. Specific examples include linear or branched ones such as methylene, ethylene, trimethylene, propylene, 1,2-butanediyl, and 2-methylpropane-1,3-diyl. Chain C _1-8 alkylene group. Preferred alkylene groups are linear or branched C _1-6 alkylene groups (for example, methylene, ethylidene, trimethylene, propylene, 2-methylpropane-1,3-di linear or branched C _1-4 alkylene group). Examples of the substituent of the hydrocarbon group include an aryl group (such as a phenyl group) and a cycloalkyl group (such as a cyclohexyl group).

Each X ¹ may be the same or different. X ¹ and X ² may be the same or different. X ¹ is preferably a linear or branched C _2-4 alkylene group (for example, a linear or branched C 2-3 alkylene group such as ethylene or propylene), and X ² is preferably a straight chain or branched C _2-3 alkylene group. Chain or branched C _1-3 alkylene group (for example, methylene, ethylene).

Examples of the dicarboxylic acid component represented by formula (1a) include 9,9-bis(carboxy C _2-6 alkyl)fluorene and their ester-forming derivatives. Specific examples include 9,9-bis(2-carboxyethyl)fluorene and 9,9-bis(2-carboxypropyl)fluorene. Examples of the dicarboxylic acid component represented by formula (1b) include 9-(dicarboxylic C _2-8 alkyl)fluorene and their ester-forming derivatives. Specific examples include 9-(1-carboxy-2-carboxyethyl)fluorene and 9-(2,3-dicarboxypropyl)fluorene.

The fluorene ring-containing polyester preferably contains 10 mol% or more (for example, 30 mol% or more), more preferably 50 mol% or more (for example,) based on the total amount of structural units derived from the dicarboxylic acid component (A). , 60 mol% or more), more preferably 70 mol% or more (for example, 80 mol% or more), particularly preferably 90 mol% or more (for example, 95 mol% or more) of the fluorenedicarboxylic acid component ( Structural unit of A1). Substantially all of the dicarboxylic acid component (A) may be a fluorenedicarboxylic acid component (A1).

The dicarboxylic acid component (A) may further contain other dicarboxylic acid components within a range that does not impair the effects of the present invention. Examples of other dicarboxylic acid components include aromatic dicarboxylic acid components (A2) [excluding the fluorene dicarboxylic acid component (A1)], alicyclic dicarboxylic acid components (A3), aliphatic dicarboxylic acid components Acid component (A4), and their ester-forming derivatives.

The diol component (B) contains the fluorene diol component (B1) represented by the following formula (2). The fluorene diol component (B1) may be a single diol compound or a combination of multiple diol compounds. [Chemical formula 4] In formula (2), Z is an aromatic hydrocarbon ring, R ³ and R ⁴ are each a substituent, p is each an integer from 0 to 4, q and r are each an integer of 0 or more than 1, and R ⁵ is an alkane. base.

In the formula (2), examples of the aromatic hydrocarbon ring (aromatic hydrocarbon ring) represented by Z include monocyclic aromatic hydrocarbon rings (monocyclic aromatic hydrocarbon rings) such as benzene rings and polycyclic aromatic hydrocarbon rings ( Polycyclic aromatic hydrocarbon rings). Examples of polycyclic aromatic hydrocarbon rings include condensed polycyclic aromatic hydrocarbon rings (fused polycyclic aromatic hydrocarbon rings) and ring-collected aromatic hydrocarbon rings (ring-collected aromatic hydrocarbon rings). C _6-12 aromatic hydrocarbon rings such as benzene ring, naphthalene ring and biphenyl ring are preferred, and C _6-10 aromatic hydrocarbon rings such as benzene ring are more preferred. Each Z can be the same or different.

In the formula (2), the substituent R ³ and the substitution number p are each the same as the substituent R ¹ and the substitution number k in the formula (1a).

