JP2009041007A - Optically isotropic acrylic resin film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optically isotropic acrylic resin film which is excellent in transparency, heat resistance, toughness and optical isotropy and exhibits durability to environmental changes such as high temperature and high humidity. <P>SOLUTION: The optically isotropic acrylic resin film contains a thermoplastic copolymer (i) containing a lactone ring-containing monomer unit and has (a) ≥120°C glass transition temperature, (b) ≥10% tensile elongation at break and (c) ≤10 nm absolute value of in-plane retardation (Re) and ≤10 nm absolute value of thickness retardation (Rth). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optically isotropic acrylic resin film and a polarizing plate protective film having excellent transparency, heat resistance, toughness, optical isotropy, and durability against changes in the external environment such as high temperature and high humidity. Is.

  In a liquid crystal display device such as a liquid crystal television or a mobile phone, it is indispensable to dispose polarizing plates on both sides of a glass substrate that forms a liquid crystal panel surface. As a polarizing plate, a polarizer using a cellulose resin film represented by triacetyl cellulose (TAC) on both sides of a polarizer made of a polyvinyl alcohol (PVA) film and a dichroic material such as iodine. A laminate with a protective film is generally used.

The cellulose resin film has excellent properties as a polarizer protective film because it has good transparency, a small retardation in the in-plane direction, practical heat resistance and excellent mechanical strength. In addition, because of its high moisture permeability, it is generally used as a polarizer protective film because it has good processability such as excellent moisture permeability of PVA and adhesive when bonded to a polarizer such as PVA (for example, (See Patent Document 1.)
In addition, in the polarizer protective film, a film having an unnecessary retardation is generally not preferable, even if the polarizer film has a highly accurate linear polarization function, the retardation of the polarizer protective film is not preferable. In addition, the deviation of the optical axis is considered to be due to giving elliptically polarized light to the linearly polarized light that has passed through the polarizer film.

  The phase difference of the film is defined as the X-axis direction in which the in-plane refractive index is maximum, the Y-axis direction perpendicular to the X-axis, and the Z-axis thickness direction of the film. Assuming that nz is the thickness of the film, d is the in-plane retardation Re = (nx−ny) × d, and the thickness direction retardation Rth = {(nx + ny) / 2−nz} × d.

  Although the cellulose-based resin film as described above basically has a small in-plane retardation, it is likely to cause a retardation due to the action of external stress, and has a relatively large thickness direction retardation. For this reason, particularly in a large-sized liquid crystal display device, there is a problem that the contrast in the peripheral portion is lowered.

  In addition, since the cellulose resin film does not have sufficient heat and moisture resistance and has high water absorption, there are problems in the performance degradation of the polarizer, dimensional stability due to water absorption, and the like. When the polarizing plate used as the protective film is used under high temperature / high humidity, there is a drawback that its optical characteristics are greatly deteriorated.

  In addition, the cellulose resin film generates a phase difference with respect to incident light in an oblique direction. Such a phase difference has an adverse effect on viewing angle characteristics as the size of liquid crystal displays increases in recent years.

  In order to solve the above problems, in recent years, development of a material excellent in transparency, heat resistance, optical isotropy and the development of a polarizer protective film using the material, which replaces the cellulose resin film, has been activated. Here, the optical isotropy is a characteristic in which the absolute value of the in-plane retardation, the absolute value of the thickness retardation, and the absolute value of the photoelastic coefficient are all small.

  However, for example, a polycarbonate film or a polyethylene terephthalate film having a small water absorption has a problem that the photoelastic constant is large, and the phase difference is changed by the action of external stress, so that the performance as a polarizing plate is deteriorated.

Moreover, although the cyclic polyolefin resin film with a small water absorption rate and a small photoelastic constant is disclosed (patent documents 2 and 3), although the water absorption rate is small, the moisture permeability is small. When a polarizer such as PVA is bonded, there is a problem that moisture in the PVA is lost and a bonding failure such as swelling or bubbles occurs.
Japanese Patent Laid-Open No. 07-120617 Japanese Patent Laid-Open No. 05-212828 Japanese Patent Laid-Open No. 06-0511117

An object of the present invention is to provide an optically isotropic acrylic resin film having excellent transparency, heat resistance, toughness, optical isotropy, and durability against changes in the external environment such as high temperature and high humidity. And

That is, the present invention is as follows.
1. It contains a thermoplastic copolymer containing (i) a lactone ring-containing monomer unit represented by the following general formula (1), and satisfies the following (a), (b) and (c): An optically isotropic acrylic resin film.
(A) The glass transition temperature is 120 ° C. or higher.
(B) Tensile breaking elongation is 10% or more.
(C) The absolute value of the in-plane retardation (Re) is 10 nm or less, and the absolute value of the thickness retardation (Rth) is 10 nm or less.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)
2. The thermoplastic copolymer is (i) 15 to 50% by weight of a lactone ring-containing monomer unit represented by the general formula (1), and (ii) an unsaturated carboxylic acid represented by the following general formula (2). 2. The optically isotropic acrylic resin film according to 1, comprising 85 to 50% by weight of an acid alkyl ester unit.

