CN118732121A - Polarizer protective film, polarizing plate and liquid crystal panel - Google Patents

Abstract

The present invention relates to a polarizer protective film, a polarizing plate and a liquid crystal panel. Provided is a polarizer protective film, comprising an acrylic resin composition, wherein the average value of the in-plane phase difference Re is greater than 0.0 nm and less than 0.7 nm, and the thickness direction phase difference Rth at a wavelength of 590 nm is greater than ‑15.0 nm and less than 0.0 nm, wherein the acrylic resin composition comprises an acrylic resin having a ring structure in the main chain, and the glass transition temperature is greater than 120° C.

Description

Polarizer protective film, polarizing plate and liquid crystal panel

Technical Field

The invention relates to a polarizing element protective film, a polarizing plate and a liquid crystal panel.

Background Art

Acrylic resins have excellent transparency, color tone, appearance, heat resistance, and processability, and are therefore used, for example, in polarizer protective films (see, for example, Patent Document 1). Here, the polarizer protective film is applied to a liquid crystal panel by being bonded to both sides of a polarizer to form a polarizing plate, and then disposed on both sides of a liquid crystal cell.

On the other hand, IPS-type liquid crystal panels are preferably used in applications such as liquid crystal televisions because of their wide viewing angle and excellent color reproducibility.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2017-25333

Summary of the invention

Problem that the invention aims to solve

However, if a polarizer protective film containing acrylic resin is applied to an IPS liquid crystal panel, a slightly yellowish color may be produced when the black liquid crystal panel is visually recognized from an oblique direction. On the other hand, when such a color tone problem is optically compensated by the phase difference of the polarizer protective film, if there is a deviation in the in-plane phase difference of the polarizer protective film, there is a possibility that the display of the liquid crystal panel will be uneven.

An object of the present invention is to provide a polarizer protection film capable of achieving both uniformity of in-plane retardation and reduction of yellowness when a liquid crystal panel is viewed from an oblique direction.

Solutions for solving problems

[1] A polarizer protective film comprising an acrylic resin composition, wherein the average in-plane phase difference is greater than 0.0 nm and less than 0.7 nm, and the thickness direction phase difference Rth at a wavelength of 590 nm is greater than -15.0 nm and less than 0.0 nm, wherein the acrylic resin composition comprises an acrylic resin having a ring structure in the main chain and has a glass transition temperature of 120° C. or higher.

[2] The polarizer protective film according to [1], wherein the thickness direction retardation Rth at a wavelength of 590 nm is not less than -13.0 nm and not more than -2.5 nm.

[3] The polarizer protective film according to [1] or [2], wherein the acrylic resin having a ring structure in the main chain has a structural unit having one or more ring structures selected from a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring and a glutaric anhydride ring in the main chain.

[4] The polarizer protective film according to [3], wherein the acrylic resin having a ring structure in a main chain has a structural unit represented by the following formula (1).

(In the formula, ^R1 and ^R2 are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and ^R3 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.)

[5] The polarizer protective film according to any one of [1] to [4], wherein the content of the structural unit derived from the aromatic vinyl group in the acrylic resin composition is 0 wt % or more and 8 wt % or less.

[6] The polarizer protective film according to [5], wherein the content of the structural unit derived from styrene in the acrylic resin composition is 0 wt % or more and 8 wt % or less.

[7] The polarizer protective film according to [6], wherein the content of the structural unit derived from styrene in the acrylic resin composition is 0.5 wt% to 5 wt%.

[8] The polarizer protective film according to any one of [1] to [7], wherein the acrylic resin composition further comprises polymethyl methacrylate or a methyl methacrylate-styrene copolymer.

[9] The polarizer protective film according to any one of [1] to [8], wherein the acrylic resin composition has a 1% weight loss temperature of 300° C. or higher.

[10] The polarizer protective film according to [9], wherein the acrylic resin composition has a 1% weight loss temperature of 305° C. or higher.

[11] The polarizer protective film according to any one of [1] to [10], which does not contain an ultraviolet absorber.

[12] The polarizer protective film according to any one of [1] to [11], which is a biaxially stretched film.

[13] The polarizer protective film according to any one of [1] to [12], which has a yellowness index of 0.01 to 5.00.

[14] The polarizer protective film according to any one of [1] to [13], wherein the absorbance at a wavelength of 380 nm is 0.01 or more and 1.00 or less.