Examples of the substituent R ⁴ include a halogen atom, a linear or branched alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkoxy group, a cycloalkyloxy group, and an aryloxy group. Aralkyloxy, alkylthio, cycloalkylthio, arylthio, aralkylthio, acyl, nitro, cyano, substituted amine, bis(alkylcarbonyl)amine. The substituent R ⁴ is preferably an alkyl group (for example, a linear or branched C _1-6 alkyl group such as methyl), a cycloalkyl group (for example, a C _5-8 cycloalkyl group such as cyclohexyl), an aryl group ( For example, a C _6-14 aryl group such as a phenyl group), an alkoxy group (such as a linear or branched C _1-4 alkoxy group such as a methoxy group), and more preferably an alkyl group (such as a methyl group, etc. Linear or branched C _1-4 alkyl group), aryl group (for example, C _6-10 aryl group such as phenyl group). In addition, when the substituent R ⁴ is an aryl group, the substituent R ⁴ and the ring Z may form an aromatic hydrocarbon ring of the above-mentioned ring set. Each R ⁴ may be the same or different.

The substitution number q of the substituent R ⁴ is, for example, an integer of 0 to 8, preferably an integer of 0 to 4 (for example, 0 to 3), and more preferably an integer of 0 to 2 (for example, 0 or 1). The substitution number q can be 0. In addition, the bonding position (substitution position) of the substituent R ⁴ is not particularly limited.

In the formula (2), examples of the substituent R ⁵ include ethylene, propylene (1,2-propanediyl), trimethylene, 1,2-butanediyl, and tetramethylene. A linear or branched C _2-6 alkylene group. A linear or branched C _2-4 alkylene group is preferred, and a linear or branched C _2-3 alkylene group (especially an ethylene group) is more preferred. The repeating number (addition molar number) r of the oxyalkylene group (OR ⁵ ) is, for example, an integer of 0 to 15 (for example, 1 to 10), preferably an integer of 0 to 8 (for example, 1 to 6), and more It is preferably an integer of 0 to 4 (for example, 1 to 2), and more preferably 0 or 1 (for example, 1). In addition, the substitution position of the group [-O-(R ⁵ O) _r -H] in formula (2) is not particularly limited.

Examples of the diol represented by the formula (2) include 9,9-bis(hydroxyaryl)fluorenes and 9,9-bis[hydroxy(poly)alkoxyaryl]fluorenes.

The diol component (B) may further contain alkanediol (B2) [or alkylene glycol ( B2)]. Examples of the alkanediol (B2) include ethylene glycol, propylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, and tetramethylene glycol (1, 4-butanediol), 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol and other linear or branched chains Like C _2-12 alkane diol. The ratio B1/B2 (molar ratio) of the structural unit derived from fluorene diol (B1) and the structural unit derived from alkane diol (B2) in the fluorene ring-containing polyester is, for example, 0/50 to 100/0 ( For example, 50/50~99/1), preferably 60/40~97/3 (for example, 65/35~95/5), more preferably 68/32~92/8 (for example, 70/30~90 /10), more preferably 73/27~88/12 (for example, 75/25~85/15).

The glycol component (B) may further contain other glycols as necessary. Examples of other diols include polyalkylene glycol (or polyalkylene glycol) (B3), alicyclic diol (B4), aromatic diol (B5) and hydrogenated products thereof. These other diols may be used individually or in combination of 2 or more types.

The fluorene ring-containing polyester contains, for example, 10 mol% or more (for example, 30 mol% to 100 mol%), preferably 50 mol% or more, based on the total amount of structural units derived from the diol component (B). (for example, 60 mol% to 99 mol%), more preferably 70 mol% or more (for example, 80 mol% to 98 mol%), further preferably 90 mol% or more (for example, 95 mol% to 95 mol%) 97 mol%) structural units derived from the fluorene diol component (B1) and the alkane diol component (B2). The diol component (B) may be substantially all a fluorene diol component (B1) and an alkane diol component (B2).