(Wherein R ⁷ represents any one selected from a hydrogen atom and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted C 1-6 aliphatic hydrocarbon group substituted with a hydroxyl group or halogen, and Any one selected from alicyclic hydrocarbon groups having 3 to 6 carbon atoms)
3. 3. The optically isotropic acrylic resin film according to 1 or 2, which is subjected to a stretching treatment.
4). 4. The optically isotropic acrylic resin film according to 3, wherein a biaxial stretching process is performed.
5. Absolute value of in-plane retardation (Re) after wet heat treatment at 60 ° C., 90% RH, 500 hours is 10 nm or less, and absolute value of thickness retardation (Rth) is 10 nm or less The optically isotropic acrylic resin film in any one of -4.
6. The optically isotropic acrylic resin film according to any one of 1 to 5, wherein a dimensional change rate after wet heat treatment at 60 ° C., 90% RH and 500 hours is 2% or less.
7. The optically isotropic acrylic resin film in any one of 1-6 whose average thickness of a film is 20-200 micrometers.
8). (I) 15 to 50% by weight of a lactone ring-containing monomer unit represented by the following general formula (1), (ii) 85 to 50% by weight of an unsaturated carboxylic acid alkyl ester unit represented by the following general formula (2) %. The method for producing an optically isotropic acrylic resin film according to any one of 1 to 7, wherein a thermoplastic copolymer containing 2% is formed and stretched.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

(Wherein R ⁷ is any one selected from a hydrogen atom and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted aliphatic hydrocarbon group having 1 to 6 carbon atoms substituted with a hydroxyl group or halogen, and carbon. Any one selected from alicyclic hydrocarbon groups of 3 to 6)
9. 9. The method for producing an optically isotropic acrylic resin film according to 8, wherein the stretching treatment is biaxial stretching.
10. A polarizing plate protective film comprising the optically isotropic acrylic resin film according to any one of 10.1 to 7.
11. A polarizing plate using the polarizing plate protective film described in 11.10.
12. A polarizing optical film, wherein the polarizing plate according to 12.11 and a retardation film are laminated.
13. A liquid crystal display device comprising at least one selected from the polarizing plate protective film according to 13.10, the polarizing plate according to 11, and the polarizing optical film according to 12.

  According to the present invention, an optically isotropic acrylic resin film having excellent transparency, heat resistance, toughness, optical isotropy, and durability against changes in the external environment such as high temperature and high humidity, and a polarizer comprising the same A protective film and a polarizing plate can be obtained.

  Hereinafter, the optically isotropic acrylic resin film of the present invention will be specifically described.

  The thermoplastic copolymer constituting the optically isotropic acrylic resin film of the present invention is (i) 15 to 50% by weight of a lactone ring-containing monomer unit represented by the following general formula (1), (ii) It is a thermoplastic copolymer comprising 50 to 85% by weight of unsaturated carboxylic acid alkyl ester units.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

  The content of the (i) lactone ring-containing unit in the thermoplastic copolymer is 15 to 50% by weight, more preferably 15 to 45% by weight, and still more preferably 20 to 100% by weight in 100% by weight of the thermoplastic copolymer. 45% by weight, most preferably 20-40% by weight. When the lactone ring-containing monomer unit is less than 15% by weight, not only the effect of improving the heat resistance is reduced, but also the optical isotropy which is the effect of the present invention is inferior.

  The content of the (ii) unsaturated carboxylic acid alkyl ester unit in the thermoplastic copolymer is 50 to 85% by weight, more preferably 55 to 85% by weight, more preferably 100% by weight of the thermoplastic copolymer. 55-80% by weight, most preferably 60-80% by weight.

  The thermoplastic copolymer is within a range not impairing the effects of the present invention, and the content of other vinyl monomer units is 0 to 10% by weight in 100% by weight of the thermoplastic copolymer, preferably 0 to 5% by weight.

  In general, an infrared spectrophotometer, a proton nuclear magnetic resonance (1H-NMR) measuring instrument, or a carbon nuclear magnetic resonance (13C-NMR) measuring instrument is used for quantification of each component unit in the thermoplastic copolymer. In infrared spectroscopy, glutaric anhydride units are characterized by absorption at 1800 cm −1 and 1760 cm −1 and can be distinguished from unsaturated carboxylic acid units and unsaturated carboxylic acid alkyl ester units. In the 1H-NMR method, the copolymer composition can be determined from the integral ratio of the spectrum. For example, in the case of a copolymer consisting of an α-methylene-γ-butyrolactone unit and a methyl methacrylate unit, the 1H-NMR spectrum measured in a deuterated chloroform solvent has a peak of 0.5 to 1.5 ppm of methacrylic acid. Α-methyl group hydrogen of methyl acid unit, 1.6 to 2.1 ppm peak is hydrogen of methylene group of polymer main chain, 3.5 ppm peak is hydrogen of carboxylic acid ester (—COOCH 3) of methyl methacrylate unit , And the peak around 4.0 ppm is methylene hydrogen inside the ring of α-methylene-γ-butyrolactone units.

  The (i) lactone ring-containing monomer unit preferably has a structure represented by the following general formula (1), more preferably is represented by the following general formula (3), and most preferably α-methylene-γ-butyrolactone unit.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

(In the above formula, R ^{9 to} R ¹² are the same or different and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

  As said (ii) unsaturated carboxylic acid alkylester unit, what has a structure represented by following General formula (2) is preferable.

(However, R ⁷ represents any one selected from hydrogen and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted aliphatic hydrocarbon group having 1 to 6 carbon atoms substituted with a hydroxyl group or halogen and carbon. Any one selected from alicyclic hydrocarbon groups of 3 to 6)

  The thermoplastic copolymer can be basically produced by copolymerizing a lactone ring-containing monomer and an unsaturated carboxylic acid alkyl ester monomer. In that case, in the range which does not impair the effect of this invention, when other vinyl-type monomer units are included, you may copolymerize the vinyl-type monomer which gives this unit.

