JP2016069434A - Imide structure-containing (meth)acrylic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imide structure-containing (meth)acrylic resin that can be suitably used as a raw material for an optical film excellent in heat resistance and having small birefringence, high surface hardness and a small photoelastic coefficient and the like, to provide a method for producing the same, to provide an optical film containing the imide structure-containing (meth)acrylic resin and to provide an image display device having the optical film.SOLUTION: The imide structure-containing (meth)acrylic resin uses a (meth)acrylic resin produced by polymerizing as a raw material a monomer component containing a (meth)acrylic monomer. The monomer component contains a (meth)acrylic acid alkyl ester having a 2-6C alkyl ester and a (meth)acrylic acid and the imide structure-containing (meth)acrylic resin has a glass transition temperature of 150°C or higher.SELECTED DRAWING: None

Description

  The present invention relates to an imide structure-containing (meth) acrylic resin. More specifically, the present invention relates to polarized light used in a polarizing plate provided in an image display device such as a protective film for a substrate of an optical disk such as VD, CD, DVD, MD, and LD, and a liquid crystal display device such as an LCD. Suitable as a raw material for optical films represented by optical protective films such as optical protective films, antireflection films used in organic EL displays (OLEDs), transparent conductive films formed with transparent conductive layers such as ITO layers, etc. The present invention relates to an imide structure-containing (meth) acrylic resin that can be used and a method for producing the same, an optical film, and an image display device.

  In recent years, there has been a demand for image display devices to develop optical materials having advanced optical characteristics in response to a demand for improvement in image sharpness. As one of the advanced optical characteristics, low birefringence is required. In general, a polymer compound used for an optical material has birefringence because the refractive index in the main chain direction of the molecule is different from the refractive index in the direction perpendicular to the main chain direction. As a polymer material for an optical film having a small birefringence, a cellulose-based resin such as triacetyl cellulose has been proposed (for example, see Patent Document 1).

  However, an optical film made of a cellulose-based resin produces a phase difference with respect to obliquely incident light, and the phase difference with respect to the obliquely incident light adversely affects viewing angle characteristics in a large liquid crystal display. Have

  On the other hand, polymethyl methacrylate has been proposed as an optical material that has excellent moldability, high surface hardness, high light transmittance, low birefringence, and low wavelength dependency (see, for example, Patent Document 2). However, since polymethyl methacrylate has a low glass transition temperature (Tg) of about 100 ° C. and is inferior in heat resistance, it is difficult to use it in applications requiring heat resistance, such as an image display device.

  Therefore, as a method for improving the heat resistance of acrylic resins such as polymethyl methacrylate, when forming an optical film by extrusion molding of an acrylic resin using an extruder, the acrylic resin is treated with methylamine. It has been proposed to imidize acrylic resins (for example, see Patent Document 3). However, a resin obtained by imidizing an acrylic resin with methylamine has a drawback of large positive birefringence.

JP 2009-265174 A Japanese Patent Laid-Open No. 06-102547 JP 2009-107180 A

  The present invention has been made in view of the above prior art, and is an imide that can be suitably used as a raw material for optical films having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient. It is an object to provide a structure-containing (meth) acrylic resin and a production method thereof, an optical film containing the imide structure-containing (meth) acrylic resin, and an image display device having the optical film.

The present invention
(1) An imide structure-containing (meth) acrylic resin using a (meth) acrylic resin obtained by polymerizing a monomer component containing a (meth) acrylic monomer as a raw material, the (meth) acrylic resin The monomer is a (meth) acrylic monomer containing a (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms in the alkyl ester and (meth) acrylic acid, and has a glass transition temperature of 150 ° C. or higher. An imide structure-containing (meth) acrylic resin,
(2) The imide structure-containing (meth) acrylic resin is represented by the formula (I):

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ³ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or an alkyl group having 3 to 12 carbon atoms. A cycloalkyl group or an aryl group having 6 to 10 carbon atoms)
Repeating units represented by the formula (II):