Aromatic polycarbonate is a polycarbonate containing a diol component (C) as a polymerization component. The diol component (C) contains at least aromatic diol (C1). Examples of the aromatic diol (C1) include the above-mentioned fluorene diols (for example, 9,9-bis(hydroxyaryl)fluorenes, 9,9-bis[hydroxy(poly)alkoxyaryl ] fluorenes), dihydroxyaromatic hydrocarbons (e.g., hydroquinone, resorcinol), aromatic aliphatic diols (e.g., benzenedimethanol), bisphenols (e.g., bisphenol A, bisphenol F, bisphenol Phenol AD, bisphenol C, bisphenol G, bisphenol S), biphenols (for example, p, p'-biphenol), and C _2-4 alkylene oxide (or alkylene group) of their diol components Carbonate, haloalkanol) adduct [for example, an adduct obtained by adding approximately 2 to 10 moles of ethylene oxide to 1 mole of bisphenol A]. These aromatic diols (C1) may be used alone or in combination of two or more types. The aromatic diol (C1) preferably contains biphenols, bisphenols or C _2-4 alkylene oxide adducts thereof.

The ratio PE/PC (weight ratio) of the fluorene ring-containing polyester to the aromatic polycarbonate in the polymer alloy is, for example, 1/99 to 99/1 (for example, 10/90 to 97/3), preferably 30/ 70~95/5, more preferably 50/50~90/10, further preferably 60/40~88/12 (for example, 65/35~85/15), particularly preferably 67/33~83/17 ( For example, 70/30~80/20).

The polymer alloy may further contain a compound represented by the following formula (3) as an additive as necessary within a range that does not impair the effects of the present invention.

[Chemical formula 5] In the formula (3), Z ¹ is each a monocyclic or fused polycyclic aromatic hydrocarbon ring, R ⁶ and R ⁷ are each a substituent, and s, t and u are integers of 0 or more.

The polymer alloy may further contain any suitable additives. Examples of additives include plasticizers (esters, phthalic acid compounds, epoxy compounds, sulfonamides, etc.), flame retardants (inorganic flame retardants, organic flame retardants, colloidal flame retardants, etc.) flammable substances, etc.), stabilizers (antioxidants, ultraviolet absorbers, heat stabilizers, etc.), antistatic agents, fillers (oxide-based inorganic fillers, non-oxide-based inorganic fillers, metal powders, etc.), foaming Agents, defoaming agents, lubricants, release agents (natural waxes, synthetic waxes, linear fatty acids or their metal salts, acid amides, etc.), slippery agents (for example, silicon dioxide, titanium oxide , calcium carbonate, clay, mica, kaolin and other inorganic particles; (meth)acrylic resin, styrene resin (cross-linked polystyrene resin, etc.) and other organic particles), solubilizer. The number, type, combination and amount of additives to be added can be appropriately set according to the purpose.

Details of the polymer alloy are described in, for example, Japanese Patent Application Laid-Open No. 2017-198956, and the description of this publication is incorporated into this specification by reference.

In an embodiment of the present invention, the in-plane retardation of the surface protection film base material is Re (550) 30 nm or less, preferably 20 nm or less, more preferably 15 nm or less, still more preferably 10 nm or less, particularly preferably 5 nm or less. The smaller the in-plane phase difference Re (550) is, the more preferable it is. The lower limit is ideally 0 nm, and may be, for example, 1 nm. When the in-plane phase difference Re (550) is within such a range, light leakage, coloration, and iridescence can be well suppressed when the surface protection film using the surface protection film base material of the present invention is subjected to optical inspection of an image display device. Uneven. As a result, the optical inspection accuracy of the image display device can be significantly improved, and the efficiency from manufacturing to shipment of the image display device can be improved. Such an in-plane retardation Re (550) can be achieved by stretching a film containing the above-mentioned specific polymer alloy under predetermined stretching conditions described below. In addition, in this specification, "Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. Regarding Re (λ), when the thickness of the layer (thin film) is d (nm), it is obtained according to the formula: Re=(nx-ny)×d. Therefore, "Re(550)" is the in-plane phase difference measured with light having a wavelength of 550 nm at 23°C. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (ie, the slow axis direction), and "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (ie, the fast axis direction).