  Preferred examples of the lactone ring-containing monomer include those represented by the following general formula (4), and more preferred examples include the monomer represented by the following general formula (5). Can do.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

(In the above formula, R ^{9 to} R ¹² are the same or different and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

  Preferred specific examples of these lactone ring-containing monomers include α-methylene-γ-butyrolactone, α-methylene-4-methyl-γ-butyrolactone, α-methylene-4,4-dimethyl-γ-butyrolactone, α -Methylene-4-ethyl-γ-butyrolactone, α-methylene-3-methyl-γ-butyrolactone, α-methylene-3-ethyl-γ-butyrolactone, α-methylene-δ-valerolactone, and more preferably α -Methylene-γ-butyrolactone and α-methylene-δ-valerolactone, most preferably α-methylene-γ-butyrolactone. These can be used alone or in combination of two or more thereof.

  When the lactone ring-containing monomers represented by the general formulas (4) and (5) are copolymerized, the lactone ring-containing monomers having the structures represented by the following general formulas (1) and (3), respectively. Gives the unit of mer (i).

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

(In the above formula, R ^{9 to} R ¹² are the same or different and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

  Preferable examples of the unsaturated carboxylic acid alkyl ester monomer include those represented by the following general formula (6).

(However, R ⁷ represents any one selected from hydrogen and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted aliphatic hydrocarbon group having 1 to 6 carbon atoms substituted with a hydroxyl group or halogen and carbon. Any one selected from alicyclic hydrocarbon groups of 3 to 6)

  Specific preferred examples of the unsaturated carboxylic acid alkyl ester monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, n-butyl acrylate, N-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, chloromethyl acrylate, chloromethyl methacrylate, 2-chloroethyl acrylate, 2-chloroethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2,3,4,5, acrylic acid 6-Penta Examples include droxyhexyl, 2,3,4,5,6-pentahydroxyhexyl methacrylate, 2,3,4,5-tetrahydroxypentyl acrylate, and 2,3,4,5-tetrahydroxypentyl methacrylate. Among them, methyl methacrylate is most preferably used. These can be used alone or in combination of two or more thereof. The unsaturated carboxylic acid monomer represented by the general formula (6) gives an unsaturated carboxylic acid alkyl ester unit (ii) having a structure represented by the general formula (2) when copolymerized.

(However, R ⁷ represents any one selected from hydrogen and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted aliphatic hydrocarbon group having 1 to 6 carbon atoms substituted with a hydroxyl group or halogen and carbon. Any one selected from alicyclic hydrocarbon groups of 3 to 6)

  Further, in the production of the thermoplastic copolymer constituting the optically isotropic acrylic resin film of the present invention, other vinyl monomers not containing an aromatic ring are used within a range not impairing the effects of the present invention. It doesn't matter. When this other vinyl monomer not containing an aromatic ring is copolymerized, the above (iv) other vinyl monomer unit not containing an aromatic ring is obtained. Preferable specific examples of other vinyl monomers not containing an aromatic ring include vinyl cyanide monomers such as acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N -Methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, acrylamide, methacrylamide, N-methylacrylamide, butoxymethylacrylamide, N-propylmethacrylamide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate , Ethylaminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine Down, 2-isopropenyl - oxazoline, 2-vinyl - oxazoline, 2-acryloyl - oxazoline, and the like. These may be used alone or in combination of two or more.

  The polymerization method of the thermoplastic copolymer constituting the optically isotropic acrylic resin film of the present invention is basically known by radical polymerization, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, precipitation polymerization, etc. The polymerization method can be used. Solution polymerization, bulk polymerization, suspension polymerization, and precipitation polymerization are preferred in terms of fewer impurities.

  In the present invention, the ratio of these monomer mixtures used in the production of the thermoplastic copolymer is 10 to 60% by weight of the lactone ring-containing monomer, preferably 100% by weight of the whole monomer mixture. Is 15-55 wt%, most preferably 15-45 wt%, unsaturated carboxylic acid alkyl ester monomer is 40-90 wt%, preferably 45-85 wt%, most preferably 55-85 wt% . The proportion of other vinyl monomers copolymerizable with these is 0 to 30% by weight, more preferably 0 to 20% by weight, still more preferably 0 to 10% by weight.

  When the content of the lactone ring-containing monomer is less than 10% by weight, the (i) lactone ring-containing monomer unit represented by the general formula (1) in the thermoplastic copolymer to be obtained The content is reduced, and the thermoplastic copolymer tends to be inferior in heat resistance and optical isotropy. On the other hand, when the content of the lactone ring-containing monomer exceeds 60% by weight, (i) the lactone ring-containing monomer represented by the general formula (1) in the obtained thermoplastic copolymer This is not preferable because the unit content increases, and the fluidity and optical isotropy of the thermoplastic copolymer tend to be inferior.

  Moreover, it is preferable that the weight average molecular weights of the thermoplastic copolymer of this invention are 10,000-200000, More preferably, it is 30,000-150,000, More preferably, it is 5-150,000.

  When the weight average molecular weight is in this range, the fluidity is excellent and the mechanical strength of the optically isotropic acrylic resin film of the present invention can be increased. In addition, the weight average molecular weight as used in the field of this invention shows the weight average molecular weight in the absolute molecular weight measured by multi-angle light scattering gel permeation chromatography (GPC-MALLS).

  Regarding the method for controlling the molecular weight of the thermoplastic copolymer, for example, the addition amount of radical polymerization initiators such as azo compounds and peroxides, or alkyl mercaptans, carbon tetrachloride, carbon tetrabromide, dimethylacetamide, dimethylformamide, triethylamine It can be controlled by the amount of chain transfer agent added. In particular, a method of controlling the amount of alkyl mercaptan added as a chain transfer agent can be preferably used from the viewpoint of stability of polymerization, ease of handling, and the like.