[15] The polarizer protective film according to any one of [1] to [14], wherein the standard deviation of the in-plane retardation Re is less than 0.2.

[16] The polarizer protective film according to any one of [1] to [15], wherein the yellowness index thereof is 50 or less when viewed from an oblique direction of a liquid crystal panel.

[17] The polarizer protective film according to any one of [1] to [16], wherein the acrylic resin composition has a weight average molecular weight of 50,000 to 200,000.

[18] The polarizer protective film according to any one of [1] to [17], wherein a ratio of a weight average molecular weight to a number average molecular weight of the acrylic resin composition is 1.5 or more and 2.5 or less.

[19] A polarizing plate comprising the polarizer protective film according to any one of [1] to [16].

[20] A liquid crystal panel comprising the polarizing plate described in [17].

Effects of the Invention

According to the present invention, it is possible to provide a polarizer protection film capable of achieving both uniformity of in-plane phase difference and reduction of yellowness when a liquid crystal panel is viewed from an oblique direction.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described.

(Polarizer protective film)

The polarizer protective film of the present embodiment contains an acrylic resin composition.

The average value of the in-plane phase difference Re of the polarizer protective film of the present embodiment is greater than 0.0nm and is less than 0.7nm, preferably less than 0.6nm. If the average value of Re is less than 0.7nm, the uniformity of the in-plane phase difference is improved. At this time, the standard deviation of the in-plane phase difference Re of the polarizer protective film of the present embodiment is preferably less than 0.2.

The thickness direction phase difference Rth of the polarizer protective film of the present embodiment at a wavelength of 590nm is greater than -15.0nm and less than 0.0nm, more preferably greater than -13.0nm and less than -2.5nm, further preferably greater than -10.0nm and less than -2.5nm, further preferably greater than -10.0nm and less than -5.0nm, particularly preferably greater than -10.0nm and less than -7.0nm. If Rth is greater than -15.0nm and less than 0.0nm, the yellowness is reduced when visually identified from the oblique direction of the liquid crystal panel. At this time, the polarizer protective film of the present embodiment preferably has a yellowness of less than 50 when visually identified from the oblique direction of the liquid crystal panel.

In addition, Re and Rth are calculated by the following formula.

Re＝(nx-ny)×d

Rth＝[(nx+ny)/2-nz]×d

Here, nx, ny and nz are the refractive indices in the X-axis direction, Y-axis direction and Z-axis direction respectively when the MD direction is the X-axis, the TD direction is the Y-axis and the thickness direction of the film is the Z-axis. In addition, d is the thickness of the film.

The yellowness of the polarizer protective film of the present embodiment is preferably 0.01 to 5.00, and more preferably 0.01 to 2.0. If the yellowness of the polarizer protective film of the present embodiment is 5.00 or less, the polarizer protective film of the present embodiment is less colored and has less influence on the color rendering of the liquid crystal display.

The absorbance of the polarizer protective film of this embodiment at a wavelength of 380 nm is preferably 0.01 to 1.00, more preferably 0.10 to 0.80. If the absorbance of the polarizer protective film of this embodiment at a wavelength of 380 nm is 1.00 or less, the polarizer protective film of this embodiment does not substantially contain an ultraviolet absorber.

The photoelastic coefficient of the polarizer protective film of the present embodiment is preferably not less than -10× ^10-12 Pa ^-1 and not more than 10× ^10-12 Pa ^-1 , more preferably not less than -5.5× ^10-12 Pa ^-1 and not more than 5.5× ^10-12 Pa ^-1 , and further preferably not less than -4.5× ^10-12 Pa ^-1 and not more than 4.5× ^10-12 Pa ^{- 1} . If the photoelastic coefficient of the polarizer protective film of the present embodiment is not less than -10× ^10-12 Pa ^-1 and not more than 10× ^10-12 Pa ^-1 , the polarizer protective film of the present embodiment is less likely to cause color unevenness, and this tendency becomes significant particularly in a high temperature and high humidity environment.

[Acrylic resin composition]

The acrylic resin composition contains an acrylic resin having a ring structure in the main chain. The glass transition temperature of the acrylic resin composition is 120°C or higher, preferably more than 120°C, more preferably 121°C or higher, and further preferably 122°C or higher. If the glass transition temperature of the acrylic resin composition is lower than 120°C, sometimes the orientation is relaxed in a high temperature and high humidity environment, and the stability of the phase difference is reduced. The glass transition temperature of the acrylic resin composition is, for example, 160°C or lower.