The thickness direction retardation Rth (550) of the surface protection film base material is preferably 95 nm or less, more preferably 85 nm or less. The thickness direction phase difference Rth (550) is preferably as small as possible, and the lower limit is ideally 0 nm. When the thickness direction phase difference Rth (550) is in such a range, light leakage, coloration, and rainbow-like unevenness in the oblique direction during the optical inspection can be satisfactorily suppressed. As a result, the accuracy can be significantly improved even in optical inspection of large-scale image display devices. The Nz coefficient of the surface protection film base material is preferably 3.0 to 10. Therefore, the refractive index characteristics of the surface protection film base material can show the relationship nx>ny>nz, for example. When the Nz coefficient is in such a range, light leakage, coloration, and rainbow-like unevenness in the oblique direction during optical inspection can be more effectively suppressed. "Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For Rth (λ), when the thickness of the layer (thin film) is d (nm), it is determined according to the formula: Rth=(nx-nz)×d. Therefore, "Rth(550)" is the phase difference in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Here, "nz" is the refractive index in the thickness direction. Furthermore, the "Nz coefficient" is found by Nz=Rth(λ)/Re(λ).

The base material for surface protection film can exhibit inverse dispersion wavelength characteristics in which the in-plane phase difference becomes larger depending on the wavelength of the measurement light, and can also exhibit positive wavelength dispersion characteristics in which the in-plane phase difference becomes smaller depending on the wavelength of the measurement light. It can display flat wavelength dispersion characteristics in which the in-plane phase difference does not change substantially with the wavelength of the measurement light.

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, particularly preferably 95% or more. Furthermore, the haze of the surface protection film base material 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. According to the embodiment of the present invention, it is possible to realize a base material for a surface protection film that has a very small in-plane phase difference Re (550) as described above and has such very excellent transparency.

In an embodiment of the present invention, the number of times the base material for surface protection film is bent before breaking in the MIT test is 500 times or more, preferably 1,000 times or more, more preferably 1,500 times or more, and still more preferably 2,000 times or more. That is, the base material for surface protection films can have extremely excellent flexibility or bending resistance. Due to such excellent flexibility or bending resistance of the surface protection film base material, it is possible to obtain a surface protection film that has excellent workability during bonding and peeling and in which cracking is suppressed. According to the embodiment of the present invention, it is possible to achieve both such excellent flexibility or bending resistance and the very small in-plane phase difference Re (550) as described above. Being able to achieve such a balance is one of the achievements of the present invention. Furthermore, the MIT test can be performed in accordance with JIS P 8115.

The elastic modulus of the base material for surface protection films is preferably 50 MPa to 350 MPa at a stretching speed of 100 mm/min. When the elastic modulus is within such a range, a surface protection film excellent in conveyability and workability can be obtained. According to the embodiment of the present invention, it is possible to achieve both excellent elastic modulus (strength) and excellent flexibility or bending resistance (flexibility) as described above. In addition, the elastic modulus is measured based on JIS K 7127:1999.

The tensile elongation of the surface protection film base material is preferably 70% to 200%. When the tensile elongation is in this range, there is an advantage that it is less likely to break during transportation. In addition, the tensile elongation is measured based on JIS K 6781.

The thickness of the base material for surface protection film is typically 10 μm to 100 μm, preferably 20 μm to 70 μm.

B. Manufacturing method of base material for surface protection film The method for producing a base material for a surface protection film according to an embodiment of the present invention includes forming the film-forming material (resin composition) containing a polymer alloy described in the above item A into a film, and stretching the formed film. stretch.

In addition to the above-mentioned polymer alloy, the film-forming material may also contain other resins, additives, or solvents. Examples of additives include those described above.

