Manufacturing method of stretched film

Abstract

A stretched film is produced by the present invention by stretching a resin film at a temperature of Tg+20°C to Tg+70°C, the resin film comprising an acrylic resin having a glass transition temperature (Tg) of 115°C or higher and acrylic rubber particles, the proportion of all the acrylic acid ester monomers used for constituting the acrylic rubber particles to the sum of the monomers used for constituting the acrylic resin and the monomers used for constituting the acrylic rubber particles being 10-40 wt%.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a stretched film that can be used in optical films and the like, a polarizer protective film, and a polarizing plate. [Background technology]

[0002] In recent years, optical films made of acrylic resin have been used as polarizer protective films to improve moisture resistance and water absorption. However, optical films made of acrylic resin have poor adhesion to polarizers, which can impair the polarizer's properties, such as color distortion and unevenness caused by warping and deformation. Therefore, research is being conducted to improve the adhesion.

[0003] For example, Patent Document 1 proposes a method for setting the number-average particle size of the rubber portion in an acrylic rubber particle within a predetermined range in a film containing an acrylic resin and acrylic rubber particles. Furthermore, Patent Document 2 proposes a method for producing a stretched film with excellent heat resistance, dimensional stability, mechanical properties, and adhesive properties by stretching a resin film containing an acrylic resin and acrylic rubber particles having a glass transition temperature of 120°C or higher within a predetermined temperature range. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-231015 [Patent Document 2] International Publication No. 2018 / 168960 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described in Patent Document 2, the mechanical properties and adhesiveness of an acrylic resin film can be improved by blending acrylic rubber particles with an acrylic resin and stretching the film. However, in Patent Document 2, the adhesiveness of an acrylic resin film is evaluated by providing an easy-adhesion layer containing urethane resin and a crosslinking agent on the film, and then further bonding it to a substrate using an adhesive (paragraphs 0156-0157). Thus, in order to obtain sufficient adhesive strength with an acrylic resin film, it was necessary to provide an easy-adhesion layer acting as a primer between the film and the adhesive layer.

[0006] An object of one aspect of the present invention is to provide a method for manufacturing a stretched film that has excellent mechanical properties and can achieve good adhesive strength without providing an easy-adhesion layer. Another object of the present invention is to provide a polarizer protective film that has excellent mechanical properties and can achieve sufficient adhesive strength with a polarizer without providing an easy-adhesion layer, and a polarizer plate including the protective film. [Means for solving the problem]

[0007] The inventors of the present invention have found that the above problem can be solved by stretching a resin film containing an acrylic resin and acrylic rubber particles at a predetermined temperature, in which the amount of acrylic acid ester monomer constituting the acrylic rubber particles is controlled to a predetermined range.

[0008] In other words, the present invention relates to a method for producing a stretched film, comprising the step of stretching a resin film containing an acrylic resin having a glass transition temperature (Tg) of 115°C or higher, and acrylic rubber particles, wherein the total amount of acrylic acid ester monomers constituting the acrylic rubber particles is 10 to 40% by weight relative to the total amount of monomers constituting the acrylic resin and monomers constituting the acrylic rubber particles, at a temperature of Tg + 20°C to Tg + 70°C. Preferably, the amount of acrylic acid ester monomer in the monomer constituting the acrylic rubber particles is 45 to 90% by weight. Preferably, the proportion of the acrylic rubber particles in the total content of the acrylic resin and acrylic rubber particles is 15 to 50% by weight. Preferably, the acrylic acid ester monomer has the following structure.

[0009] [Chemical formula]

[0010] (In the formula, R 1 represents a linear or branched alkyl group having 1 to 10 carbon atoms.) Preferably, the acrylic rubber particles are a core-shell type elastomer containing a soft core layer and a hard shell layer, and the core layer is formed from a monomer component (a) composed of a polyfunctional monomer (a1) having two or more polymerizable functional groups in the molecule and a monomer (a2) other than the polyfunctional monomer, and the monomer (a2) other than the polyfunctional monomer contains 40 to 100% by weight of an acrylic acid ester monomer. Preferably, the shell layer is formed from a monomer component (b) containing 1 to 50% by weight of an acrylic acid ester monomer. Preferably, the amount of the polyfunctional monomer (a1) with respect to 100 parts by weight of the monomer (a2) other than the polyfunctional monomer is 0.5 to 3.0 parts by weight. Preferably, the average particle diameter of the core layer is 25 to 300 nm. Preferably, the number of MIT reciprocating bends of the stretched film is 150 or more. Preferably, the stretched film is attached to a PET film with an active energy ray curable adhesive, and the 90-degree peel strength value measured in an atmosphere of 23°C and 55% RH is 1.0 N / 20 mm or more. The present invention also relates to a polarizer protection film containing an acrylic resin having a Tg of 115°C or higher and acrylic rubber particles, where the total amount of the acrylic acid ester monomers constituting the acrylic rubber particles is 10 to 40% by weight with respect to the total amount of the monomers constituting the acrylic resin and the monomers constituting the acrylic rubber particles, and the amount of the acrylic acid ester monomer in the monomers constituting the acrylic rubber particles is 45 to 90% by weight. The present invention also relates to a polarizer protective film in which the polarizer protective film is attached to a PET film with an active energy ray curable adhesive, and the 90-degree peel strength measured at 23°C and a 55% RH atmosphere is 1.0 N / 20 mm or more. Preferably, the polarizer protective film has a MIT (Mid-Integrated Time) folding count of 150 or more. Furthermore, the present invention also relates to a polarizing plate comprising the polarizer protective film, adhesive layer, and polarizer laminated in this order. Preferably, the polarizing plate does not include an easy-adhesion layer. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to provide a method for manufacturing a stretched film that has excellent mechanical properties and can achieve good adhesive strength without providing an easy-adhesion layer. According to another aspect of the present invention, a polarizer protective film that has excellent mechanical properties and can achieve sufficient adhesive strength with a polarizer without providing an easy-adhesion layer, and a polarizer plate including the protective film can be provided. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described in detail below, but the present invention is not limited to these embodiments. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims, and embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention.

