CN110862664A

CN110862664A - Base material for surface protection film, method for producing the base material, and surface protection film using the base material

Info

Publication number: CN110862664A
Application number: CN201910801816.7A
Authority: CN
Inventors: 中原步梦; 清水享
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2018-08-28
Filing date: 2019-08-28
Publication date: 2020-03-06
Also published as: JP7193272B2; TW202020045A; JP2020033419A; TWI812749B; KR20200024715A; JP2023016970A

Abstract

The invention provides a substrate for a surface protection film, a method for producing the substrate, and a surface protection film using the substrate. Provided is a substrate for a surface protective film, which has excellent flexibility and bending resistance and can well inhibit light leakage, coloring and rainbow unevenness during optical inspection. The substrate 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, and has an in-plane retardation Re (550) of 30nm or less and a number of bending times to break in an MIT test of 500 or more. The method for producing a substrate for a surface protective film of the present invention comprises: forming a film-forming material containing a polymer alloy containing a fluorene-ring-containing polyester and an aromatic polycarbonate into a film; and subjecting the film obtained by the molding to sequential biaxial stretching or simultaneous biaxial stretching.

Description

Base material for surface protection film, method for producing the base material, and surface protection film using the base material

Technical Field

The present invention relates to a substrate for a surface protective film, a method for producing the substrate, a surface protective film using the substrate, and an optical film with a surface protective film.

Background

An optical film (for example, a polarizing plate or a laminate including a polarizing plate) is bonded with a surface protective film in a peelable manner so as to protect the optical film (eventually, an image display device) until the image display device to which the optical film is applied is actually used. In practical use, an image display device is manufactured by bonding a laminate of an optical film and a surface protective film to a display unit, the image display device is subjected to an optical test (for example, a lighting test) in a state where the laminate is bonded, and the surface protective film is peeled off and removed at an appropriate time thereafter. The surface protective film typically has a resin film as a substrate and an adhesive layer. With conventional surface protective films, light leakage, coloration, rainbow unevenness, and the like may occur during optical inspection, which may cause a reduction in the accuracy of optical inspection. As a result, the image display device itself may be determined to be defective even in the optical inspection before shipment, and thus the efficiency from the manufacture of the image display device to shipment may be reduced. Further, the surface protective film (substantially, the base material) is required to have excellent flexibility in consideration of workability at the time of bonding and peeling.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-190406

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a substrate for a surface protective film which has excellent flexibility and bending resistance and can satisfactorily suppress light leakage, coloring and rainbow unevenness in optical inspection.

Means for solving the problems

The substrate for a surface protection film according to an embodiment of the present invention is composed of a film containing a polymer alloy of a fluorene-containing polyester and an aromatic polycarbonate, and has an in-plane retardation Re (550) of 30nm or less and a number of bending times to break in an MIT test of 500 or more.

In 1 embodiment, the fluorene ring-containing polyester comprises, as copolymerized components, a dicarboxylic acid component (A) comprising a fluorene dicarboxylic acid component (A1) and a diol component (B), wherein the fluorene dicarboxylic acid component (A1) is at least 1 selected from dicarboxylic acids represented by the following formulae (1a) and (1B),

in the formulae (1a) and (1b), R¹And R²Each is a substituent, k, m and n are each an integer of 0 to 4, X¹And X²Each is a substituted or unsubstituted 2-valent hydrocarbon group.

In 1 embodiment, the fluorene ring-containing polyester contains 50 mol% or more of a structural unit derived from the fluorene dicarboxylic acid component (a1) based on the total amount of structural units derived from the dicarboxylic acid component (a).

In 1 embodiment, the diol component (B) contains a fluorene diol component (B1) represented by the following formula (2),

in the formula (2), Z is an aromatic hydrocarbon ring, R³And R⁴Each represents a substituent, p is an integer of 0 to 4, q and R are each an integer of 0 or 1 or more, R⁵Each is an alkylene group.

In 1 embodiment, the surface-protecting-film substrate 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 producing the substrate for a surface protective film. The manufacturing method comprises the following steps: forming a film-forming material containing a polymer alloy containing a fluorene-ring-containing polyester and an aromatic polycarbonate into a film; and subjecting the film obtained by the molding to sequential biaxial stretching or simultaneous biaxial stretching.

In 1 embodiment, in the production method, the stretching speed in the sequential biaxial stretching or simultaneous biaxial stretching is 10%/second or less.

According to still another aspect of the present invention, a surface protective film is provided. The surface-protecting film comprises the substrate for a surface-protecting film and an adhesive layer.

According to still another aspect of the present invention, there is provided an optical film with a surface protective film. The optical film with a surface protective film comprises: an optical film and the surface protective film releasably attached to the optical film.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the embodiment of the present invention, a substrate for a surface protective film can be realized which can achieve both a very small in-plane retardation and excellent flexibility or bending resistance by stretching a film containing a polymer alloy of a fluorene ring-containing polyester and an aromatic polycarbonate under predetermined stretching conditions (typically, a stretching speed).