  Examples of the alkyl mercaptan used in the present invention include n-octyl mercaptan, t-dodecyl mercaptan, n-dodecyl mercaptan, n-tetradecyl mercaptan, n-octadecyl mercaptan, etc., among which t-dodecyl mercaptan or n-dodecyl mercaptan is preferably used.

  The amount of the alkyl mercaptan added is preferably 0.2 to 5.0 parts by weight, more preferably 0.3 to 4 parts by weight based on 100 parts by weight of the total amount of the monomer mixture in order to control the molecular weight to a preferable level. 0.0 part by weight, more preferably 0.4 to 3.0 parts by weight.

  The optically isotropic acrylic resin film of the present invention thus obtained preferably has a glass transition temperature (Tg) of 110 ° C. or more in terms of heat resistance. The glass transition temperature is more preferably 115 ° C. or higher, and particularly preferably 120 ° C. or higher. Moreover, as an upper limit, it is about 170 degreeC normally. In addition, the glass transition temperature here is a glass transition temperature (Tg) measured at a heating rate of 20 ° C./min using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer).

  Further, the thermoplastic copolymer constituting the optically isotropic acrylic resin film of the present invention includes other thermoplastic resins such as a polyethylene resin, a polypropylene resin, an acrylic resin, and a polyamide as long as the object of the present invention is not impaired. Resin, polyphenylene sulfide resin, polyether ether ketone resin, polyester resin, polysulfone resin, polyphenylene oxide resin, polyacetal resin, polyimide resin, polyetherimide resin, etc., thermosetting resins such as phenol resin, melamine resin, polyester resin, One or more selected from silicone resins, epoxy resins and the like can be further contained. In this case, the preferable content of the other thermoplastic resin is 99 parts by weight or less, more preferably 95 parts by weight or less, and most preferably 90 parts by weight or less with respect to 100 parts by weight of the thermoplastic copolymer.

  In addition, hindered phenol, benzotriazole, benzophenone, benzoate, and cyanoacrylate UV absorbers and antioxidants, higher fatty acids, acid esters and acid amides, and higher alcohol and other lubricants and plasticizers , Montanic acid and its salts, its esters, its half esters, release agents such as stearyl alcohol, stearamide and ethylene wax, anti-coloring agents such as phosphites and hypophosphites, halogen flame retardants, phosphorus And additives such as coloring agents such as non-halogen flame retardants, nucleating agents, amines, sulfonic acids, and polyethers, pigments, dyes, and optical brighteners. May be. However, in light of the characteristics required by the application to be applied, it is preferable to add the additive within a range where the color of the additive does not adversely affect the thermoplastic polymer and the transparency is not lowered.

  There is no restriction | limiting in the method of containing additives, such as said other resin, a plasticizer, a flame retardant, A well-known melt-kneading method is used, for example, it can carry out in the extruder heated up to 150-300 degreeC of preset temperature. . Examples of the extruder include a single screw extruder with a vent, a twin screw extruder, and the like.

  Here, in the present specification, for convenience, a film after the thermoplastic copolymer is formed into a film and before being stretched may be referred to as an “unstretched film”.

  A well-known method can be used for the manufacturing method of the unstretched film of the optically isotropic acrylic resin film of this invention. That is, a production method such as an inflation method, a T-die method, a calendar method, a cutting method, a solution casting method, an emulsion method, or a hot press method can be used. Preferably, a T-die method, a solution cast method, or a hot press method can be used. In the case of a production method using an inflation method or a T-die method, an extruder type melt extrusion apparatus equipped with a single screw or twin screw can be used. The melt extrusion temperature for producing the optically isotropic acrylic resin film of the present invention is preferably 150 to 350 ° C, more preferably 200 to 300 ° C. Moreover, when melt-kneading using a melt-extrusion apparatus, it is preferable to perform the melt-kneading under a reduced pressure or the melt-kneading under nitrogen stream from a viewpoint of coloring suppression using a vent. Moreover, when manufacturing the acrylic resin film of this invention by a solution cast method, solvents, such as tetrahydrofuran, acetone, methyl ethyl ketone, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, can be used. Preferred solvents are acetone, methyl ethyl ketone, N-methylpyrrolidone and the like. When the acrylic resin film of the present invention is produced by the solution casting method, the thermoplastic copolymer is dissolved in one or more of the above solvents, and the solution is used as a bar coater, a T-die, a T-die with a bar, or a die coat. Etc., using a dry method in which the solvent is evaporated and cast on a heat-resistant film such as polyethylene terephthalate, a steel belt, a flat plate or a curved plate (roll) such as a metal foil, or a wet method in which the solution is solidified with a coagulating liquid. Etc. can be used.

  The optically isotropic acrylic resin film of the present invention may be a single layer or a multilayer.

  The optically isotropic acrylic resin film of the present invention may be left as it is without being stretched, but from the viewpoint of toughness of the resulting film, after forming an unstretched film, it is uniaxially stretched or biaxially stretched to have a predetermined thickness. It is preferable to produce the film. By stretching, the toughness of the film can be improved.