In the present specification and claims, an acrylic resin refers to a polymer of a monomer having an acryloyl group and/or a monomer having a methacryloyl group. In this case, the acrylic resin may be any of a homopolymer and a copolymer. When the acrylic resin is a copolymer, the acrylic resin may be a copolymer of a monomer having no acryloyl group or methacryloyl group.

The acrylic resin composition may further contain, for example, polymethyl methacrylate or a methyl methacrylate-styrene copolymer. It should be noted that the acrylic resin contained in the acrylic resin composition preferably does not have a structural unit derived from an aromatic vinyl group.

In addition, the acrylic resin composition may further include additives as long as it is within the range that does not impair the purpose of the present invention. The additives are not particularly limited, and examples thereof include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, specific wavelength absorbers or specific wavelength absorbing pigments for the purpose of blue light cutoff, free radical scavengers and other light resistance stabilizers, phase difference adjusters, catalysts, plasticizers, lubricants, antistatic agents, colorants, shrinkage inhibitors, antibacterial/deodorizing agents, fluorescent whitening agents, solubilizing agents, and two or more thereof may be used in combination.

The birefringence expression Δnxy of the acrylic resin composition is preferably -1.0×10 ^-3 or more and -0.1×10 ^-3 or less, more preferably -0.8×10 ^-3 or more and -0.25×10 ^-3 or less, more preferably -0.8×10 ^-3 or more and -0.20×10 ^-3 or less, and further preferably -0.8×10 ^-3 or more and -0.12×10 ^-3 or less. When Δnxy is -1.0×10 ^-3 or more, a desired thickness direction retardation is easily expressed during biaxial stretching, and when it is -0.1×10 ^-3 or less, the in-plane retardation is easily uniform during biaxial stretching.

In the present specification and claims, the birefringence expression Δnxy of the acrylic resin composition refers to the birefringence expressed when a film of the acrylic resin composition in an unstretched state is subjected to free-end uniaxial stretching at a temperature 5°C higher than the glass transition temperature of the acrylic resin composition so that the stretch ratio in the longitudinal direction becomes 2 times.

It should be noted that Δnxy is calculated by the following formula.

Δnxy＝nx-ny＝Re/d

Here, nx and ny are the refractive indices in the X-axis direction and the Y-axis direction, respectively, when the MD direction is the X-axis, the TD direction is the Y-axis, and the thickness direction of the film is the Z-axis. In addition, Re is the in-plane phase difference of the film, and d is the thickness of the film.

The content of the structural unit derived from the aromatic vinyl (such as styrene) in the acrylic resin composition is preferably 0% by weight or more and 8% by weight or less, more preferably 0.5% by weight or more and 5% by weight or less, further preferably 0.5% by weight or more and 3% by weight or less, further preferably 0.5% by weight or more and 2.5% by weight, and particularly preferably 1.0% by weight or more and 2.5% by weight or less. If the content of the structural unit derived from the aromatic vinyl (such as styrene) in the acrylic resin composition is 8% by weight or less, the uniformity of the in-plane phase difference of the polarizer protective film of the present embodiment is improved.

The 1% weight loss temperature of the acrylic resin composition is preferably 300°C or higher, more preferably 302°C or higher, and further preferably 305°C or higher. When the 1% weight loss temperature of the acrylic resin composition is 300°C or higher, contamination of the cooling roll during production of the stock film is suppressed, and the film forming properties of the stock film are improved. The 1% weight loss temperature of the acrylic resin composition is, for example, 380°C or lower.

The weight average molecular weight of the acrylic resin composition is preferably 50,000 to 200,000, more preferably 90,000 to 150,000. When the weight average molecular weight of the acrylic resin composition is 50,000 or more, the mechanical properties of the molded article of the acrylic resin composition tend to be improved, and when it is 200,000 or less, the moldability of the acrylic resin composition tends to be improved.

The ratio of the weight average molecular weight to the number average molecular weight (polydispersity) of the acrylic resin composition is preferably 1.5 or more and 2.5 or less, and more preferably 1.5 or more and 2.2 or less. When the polydispersity of the acrylic resin composition is 1.5 or more, the flowability of the acrylic resin composition tends to be improved, thereby facilitating molding, and when it is 2.5 or less, the mechanical properties such as impact resistance, toughness, and complete resistance of the molded body of the acrylic resin composition tend to be improved.