Detailed Description

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

A. Base material for surface protective film

The surface protective film substrate according to the embodiment of the present invention is composed of a film containing a polymer alloy containing a fluorene ring-containing polyester and an aromatic polycarbonate. The polymer alloy may be a polymer blend or a copolymer. Preferably a polymer blend. The fluorene ring-containing polyester and the aromatic polycarbonate are different polymers, but they are completely compatible or stably microphase-separated when mixed, and can easily form a polymer blend without using a compatibilizer. Any suitable method can be employed for mixing the fluorene-containing cyclic polyester and the aromatic polycarbonate. Specific examples of the mixing method include a method of dissolving the fluorene ring-containing polyester and the aromatic polycarbonate in a solvent, and a method of melt-mixing the fluorene ring-containing polyester and the aromatic polycarbonate using a kneader or an extruder. Melt mixing is preferred. This is because the reduction of optical properties (for example, phase difference, wavelength dispersion properties, and the like) due to the residual solvent after the production of the substrate for a surface protective film can be prevented.

The fluorene ring-containing polyester contains a dicarboxylic acid component (A) and a diol component (B) as copolymerization components. The dicarboxylic acid component (a) contains a fluorene dicarboxylic acid component (a 1). Examples of the fluorene dicarboxylic acid component include dicarboxylic acids represented by the following formulae (1a) and (1 b). These dicarboxylic acids may be used alone or in combination.

In the formula (1a), as the substituent R¹Examples thereof include a cyano group, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom), a hydrocarbon group [ e.g., an alkyl group, an aryl group (e.g., C such as a phenyl group, etc. ]_6-10Aryl radical)]And the like. Examples of the alkyl group include C such as methyl, ethyl, n-propyl, isopropyl, n-butyl and tert-butyl_1-12An alkyl group. Preferably C_1-8Alkyl, more preferably C_1-4Alkyl (e.g., methyl). Each substituent R¹May be the same or different. Further, a substituent R¹When the number of substitution (k) is 2 or more, 2 or more groups R in the same phenyl ring in the fluorene ring¹May be the same or different. The substituent R in 2 benzene rings constituting the fluorene ring¹Examples of the bonding position (substitution position) include the 2-position, 7-position, 2-and 7-positions of the fluorene ring.

Substituent R¹The number of substitution (k) is, for example, an integer of 0 to 2, preferably 0 or 1, and more preferably 0. Wherein the fluorene ring is formedThe number of substitution k in the 2 benzene rings may be the same or different.

In the formula (1b), the substituent R²And the number of substitution m is each independently the substituent R in the formula (1a)¹The same applies to the number of substitutions k.

In the 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 formulae (1a) and (1b), X is¹And X²Examples of the hydrocarbon group include a linear or branched alkylene group. Specific examples thereof include linear or branched C groups such as methylene, ethylene, trimethylene, propylene, 1, 2-butanediyl and 2-methylpropane-1, 3-diyl_1-8An alkylene group. Preferred alkylene groups are linear or branched C_1-6Alkylene (e.g., linear or branched C such as methylene, ethylene, trimethylene, propylene, 2-methylpropane-1, 3-diyl)_1-4Alkylene). Examples of the substituent for the hydrocarbon group include an aryl group (e.g., phenyl group) and a cycloalkyl group (e.g., cyclohexyl group).

Each X¹May be the same or different. X¹And X²May be the same or different. X¹Preferably straight-chain or branched C_2-4Alkylene (e.g., ethylene, propylene, etc. straight or branched C_2-3Alkylene) group, X²Preferably straight-chain or branched C_1-3Alkylene (e.g., methylene, ethylene).

As the dicarboxylic acid component represented by the formula (1a), for example, 9-bis (carboxy C)_2-6Alkyl) fluorenes and their ester-forming derivatives. Specific examples thereof include 9, 9-bis (2-carboxyethyl) fluorene and 9, 9-bis (2-carboxypropyl) fluorene. As the dicarboxylic acid component represented by the formula (1b), for example, 9- (dicarboxyc) can be mentioned_2-8Alkyl) fluorenes and their ester-forming derivatives. Specific examples thereof include 9- (1-carboxy-2-carboxyethyl) fluorene and 9- (2, 3-dicarboxypropyl) fluorene.

The fluorene ring-containing polyester contains the structural unit derived from the fluorene dicarboxylic acid component (a1) in an amount of preferably 10 mol% or more (e.g., 30 mol% or more), more preferably 50 mol% or more (e.g., 60 mol% or more), still more preferably 70 mol% or more (e.g., 80 mol% or more), and particularly preferably 90 mol% or more (e.g., 95 mol% or more) based on the total amount of the structural units derived from the dicarboxylic acid component (a). The dicarboxylic acid component (a) may be substantially all the fluorene dicarboxylic acid component (a 1).