[0013] A method for manufacturing a stretched film according to this disclosure includes a step of stretching a resin film containing an acrylic resin having a glass transition temperature (Tg) of 115°C or higher, and acrylic rubber particles, wherein the total amount of acrylic acid ester monomers constituting the acrylic rubber particles is 10% to 40% by weight relative to the total amount of monomers constituting the acrylic resin and monomers constituting the acrylic rubber particles, at a temperature of Tg+20°C to Tg+70°C.

[0014] (Acrylic resin) The aforementioned resin film contains an acrylic resin. The glass transition temperature (Tg) of the acrylic resin is not particularly limited as long as it is 115°C or higher, but is preferably 117°C or higher, more preferably 118°C or higher, and even more preferably 119°C or higher. The glass transition temperature of the acrylic resin may be 120°C or higher, 125°C or higher, or 130°C or higher. There is no particular upper limit, but it may be 170°C or lower, or 160°C or lower.

[0015] The glass transition temperature of an acrylic resin is the peak temperature in the DSC curve measured for that acrylic resin. Furthermore, when measuring the DSC curve for a resin film containing acrylic resin and acrylic rubber particles, two peaks may appear. The higher-temperature peak can be determined to be the glass transition temperature of the acrylic resin. Alternatively, the glass transition temperature of the acrylic resin may be determined by dissolving the resin film in a suitable solvent, separating the acrylic resin and acrylic rubber particles by centrifugation, and measuring the DSC curve for the acrylic resin.

[0016] The acrylic resin is preferably a polymer mainly composed of alkyl methacrylate. For example, it may be a copolymer of 50% by weight or more of alkyl methacrylate and 50% by weight or less of a monomer other than alkyl methacrylate, or it may be a homopolymer of alkyl methacrylate. As the alkyl methacrylate, those with 1 to 8 carbon atoms in the alkyl group are usually used, with those with 1 to 4 carbon atoms being preferred, and among these, methyl methacrylate with 1 carbon atom is preferred.

[0017] The monomers other than the alkyl methacrylates may be monofunctional monomers having one polymerizable carbon-carbon double bond in the molecule, or polyfunctional monomers having two or more polymerizable carbon-carbon double bonds in the molecule, but monofunctional monomers are preferred here. Specifically, examples include (meth)acrylate esters other than alkyl (meth)acrylates such as benzyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate; styrene monomers such as styrene and alkylstyrene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; and maleimide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide.

[0018] From the viewpoint of mechanical properties, heat resistance, and transparency, the monomer composition of the acrylic resin is preferably such that the proportion of alkyl methacrylate is 70% or more by weight, more preferably 80% or more by weight, and even more preferably 90% or more by weight, based on 100% by weight of the total monomers. Furthermore, it is preferably 99% or less by weight.

[0019] (Acrylic rubber particles) The aforementioned resin film contains acrylic rubber particles. The acrylic rubber particles preferably have a total content of acrylic acid ester monomers of 45% to 90% by weight relative to the total amount of monomers constituting the particles. From the viewpoint of mechanical strength and heat resistance, 48% to 85% by weight is more preferable, 50% to 80% by weight is even more preferable, and 55% to 75% by weight is particularly preferable.

[0020] The acrylic acid ester monomer is not particularly limited, but it is preferable from the viewpoint of mechanical strength that it has the following structure.

[0021] [ka]

[0022] In the formula, R 1 This represents a linear or branched alkyl group having 1 to 10 carbon atoms. Specifically, examples include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate. Butyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate are preferred, and among these, butyl acrylate is particularly preferred from the viewpoint of mechanical strength and adhesion. These may be used individually or in combination of two or more.

[0023] The acrylic rubber particles are preferably a core-shell type elastic body comprising a soft core layer and a hard shell layer.

[0024] The core layer's Tg is preferably 20°C or lower, more preferably -60°C to 20°C, and even more preferably -60°C to 10°C. When the core layer's Tg is 20°C or lower, the resulting stretched film may have good mechanical strength.

[0025] The Tg of the shell layer is preferably 50°C or higher, more preferably 50°C to 140°C, and even more preferably 60°C to 130°C. When the Tg of the shell layer is 50°C or higher, the resulting stretched film may have good heat resistance.

[0026] The core layer is a layer formed from monomer components (a) consisting of a polyfunctional monomer (a1) having two or more polymerizable functional groups in its molecule and monomers other than the polyfunctional monomer (a2).

[0027] The content of the core layer in the acrylic rubber particles is preferably 30% to 95% by weight, more preferably 50% to 90% by weight, even more preferably 60% to 85% by weight, and particularly preferably 60% to 80% by weight. The content of the shell layer in the acrylic rubber particles is preferably 5% to 70% by weight, more preferably 10% to 50% by weight, even more preferably 15% to 40% by weight, and particularly preferably 20% to 40% by weight. The acrylic rubber particles may contain any other suitable components as long as they do not impair the effects of the invention.