It should be noted that the number average molecular weight and weight average molecular weight of the acrylic resin composition are values converted to standard polystyrene measured by gel permeation chromatography (GPC). In addition, the number average molecular weight and weight average molecular weight of the acrylic resin composition can be controlled by the type and amount of the polymerization initiator and chain transfer agent used in the synthesis of the acrylic resin.

The polarizer protective film of the present embodiment can be attached to the polarizer to form a polarizer. As the polarizer, there is no particular limitation, and a known polarizer can be used. In addition, the polarizer can be combined with a liquid crystal cell to form a liquid crystal panel. In this case, it is preferred to use an IPS liquid crystal cell with a wide viewing angle. In addition, the polarizer protective film of the present embodiment may not contain a UV absorber, or may not substantially contain a UV absorber when it is disposed on a side opposite to the liquid crystal cell.

(Acrylic resin having a ring structure in the main chain)

The acrylic resin having a ring structure in the main chain (hereinafter referred to as acrylic resin) preferably has a structural unit containing one or more ring structures selected from a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring and a glutaric anhydride ring in the main chain.

The structural unit containing a glutarimide ring in the main chain is represented by, for example, the following formula (1).

(In the formula, ^R1 and ^R2 are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and ^R3 is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.)

The acrylic resin having the structural unit represented by formula (1) can be produced by a known method. An example of a method for producing the acrylic resin having the structural unit represented by formula (1) is described below.

First, a twin-screw extruder having a die at the outlet is used to melt the methyl methacrylate resin, imidize it, and extrude strands from the die. Next, the strands are cooled using a water tank, and the strands are pelletized using a granulator to obtain imidized methyl methacrylate resin. Next, a twin-screw extruder having a die at the outlet is used to melt the imidized methyl methacrylate resin, and esterify it, and extrude strands from the die. Next, the strands are cooled using a water tank, and the strands are pelletized using a granulator to obtain an acrylic resin having a structural unit represented by formula (1).

Examples of the imidizing agent include ammonia and a primary amine represented by the following formula (2). Among them, monomethylamine is preferred.

R ³ NH ₂ (2)

(In the formula, R ³ has the same meaning as in formula (1).)

Examples of the esterification agent include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluenesulfonate, methyl trifluoromethylsulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl tert-butylchlorosilane, isopropenyl acetate, dimethylurea, tetramethylammonium hydroxide, dimethyldiethoxysilane, tetra-n-butoxysilane, dimethyl (trimethylsilane) phosphite, trimethylphosphite, trimethylphosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether. Among them, dimethyl carbonate is preferred.

The content of the structural unit containing a ring structure in the main chain in the acrylic resin is preferably 1% by weight or more and 80% by weight or less. The glass transition temperature of the acrylic resin is preferably 120° C. or more and 160° C. or less.

The acrylic resin may further have a structural unit derived from a (meth)acrylate.

Examples of (meth)acrylates include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate; aryl (meth)acrylates such as benzyl (meth)acrylate; and cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate. Two or more of these may be used in combination. Among these, alkyl methacrylates are preferred, and methyl methacrylate is particularly preferred.

The content of the structural unit derived from the alkyl methacrylate in the acrylic resin is preferably 50% by weight or more, more preferably 75% by weight or more, particularly preferably 90% by weight or more.

The content of the structural unit derived from acrylic acid ester in the acrylic resin is preferably less than 1% by weight, more preferably less than 0.5% by weight, and particularly preferably less than 0.3% by weight.

The acrylic resin may further have a structural unit derived from other monomers. The other monomers are not particularly limited, and examples thereof include aromatic monomers such as styrene and methylstyrene; and nitrile monomers such as acrylonitrile and methacrylonitrile.

(Method for manufacturing polarizer protective film)

The polarizer protective film of the present embodiment can be produced using a known method. Hereinafter, an example of a method for producing the polarizer protective film of the present embodiment will be described.