The dicarboxylic acid component (a) may further contain other dicarboxylic acid components within a range not impairing the effects of the present invention. Examples of the other dicarboxylic acid component include an aromatic dicarboxylic acid component (a2) [ excluding the fluorene dicarboxylic acid component (a1) ], an alicyclic dicarboxylic acid component (A3), an aliphatic dicarboxylic acid component (a4), and ester-forming derivatives thereof.

The diol component (B) contains a 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 a plurality of diol compounds.

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) and polycyclic aromatic hydrocarbon rings (polycyclic aromatic hydrocarbon rings) such as benzene rings. Examples of the polycyclic aromatic hydrocarbon ring include a condensed polycyclic aromatic hydrocarbon ring (condensed polycyclic aromatic hydrocarbon ring) and a ring-assembled aromatic hydrocarbon ring (ring-assembled aromatic hydrocarbon ring). Preferably C such as benzene ring, naphthalene ring, biphenyl ring, etc_6-12Aromatic hydrocarbon ring, more preferably C such as benzene ring_6-10An aromatic hydrocarbon ring. Each Z may be the same or different.

In the formula (2), the substituent R³And the number of substitution p is each independently the substituent R in formula (1a)¹The same applies to the number of substitutions k.

As substituents R⁴Examples thereof include a halogen atom, a linear or branched alkyl group, a cycloalkyl group and an aryl groupAralkyl, alkoxy, cycloalkyloxy, aryloxy, aralkyloxy, alkylthio, cycloalkylthio, arylthio, aralkylthio, acyl, nitro, cyano, substituted amino, bis (alkylcarbonyl) amino. Substituent R⁴Preferably an alkyl group (e.g., a linear or branched C such as methyl group)_1-6Alkyl), cycloalkyl (e.g. C such as cyclohexyl)_5-8Cycloalkyl), aryl (e.g. phenyl, etc. C_6-14Aryl group), alkoxy group (e.g., methoxy group, linear or branched C_1-4Alkoxy), more preferably an alkyl group (e.g., a linear or branched C such as methyl group)_1-4Alkyl), aryl (e.g. C such as phenyl)_6-10Aryl). In addition, the substituent R⁴In the case of aryl, the substituent R⁴The above ring-assembled aromatic hydrocarbon ring may be formed together with ring Z. Each R is⁴May be the same or different.

Substituent R⁴The number of substitution q in (b) is, for example, an integer of 0 to 8, preferably an integer of 0 to 4 (e.g., 0 to 3), and more preferably an integer of 0 to 2 (e.g., 0 or 1). The number of substitutions q may be 0. In addition, the substituent R⁴The bonding position (substitution position) of (2) is not particularly limited.

In the formula (2), as the substituent R⁵Examples thereof include linear or branched C groups such as ethylene, propylene (1, 2-propanediyl), trimethylene, 1, 2-butanediyl and tetramethylene_2-6An alkylene group. Preferably straight-chain or branched C_2-4Alkylene, more preferably straight-chain or branched C_2-3Alkylene (especially ethylene). Oxyalkylene Radical (OR)⁵) The number of repetitions (number of moles added) r is, for example, an integer of 0 to 15 (e.g., 1 to 10), preferably an integer of 0 to 8 (e.g., 1 to 6), more preferably an integer of 0 to 4 (e.g., 1 to 2), and still more preferably 0 or 1 (e.g., 1). The group [ -O- (R) in the formula (2)⁵O)_r-H]The substitution position of (3) 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.

For the diol component(B) The fluorene ring-containing polyester may further contain an alkanediol (B2) [ or an alkylene diol (B2) ] in order to improve polymerization reactivity, impart flexibility to the fluorene ring-containing polyester and improve moldability]. Examples of the alkanediol (B2) include linear or branched C-diols such as ethylene glycol, propylene glycol, trimethylene glycol, 1, 2-butanediol, 1, 3-butanediol, tetramethylene glycol (1, 4-butanediol), 1, 5-pentanediol, neopentyl glycol, 1, 6-hexanediol, 1, 8-octanediol, and 1, 10-decanediol_2-12An alkane diol. The ratio B1/B2 (molar ratio) of the structural unit derived from the fluorene diol (B1) to the structural unit derived from the alkane diol (B2) in the fluorene ring-containing polyester is, for example, 0/50 to 100/0 (e.g., 50/50 to 99/1), preferably 60/40 to 97/3 (e.g., 65/35 to 95/5), more preferably 68/32 to 92/8 (e.g., 70/30 to 90/10), and still more preferably 73/27 to 88/12 (e.g., 75/25 to 85/15).