  The film may be continuously stretched immediately after the unstretched film is formed. Here, the “unstretched film” state may exist only momentarily. If it exists only momentarily, the momentary state after the film is formed and then stretched is referred to as an unstretched film. In addition, the unstretched film only needs to be in a film shape sufficient to be stretched thereafter, and does not need to be in a complete film state. Of course, it does not have performance as a completed film. May be. Further, if necessary, after forming an unstretched film, the film may be temporarily stored or moved, and then the film may be stretched. As a method of stretching the unstretched film, any conventionally known stretching method can be adopted. Specifically, for example, there are longitudinal stretching using a roll or a hot stove, transverse stretching using a tenter, and sequential biaxial stretching in which these are sequentially combined. Moreover, the simultaneous biaxial stretching method of extending | stretching length and width simultaneously is also employable. You may employ | adopt the method of performing horizontal extending | stretching by a tenter after performing roll longitudinal stretching.

  The optically isotropic acrylic resin film of the present invention can be made into a final product in the state of a uniaxially stretched film. Furthermore, it is good also as a biaxially stretched film by combining and extending | stretching a process. When biaxial stretching is performed, the stretching conditions such as the temperature and the magnification of the longitudinal stretching and the lateral stretching may be equivalent or intentionally changed within a range not impairing the object of the present invention.

  The stretching temperature and stretching ratio of the film can be adjusted as appropriate using the phase difference, mechanical strength and surface properties, and thickness accuracy of the obtained film as indices. The range of the stretching temperature is preferably in the range of Tg-30 ° C to Tg + 30 ° C, where Tg is the glass transition temperature of the film obtained by the DSC method. More preferably, it is the range of Tg-10 degreeC-Tg + 30 degreeC. More preferably, it is the range of Tg-Tg + 30 degrees C or less. When the stretching temperature is too high, the film tends to be softened and melted, and it becomes difficult to stretch the film. When the stretching temperature is Tg−30 ° C. or less, stress is applied to the film at the time of stretching, and it is not preferable because problems on the process such as tearing of the film are likely to occur.

  Moreover, although a preferable draw ratio also depends on the drawing temperature, it is in the range of 1.1 times to 5.0 times, more preferably 1.1 times to 4.0 times, and still more preferably 1.1 times to 5.0 times. Times to 3.0 times, and most preferably 1.1 to 2.5 times.

  The thickness of the optically isotropic optically isotropic acrylic resin film of the present invention thus obtained is preferably 10 to 200 μm, more preferably 15 to 170 μm, and most preferably 20 to 150 μm. The film thickness can be controlled within the above range by adjusting the thickness of the “unstretched film” before stretching.

  Here, the thickness of the optically isotropic optically isotropic acrylic resin film of the present invention is an average value obtained by measuring the thickness of a film obtained by cutting the film into a 50 mm × 50 mm square.

  In addition, when forming a film, it contains known additives such as heat stabilizers, ultraviolet absorbers, lubricants, processability improvers such as lubricants, and other polymers and other polymers, as long as the object of the present invention is not impaired. You can do it.

  In addition to improving the weather resistance by adding an ultraviolet absorber to the optically isotropic acrylic resin film of the present invention, the durability of the liquid crystal display device using the optically isotropic acrylic resin film of the present invention can also be improved. And practically preferable. Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers such as 2- (2H-benzotriazol-2-yl) -p-cresol and 2-benzotriazol-2-yl-4,6-di-t-butylphenol, Triazine-based UV absorbers such as 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol, benzophenone-based UV absorbers such as octabenzone, etc. Benzoate light stabilizers such as 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate and bis (2,2,6,6-tetramethyl) Light stabilizers such as hindered amine light stabilizers such as -4-piperidyl) sebacate can also be used.

  In the optically isotropic acrylic resin film of the present invention, the absolute value of the in-plane retardation (Re) with respect to the wavelength of 580 nm is preferably 10 nm or less, more preferably 7 nm or less, and most preferably 5 nm or less. The absolute value of the thickness retardation (Rth) with respect to the wavelength of 580 nm is preferably 10 nm or less, more preferably 7 nm or less, and most preferably 5 nm or less.

Here, Re and Rth for light having a wavelength of 580 nm are samples (40 mm × 40 mm × 40 mm) obtained by the parallel Nicol rotation method using an elliptical polarization measuring device (product name “KOBRA-WPR” manufactured by Oji Scientific Instruments). (About 40 μm thickness) The value at the center is measured and is represented by the following formula.
Re = (nx−ny) × d (1)
Rth = {(nx + ny) / 2−nz} × d (2)
here,
nx: refractive index in the direction (x axis) in which the refractive index of the plane is maximum ny: refractive index in the direction perpendicular to the x axis (y axis) nz: refractive index in the thickness direction (z axis) d: film thickness ( nm)
It is.

  Here, the film thickness d when measuring Re and Rth is a value measured according to JIS K 7130-1999, and is preferably within 40 ± 8 μm, and more preferably within 40 ± 5 μm.

About the acrylic resin film of this invention, it is preferable that the absolute value of the photoelastic coefficient with respect to the light of wavelength 580nm is 10 * 10 <^-12> Pa < ^{-1 >} or less, More preferably, it is 7 * 10 <^-12> Pa <^-1> or less. Preferably it is 5 * 10 <^-12> Pa < ^{-1 >} or less. When the absolute value of the photoelastic coefficient is 10 × 10 ⁻¹² Pa ⁻¹ or less, for example, when a stress is applied to the film, the change in phase difference does not increase, which is preferable. The photoelastic coefficient with respect to light having a wavelength of 580 nm here is that of a sample (size 15 mm × 100 mm × about 40 μm thickness) using an elliptical polarization measuring device (product name “KOBRA-WPR” manufactured by Oji Scientific Instruments). This is a value calculated from the slope of the function of stress and phase difference by measuring the phase difference value (23 ° C./580 nm) at the center of the sample while applying stress (0.01 to 10 N) across both ends.