First, an extruder having a die at the outlet is used to mix an acrylic resin with a methyl methacrylate-styrene copolymer as needed, and then a strand is extruded from the die. Next, after the strand is cooled using a water tank, the strand is granulated using a granulator to obtain an acrylic resin composition. Next, an extruder having a T-die at the outlet is used to melt the acrylic resin composition, and then a sheet is extruded from the T-die, and cooled with a cooling roller to obtain an original film. Next, the original film is biaxially stretched to obtain the polarizer protective film of the present embodiment. At this time, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

Regarding the temperature when the original film is biaxially stretched, when the glass transition temperature of the acrylic resin composition is set to Tg, it is preferably above (Tg+5)°C and below (Tg+20)°C, more preferably above (Tg+6)°C and below (Tg+18)°C, and further preferably above (Tg+7)°C and below (Tg+15)°C. In addition, there is no particular limitation on the surface ratio when the original film is biaxially stretched, for example, it is above 2 times and below 10 times. There is no particular limitation on the stretching speed when the original film is biaxially stretched, for example, it is above 1.1 times/minute and below 100 times/minute. In the case of sequential biaxial stretching of the original film, the stretching speed in the first stage may be the same as or different from the stretching speed in the second stage. It should be noted that in the sequential biaxial stretching, the stretching in the first stage is usually the stretching in the length direction (MD direction), and the stretching in the second stage is the stretching in the width direction (TD direction).

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, and the said embodiment can also be modified suitably within the range of the summary of this invention.

Example

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

(Content ratio of structural units containing glutarimide ring in the main chain)

The ¹ H-NMR spectrum of the acrylic resin was measured using a nuclear magnetic resonance device Avance III (manufactured by BRUKER) with a proton resonance frequency of 400 MHz. The molar ratio of the structural unit derived from methyl methacrylate to the structural unit containing a glutarimide ring in the main chain was converted by weight to calculate the content of the structural unit containing a glutarimide ring in the main chain. At this time, the molar ratio was calculated from the peak area A of O-CH ₃ protons derived from methyl methacrylate near 3.5 to 3.8 ppm and the peak area B of N-CH ₃ protons derived from glutarimide near 3.0 to 3.3 ppm.

(Glass transition temperature)

Using a high-sensitivity differential scanning calorimeter DSC 7000X (manufactured by Hitachi High-Tech Science Corporation), 10 mg of the acrylic resin or acrylic resin composition was heated at a heating rate of 10° C./min in a nitrogen atmosphere, and the glass transition temperature was determined by a midpoint method.

(1% weight loss temperature)

Using a differential thermal and thermogravimetric simultaneous measuring apparatus STA 7200 (manufactured by Hitachi High-Tech Science Corporation), 10 mg of the acrylic resin composition was heated from room temperature at a heating rate of 10° C./min in a nitrogen atmosphere to determine the 1% weight loss temperature.

(Birefringence appearance Δnxy)

After cutting out a 30×100 mm range from the original film roll, the film was subjected to free-end uniaxial stretching at a temperature 5°C higher than the glass transition temperature of the original film roll so that the stretching ratio in the longitudinal direction was 2 times to obtain a uniaxially stretched film. Next, the in-plane retardation of the central portion of the uniaxially stretched film was measured using a retardation measuring device KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.), and the result was divided by the thickness of the uniaxially stretched film to obtain the birefringence expression Δnxy.

(Thickness direction phase difference Rth)

The thickness direction retardation Rth of the polarizer protective film at a wavelength of 590 nm was measured using a retardation measuring device KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.).

(Average value and standard deviation of in-plane phase difference Re)

After cutting out a central area of 150×150 mm from the polarizer protective film, the average value and standard deviation of the in-plane phase difference Re were measured using a two-dimensional birefringence evaluation system WPA-200 (manufactured by Photonic Lattice, Inc.). At this time, three lines were drawn in the MD direction and TD direction respectively, and the average value and standard deviation of the in-plane phase difference Re were obtained using the line analysis function.

(Yellowness)

The polarizer protective film was cut into 3 cm squares, and then the yellowness (YI) was measured in accordance with JIS K7373:2006 using a colorimeter SC-P (manufactured by Suga Test Instruments Co., Ltd.).

(Absorbance at 380nm wavelength)

The absorbance of the polarizer protective film at a wavelength of 380 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer V-560 (manufactured by JASCO Corporation).

(Photoelastic coefficient)

The photoelastic coefficient of the polarizer protective film was measured using a phase difference measuring device KOBRA (manufactured by Oji Scientific Instruments Co., Ltd.). Specifically, the polarizer protective film was cut into a film of 15 mm × 60 mm, and the change in phase difference when the tensile load was changed from 0 g to 1100 g per 100 g was measured. The stress calculated from the tensile load value was set as the X-axis, and the birefringence calculated from the measured value of the phase difference and the thickness of the film was set as the Y-axis, and the slope of the straight line of the drawn image was calculated as the photoelastic coefficient.