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

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

The aromatic polycarbonate is a polycarbonate having a diol component (C) as a polymerization component. The diol component (C) contains at least an aromatic diol (C1). Examples of the aromatic diol (C1) include the fluorene diols (e.g., 9, 9-bis (hydroxyaryl) fluorenes, 9, 9-bis [ hydroxy (poly) alkoxyaryls)]Fluorenes), dihydroxy aromatic hydrocarbons (e.g., hydroquinone, resorcinol), araliphatic diols (e.g., benzenedimethanol), bisPhenols (e.g., bisphenol A, bisphenol F, bisphenol AD, bisphenol C, bisphenol G, bisphenol S), diphenols (e.g., p, p' -biphenol), and C of diol component thereof_2-4Alkylene oxide (or alkylene carbonate, halogenated alkanol) adduct [ for example, adduct obtained by adding about 2 to 10 moles of ethylene oxide to 1 mole of bisphenol A]. These aromatic diols (C1) may be used alone, or 2 or more thereof may be used in combination. The aromatic diol (C1) preferably comprises biphenols, bisphenols or C thereof_2-4An alkylene oxide adduct.

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 (e.g., 10/90 to 97/3), preferably 30/70 to 95/5, more preferably 50/50 to 90/10, still more preferably 60/40 to 88/12 (e.g., 65/35 to 85/15), and particularly preferably 67/33 to 83/17 (e.g., 70/30 to 80/20).

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

In the formula (3), Z¹Each being a monocyclic or fused polycyclic aromatic hydrocarbon ring, R⁶And R⁷Each is a substituent, and s, t and u are integers of 0 or more.

The polymer alloy may further comprise any suitable additive. Examples of the additives include plasticizers (esters, phthalic acid compounds, epoxy compounds, sulfonamides, etc.), flame retardants (inorganic flame retardants, organic flame retardants, colloidal flame retardant 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, antifoaming agents, lubricants, mold release agents (natural waxes, synthetic waxes, straight chain fatty acids, metal salts thereof, acid amides, etc.), slipping property imparting agents (inorganic fine particles such as silica, titanium oxide, calcium carbonate, clay, mica, kaolin, etc., (organic fine particles such as (meth) acrylic resins, styrene resins (crosslinked polystyrene resins, etc.)), and compatibilizers. The amount, kind, combination and addition amount of the additive to be added can be appropriately set according to the purpose.

Details of the polymer alloy are described in, for example, Japanese patent laid-open publication No. 2017-198956, the disclosure of which is incorporated herein by reference.

In the embodiment of the present invention, the in-plane retardation of the substrate for a surface protective film is Re (550)30nm or less, preferably 20nm or less, more preferably 15nm or less, still more preferably 10nm or less, and particularly preferably 5nm or less. The smaller the in-plane retardation Re (550) is, the more preferable the lower limit thereof is 0nm, and for example, it may be 1 nm. When the in-plane retardation Re (550) is in such a range, light leakage, coloration, and rainbow unevenness can be favorably suppressed when the surface protection film using the substrate for a surface protection film of the present invention is subjected to optical inspection of an image display device. As a result, the accuracy of optical inspection of the image display device can be significantly improved, and the efficiency from the manufacture to the 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-described specific polymer alloy under predetermined stretching conditions as described later. In the present specification, "Re (λ)" is an in-plane retardation measured at 23 ℃ with light having a wavelength of λ nm. For Re (λ), assuming that the thickness of the layer (film) is d (nm), according to the formula: re ═ x-ny) × d. Thus, "Re (550)" is an in-plane retardation measured at 23 ℃ with light having a wavelength of 550 nm. Here, "nx" is a refractive index in a direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), and "ny" is a refractive index in a direction orthogonal to the slow axis (i.e., the fast axis direction) in the plane.

The retardation Rth (550) in the thickness direction of the substrate for a surface protective film is preferably 95nm or less, more preferably 85nm or less. The lower the thickness direction retardation Rth (550) is, the more preferable, the lower limit thereof is preferably 0 nm. When the thickness direction retardation Rth (550) is in such a range, the light leakage in the oblique direction, coloring, and rainbow unevenness in the optical inspection can be favorably suppressed. As a result, the accuracy can be significantly improved even in the optical inspection of a large-sized image display device. The surface-protecting film substrate preferably has an Nz coefficient of 3.0 to 10. Therefore, the refractive index characteristics of the substrate for a surface protection film can show a relationship of, for example, nx > ny > nz. When the Nz coefficient is in such a range, light leakage in an oblique direction, coloring, and rainbow unevenness in optical inspection can be further favorably suppressed. "Rth (λ)" is a phase difference in the thickness direction measured at 23 ℃ with light having a wavelength of λ nm. With respect to Rth (λ), when the thickness of the layer (film) is d (nm), according to the formula: and Rth ═ x-nz) × d. Thus, "Rth (550)" is a retardation in the thickness direction measured at 23 ℃ with light having a wavelength of 550 nm. Here, "nz" is a refractive index in the thickness direction. The "Nz coefficient" is obtained by Nz ═ Rth (λ)/Re (λ).