  For example, for an optically isotropic acrylic resin film that is one of optical films, it is required that the optical isotropy is excellent, that is, the absolute value of the in-plane / thickness phase difference and the photoelastic coefficient is small, The optically isotropic acrylic resin film of the present invention can be suitably used for such applications.

  The absolute value of Re of the optically isotropic acrylic resin film of the present invention after the wet heat treatment at 60 ° C. and 90% RH for 500 hours is preferably 10 nm or less, more preferably 7 nm or less, and most preferably 5 nm or less. , Rth is preferably 10 nm or less, more preferably 7 nm or less, and most preferably 5 nm or less.

  The elongation at break in the tensile test of the optically isotropic acrylic resin film of the present invention is preferably 10% or more, more preferably 12% or more. The elongation at break here means that a sample (20 mm × 50 mm) is attached to the chuck using a tensile tester (product name “RTA-1T” manufactured by Orientec Co., Ltd.), the distance between chucks is 20 mm, and the tensile speed is It is the average value of the breaking elongation in the MD direction (film flow direction) and the TD direction (direction perpendicular to the film flow) when the tensile test was performed at 200 mm / min. If the elongation at break is less than 10%, the film may be broken during the molding process, which is not preferable in the production process.

The dimensional change rate of the optically isotropic acrylic resin film of the present invention after wet heat treatment at 60 ° C. and 90% RH for 500 hours is preferably 2% or less, more preferably 1.0% or less, and still more preferably 0. .5% or less. When the dimensional change rate is 2% or more, there is a problem that the change in optical characteristics at high temperature and high humidity becomes large. The dimensional change rate here means that a 30 mm × 30 mm square is drawn on the film, the exact length of the four sides before wet heat treatment is measured with a universal projector (Nikon V-12), and the average value is calculated. Calculate (D0). The film was placed in a constant temperature and humidity chamber (LHL-112 manufactured by Tabai Co., Ltd.) at 60 ° C. × 90% RH, and after processing for 500 hours, the exact length of the four sides of the square was measured again with a universal projector, The average value is calculated (D1), and the dimensional change rate is calculated by the following equation.
Dimensional change rate (%) = (D1-D0) / D0 × 100 (3)

  The application of the optically isotropic acrylic resin film of the present invention is not particularly limited, but an application that can make use of excellent transparency, heat resistance, toughness, and optical characteristics is preferable. Preferred examples of applications include, for example, liquid crystal displays, flat panel displays, polarizing plates for plasma displays, polarizer protective films, retardation films, light diffusion films, viewing angle widening films, reflective films, antireflection films, antiglare films, and brightness. Examples include optical films such as improvement films, prism sheets, light guide films for touch panels, and substrate protective films for various optical disks (VD, CD, DVD, MD, LD, etc.). Especially, since it has the outstanding optical isotropy and durability at high temperature and humidity, it is very useful as a polarizer protective film.

  Hereinafter, the configuration and effects of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Reference example 1
Preparation of thermoplastic copolymer (A-1) 20 parts by weight of methyl methacrylate, 80 parts by weight of acrylamide, 0.3 part by weight of potassium persulfate and 1500 parts by weight of ion-exchanged water were charged into the reactor. The temperature was kept at 70 ° C. while replacing with nitrogen gas. The reaction was continued until the monomer was completely converted into a polymer to obtain an aqueous solution of methyl methacrylate / acrylamide copolymer. The resulting aqueous solution was used as a suspending agent. A solution prepared by dissolving 0.05 parts by weight of the above-mentioned methyl methacrylate / acrylamide copolymer suspension in 165 parts by weight of ion-exchanged water in a stainless steel autoclave having a volume of 5 liters and equipped with a baffle and a foudra-type stirring blade. The mixture was supplied and stirred at 400 rpm, and the inside of the system was replaced with nitrogen gas. Next, the following mixed substances were added while stirring the reaction system, and the temperature was raised to 70 ° C. The time when the internal temperature reached 70 ° C. was set as the start of polymerization, and kept for 180 minutes to complete the polymerization. Thereafter, the reaction system was cooled, the polymer was separated, washed and dried according to the usual method to obtain a bead-shaped copolymer (a-1). The polymerization rate of this copolymer (A-1) was 98%.
α-methylene-γ-butyrolactone 25 parts by weight Methyl methacrylate 75 parts by weight n-dodecyl mercaptan 0.6 parts by weight Laurolyl peroxide 0.4 parts by weight.

  Next, the obtained (A-1) was kneaded using a twin-screw extruder (TEX30 (manufactured by Nippon Steel Co., Ltd., L / D = 44.5)) at a cylinder temperature of 280 ° C. and a screw rotation speed of 100 rpm. Then, a thermoplastic copolymer was obtained, and the pellets were dried at 80 ° C. for 8 hours and analyzed by 1H-NMR, and as a result, 22% by weight of α-methylene-γ-butyrolactone (MBL) unit, methyl methacrylate was obtained. The unit was 78% by weight, Mw by GPC measurement was 111,000, and the glass transition temperature by DSC measurement was 123 ° C.

Reference example 2
Preparation of thermoplastic copolymer (A-2) A pellet-shaped thermoplastic copolymer (A-2) was obtained in the same manner as in Reference Example 1 except that the mixed composition was changed to the following.
α-methylene-γ-butyrolactone 35 parts by weight Methyl methacrylate 65 parts by weight n-dodecyl mercaptan 0.6 parts by weight Laurolyl peroxide 0.4 parts by weight.

  The obtained thermoplastic copolymer (A-2) pellets were dried at 80 ° C. for 8 hours and subjected to composition analysis by 1H-NMR. As a result, 31% by weight of α-methylene-γ-butyrolactone (MBL) unit was obtained. The methyl methacrylate unit was 69% by weight. Mw by GPC measurement was 122,000, and the glass transition temperature by DSC measurement was 132 ° C.