(Yellowness when viewing the LCD panel from an oblique angle)

The liquid crystal panel simulation was performed using a liquid crystal simulator LCD Master (manufactured by SHINTECH Co., Ltd.). At this time, a polarizing plate configured on the light source side, an IPS-type liquid crystal cell with an in-plane phase difference Re of 295 nm, and a polarizing plate configured on the visual recognition side were sequentially configured. As the optical properties of the polarizer protective film on the side of the polarizing plate configured on the light source side and the visual recognition side opposite to the liquid crystal cell, the measurement result of the thickness direction phase difference Rth was input. Next, the value of the XYZ color when the liquid crystal cell is set to a dark state from a polar angle of 70° and an azimuth angle of 40° was obtained by simulation, and the yellowness (YI) was obtained by the following formula according to JIS K7373:2006.

YI＝100(1.2985X-1.1335Z)/Y

(Weight average molecular weight, number average molecular weight and polydispersity)

The weight average molecular weight (Mw), number average molecular weight (Mn) and polydispersity (Mw/Mn) of the acrylic resin composition were calculated using gel permeation chromatography (GPC). At this time, the analysis was performed under the following conditions using a sample solution prepared by dissolving 20 mg of the acrylic resin composition in 10 mL of tetrahydrofuran.

Measuring machine: HLC-8420GPC (manufactured by Tosoh Corporation)

Detector: RI detector

Eluent: Tetrahydrofuran

Guard column: TSKgel guardcolumn SuperH-L (manufactured by Tosoh Corporation)

Analytical columns: TSKgel SuperH5000, SuperH4000, SuperH3000, SuperH2000 (manufactured by Tosoh Corporation) (connected in series)

Eluent flow rate: 0.6mL/min

Measurement temperature: 40℃

Standard material: Standard polystyrene (manufactured by Tosoh Corporation)

(Manufacture of acrylic resin 1)

The temperature setting of each temperature control zone of an intermeshing type co-rotating twin-screw extruder (L/D=90) equipped with a die of 40 mm in diameter at the outlet was set to 250-280° C., and the screw speed was set to 85 rpm. Methyl methacrylate resin PARAPET HM (manufactured by Kuraray Co., Ltd.) was melted and filled with a kneading block. Then, 1.8% by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added to the methyl methacrylate resin from a nozzle to imidize the methyl methacrylate resin. Then, the strands extruded from the die were cooled in a water tank, and then pelletized using a pelletizer to obtain resin (I).

The set temperature of each temperature control zone of an intermeshing type co-rotating twin-screw extruder (L/D=90) with a die of 40 mm in diameter at the outlet was set to 240-260°C, the screw speed was set to 85 rpm, and the resin (I) was melted and filled using a kneading block. Next, 0.56 wt% of dimethyl carbonate was added to the resin (I) from a nozzle to esterify the carboxyl groups in the resin (I). At this time, the by-products and excess dimethyl carbonate after the reaction were removed. Next, the strands extruded from the die were cooled using a water tank, and then the strands were pelletized using a pelletizer to obtain acrylic resin 1. The glass transition temperature of acrylic resin 1 is 123°C, and the content of structural units containing glutarimide rings in the main chain is 6 wt%.

(Manufacture of acrylic resin 2)

Acrylic resin 2 was obtained in the same manner as acrylic resin 1 except that the amount of monomethylamine added was changed to 4.3% by weight relative to methyl methacrylate resin. Acrylic resin 2 had a glass transition temperature of 125° C. and a content of structural units containing glutarimide rings in the main chain of 15% by weight.

(Manufacture of acrylic resin 3)

Acrylic resin 3 was obtained in the same manner as acrylic resin 1 except that methyl methacrylate-styrene copolymer TX-100 (manufactured by Denka Co., Ltd.) having a content of 40% by weight of structural units derived from styrene was used instead of methyl methacrylate resin and the amount of monomethylamine added was 8.2% by weight relative to the methyl methacrylate-styrene copolymer. Acrylic resin 5 had a glass transition temperature of 125° C. and a content of structural units containing a glutarimide ring in the main chain of 45% by weight.

Table 1 shows the properties of the acrylic resin.