The surface protective film substrate can exhibit reverse dispersion wavelength characteristics in which the in-plane retardation increases according to the wavelength of the measurement light, can exhibit positive wavelength dispersion characteristics in which the in-plane retardation decreases according to the wavelength of the measurement light, and can exhibit flat wavelength dispersion characteristics in which the in-plane retardation does not substantially change depending on the wavelength of the measurement light.

The total light transmittance of the surface-protecting-film substrate is preferably 80% or more, more preferably 85% or more, further preferably 90% or more, and particularly preferably 95% or more. Further, the haze of the substrate for a surface protective film is preferably 1.0% or less, more preferably 0.7% or less, further preferably 0.5% or less, and particularly preferably 0.3% or less. According to the embodiment of the present invention, a substrate for a surface protective film having such a very excellent transparency as having the very small in-plane retardation Re (550) as described above can be realized.

In the embodiment of the present invention, the number of times of bending until breakage in the MIT test is 500 or more, preferably 1000 or more, more preferably 1500 or more, and further preferably 2000 or more times with respect to the substrate for a surface protective thin film. That is, the substrate for a surface protective film can have very excellent flexibility or bending resistance. Due to such excellent flexibility and bending resistance of the substrate for a surface protection film, a surface protection film which is excellent in handling property at the time of bonding and peeling and is suppressed in breakage can be obtained. According to the embodiment of the present invention, such excellent flexibility and bending resistance can be achieved at the same time as well as the very small in-plane retardation Re (550) described above. The achievement of such a compromise is one of the achievements of the present invention. The MIT test can be performed according to JIS P8115.

The elastic modulus of the surface-protecting-film substrate is preferably 50MPa to 350MPa at a stretching speed of 100 mm/min. When the elastic modulus is in such a range, a surface protection film excellent in transportability and handling properties can be obtained. According to the embodiments of the present invention, it is possible to achieve both of excellent elastic modulus (strength) and excellent flexibility or bending resistance (flexibility) as described above. The elastic modulus was measured in accordance with JIS K7127: 1999.

The tensile elongation of the surface-protecting film substrate is preferably 70% to 200%. When the tensile elongation is in such a range, there is an advantage that the sheet is not easily broken during conveyance. The tensile elongation is measured according to JIS K6781.

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

B. Method for producing substrate for surface protective film

The method for producing a substrate for a surface protection film according to an embodiment of the present invention includes: the method for producing a film of the present invention comprises the steps of forming a film-forming material (resin composition) comprising the polymer alloy as set forth in item a into a film, and stretching the film obtained by the forming.

The film-forming material may contain other resins, additives, and solvents in addition to the polymer alloy. The additives mentioned above may be used.

As a method of forming a thin film from the thin film forming material, any appropriate forming process may be employed. Specific examples thereof include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, casting coating (for example, casting), calendering, and hot pressing. Extrusion molding or cast coating is preferred. This is because the smoothness of the obtained film can be improved and good optical uniformity can be obtained. The molding conditions may be appropriately set depending on the composition and type of the resin used, the desired properties of the substrate for a surface protective film, and the like.

The stretching method of the film is typically biaxial stretching, and more specifically, sequential biaxial stretching or simultaneous biaxial stretching. This is because a substrate for a surface protective film having a small in-plane retardation Re (550) and excellent flexibility and bending resistance can be obtained. Sequential biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter. Therefore, the stretching direction of the film is typically the longitudinal direction and the width direction of the film.

The stretching temperature may vary depending on the in-plane retardation and thickness desired for the substrate for a surface protective film, the type of resin used, the thickness of the film used, the stretching magnification, and the like. Specifically, the stretching temperature is preferably from Tg +5 ℃ to Tg +50 ℃ and more preferably from Tg +10 ℃ to Tg +30 ℃ relative to the glass transition temperature (Tg) of the film. By stretching at such a temperature, a surface protective film substrate having appropriate characteristics can be obtained in the embodiment of the present invention.

The stretch ratio may vary depending on the in-plane retardation and thickness desired for the substrate for a surface protective film, the type of resin used, the thickness of the film used, the stretching temperature, and the like. In the case of biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching), the difference between the stretch ratio in the 1 st direction (for example, the longitudinal direction) and the stretch ratio in the 2 nd direction (for example, the width direction) is preferably as small as possible, and more preferably substantially equal. With such a configuration, a substrate for a surface protective film having a small in-plane retardation Re (550) and excellent flexibility and bending resistance can be obtained. In the case of biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching), the stretching ratio may be, for example, 1.1 to 3.0 times in each of the 1 st direction (for example, the longitudinal direction) and the 2 nd direction (for example, the width direction).