As a method of forming a thin film from a thin film forming material, any appropriate forming processing method can be used. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (for example, tape casting), and calendaring. Forming method, hot pressing method, etc. Extrusion molding or cast coating is preferred. This is because the smoothness of the resulting film can be improved and good optical uniformity can be obtained. The molding conditions can be appropriately set according to the composition and type of the resin used, the desired characteristics of the base material for the surface protection film, and the like.

The stretching method of the film is typically biaxial stretching, and more specifically, it is sequential biaxial stretching or simultaneous biaxial stretching. This is because it is possible to obtain a base material for a surface protection film that has a small in-plane phase difference Re (550) and is excellent in flexibility or bending resistance. Sequential biaxial stretching or simultaneous biaxial stretching represents the use of a tenter frame. Therefore, the stretching direction of the film is typically the longitudinal direction and the width direction of the film.

The stretching temperature can be changed depending on the desired in-plane retardation and thickness of the surface protection film base material, 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+50°C, and more preferably Tg+10°C to Tg+30°C relative to the glass transition temperature (Tg) of the film. By stretching at such a temperature, in the embodiment of the present invention, a surface protection film base material having appropriate characteristics can be obtained.

The stretching ratio can be changed depending on the desired in-plane phase difference and thickness of the surface protection film base material, the type of resin used, the thickness of the film used, stretching temperature, and the like. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching ratio in the first direction (for example, the length direction) and the stretching ratio in the second direction (for example, the width direction) It is preferable that the difference between the magnification ratios is as small as possible, and it is more preferable that they are substantially equal. With such a structure, a surface protection film substrate having a small in-plane phase difference Re (550) and excellent flexibility or bending resistance can be obtained. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching ratio is for each of the first direction (for example, the length direction) and the second direction (for example, the width direction). , for example, it can be 1.1 times to 3.0 times.

In the embodiment of the present invention, the stretching speed is preferably 10%/second or less, more preferably 7%/second or less, further preferably 5%/second or less, and particularly preferably 2.5%/second or less. By stretching a film containing the specific polymer alloy as described above at such a low stretching speed, it is possible to obtain surface protection with a small in-plane phase difference Re (550) and excellent flexibility or bending resistance. Film base material. The lower limit of the stretching speed may be, for example, 1.2%/second. If the stretching speed is too small, productivity may become impractical. Furthermore, when biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching speed in the first direction (for example, the length direction) and the stretching speed in the second direction (for example, the width direction) The difference in stretching speed is preferably as small as possible, and more preferably is substantially equal. With such a configuration, the in-plane phase difference Re (550) can be further reduced and the flexibility and bending resistance can be further improved.

C. Surface protection film The base materials for surface protection films described in the above items A and B can be suitably used for surface protection films. Therefore, embodiments of the present invention also include surface protection films. The surface protection film according to the embodiment of the present invention includes the base material for surface protection films described in the above items A and B and an adhesive layer.

As the adhesive forming the adhesive layer, any appropriate adhesive can be used. Examples of the base resin of the adhesive include acrylic resin, styrene resin, siloxane resin, urethane resin, and rubber resin. Such a base resin is described in, for example, Japanese Patent Application Laid-Open No. 2015-120337 or Japanese Patent Application Laid-Open No. 2011-201983. The descriptions of these publications are incorporated into this specification as references. Acrylic resins are preferred from the viewpoints of chemical resistance, adhesion to prevent intrusion of treatment liquid during immersion, and freedom from adherends. Examples of cross-linking agents that may be included in the adhesive include isocyanate compounds, epoxy compounds, and aziridine compounds. The adhesive may include, for example, a silane coupling agent. The compounding formula of the adhesive can be appropriately set according to the purpose and desired properties.

The storage elastic 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. When the storage elastic modulus of the adhesive layer is within this range, blocking during roll formation can be suppressed. In addition, the storage elastic modulus can be obtained, for example, from 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, and more preferably 3 μm to 30 μm. If the thickness is too thin, the adhesiveness may become insufficient and air bubbles may be mixed in the adhesive interface. If the thickness is too thick, problems such as adhesive leakage may easily occur.