[0028] As monomers other than polyfunctional monomers (a2), any suitable polymerizable monomer may be used, but it is preferable to use at least an acrylic acid ester monomer. The content of acrylic acid ester monomer in the monomer component (a2) forming the core layer is preferably 40% to 100% by weight, more preferably 50% to 100% by weight, even more preferably 60% to 100% by weight, and particularly preferably 70% to 100% by weight. The upper limit may be 95% by weight or less, or 90% by weight or less.

[0029] The core layer contains a polyfunctional monomer (a1) having two or more polymerizable functional groups in its molecule. The content of the polyfunctional monomer (a1) is preferably 0.5 to 3.0 parts by weight, more preferably 0.7 to 2.5 parts by weight, even more preferably 0.8 to 2.2 parts by weight, and particularly preferably 1.0 to 2.0 parts by weight, per 100 parts by weight of monomer (a2) other than the polyfunctional monomer.

[0030] Examples of polyfunctional monomers (a1) include aromatic divinyl monomers such as divinylbenzene, poly(meth)acrylic acid alkane polyols such as ethylene di(meth)acrylate, butylene di(meth)acrylate, hexylene di(meth)acrylate, oligoethylene di(meth)acrylate, trimethylolpropane di(meth)acrylate, and trimethylolpropane tri(meth)acrylate, as well as di(meth)acrylic acid urethane and di(meth)acrylic acid epoxy. Examples of polyfunctional monomers having vinyl groups with different reactivity include allyl (meth)acrylate, diallyl maleate, diallyl fumarate, and diallyl itaconic acid. Among these, ethylene dimethacrylate, butylene diacrylate, and allyl methacrylate are preferred. These may be used individually or in combination of two or more.

[0031] The monomer (a2) other than the polyfunctional monomer may include the acrylic acid ester monomer and other polymerizable monomers copolymerizable with the polyfunctional monomer having two or more polymerizable functional groups in its molecule. In the monomer component (a) forming the core layer, the other polymerizable monomer is preferably present in an amount of 0% to 60% by weight, more preferably in an amount of 5% to 40% by weight, and preferably in an amount of 10% to 30% by weight.

[0032] Examples of other polymerizable monomers include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, lauroyl methacrylate, stearyl methacrylate, and other methacrylic acid esters with 1 to 20 C1 alkyl groups, aromatic vinyls such as styrene, vinyltoluene, and α-methylstyrene, aromatic vinylidene, vinyl cyanide such as acrylonitrile and methacrylonitrile, vinylidene cyanide, methyl methacrylate, urethane acrylate, and urethane methacrylate. Other polymerizable monomers may also be monomers having functional groups such as epoxy groups, carboxyl groups, hydroxyl groups, and amino groups. Specifically, examples of monomers having epoxy groups include glycidyl methacrylate. Examples of monomers having carboxyl groups include methacrylic acid, acrylic acid, maleic acid, and itaconic acid. Examples of monomers having a hydroxyl group include 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate. Examples of monomers having an amino group include diethylaminoethyl (meth)acrylate. These may be used individually or in combination of two or more.

[0033] Furthermore, the average particle size of the core layer is preferably 25 nm to 300 nm, and more preferably 80 nm to 230 nm, from the viewpoint of dispersibility and handling.

[0034] The shell layer is formed from a monomer component (b) that does not contain polyfunctional monomers. Any suitable polymerizable monomer may be used as monomer component (b), but the content of acrylic acid ester monomer in monomer component (b) is preferably 1% to 50% by weight, more preferably 5% to 40% by weight, and particularly preferably 8% to 30% by weight.

[0035] The monomer component (b) forming the shell layer preferably contains at least one monomer selected from methacrylic acid esters and aromatic vinyl monomers. It is preferable that at least one selected from methacrylic acid esters and aromatic vinyl monomers is present in an amount of 50% to 99% by weight, more preferably 60% to 95% by weight, and particularly preferably 70% to 92% by weight of 100% by weight of the monomer component (b) forming the shell layer.

[0036] The methacrylate esters mentioned above are preferably those with an alkyl group having 1 to 4 carbon atoms, such as methyl methacrylate and ethyl methacrylate, with methyl methacrylate being more preferred. These may be used individually or in combination of two or more.

[0037] Examples of the aromatic vinyl monomers include styrene, vinyltoluene, and α-methylstyrene. Among these, styrene is preferred. These may be used individually or in combination of two or more.

[0038] The monomer component (b) forming the shell layer may also contain other polymerizable monomers copolymerizable with the acrylic acid ester monomer, methacrylic acid ester, and aromatic vinyl monomer. Preferably, the other polymerizable monomer is present in an amount of 0% to 50% by weight, and more preferably 0% to 40% by weight, of 100% by weight of the monomer component (b) forming the shell layer.

[0039] Examples of other polymerizable monomers include vinyl cyanides such as acrylonitrile and methacrylonitrile, vinylidene cyanide, methacrylic acid esters other than those mentioned above, urethane acrylates, and urethane methacrylates. They may also have functional groups such as epoxy groups, carboxyl groups, hydroxyl groups, and amino groups. Examples of monomers having epoxy groups include glycidyl methacrylate. Examples of monomers having carboxyl groups include methacrylic acid, acrylic acid, maleic acid, and itaconic acid. Examples of monomers having hydroxyl groups include 2-hydroxymethacrylate and 2-hydroxyacrylate. Examples of monomers having amino groups include diethylaminoethyl methacrylate and diethylaminoethyl acrylate. These may be used individually or in combination of two or more.