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 comprising the specific polymer alloy as described above at such a small stretching speed, a substrate for a surface protection film having a small in-plane retardation Re (550) and excellent flexibility or bending resistance can be obtained. The lower limit of the drawing speed may be, for example, 1.2%/second. If the stretching speed is too low, the productivity may become impractical. In the case of biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching), the difference between the stretching speed in the 1 st direction (for example, the longitudinal direction) and the stretching speed in the 2 nd direction (for example, the width direction) is preferably as small as possible, and more preferably substantially equal. With such a configuration, the in-plane retardation Re (550) can be further reduced, and the flexibility and the bending resistance can be further improved.

C. Surface protective film

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

As the adhesive for forming the adhesive layer, any suitable adhesive can be used. Examples of the base resin of the binder include acrylic resins, styrene resins, silicone resins, urethane resins, and rubber resins. Such a base resin is described in, for example, Japanese patent laid-open Nos. 2015-120337 and 2011-201983. The descriptions of these publications are incorporated herein by reference. From the viewpoints of chemical resistance, adhesion for preventing the entry of a treatment liquid during immersion, freedom in adhesion to an adherend, and the like, an acrylic resin is preferred. Examples of the crosslinking agent that can be contained in the adhesive include isocyanate compounds, epoxy compounds, and aziridine compounds. The binder may, for example, comprise a silane coupling agent. The compounding recipe of the adhesive can be appropriately set according to the purpose and the desired characteristics.

The storage modulus of the adhesive layer is preferably 1.0X 10⁴Pa～1.0×10⁷Pa, more preferably 2.0X 10⁴Pa～5.0×10⁶Pa. When the storage modulus of the adhesive layer is in such a range, blocking at the time of roll formation can be suppressed. The storage modulus can be determined by, for example, dynamic viscoelasticity measurement at a temperature of 23 ℃ and an angular velocity of 0.1 rad/s.

The thickness of the pressure-sensitive adhesive layer is preferably 1 to 60 μm, more preferably 3 to 30 μm. If the thickness is too thin, the adhesiveness may become insufficient, and air bubbles may be mixed in the adhesion interface. If the thickness is too large, problems such as bleeding of the adhesive tend to occur.

In practice, the surface protective film is temporarily attached to a separator in a releasable manner on the surface of the pressure-sensitive adhesive layer before the film is actually used (i.e., attached to an optical film or an image display device). By providing the separator, the adhesive layer can be protected and the surface protection film can be wound up in a roll shape. Examples of the separator include a plastic (for example, polyethylene terephthalate (PET), polyethylene, and polypropylene) film, a nonwoven fabric, and paper, which are surface-coated with a release agent such as a silicone release agent, a fluorine release agent, and a long-chain alkyl acrylate release agent. As for the thickness of the separator, any appropriate thickness may be adopted according to the purpose. The thickness of the separator is, for example, 10 μm to 100 μm.

D. Optical film with surface protective film

The surface protective film described in the above item C is used for protecting an optical film (ultimately, an image display device) before the optical film is actually used. Accordingly, embodiments of the present invention also include optical films with surface protective films. An optical film with a surface protective film according to an embodiment of the present invention includes: an optical film, and the surface protective film described in the above item C releasably attached to the optical film.

The optical film may be a single film or a laminate. Specific examples of the optical film include a polarizer, a retardation film, a polarizing plate (typically, a laminate of a polarizer and a protective film), a conductive film for a touch panel, a surface-treated film, and a laminate obtained by appropriately laminating them according to the purpose (for example, a circular polarizing plate for antireflection, a conductive layer-equipped polarizing plate for a touch panel, a polarizing plate with a retardation layer, and a prism sheet-integrated polarizing plate).

[ examples ]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods of the characteristics in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) In-plane retardation Re (550) and thickness direction retardation Rth (550)

The surface-protecting-film base materials (biaxially stretched films) obtained in examples and comparative examples were cut into a length of 4cm and a width of 4cm to obtain measurement samples. The in-plane retardation and the thickness direction retardation were measured using a sample manufactured by Axometrics under the product name "Axoscan". The measurement wavelength was 550nm and the measurement temperature was 23 ℃.

(2) Haze degree

The haze was measured using a haze meter (HM-150, model, manufactured by Kimura color technology research Co., Ltd.) on the same measurement sample as in (1). The measurement temperature was 23 ℃.

(3) MIT test

MIT test was performed according to JIS P8115. Specifically, the surface-protecting-film base materials (biaxially stretched films) obtained in examples and comparative examples were cut into pieces each having a length of 15cm and a width of 1.5cm, and the pieces were used as measurement samples. The measurement sample was mounted on an MIT bending fatigue TESTER BE-202 type (manufactured by TESTER SANGYO CO, LTD.) (load 1.0kgf, R: 0.38mm of a jig), and bending was repeated at a test speed of 90cpm and a bending angle of 90 DEG, with 2000 times as an upper limit, and the number of times of bending when the measurement sample broke was taken as a test value.