(Wherein R ⁴ and R ⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 2 to 6 carbon atoms)
The imide structure-containing (meth) acrylic resin according to the above (1) having a repeating unit represented by:
(3) The imide structure-containing (meth) acrylic resin according to (2), wherein in formula (I), R ³ is a cycloalkyl group having 3 to 12 carbon atoms or an aryl group having 6 to 10 carbon atoms,
(4) The above (1) to (3) wherein the (meth) acrylic resin has 5 to 85% by weight of the repeating unit represented by the formula (I) and 15 to 95% by weight of the repeating unit represented by the formula (II). The imide structure-containing (meth) acrylic resin according to any one of the above,
(5) The imide structure-containing (meth) acrylic resin according to any one of (1) to (4), wherein the absolute value of the stress optical coefficient (Cr) is 0.3 × 10 ⁻⁹ Pa ⁻¹ or less,
(6) A method for producing an imide structure-containing (meth) acrylic resin using a (meth) acrylic resin obtained by polymerizing a monomer component containing a (meth) acrylic monomer as a raw material, the monomer component A method for producing an imide structure-containing (meth) acrylic resin, comprising using a monomer component containing (meth) acrylic acid alkyl ester and (meth) acrylic acid, wherein the alkyl ester has 2 to 6 carbon atoms,
(7) An optical film comprising the imide structure-containing (meth) acrylic resin according to any one of (1) to (5),
(8) The optical film according to (7), in which a transparent conductive layer is formed on at least one surface, and (9) the image display device having the optical film according to (7) or (8).

  In the present specification, “(meth) acryl” means “acryl” or “methacryl”.

  According to the present invention, an imide structure-containing (meth) acrylic resin that can be suitably used as a raw material for an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient, and the like A production method, an optical film containing the imide structure-containing (meth) acrylic resin, and an image display device having the optical film are provided.

  As described above, the (meth) acrylic resin obtained by polymerizing the monomer component containing the (meth) acrylic monomer as a raw material was used for the imide structure-containing (meth) acrylic resin of the present invention. (Meth) acrylic resin containing an imide structure, wherein the (meth) acrylic monomer contains (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms and (meth) acrylic acid (meth) It is an acrylic monomer and has a glass transition temperature of 150 ° C. or higher.

  In the present invention, the monomer component used as a raw material for the (meth) acrylic resin includes (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms of alkyl ester among various (meth) acrylic monomers and Since (meth) acrylic acid is used, the imide structure-containing (meth) acrylic resin of the present invention has excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient. It can be suitably used as a raw material for optical films having a low water absorption, a small change in thickness direction retardation Rth, and excellent dimensional stability.

  The imide structure-containing (meth) acrylic resin of the present invention is, for example, cyclized and condensed by heating the (meth) acrylic resin under reduced pressure, and the resulting ring structure-containing (meth) acrylic resin is imidized. It can be prepared by imidizing with an agent.

  The (meth) acrylic resin used as a raw material of the imide structure-containing (meth) acrylic resin of the present invention can be prepared by polymerizing a monomer component containing a (meth) acrylic monomer.

  As the (meth) acrylic monomer, (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms and (meth) acrylic acid are used.

  Suitable alkyl ester (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms is represented by formula (III):

(Wherein R ⁴ and R ⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 2 to 6 carbon atoms)
(Meth) acrylic acid alkyl esters represented by the formula:

In the (meth) acrylic acid alkyl ester represented by the formula (III), R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, n- Examples include a hexyl group, an isohexyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, and a 2-ethylhexyl group, but the present invention is not limited to such examples. Among these alkyl groups, an alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient.

In the repeating unit represented by the formula (III), R ⁶ is an alkyl group having 2 to 6 carbon atoms. Examples of the alkyl group having 2 to 6 carbon atoms include an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, and a hexyl group. Is not limited to such examples. Among these, an alkyl group having 2 to 4 carbon atoms is preferable from the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient, and includes an ethyl group and an n-butyl group. Is more preferable.

In the repeating unit represented by the formula (III), R ⁴ and R ⁵ are each independently from the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient. A hydrogen atom or an alkyl group having 1 to 8 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or a methyl group, and R ⁶ is an alkyl group having 2 to 6 carbon atoms, Preferably it is a C2-C4 alkyl group, More preferably, it is an ethyl group or n-butyl group.

  Examples of the (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms in the alkyl group include, for example, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, Examples include isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, and the like, but the present invention is not limited to such examples. These (meth) acrylates may be used alone or in combination of two or more.

  Ratio of (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms of alkyl ester and (meth) acrylic acid [(meth) acrylic acid alkyl ester having 2 to 6 carbon atoms of alkyl ester / (meth) Acrylic acid (mass ratio)] is preferably 40/60 or more, more preferably 50/50 or more, from the viewpoint of improving the moldability to the film, increasing the mechanical strength, and obtaining an optical film having a small birefringence. From the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness and low photoelastic coefficient, it is preferably 90/10 or less, more preferably 80/20 or less.