Practically, before the surface protection film is actually used (that is, attached to an optical film or image display device), the separation piece is temporarily adhered to the surface of the adhesive layer in a peelable manner. By providing the separator, the surface protection film can be rolled into a roll while protecting the adhesive layer. Examples of the separator include plastics (for example, polyethylene terephthalate) whose surface is coated with a release agent such as a silicone-based release agent, a fluorine-based release agent, or a long-chain alkyl acrylate release agent. ester (PET), polyethylene, polypropylene) film, non-woven fabric or paper, etc. As for the thickness of the separation member, any suitable thickness may be adopted depending on the purpose. The thickness of the separation member is, for example, 10 μm to 100 μm.

D. Optical film with surface protection film The surface protection film described in the above item C is used to protect the optical film before it is actually used (finally, an image display device). Therefore, embodiments of the present invention also include optical films with surface protection films. The optical film with a surface protection film according to an embodiment of the present invention includes an optical film and the surface protection film described in the above item C that is releasably bonded to the optical film.

The optical film may be a single film or a laminated body. Specific examples of optical films include polarizers, retardation films, polarizing plates (typically, a laminate of polarizers and protective films), conductive films for touch panels, surface treatment films, and, depending on the purpose, A laminate obtained by appropriately stacking these layers (for example, an anti-reflection circular polarizing plate, a conductive layer-attached polarizing plate for touch panels, a retardation layer-attached polarizing plate, a prism sheet-integrated polarizing plate). Example

Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these examples. The measurement methods of each characteristic in the Examples are as follows. In addition, unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) In-plane phase difference Re(550) and thickness direction phase difference Rth(550) The surface protection film substrate (biaxially stretched film) obtained in the Examples and Comparative Examples was cut into a length of 4 cm and a width of 4 cm to prepare a measurement sample. The in-plane retardation and the thickness direction retardation were measured using the product name "Axoscan" manufactured by Axometrics Co., Ltd. on this measurement sample. The measurement wavelength is 550 nm and the measurement temperature is 23°C. (2)Haze For the same measurement sample as in the above (1), the haze was measured using a haze meter (HM-150 model manufactured by Murakami Color Technology Research Institute). The measured temperature is 23°C. (3)MIT test The MIT test is conducted in accordance with JIS P 8115. Specifically, the base material for surface protection films (biaxially stretched film) obtained in Examples and Comparative Examples was cut into a length of 15 cm and a width of 1.5 cm to prepare a measurement sample. The measurement sample was mounted on the MIT bending fatigue testing machine BE-202 (manufactured by TESTER SANGYO CO, LTD.) (load 1.0kgf, clamp R: 0.38mm), and the test specimen was tested at a test speed of 90cpm and a bending angle of 90°. The bending is repeated with an upper limit of 2000 times, and the number of bends when the sample breaks is taken as the test value. (4) Rainbow-like unevenness The surface protection film substrate (biaxially stretched film) obtained in the Examples and Comparative Examples was placed between two polarizing plates in a crossed state. At this time, the surface protection film base material is arranged so that the longitudinal direction of the surface protection film base material is parallel to the transmission axis direction of one polarizing plate. In this state, fluorescent light is irradiated from the lower side of the lower polarizing plate, and the presence or absence of rainbow-like unevenness is visually observed. Evaluation is based on the following criteria. ○: Rainbow-like unevenness is not observed △: Rainbow-like unevenness is slightly observed ×: Rainbow-like unevenness is significantly observed (5) Flexibility or bending resistance Repeat the 180° bending test 100 times on the base material for surface protection film (biaxially stretched film) to confirm whether there is any breakage. Evaluation is based on the following criteria. ○: No cracking was observed ×: Fracture is observed