(4) Rainbow unevenness

The surface-protecting-film substrates (biaxially stretched films) obtained in examples and comparative examples were placed between 2 polarizing plates in a cross-prism state. In this case, the surface protective film substrate is disposed so that the longitudinal direction of the surface protective film substrate is parallel to the transmission axis direction of one polarizing plate. In this state, the fluorescent lamp was irradiated with light from below the lower polarizing plate, and the presence or absence of rainbow unevenness was visually observed. Evaluation was performed according to the following criteria.

○ rainbow unevenness was not observed

△ slight rainbow unevenness was observed

X: rainbow-like unevenness was observed remarkably

(5) Flexibility or resistance to bending

The 180 ° bending test was repeated 100 times on the surface protective film substrate (biaxially stretched film), and the presence or absence of breakage was confirmed. Evaluation was performed according to the following criteria.

○ No break observed

X: fracture was observed

< example 1>

1-1 preparation of Polymer alloys

As the raw materials, the following were used.

FDPM: 9, 9-bis (2-methoxycarbonylethyl) fluorene [9, 9-bis (2-carboxyethyl) fluorene (or dimethyl ester of fluorene-9, 9-dipropionic acid) ] was synthesized in the same manner as described in example 1 of Japanese patent laid-open publication No. 2005-89422 (except that t-butyl acrylate was changed to methyl acrylate [37.9g (0.44 mol) ]

And BPEF: 9, 9-bis [4- (2-hydroxyethoxy) phenyl ] fluorene, Osaka Gas Chemicals Co., Ltd

EG: ethylene glycol

PC: bisphenol A type polycarbonate resin, "Iipilon H-4000" manufactured by Mitsubishi Engineering-Plastics Corporation "

Manganese acetate tetrahydrate 2X 10 as a transesterification catalyst was added to FDPM 1.00 mol, BPEF 0.80 mol and EG 2.20 mol^-4Mole and calcium acetate monohydrate 8X 10^-4And (3) slowly heating and melting while stirring. After the temperature is raised to 230 ℃, 14 multiplied by 10 trimethyl phosphate is added^-4Mole, germanium oxide20×10^-4The temperature was gradually raised to 270 ℃ and the pressure was reduced to 0.13kPa or less to remove EG at the same time. After the stirring torque reached a predetermined value, the contents were taken out of the reactor to prepare pellets of the fluorene ring-containing polyester. By passing¹The obtained pellets were analyzed by H-NMR, and as a result, 100 mol% of the dicarboxylic acid component introduced into the fluorene ring-containing polyester was derived from FDPM, 80 mol% of the diol component introduced was derived from BPEF, and 20 mol% was derived from EG. The obtained fluorene ring-containing polyester had a glass transition temperature Tg of 126 ℃ and a weight-average molecular weight Mw of 43600.

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

1-2 preparation of Polymer alloy film

The obtained polymer alloy was vacuum-dried at 80 ℃ for 5 hours, and then a polymer alloy film having a thickness of 160 μm was produced using a film forming apparatus equipped with a single-screw extruder (manufactured by Isuzu Chemical Industries, screw diameter 25mm, cylinder set temperature: 255 ℃), T-die (width 200mm, set temperature: 255 ℃), chill roll (set temperature: 120 to 130 ℃) and winder.

1-3 preparation of base Material for surface protective film

The polymer alloy thin film obtained in the above was biaxially stretched 2 times in the longitudinal direction and the width direction, respectively. The stretching temperature was [ Tg +20 ℃ C. ] (i.e., 146 ℃ C.), and the stretching speed was 1.4%/sec in both the longitudinal direction and the width direction. Thus, a substrate for a surface protective film (thickness: 40 μm) was obtained. The obtained surface protection film substrate had Re (550) of 8nm, Rth (550) of 80nm, haze of 0.3%, and MIT test value exceeding 2000 times as an upper limit. The obtained surface-protecting-film substrate was subjected to the evaluations (4) and (5). The results are shown in Table 1.

< example 2>

A surface protection film substrate was obtained in the same manner as in example 1, except that the stretching speed was set to 3.1%/second in both the longitudinal direction and the width direction. The obtained surface protection film substrate had Re (550) of 10nm, Rth (550) of 81nm, haze of 0.2%, and MIT test value exceeding 2000 times as an upper limit. The obtained surface-protecting-film substrate was subjected to the evaluations (4) and (5). The results are shown in Table 1.

< example 3>

A surface protection film substrate was obtained in the same manner as in example 1, except that the stretching speed was set to 6.5%/second in both the longitudinal direction and the width direction. The obtained surface protection film substrate had Re (550) of 20nm, Rth (550) of 85nm, haze of 0.3%, and MIT test value exceeding 2000 times as an upper limit. The obtained surface-protecting-film substrate was subjected to the evaluations (4) and (5). The results are shown in Table 1.