[0040] As a method for manufacturing the aforementioned core-shell type elastic body, any suitable method capable of producing core-shell type particles can be employed.

[0041] For example, one method involves suspending or emulsion polymerizing a monomer component (a) that forms the core layer to produce a suspension or emulsion dispersion containing core layer particles, and then adding a monomer component (b) that forms the shell layer to the suspension or emulsion dispersion and performing radical polymerization to obtain a core-shell type elastic body having a multilayer structure in which the shell layer covers the surface of the core layer. Here, the monomer component (a) that forms the core layer and the monomer component (b) that forms the shell layer may each be polymerized in one step, or they may be polymerized in two or more steps by changing their composition ratio.

[0042] (Resin film) The resin film contains an acrylic resin having a glass transition temperature (Tg) of 115°C or higher, and acrylic rubber particles, wherein the total amount of acrylic acid ester monomers constituting the acrylic rubber particles relative to the total amount of monomers constituting the acrylic resin and monomers constituting the acrylic rubber particles is 10% to 40% by weight. From the viewpoint of adhesion and heat resistance, 12% to 35% by weight is preferred, and 14% to 30% by weight is more preferred.

[0043] The content of acrylic resin and acrylic rubber particles in the resin film is not particularly limited, but from the viewpoint of mechanical properties and optical properties, the proportion of the acrylic rubber particles in the total content of the acrylic resin and acrylic rubber particles is preferably 15% to 50% by weight. From the viewpoint of adhesion, moisture permeability, and viscosity, 20% to 45% by weight is preferred, 25% to 42% by weight is more preferred, and 30% to 40% by weight is even more preferred.

[0044] The thickness of the resin film is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, and especially preferably 200 μm or less. It is also preferably 10 μm or more, more preferably 30 μm or more, even more preferably 50 μm or more, and especially preferably 60 μm or more. If the film thickness is within the above range, it has the advantage of being less prone to deformation when vacuum forming is performed using the film, and less likely to break in the deep-drawn section. Furthermore, it is possible to manufacture a film with uniform optical properties and good transparency. On the other hand, if the film thickness exceeds the above range, the cooling of the film after molding becomes uneven, and the optical properties tend to become uneven. Also, if the film thickness falls below the above range, the film may become difficult to handle.

[0045] (Method of manufacturing resin film) One embodiment of the method for manufacturing the resin film described above will be described, but the present invention is not limited thereto, and any conventionally known method can be used. Specifically, examples include injection molding, melt extrusion molding, inflation molding, blow molding, and compression molding. Furthermore, the resin film can be manufactured by a solution casting method or a spin coating method, in which the acrylic resin and acrylic rubber particles are dissolved and dispersed in a solvent before molding.

[0046] In particular, it is preferable to use a melt extrusion method that does not use solvents. The melt extrusion method reduces manufacturing costs and the burden on the global environment and working environment caused by solvents. When forming the aforementioned resin film into a film by melt extrusion, first, the resin composition containing the acrylic resin and acrylic rubber particles is pre-dried, then supplied to an extruder, where the resin composition is heated and melted. Furthermore, it is supplied to a die such as a T-die through a gear pump or filter. Next, the resin composition supplied to the T-die is extruded as a sheet of molten resin, and cooled and solidified using a cooling roll or the like to obtain an unstretched film (also called a raw film roll). At this time, in order to improve the surface properties (smoothness) of the film, it is also possible to sandwich it between a metal roll and a flexible roll equipped with a metal elastic outer cylinder.

[0047] (Stretched film) According to the manufacturing method of this disclosure, a stretched film is obtained by stretching the resin film at a stretching temperature of Tg+20°C to Tg+70°C. Due to the high stretching temperature, the acrylic resin and acrylic rubber particles can move more flexibly during stretching, resulting in more gaps between molecular chains, creating an open state. This makes it easier for the adhesive to penetrate, potentially improving adhesion.

[0048] The stretching temperature is preferably between Tg+25°C and Tg+65°C, more preferably between Tg+30°C and Tg+60°C, even more preferably between Tg+35°C and Tg+55°C, and particularly preferably between Tg+40°C and Tg+50°C. Note that Tg, as mentioned in relation to the stretching temperature, refers to the glass transition temperature of the acrylic resin.

[0049] The stretching may be uniaxial or biaxial. Biaxial stretching is preferred to impart excellent mechanical properties in both the longitudinal (MD) and widthwise (TD) directions. The biaxial stretching may be simultaneous or sequential. In the case of sequential biaxial stretching, it is preferable that the stretching temperature of the second stage is within the temperature range described above.

[0050] The stretching ratio of a stretched film is not particularly limited and should be determined according to the mechanical strength, surface properties, thickness accuracy, etc., of the stretched film being manufactured. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected in the range of 1.1 to 5 times, more preferably in the range of 1.3 to 4 times, and even more preferably in the range of 1.5 to 3 times. If the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and resistance to kneading fatigue, can be greatly improved.

[0051] By annealing the film in the stretcher for at least one minute, more preferably three minutes or more, and even more preferably five minutes or more, as a preheating step before stretching, film breakage and unevenness in stretching can be suppressed.