[Table 1]

(Example 1)

Using an intermeshing co-rotating twin-screw extruder (L/D=45) with a die having a diameter of 15 mm at the outlet, 95% by weight of acrylic resin 1 and 5% by weight of methyl methacrylate-styrene copolymer KT-89 (manufactured by Denka Co., Ltd.) having a content of 11% by weight of structural units derived from styrene were kneaded. Then, the strands extruded from the die set at the outlet of the extruder were cooled in a water tank, and the strands were pelletized using a pelletizer to obtain an acrylic resin composition. The acrylic resin composition had a glass transition temperature of 123°C, a 1% weight loss temperature of 308°C, an Mw of 81,000, and an Mw/Mn of 1.62.

After drying the acrylic resin composition at 100°C for 5 hours, the acrylic resin composition was melted using an intermeshing co-rotating twin-screw extruder (L/D=45) equipped with a T-die with a diameter of 15 mm at the outlet. Then, the sheet extruded from the T-die was cooled using a cooling roll to obtain an original film with a width of 160 mm and a thickness of 160 μm.

Using a film biaxial stretching device IMC-1905 (manufactured by Imoto machinery Co., LTD), the original roll film was simultaneously biaxially stretched at a temperature 15°C higher than the glass transition temperature of the acrylic resin composition so that the stretching ratio in the longitudinal and transverse directions became 2 times to obtain a 280 mm×280 mm polarizer protective film.

(Example 2)

A polarizer protective film was obtained in the same manner as in Example 1 except that the mixing ratio of acrylic resin 1 and KT-89 (manufactured by Denka Co., Ltd.) was changed to 90 wt % and 10 wt %, respectively. At this time, the acrylic resin composition had a glass transition temperature of 123° C., a 1% weight loss temperature of 308° C., a Mw of 81,000, and a Mw/Mn of 1.62.

(Example 3)

A polarizer protective film was obtained in the same manner as in Example 2, except that the original film was simultaneously biaxially stretched at a temperature 7° C. higher than the glass transition temperature of the acrylic resin composition.

(Example 4)

A polarizer protective film was obtained in the same manner as in Example 2 except that a methyl methacrylate-styrene copolymer MS-750 (manufactured by TOYO STYRENE Co., Ltd.) having a content of 25% by weight of a structural unit derived from styrene was used instead of KT-89 (manufactured by DENKA Co., Ltd.), and the original film was simultaneously biaxially stretched at a temperature 10°C higher than the glass transition temperature of the acrylic resin composition. At this time, the glass transition temperature of the acrylic resin composition was 122°C, the 1% weight loss temperature was 306°C, the Mw was 76,000, and the Mw/Mn was 1.59.

(Example 5)

A polarizer protective film was obtained in the same manner as in Example 4 except that 10 wt % of methyl methacrylate resin PARAPET HM (manufactured by Kuraray Co., Ltd.) was added instead of KT-89 (manufactured by Denka Co., Ltd.). At this time, the acrylic resin composition had a glass transition temperature of 120° C., a 1% weight loss temperature of 302° C., a Mw of 81,000, and a Mw/Mn of 1.59.

(Comparative Example 1)

A polarizer protective film was obtained in the same manner as in Example 1 except that KT-89 (manufactured by DENKA CO., LTD.) was not used. At this time, the acrylic resin composition had a glass transition temperature of 123°C and a 1% weight loss temperature of 310°C.

(Comparative Example 2)

A polarizer protective film was obtained in the same manner as in Comparative Example 1 except that acrylic resin 2 was used instead of acrylic resin 1. At this time, the acrylic resin composition had a glass transition temperature of 125°C and a 1% weight loss temperature of 315°C.

(Comparative Example 3)

A polarizer protective film was obtained in the same manner as in Example 1 except that the original film was simultaneously biaxially stretched at a temperature 20°C higher than the glass transition temperature of the acrylic resin composition without using acrylic resin 1. At this time, the glass transition temperature of the acrylic resin composition was 117°C and the 1% weight loss temperature was 297°C.

(Comparative Example 4)

A polarizer protective film was obtained in the same manner as in Comparative Example 3 except that methyl methacrylate-styrene copolymer MS800 (manufactured by Nippon Steel Chemical Co., Ltd.) having a content of 20% by weight of structural units derived from styrene was used instead of KT-89 (manufactured by Denka Co., Ltd.) and the original film was simultaneously biaxially stretched at a temperature 30°C higher than the glass transition temperature of the acrylic resin composition. At this time, the glass transition temperature of the acrylic resin composition was 115°C and the 1% weight loss temperature was 296°C.