Reference example 3
Preparation of thermoplastic copolymer (A-3) A pellet-shaped thermoplastic copolymer (A-3) was obtained in the same manner as in Reference Example 1 except that the mixed composition was changed to the following.
α-methylene-γ-butyrolactone 50 parts by weight Methyl methacrylate 50 parts by weight n-dodecyl mercaptan 0.6 parts by weight Laurolyl peroxide 0.4 parts by weight.

  The obtained thermoplastic copolymer (A-3) pellets were dried at 80 ° C. for 8 hours and subjected to composition analysis by 1H-NMR. As a result, α-methylene-γ-butyrolactone (MBL) unit was 45% by weight, The methyl methacrylate unit was 55% by weight. The Mw by GPC measurement was 115,000, and the glass transition temperature by DSC measurement was 141 ° C.

Reference example 4
Preparation of thermoplastic copolymer (A-4) A pellet-shaped thermoplastic copolymer (A-4) was obtained in the same manner as in Reference Example 1 except that the mixed composition was changed to the following.
α-methylene-γ-butyrolactone 5 parts by weight Methyl methacrylate 95 parts by weight n-dodecyl mercaptan 0.6 parts by weight Laurolyl peroxide 0.4 parts by weight

  The resulting thermoplastic copolymer (A-4) pellets were dried at 80 ° C. for 8 hours and subjected to composition analysis by 1H-NMR. As a result, 5% by weight of α-methylene-γ-butyrolactone (MBL) unit was obtained. The methyl methacrylate unit was 95% by weight. The Mw by GPC measurement was 115,000, and the glass transition temperature by DSC measurement was 112 ° C.

Reference Example 5
Preparation of thermoplastic copolymer (A-5) A pellet-shaped thermoplastic copolymer (A-5) was obtained in the same manner as in Reference Example 1 except that the mixed composition was changed to the following.
α-methylene-γ-butyrolactone 65 parts by weight Methyl methacrylate 35 parts by weight n-dodecyl mercaptan 0.6 parts by weight Laurol peroxide 0.4 parts by weight.

  The obtained thermoplastic copolymer (A-5) pellets were dried at 80 ° C. for 8 hours and subjected to composition analysis by 1H-NMR. As a result, 60% by weight of α-methylene-γ-butyrolactone (MBL) unit was obtained. The methyl methacrylate unit was 40% by weight. The Mw by GPC measurement was 116,000, and the glass transition temperature by DSC measurement was 152 ° C.

Reference Example 6
Preparation of the thermoplastic copolymer (A-6) A pellet-like thermoplastic copolymer (A-6) was obtained in the same manner as in Reference Example 1 except that the mixed composition was changed as follows.
Methyl methacrylate 100 parts by weight n-dodecyl mercaptan 0.6 parts by weight Laurolyl peroxide 0.4 parts by weight.

  Mw by GPC measurement was 112,000, and the glass transition temperature by DSC measurement was 108 ° C.

Examples 1-3, Comparative Examples 1-3
A biaxial melt kneader HK-25D (Parker) with a T-die in which the pellet-shaped thermoplastic copolymers (A-1 to A-3) obtained in Reference Examples 1 to 6 were adjusted to a lip interval of 0.6 mm. (Corporation Corporation), and melt film formation was performed at a temperature of glass transition temperature (Tg) + 130 ° C. A film having a thickness of about 80 μm was obtained by setting the drum temperature to 130 ° C. and adjusting the winding speed. The obtained film was subjected to a film automatic biaxial stretching apparatus IMC-11A9 type (manufactured by Imoto Seisakusho), and subjected to 1.5 times simultaneous biaxial stretching at a temperature of Tg + 10 ° C. to obtain a film having an average thickness of 40 μm.

Comparative Example 4
A triacetyl cellulose (TAC) film (Fuji Photo Film, Fujitac: average thickness 40 μm) was formed from a mixed solvent of methylene chloride and methanol by a solution casting method and evaluated.

  The measuring method of various physical properties of the film obtained by the above is described below.

(1) Transparency (total light transmittance and haze)
The obtained film was subjected to a direct reading haze meter manufactured by Toyo Seiki Co., Ltd., and the total light transmittance (%) and haze (cloudiness) (%) at 23 ° C. were measured to evaluate transparency.

(2) Optical isotropy (photoelastic coefficient, in-plane retardation and thickness retardation)
The obtained film was cut into a size of 15 mm × 100 mm, and subjected to an elliptical polarization measuring device (product name “KOBRA-WPR” manufactured by Oji Scientific Instruments), and stress (0. The retardation value (23 ° C./580 nm) at the center of the sample was measured while applying 01 to 10 N), and calculated from the slope of the function of stress and retardation.

  In addition, the obtained film was cut into a size of 40 mm × 40 mm, subjected to an elliptical polarization measuring device (product name “KOBRA-WPR” manufactured by Oji Scientific Instruments), and with respect to a wavelength of 580 nm by a parallel Nicol rotation method. The in-plane retardation (Re) and thickness retardation (Rth) were measured at the center of the film.

(3) Toughness (tensile elongation at break)
The obtained film was cut to 20 mm × 100 mm and used for a tensile tester (product name “RTA-1T” manufactured by Orientec Co., Ltd.), and a tensile test was performed at a distance between chucks of 20 mm and a tensile speed of 200 mm / min. The elongation at break in each of the MD direction (film flow direction) and TD direction (direction perpendicular to the film flow) was measured, and the average value of a total of 10 was calculated.