[0052] Regarding the stretching speed, it is preferable to perform it at 50 mm / min or more, and more preferably at 75 mm / min or more. Furthermore, it is preferable to be 300 mm / min or less, and more preferably 200 mm / min or less. In the case of sequential biaxial stretching, the stretching speed of the first stage and the stretching speed of the second stage may be the same or different, but it is preferable that the stretching speed of the second stage is equal to or greater than the stretching speed of the first stage. In sequential biaxial stretching, the stretching in the first stage is usually in the longitudinal direction (MD direction), and the stretching in the second stage is in the width direction (TD direction).

[0053] The stretched film according to this disclosure may have improved adhesive strength when bonded to a PET film via an active energy ray curable adhesive. The adhesive strength is preferably such that the 90-degree peel strength measured at 23°C and a 55% RH atmosphere is 1.0 N / 20 mm or more, more preferably 1.5 N / 20 mm or more, even more preferably 2.0 N / 20 mm or more, even more preferably 2.5 N / 20 mm or more, and particularly preferably 3.0 N / 20 mm or more. A peel strength of 2.0 N / 20 mm or more is good in terms of reworkability and durability after bonding with a polarizer. The peel strength can be determined by recording it using a Force Logger and calculating the average value of the stable region of the obtained measurement data.

[0054] The stretched film according to this disclosure can improve the number of MIT reciprocal folds (hereinafter also referred to as the number of folds) before breakage in the MIT bending resistance test. Preferably, the number of folds in the longitudinal direction (MD direction) of the stretched film is 150 or more, more preferably 500 or more, even more preferably 1000 or more, and most preferably 2000 or more. A number of folds of 150 or more is advantageous in terms of reducing the risk of breakage during the long film manufacturing process and the reworkability after lamination to a liquid crystal panel. Uniaxial stretching or biaxial stretching of the stretched film can be performed as desired. Generally, the width direction (TD direction) tends to be more prone to breakage, but stretching can increase the number of MIT reciprocal folds before breakage in the MIT bending resistance test in both the MD and TD directions.

[0055] The stretched film according to this disclosure preferably has a total light transmittance of 85% or more, more preferably 88% or more, and even more preferably 90% or more, when measured at a film thickness of 50 μm. If the total light transmittance is within the above range, it has high transparency and can be suitably used in optical components, decorative applications, interior applications, and vacuum forming applications where light transmission is required.

[0056] The glass transition temperature of the stretched film according to this disclosure may be 115°C or higher, preferably 117°C or higher, more preferably 118°C or higher, and even more preferably 119°C or higher. It may also be 120°C or higher, 125°C or higher, or 130°C or higher. If the glass transition temperature is within the above range, a stretched film with excellent heat resistance can be obtained. There is no particular upper limit, but it may be 170°C or lower, or 160°C or lower.

[0057] The average refractive index of the stretched film according to this disclosure is preferably 1.48 or higher. The refractive index difference between the acrylic resin and the acrylic rubber particles is preferably 0.02 or less, and more preferably 0.01 or less. Since the stretched film is a state in which acrylic rubber particles are dispersed in an acrylic resin, the internal haze of the stretched film tends to decrease as the refractive index difference between the acrylic resin and the acrylic rubber particles decreases. The average refractive index can be measured using an Abbe refractometer.

[0058] The stretched film according to this disclosure preferably has a haze of 2.0% or less, more preferably 1.5% or less, even more preferably 1.3% or less, and particularly preferably 1.0% or less when measured at a film thickness of 50 μm. The haze consists of haze inside the film and haze on the film surface (outside), which are referred to as internal haze and external haze, respectively. The resin film further preferably has an internal haze of 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less. If the haze and internal haze are within the above ranges, the transparency is high, making it suitable for optical components requiring light transmittance, decorative applications, interior applications, and vacuum forming applications.

[0059] The stretched film according to this disclosure can be used as an optical film in various applications, but when used as a polarizer protective film, it is preferable that it has low optical anisotropy. In particular, it is preferable that the optical anisotropy is small not only in the in-plane direction (length direction and width direction) of the film, but also in the thickness direction. That is, it is preferable that the absolute values ​​of both the in-plane phase difference and the thickness direction phase difference are small. More specifically, the absolute value of the in-plane phase difference is preferably 10 nm or less, more preferably 6 nm or less, even more preferably 5 nm or less, and particularly preferably 3 nm or less.

[0060] Furthermore, the absolute value of the phase difference in the thickness direction is preferably 50 nm or less, more preferably 20 nm or less, even more preferably 15 nm or less, even more preferably 10 nm or less, and most preferably 5 nm or less. A film having such a phase difference can be suitably used as a polarizer protective film for the polarizer plate of a liquid crystal display device. On the other hand, if the absolute value of the in-plane phase difference of the film exceeds 10 nm, or if the absolute value of the phase difference in the thickness direction exceeds 50 nm, problems such as a decrease in contrast may occur in the liquid crystal display device when used as a polarizer protective film for the polarizer plate of a liquid crystal display device.

[0061] Phase difference is an index value calculated based on birefringence, and the in-plane phase difference (Re) and the thickness-direction phase difference (Rth) can be calculated using the following formulas, respectively. In an ideal film that is perfectly optically isotropic in three dimensions, both the in-plane phase difference Re and the thickness-direction phase difference Rth are 0. Re=(nx-ny)×d Rth = ((nx + ny) / 2 - nz) × d In the above formula, nx, ny, and nz respectively represent the refractive indices in the axial directions, where the stretching direction (the orientation direction of the polymer chain) in the plane is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the film thickness direction is the Z-axis. Also, d represents the film thickness, and nx - ny represents the orientation birefringence. Note that the MD direction of the film is taken as the X-axis, and in the case of a stretched film, the stretching direction is taken as the X-axis.