(Comparative Example 5)

A polarizer protective film was obtained in the same manner as in Comparative Example 1 except that acrylic resin 3 was used instead of acrylic resin 1 and the original film was simultaneously biaxially stretched at a temperature 35°C higher than the glass transition temperature of the acrylic resin composition. At this time, the glass transition temperature of the acrylic resin composition was 125°C and the 1% weight loss temperature was 320°C.

Table 2 shows the properties and evaluation results of the acrylic resin composition and the polarizer protective film.

[Table 2]

As shown in Table 2, the polarizer protective films of Examples 1 to 5 take into account both the standard deviation of Re and the reduction of YI when visually identified from the oblique direction of the liquid crystal panel. In contrast, the Rth of the polarizer protective films of Comparative Examples 1 and 2 is 0.0nm and 10.2nm, respectively, so the YI when visually identified from the oblique direction of the liquid crystal panel becomes larger. The average values of Re of the polarizer protective films of Comparative Examples 3 to 5 are 0.8, 0.9, and 1.0, respectively, so the standard deviation of Re becomes larger.

Claims (20)

1. A polarizing element protective film comprising an acrylic resin composition having a ring structure in the main chain, wherein the average value of the in-plane retardation Re of the polarizing element protective film is greater than 0.0nm and 0.7nm or less, the thickness direction retardation Rth at a wavelength of 590nm is-15.0 nm or more and less than 0.0nm, and the acrylic resin composition has a glass transition temperature of 120 ℃ or more.

2. The polarizing-element protective film according to claim 1, wherein the retardation Rth in the thickness direction at a wavelength of 590nm is-13.0 nm or more and-2.5 nm or less.

3. The polarizing element protective film according to claim 1 or 2, wherein the acrylic resin having a ring structure in a main chain has: the main chain contains a structural unit having at least one ring structure selected from the group consisting of a glutarimide ring, a lactone ring, a maleic anhydride ring, a maleimide ring and a glutarimide ring.

4. The polarizing-element protective film according to claim 3, wherein the acrylic resin having a ring structure in the main chain has a structural unit represented by the following formula (1),

Wherein R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ³ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.

5. The polarizing-element protective film according to any one of claims 1 to 4, wherein the acrylic resin composition has a content of structural units derived from an aromatic vinyl group of 0% by weight or more and 8% by weight or less.

6. The polarizing element protective film according to claim 5, wherein the acrylic resin composition has a content of structural units derived from styrene of 0wt% or more and 8 wt% or less.

7. The polarizing element protective film according to claim 6, wherein the acrylic resin composition has a content of structural units derived from styrene of 0.5% by weight or more and 5% by weight or less.

8. The polarizing element protective film according to any one of claims 1 to 7, wherein the acrylic resin composition further comprises polymethyl methacrylate or a methyl methacrylate-styrene copolymer.

9. The polarizing element protective film according to any one of claims 1 to 8, wherein the acrylic resin composition has a 1% weight loss temperature of 300 ℃ or higher.

10. The polarizing protective film according to claim 9, wherein the acrylic resin composition has a 1% weight loss temperature of 305 ℃ or higher.

11. The polarizing element protective film according to any one of claims 1 to 10, which does not contain an ultraviolet absorber.

12. The polarizing element protective film according to any one of claims 1 to 11, which is a biaxially stretched film.

13. The polarizing plate protective film according to any one of claims 1 to 12, which has a yellowness of 0.01 or more and 5.00 or less.

14. The polarizing plate protective film according to any one of claims 1 to 13, which has an absorbance at 380nm of 0.01 or more and 1.00 or less.

15. The polarizing element protective film according to any one of claims 1 to 14, wherein the standard deviation of the in-plane retardation Re is less than 0.2.

16. The polarizing protective film according to any one of claims 1 to 15, which has a yellowness of 50 or less when visually recognized from an oblique direction of a liquid crystal panel.

17. The polarizing element protective film according to any one of claims 1 to 16, wherein the acrylic resin composition has a weight average molecular weight of 5 to 20 ten thousand.

18. The polarizing protective film according to any one of claims 1 to 17, wherein a ratio of a weight average molecular weight to a number average molecular weight of the acrylic resin composition is 1.5 or more and 2.5 or less.

19. A polarizing plate comprising the polarizing material protective film according to any one of claims 1 to 18.

20. A liquid crystal panel comprising the polarizing plate according to claim 19.