(4) Heat resistance (dimensional change rate after dry heat treatment)
A square of 30 mm × 30 mm was drawn on the obtained film, the exact length of the four sides before processing was measured with a universal projector (V-12 manufactured by Nikon Corporation), and the average value was calculated as D0. The film was placed in a high-temp oven at 90 ° C. (HPS-222 manufactured by Tabai Co., Ltd.), and after 48 hours of dry heat treatment, the exact length of the four sides of the square was measured again with a universal projector, and the average value was calculated. Calculated (D1), the dimensional change rate was calculated by the following equation.
Dimensional change rate (%) = (D1-D0) / D0 × 100.

(5) Durability (in-plane retardation, thickness retardation, dimensional change rate after wet heat treatment)
The film of which Re and Rth were measured according to the above item (2) was subjected to a thermothermal treatment at 500C for 90 hours by using a constant temperature and humidity chamber (LHL-112 manufactured by Tabai Co., Ltd.) at 60 ° C and 90% RH. The Re and Rth of the film after the wet heat treatment were evaluated in the same manner as in the above item (2).

  Further, in the same manner as in the above (4), a square of 30 mm × 30 mm was drawn on the obtained film, and the exact length of the four sides before processing was measured with a universal projector (Nikon Corporation V-12). . The film was used in a constant temperature and humidity bath (LHL-112 manufactured by Tabai Co., Ltd.) at 60 ° C. and 90% RH, and subjected to a wet heat treatment for 500 hours. The dimensional change rate after the wet heat treatment for 500 hours was calculated in the same manner as in the above item (4).

  From Examples 1 to 3, the optically isotropic acrylic resin film of the present invention is excellent in balance with transparency, optical isotropy, toughness and heat resistance, and is excellent in durability during wet heat treatment. It is extremely useful as an optical film such as a protective film.

  On the other hand, as in Comparative Examples 1 and 2, when the copolymerization amount of the α-methylene-γ-butyrolactone unit is not in the range of 50% by weight, the toughness is excellent, but the optical isotropy is inferior, and the optical film is obtained. Deployment is difficult.

  Further, as in Comparative Examples 3 and 4, in the case of an optically isotropic acrylic resin film made of a copolymer containing no α-methylene-γ-butyrolactone unit, although it is excellent in transparency, it is optically isotropic and heat resistant. In addition, a film satisfying any of the durability cannot be obtained, and development to an optical film is extremely difficult.

Claims (13)

(I) a thermoplastic copolymer containing a lactone ring-containing monomer unit represented by (1), and satisfying the following (a), (b) and (c): Isotropic acrylic resin film.
(A) The glass transition temperature is 120 ° C. or higher.
(B) Tensile breaking elongation is 10% or more.
(C) The absolute value of the in-plane retardation (Re) is 10 nm or less, and the absolute value of the thickness retardation (Rth) is 10 nm or less.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms) The thermoplastic copolymer is (i) 15 to 50% by weight of a lactone ring-containing monomer unit represented by the general formula (1), and (ii) an unsaturated carboxylic acid represented by the following general formula (2). The optically isotropic acrylic resin film according to claim 1, comprising 85 to 50% by weight of an acid alkyl ester unit.

(Wherein R ⁷ represents any one selected from a hydrogen atom and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted C 1-6 aliphatic hydrocarbon group substituted with a hydroxyl group or halogen, and Any one selected from alicyclic hydrocarbon groups having 3 to 6 carbon atoms) 3. The optically isotropic acrylic resin film according to claim 1 or 2, which has been subjected to a stretching treatment. The optically isotropic acrylic resin film according to claim 3, which is biaxially stretched. The absolute value of the in-plane retardation (Re) after the wet heat treatment at 60 ° C., 90% RH and 500 hours is 10 nm or less, and the absolute value of the thickness retardation (Rth) is 10 nm or less. The optically isotropic acrylic resin film in any one of -4. 6. The optically isotropic acrylic resin film according to claim 1, wherein a dimensional change rate after wet heat treatment at 60 ° C., 90% RH and 500 hours is 2% or less. The optically isotropic acrylic resin film according to claim 1, wherein the film has an average thickness of 20 to 200 μm. (I) 15 to 50% by weight of a lactone ring-containing monomer unit represented by the following general formula (1), (ii) 85 to 50% by weight of an unsaturated carboxylic acid alkyl ester unit represented by the following general formula (2) %. The method for producing an optically isotropic acrylic resin film according to claim 1, wherein a thermoplastic copolymer containing 2% is formed and stretched.

(In the above formula, m is 0 or ¹ and R ^{1 to} R ⁶ are the same or different, and represent any one selected from a hydrogen atom and an organic residue having 1 to 20 carbon atoms)

(However, R ⁷ is any one selected from a hydrogen atom and an alkyl group having 1 to 5 carbon atoms, and R ⁸ is an unsubstituted or substituted C 1-6 aliphatic hydrocarbon group and carbon atom substituted with a hydroxyl group or halogen. Any one selected from alicyclic hydrocarbon groups of 3 to 6) The method for producing an optically isotropic acrylic resin film according to claim 8, wherein the stretching treatment is biaxial stretching. A polarizing plate protective film comprising the optically isotropic acrylic resin film according to claim 1. A polarizing plate using the polarizing plate protective film according to claim 10. A polarizing optical film, wherein the polarizing plate according to claim 11 and a retardation film are laminated. A liquid crystal display device comprising at least one selected from the polarizing plate protective film according to claim 10, the polarizing plate according to claim 11, and the polarizing optical film according to claim 12.