[0062] The resin film according to the present disclosure preferably has an orientation birefringence value of -2.6×10 -4 ~2.6×10 -4 , more preferably -2.1×10 -4 ~2.1×10 -4 , even more preferably -1.7×10 -4 ~1.7×10 -4 , still more preferably -1.6×10 -4 ~1.6×10 -4 [[ID=二十]]Even more preferably -1.5×10 -4 ~1.5×10 -4 , even more preferably -1.0×10 -4 ~1.0×10 -4 , particularly preferably -0.5×10 -4 ~0.5×10 -4 , most preferably -0.2×10 -4 ~0.2×10 -4 . If the orientation birefringence is within the above range, no birefringence will occur during the molding process, and stable optical properties can be obtained. It is also very suitable as an optical film used in liquid crystal displays and the like.

[0063] Also, it is preferable that the absolute values of both the photoelastic coefficients are smaller. More specifically, the value of the photoelastic coefficient is preferably -6.0×10 -12 ~6.0×10 -12 , more preferably -5.0×10 -12 ~5.0×10 -12 , even more preferably -4.0×10 -12 ~4.0×10 -12 , still more preferably -3.0×10 -12 ~3.0×10 -12 , even more preferably -2.0×10-12 ~2.0×10 -12 This is even more preferable, -1.0 × 10 -12 ~1.0×10 -12 This is the most preferable. When a phase difference film laminated to different materials in a liquid crystal display device is subjected to temperature changes, stress is generated in the phase difference film due to the difference in the dimensional change rates of each material, causing a change in the phase difference and affecting the display. Therefore, a material within the aforementioned range, which has less stress influence, i.e., a small photoelastic coefficient, is suitable.

[0064] (Application) The stretched film can be used as a polarizer protective film. In this case, a polarizer plate can be formed by bonding the stretched film to a polarizer via an active energy ray curable adhesive.

[0065] The aforementioned active energy ray curable adhesive is a resin that hardens when irradiated with active energy rays, and examples of active energy rays include ultraviolet light, visible light, electron beams, or X-rays. The active energy ray curable resin may contain, for example, a cationic curable compound or a radical curable compound. Examples of cationically polymerizable curable compounds include compounds having epoxy groups and compounds having oxetanyl groups. Examples of radically polymerizable curable compounds include compounds having carbon-carbon double bonds such as (meth)acryloyl groups and vinyl groups, and (meth)acrylamide derivatives having (meth)acrylamide groups.

[0066] Furthermore, adhesion can be improved by using an easy-to-adhere layer. The easy-to-adhere layer can be formed using known techniques described in Japanese Patent Publication No. 2009-193061, Japanese Patent Publication No. 2010-55062, and others. Specific examples of easy-to-adhere adhesives that can form an easy-to-adhere layer include easy-to-adhere adhesive compositions that contain a urethane resin or epoxy resin having a carboxyl group as a main component, and further contain a crosslinking agent. Examples of the crosslinking agent include epoxy crosslinking agents, oxazoline crosslinking agents, and carbodiimide crosslinking agents. However, since the stretched film according to this disclosure has good adhesion, it can be bonded to a polarizer without the need for an easy-adhesion layer. By not using an easy-adhesion layer, the cost of forming the easy-adhesion layer can be reduced, and bonding to a polarizer can be achieved with high productivity.

[0067] The polarizer is not particularly limited, and any conventionally known polarizer can be used. For example, a polarizer obtained by containing iodine in stretched polyvinyl alcohol can be used.

[0068] This polarizing plate can be further laminated with various films and used in a variety of products. Its applications are not particularly limited, but it can be suitably used in image display devices such as liquid crystal displays and organic EL displays. [Examples]

[0069] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Hereinafter, "parts" and "%" mean "parts by weight" and "weight %" respectively, unless otherwise specified. The test methods for each physical property described in the examples and comparative examples are as follows.

[0070] <Testing Method> <Manufacturing of acrylic resins> (Acrylic resin (A1)) As the acrylic resin, a polymethyl methacrylate resin with a weight-average molecular weight of 60,000, manufactured by bulk polymerization, was used. The glass transition temperature was 120°C.

[0071] <Measurement of glass transition temperature> The glass transition temperature (Tg) of each sample was determined in accordance with the provisions of JIS K7121. Specifically, using a differential scanning calorimeter (Hitachi, DSC7000X), approximately 5 mg of the sample was heated from 40°C to 200°C at a heating rate of 10°C / min under a nitrogen gas atmosphere, and then cooled down to 40°C at a cooling rate of 60°C / min. The sample was then heated again from 40°C to 200°C at a heating rate of 10°C / min, and the Tg was calculated from the DSC curve obtained from this second heating cycle.