>Example 1> 1-1. Preparation of polymer alloy As raw materials, the following materials were used. FDPM: 9,9-bis(2-methoxycarbonylethyl)fluorene [dimethyl ester of 9,9-bis(2-carboxyethyl)fluorene (or fluorene-9,9-dipropionic acid)] , was synthesized in the same manner except that tert-butyl acrylate described in Example 1 of Japanese Patent Application Laid-Open No. 2005-89422 was replaced with methyl acrylate [37.9 g (0.44 mol)]. BPEF: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, manufactured by Osaka Gas Chemicals Co., Ltd. EG: ethylene glycol PC: Bisphenol A type polycarbonate resin, "Iupilon H-4000" manufactured by Mitsubishi Engineering-Plastics Corporation

Add 1.00 mole of FDPM, 0.80 mole of BPEF, and 2.20 mole of EG as transesterification catalysts: 2×10 ^-4 mole of manganese acetate tetrahydrate and 8×10 ^-4 mole of calcium acetate monohydrate. Heat slowly while stirring to melt. After the temperature was raised to 230°C, 14×10 ^-4 moles of trimethyl phosphate and 20×10 ^-4 moles of germanium oxide were added, and the temperature was slowly raised to 270°C and below 0.13 kPa, and EG was removed while reducing the pressure. After reaching the predetermined stirring torque, the contents are taken out of the reactor to prepare fluorene ring-containing polyester pellets. The obtained pellets were analyzed by ¹ H-NMR. It was found that 100 mol% of the dicarboxylic acid component introduced into the fluorene ring-containing polyester was derived from FDPM, and 80 mol% of the introduced diol component was derived from BPEF, 20 Mol% is derived from EG. The obtained fluorene ring-containing polyester had a glass transition temperature Tg of 126°C and a weight average molecular weight Mw of 43,600.

The obtained fluorene ring-containing polyester and PC were kneaded in a twin-screw mixer at a ratio of 20/80 (weight ratio) to prepare polymer alloy pellets.

1-2. Production of polymer alloy film The obtained polymer alloy was vacuum-dried at 80° C. for 5 hours, and then used a single-screw extruder (manufactured by Isuzu Chemical Industries, screw diameter 25 mm, barrel set temperature: 255° C.) and a T-die (width 200 mm, set temperature : 255℃), cooling roll (set temperature: 120~130℃) and the film forming device of the coiler to produce a polymer alloy film with a thickness of 160μm.

1-3. Preparation of base material for surface protection film The polymer alloy film obtained above is biaxially stretched simultaneously in the length direction and width direction to 2 times. The stretching temperature is [Tg+20°C] (i.e. 146°C), and the stretching speed is 1.4%/second in both the length and width directions. In this way, a surface protection film base material (thickness 40 μm) was obtained. The obtained base material for surface protection film had Re (550) of 8 nm, Rth (550) of 80 nm, a haze of 0.3%, and the MIT test value exceeded the upper limit of 2000 times. The obtained base material for surface protection films was used for the evaluation of the above (4) and (5). The results are shown in Table 1.

>Example 2> Except that the stretching speed was set to 3.1%/second in both the length direction and the width direction, the same operation was performed as in Example 1 to obtain a surface protection film base material. The obtained base material for surface protection film had Re (550) of 10 nm, Rth (550) of 81 nm, a haze of 0.2%, and the MIT test value exceeded the upper limit of 2000 times. The obtained base material for surface protection films was used for the evaluation of the above (4) and (5). The results are shown in Table 1.

>Example 3> Except that the stretching speed was set to 6.5%/second in both the length direction and the width direction, the same operation was performed as in Example 1 to obtain a surface protection film base material. The obtained base material for surface protection film had Re (550) of 20 nm, Rth (550) of 85 nm, a haze of 0.3%, and the MIT test value exceeded the upper limit of 2000 times. The obtained base material for surface protection films was used for the evaluation of the above (4) and (5). The results are shown in Table 1.

>Example 4> Except that the stretching speed was set to 10%/second in both the length direction and the width direction, the same operation was performed as in Example 1 to obtain a surface protection film base material. The obtained base material for surface protection film had Re (550) of 30 nm, Rth (550) of 91 nm, a haze of 0.2%, and the MIT test value exceeded the upper limit of 2000 times. The obtained base material for surface protection films was used for the evaluation of the above (4) and (5). The results are shown in Table 1.