< example 4>

A surface protection film substrate was obtained in the same manner as in example 1, except that the stretching speed was 10%/second in both the longitudinal direction and the width direction. The obtained surface protection film substrate had Re (550) of 30nm, Rth (550) of 91nm, haze of 0.2%, and MIT test value exceeding 2000 times as an upper limit. The obtained surface-protecting-film substrate was subjected to the evaluations (4) and (5). The results are shown in Table 1.

< comparative example 1>

A surface protection film substrate was obtained in the same manner as in example 1 except that a commercially available norbornene resin film (trade name "ZEONOR", Tg: 150 ℃ C., manufactured by Zeon Corporation) was used instead of the polymer alloy film. The obtained substrate for a surface protection film had Re (550) of 2nm, Rth (550) of 8nm, haze of 0.1% and MIT test value of 150. The obtained surface-protecting-film substrate was subjected to the evaluations (4) and (5). The results are shown in Table 1.

< comparative example 2>

A substrate for a surface protective film was obtained in the same manner as in example 1 except that an ultra-high retardation polyethylene terephthalate film (product name "Diafil" manufactured by Mitsubishi chemical Corporation, Tg: 81 ℃) was used instead of the polymer alloy film. The obtained surface protection film substrate had Re (550) of 4500nm, Rth (550) of 6000nm, haze of 1.3%, and MIT test value exceeding 2000 times as an upper limit. The obtained surface-protecting-film substrate was subjected to the evaluations (4) and (5). The results are shown in Table 1.

[ Table 1]

Example 1

Example 2

Example 3

Example 4

Comparative example 1

Comparative example 2

Constituent Material

Polymer alloy

Norbornene based on carbon dioxide

PET

Tensile Rate (%/second)

1.4

3.1

6.5

10.1

1.4

Stretching temperature (. degree.C.)

Tg+20

Draw ratio (Length/Width)

2/2

Re(550)(nm)

8

10

20

30

2

4500

Rth(550)(nm)

80

81

85

91

8

6000

Haze (%)

0.3

0.2

0.3

0.2

0.1

1.3

MIT test (number of times)

>2000

150

＞2000

Rainbow unevenness

○

△

○

×

Resistance to bending

○

×

○

< evaluation >

As is clear from table 1, the substrate for a surface protection film of the examples of the present invention can prevent rainbow unevenness and has excellent bending resistance (or flexibility). This is presumably achieved by stretching a film comprising a specific polymer alloy at a stretching speed of a predetermined value or less. Further, as is clear from comparison of examples 1 to 4, as the stretching speed is reduced, excellent characteristics (small in-plane retardation) can be obtained. It was confirmed that the same result as that of rainbow unevenness was obtained with respect to light leakage and coloring.

Industrial applicability

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

Claims

1. A substrate for a surface protective film, which comprises a film comprising a polymer alloy of a fluorene ring-containing polyester and an aromatic polycarbonate, and which has an in-plane retardation Re (550) of 30nm or less and a number of bends until breakage in an MIT test of 500 or more.

2. The substrate for a surface protection film according to claim 1, wherein the fluorene ring-containing polyester comprises a dicarboxylic acid component A comprising a fluorene dicarboxylic acid component A1 and a diol component B as copolymerization components, the fluorene dicarboxylic acid component A1 is at least 1 selected from dicarboxylic acids represented by the following formulae (1a) and (1B),

3. The substrate for a surface protection film according to claim 2, wherein the fluorene ring-containing polyester contains 50 mol% or more of a structural unit derived from the fluorene dicarboxylic acid component A1 relative to the total amount of structural units derived from the dicarboxylic acid component A.

4. The substrate for a surface protection film according to claim 2 or 3, wherein the diol component B comprises a fluorene diol component B1 represented by the following formula (2),

5. The substrate for a surface protection film according to any one of claims 1 to 4, wherein the total light transmittance is 80% or more and the haze is 1.0% or less.

6. A method for producing the substrate for a surface protective film according to any one of claims 1 to 5, comprising: forming a film-forming material containing a polymer alloy containing a fluorene-ring-containing polyester and an aromatic polycarbonate into a film; and subjecting the film obtained by the molding to sequential biaxial stretching or simultaneous biaxial stretching.

7. The method for producing a substrate for a surface protection film according to claim 6, wherein a stretching speed in the sequential biaxial stretching or simultaneous biaxial stretching is 10%/second or less.

8. A surface protective film comprising the substrate for a surface protective film according to any one of claims 1 to 5 and an adhesive layer.

9. An optical film with a surface protective film, comprising: an optical film, and the surface protective film according to claim 8 releasably attached to the optical film.