[0072] <Manufacturing of acrylic rubber particles> (Manufacturing Example 1) (Manufacturing of acrylic rubber particles (B1)) The following substances were charged into an 8L polymerization apparatus equipped with a stirrer. Deionized water, 180 units 0.04 parts of polyoxyethylene lauryl ether phosphate Boric acid 0.5 parts Sodium carbonate 0.05 parts After thoroughly purging the polymer chamber with nitrogen gas, the internal temperature was set to 80°C, and 0.01 parts of 2% sodium hydroxide aqueous solution and 0.107 parts of 2% potassium persulfate aqueous solution were added. Then, the material mixture shown in polymerization stage (II) of Table 1 was continuously added over 230 minutes. 60 minutes after addition, an additional 0.03 parts of 2% sodium hydroxide aqueous solution was added. After the addition was complete, 0.015 parts of 2% potassium persulfate aqueous solution were added, and polymerization was carried out for 120 minutes to obtain polymer (II). The polymerization conversion rate was 98.5%, and the average particle size was 109 nm.

[0073] Next, the material mixture shown in polymerization step (III) of Table 1 was continuously added over 70 minutes. After the addition was complete, polymerization was carried out for 60 minutes to obtain latex. The latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain white powdery acrylic rubber particles (B1).

[0074] (Manufacturing examples 2-3) (Manufacturing of acrylic rubber particles (B2) to (B3)) Acrylic rubber particles (B2) to (B3) were manufactured in the same manner as in Manufacturing Example 1, except that the types and amounts of raw materials used were changed as shown in Table 1.

[0075] (Manufacturing example 4) (Manufacturing of acrylic rubber particles (B4)) Deionized water, 180 units Polyoxyethylene lauryl ether phosphate 0.003 parts Boric acid 0.5 parts Sodium carbonate 0.05 parts 0.01 part sodium hydroxide

[0076] After thoroughly purging the polymer chamber with nitrogen gas, the internal temperature was set to 80°C, and 0.03 parts of potassium persulfate were added in a 2% aqueous solution. Subsequently, the material mixture shown in polymerization step (I) of Table 1 was continuously added over 81 minutes. Polymerization was continued for another 60 minutes to obtain the polymer. The polymerization conversion rate was 89.9%.

[0077] Subsequently, 0.03 parts of sodium hydroxide were added in a 2% aqueous solution, followed by 0.08 parts of potassium persulfate in a 2% aqueous solution. Then, the material mixture shown in polymerization step (II) of Table 1 was continuously added over 150 minutes. After the addition was complete, 0.02 parts of pure potassium persulfate were added in a 2% aqueous solution, and polymerization was continued for 120 minutes to obtain polymer (II). The polymerization conversion rate was 97.5%, and the average particle size was 221 nm.

[0078] Subsequently, 0.02 parts of potassium persulfate were added in a 2% aqueous solution, and then the material mixture shown in polymerization step (III) of Table 1 was continuously added over 70 minutes. After the addition was complete, polymerization was carried out for 60 minutes to obtain latex. The polymerization conversion rate was 99.9%. The obtained latex was salted out with magnesium chloride, solidified, washed with water, and dried to obtain white powdery acrylic rubber particles (B4).

[0079] [Table 1]

[0080] <Measurement of average particle size> The average particle size of the acrylic rubber particles was calculated by measuring light scattering at a wavelength of 546 nm using a HITACHI U-5100 spectrophotometer.

[0081] <Adhesion measurement> Adhesion evaluation samples were prepared as follows. First, the stretched films obtained in each example or comparative example were subjected to corona discharge treatment (13V) using a Corona Master (PS-1M) manufactured by Shinko Electric Instrumentation Co., Ltd. An active energy ray curable adhesive (N-(2-hydroxyethyl)acrylamide / 4-acryloylmorpholine / phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide = 40 / 60 / 3 (weight ratio)) was applied to the stretched film and spread uniformly with a No. 3 bar coater (wet film thickness 6.87 μm). Then, the easily adhering side (uneven surface, not the aforementioned easily adhering layer) of a PET film (product name: Cosmoshine 50A4100, manufactured by Toyobo Co., Ltd.) was placed over it and uniformly bonded using a rubber roller. The PET film side of the resulting laminate was attached to a glass plate using adhesive tape, preheated at 50°C for 1 minute, and then treated with UV irradiation (1000 mJ / cm²) using a UV irradiation machine manufactured by I-Graphics Co., Ltd. 2 The sample was obtained by irradiating it with ) and annealing it at 80°C for 3 minutes. The obtained samples were cut into strips 2 cm wide, and the samples were attached to a stainless steel stand using "PE Cross Double-Sided Tape (0.23 mm x 25 mm x 15 m)" manufactured by Sekisui Chemical Co., Ltd., with the stretched film facing downwards and the PET film facing upwards. The 90-degree peel strength when peeling the PET film from the stretched film was measured at 23°C and in a 55% RH atmosphere and evaluated as adhesive strength.

[0082] <Measurement of number of folds> The stretched films obtained in each example or comparative example were cut into strips with a width of 1.5 mm, and these were used as test specimens. A Toyo Seiki Co., Ltd. MIT Flexible Fatigue Tester Model D was used, with a test load of 200 g, a speed of 175 cycles / min, a bending clamp radius R of 0.38 mm, and a bending angle of 135° to the left and right. The arithmetic mean of the values ​​measured in the MD direction was used as the number of folds.

[0083] [Example 1] A mixture of 80 parts by weight of the aforementioned acrylic resin (A1) and 20 parts by weight of acrylic rubber particles (B1) was kneaded in a 15 mm diameter, coaxial twin-screw extruder (L / D=45). The resin mixture was supplied from the hopper at a rate of 1.5 kg / hr, and the temperature of each temperature control zone of the extruder was set to 230°C and the screw rotation speed to 120 rpm. After cooling the strands coming out of the die in a water bath, they were pelletized in a pelletizer.