>Comparative Example 1> A surface protection film was obtained in the same manner as in Example 1, except that a commercially available norbornene-based resin film (manufactured by Zeon Corporation, trade name "ZEONOR", Tg: 150°C) was used instead of the polymer alloy film. base material. The obtained base material for surface protection film had Re(550) of 2 nm, Rth(550) of 8 nm, haze of 0.1%, and MIT test value of 150 times. The obtained base material for surface protection films was used for the evaluation of the above (4) and (5). The results are shown in Table 1.

>Comparative example 2> The same procedure as in Example 1 was performed except that an ultra-high phase difference polyethylene terephthalate film (manufactured by Mitsubishi Chemical Corporation, trade name "Diafoil", Tg: 81°C) was used instead of the polymer alloy film. , to obtain a base material for surface protection film. The obtained base material for surface protection film had Re (550) of 4500 nm, Rth (550) of 6000 nm, a haze of 1.3%, and the MIT test value exceeded the upper limit of 2000 times. The obtained base material for surface protection films was used for the evaluation of the above (4) and (5). The results are shown in Table 1.

[Table 1]

>Evaluation> As is clear from Table 1, the base materials for surface protection films according to Examples of the present invention can prevent rainbow-like unevenness and have excellent bending resistance (or flexibility). Presumably this can be achieved by stretching a film containing a specific polymer alloy at a stretching speed below a predetermined value. Furthermore, when Examples 1 to 4 are compared, it is clear that the lower the stretching speed, the more excellent characteristics (small in-plane phase difference) can be obtained. Furthermore, regarding light leakage and coloration, it has been confirmed that the same results as rainbow-like unevenness are obtained. Industrial availability

The base material for surface protection films of the present invention is suitable for use in surface protection films. The surface protection film of the present invention can be used to protect the optical film (and ultimately the image display device) before it is actually used. By using the base material for surface protection film and the surface protection film of the present invention, the optical inspection accuracy of the image display device can be significantly improved.

(without)

Claims (6)

A surface protection film, comprising: a base material for a surface protection film, which is composed of a film containing a polymer alloy. The polymer alloy is a polymer alloy containing a fluorene ring-containing polyester and an aromatic polycarbonate. The surface protection film The in-plane phase difference Re (550) of the base material is 30 nm or less, and the number of bends until fracture in the MIT test is more than 500 times; and an adhesive layer. The surface protection film of claim 1, wherein the fluorene ring-containing polyester contains dicarboxylic acid component A and diol component B as copolymer components, and the dicarboxylic acid component A contains fluorenedicarboxylic acid component A1, and the fluorenedicarboxylic acid component Component A1 is at least one selected from the dicarboxylic acids represented by the following formulas (1a) and (1b):

In formula (1a) and formula (1b), R ¹ and R ² are each a substituent, k, m and n are each an integer from 0 to 4, and X ¹ and X ² are each a substituted or unsubstituted divalent hydrocarbon group. The surface protection film of claim 2, wherein the fluorene ring-containing polyester contains 50 mol% or more of the structural units derived from the fluorene dicarboxylic acid component A1 relative to the total amount of structural units derived from the dicarboxylic acid component A. structural unit. The surface protection film of claim 2, wherein the diol component B includes the fluorene diol component B1 represented by the following formula (2),

In formula (2), Z is an aromatic hydrocarbon ring, R ³ and R ⁴ are each a substituent, p is each an integer from 0 to 4, q and r are each an integer of 0 or more than 1, and R ⁵ is an alkane. base. For example, the surface protection film of requirement 1 has a total light transmittance of more than 80% and a haze of less than 1.0%. An optical film with a surface protection film, including: an optical film; and the surface protection film according to any one of claims 1 to 5, which is attached to the optical film in a peelable manner.