[0084] The obtained pellets were dried at 90°C for 5 hours, and then a film was formed using a 15mm diameter, co-rotating twin-screw extruder (L / D=30) equipped with a T-die at the extruder outlet. The pellets were supplied from the hopper at a rate of 1.5 kg / hr, with the temperature of each temperature control zone of the extruder set to 230°C, the T-die set to 255°C, and the screw rotation speed set to 100 rpm. The sheet-like molten resin extruded from the T-die at the extruder outlet was cooled on a cooling roll temperature-controlled to 90°C to obtain a resin film with a width of 120 mm and a thickness of 160 μm.

[0085] The obtained resin film was preheated at 145°C for 5 minutes inside an ESPEC Corporation simultaneous biaxial stretching machine (PHH-302), and then 2x2 simultaneous biaxial stretching was performed at a stretching speed of 100 mm / min to obtain a stretched film. Adhesion and number of folds were measured according to the above method, and the results are shown in Table 2.

[0086] [Examples 2-14, Comparative Examples 1-13] A stretched film was prepared by performing the same procedure as in Example 1, except that the acrylic resin content, the type or content of acrylic rubber particles, or the stretching temperature were changed according to Table 2. The adhesion and number of folds were measured according to the method described above, and the results are shown in Table 2.

[0087] [Table 2]

[0088] Table 2 shows that the stretched films obtained in Examples 1-14 achieved both high adhesion and good bending resistance, while the stretched films obtained in Comparative Examples 1-13 lacked sufficient adhesion or bending resistance. The reason for the good results obtained in Examples 1-14 is presumed to be that stretching at a stretching temperature that allowed sufficient molecular chain movement facilitated the penetration of the adhesive, and that the amount of acrylic acid ester monomer contained in the acrylic resin and acrylic rubber particles was appropriate. Among these, Examples 2-5, 8, 9, and 12 exhibit particularly excellent adhesion, and Examples 2, 4, 5, 9, and 12 are particularly preferred in terms of the balance between adhesion and bending resistance.

Claims

1. A method for producing a stretched film, comprising the step of stretching a resin film containing an acrylic resin having a glass transition temperature (Tg) of 115°C or higher, and acrylic rubber particles, wherein the total amount of acrylic acid ester monomers constituting the acrylic rubber particles is 12 to 40% by weight relative to the total amount of monomers constituting the acrylic resin and monomers constituting the acrylic rubber particles, at a temperature of Tg + 20°C to Tg + 70°C.

2. The method for producing a stretched film according to claim 1, wherein the amount of acrylic acid ester monomer in the monomer constituting the acrylic rubber particles is 45 to 90% by weight.

3. A method for producing a stretched film according to claim 1 or 2, wherein the proportion of the acrylic rubber particles in the total content of the acrylic resin and the acrylic rubber particles is 15 to 50% by weight.

4. A method for producing a stretched film according to any one of claims 1 to 3, wherein the acrylic acid ester monomer has the following structure. 【Chemistry 1】 (In the formula, R １ (This represents a linear or branched alkyl group having 1 to 10 carbon atoms.)

5. The method for producing a stretched film according to any one of claims 1 to 4, wherein the acrylic rubber particles are a core-shell type elastic body comprising a soft core layer and a hard shell layer, the core layer is formed from a monomer component (a) consisting of a polyfunctional monomer (a1) having two or more polymerizable functional groups in its molecule and a monomer other than the polyfunctional monomer (a2), and the monomer other than the polyfunctional monomer (a2) contains 40 to 100% by weight of an acrylic acid ester monomer.

6. The method for producing a stretched film according to claim 5, wherein the shell layer is formed from a monomer component (b) containing 1 to 50% by weight of an acrylic acid ester monomer.

7. A method for producing a stretched film according to claim 5 or 6, wherein the amount of the polyfunctional monomer (a1) is 0.5 to 3.0 parts by weight relative to 100 parts by weight of monomer (a2) other than the polyfunctional monomer.

8. A method for producing a stretched film according to any one of claims 5 to 7, wherein the average particle size of the core layer is 25 to 300 nm.

9. A method for manufacturing a stretched film according to any one of claims 1 to 8, wherein the stretched film undergoes 150 or more MIT reciprocating folds.

10. A method for producing a stretched film according to any one of claims 1 to 9, wherein the stretched film is attached to a PET film with an active energy ray curable adhesive, and the value of the 90-degree peel strength measured at 23°C and a 55% RH atmosphere is 1.0 N / 20 mm or more.

11. A polarizer protective film containing an acrylic resin with a Tg of 115°C or higher, and acrylic rubber particles, The total amount of acrylic acid ester monomers constituting the acrylic rubber particles is 12 to 40% by weight relative to the total amount of monomers constituting the acrylic resin and monomers constituting the acrylic rubber particles. The amount of acrylic acid ester monomer in the monomer constituting the acrylic rubber particles is 45 to 90% by weight. A polarizer protective film wherein the polarizer protective film is attached to a PET film with an active energy ray curable adhesive, and the 90-degree peel strength measured at 23°C and a 55% RH atmosphere is 1.0 N / 20 mm or more.

12. The polarizer protective film according to claim 11, wherein the number of MIT reciprocating folds is 150 or more.

13. A polarizing plate comprising a polarizer protective film, an adhesive layer, and a polarizer, laminated in the order described in claim 11 or 12.

14. A polarizing plate according to claim 13, which does not include an easy-adhesion layer.

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