  The (meth) acrylic monomer may be composed of (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms of alkyl ester and (meth) acrylic acid, and within a range not hindering the object of the present invention. The (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms in the alkyl ester and (meth) acrylic monomers other than (meth) acrylic acid, for example, methyl (meth) acrylate may be contained.

  In addition, the monomer component may be composed of a (meth) acrylic monomer, and includes a monomer other than a (meth) acrylic monomer such as styrene, for example, within a range that does not impair the object of the present invention. Also good.

  Examples of the method for polymerizing the monomer component include a bulk polymerization method, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and the like, but the present invention is not limited to such examples.

  Next, the (meth) acrylic resin obtained by polymerizing the monomer component is heated under reduced pressure and subjected to cyclization condensation to obtain a ring structure-containing (meth) acrylic resin.

  Generally, a glutarimide resin is obtained by imidizing a (meth) acrylic resin such as polymethyl methacrylate (PMMA) with a primary amine. In the imidation of the (meth) acrylic resin, it is known to go through a glutaric anhydride structure. In order to produce a (meth) acrylic resin having a high content of glutarimide structure, it is important to efficiently produce a glutaric anhydride structure in the (meth) acrylic resin. High temperature and reduced pressure conditions are effective in promoting the reaction of cyclization of (meth) acrylic resin (anhydrous glutaroxidation). It is known to do.

  The degree of pressure reduction when heating the (meth) acrylic resin under reduced pressure is preferably 200 hPa or more, more preferably 600 hPa or more, further preferably 800 hPa or more, from the viewpoint of promoting the cyclization reaction of the (meth) acrylic resin. It is. Further, the heating temperature of the (meth) acrylic resin is preferably 240 ° C. or higher, more preferably 260 ° C. or higher, and further preferably 280 ° C. or higher, from the viewpoint of promoting the cyclization reaction of the (meth) acrylic resin. From the viewpoint of suppressing decomposition and coloring of the (meth) acrylic resin, it is preferably 350 ° C. or lower, more preferably 330 ° C. or lower.

  (When heating the (meth) acrylic resin under reduced pressure, it is preferable to use an extruder from the viewpoint of promoting the cyclization reaction of the (meth) acrylic resin and improving the productivity. It is more preferable to use a machine.

  In addition, when the (meth) acrylic resin is cyclized and condensed, a cyclization catalyst is preferably used from the viewpoint of promoting the cyclized condensation. As the cyclization catalyst, at least one selected from the group consisting of acids, bases and salts thereof can be used. Kinds of acids, bases and salts thereof are not particularly limited. The catalyst is preferably used within the range where the (meth) acrylic resin is not adversely affected such as coloring and the transparency of the (meth) acrylic resin is not lowered.

  Examples of the acid include hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, phosphoric acid, phosphorous acid, phenylphosphonic acid, methyl phosphate, and the like, but the present invention is not limited to such examples. . Examples of the base include metal hydroxides, amines, imines, alkali metal derivatives, alkoxides, ammonium hydroxide salts, and the like, but the present invention is not limited to such examples. Examples of the acid and base salts include metal acetates, metal stearates, metal carbonates, etc., but the present invention is not limited to such examples.

  Among the cyclization catalysts, a compound having an alkali metal is preferable because an excellent reaction promoting effect is exhibited in a small amount. Examples of the compound having an alkali metal include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, sodium methoxide, sodium ethoxide, sodium phenoxide, potassium methoxide, potassium ethoxide and potassium phenoxide. Examples of the alkali metal alkoxide compound such as lithium acetate, sodium acetate, potassium acetate, and sodium stearate include organic carboxylic acid alkali metal salts, but the present invention is not limited to such examples. Among the compounds having an alkali metal, sodium hydroxide, sodium methoxide, lithium acetate and sodium acetate are more preferable because they exhibit an excellent reaction promoting effect with a relatively small amount of addition and suppress resin coloring. Sodium methoxide and lithium acetate are more preferred.

  The amount of the cyclization catalyst is 0.01 to 1 weight per 100 parts by weight of the (meth) acrylic resin from the viewpoint of accelerating the cyclization reaction and obtaining an imide structure-containing (meth) acrylic resin having a high glass transition temperature. It is preferable that it is about a part.

  Since the time required for the cyclization condensation reaction of the (meth) acrylic resin varies depending on the conditions of the cyclization condensation reaction and the like, it cannot be determined unconditionally. Usually, the cyclization condensation of the (meth) acrylic resin is performed until the reaction rate of the cyclization condensation of the (meth) acrylic resin reaches a desired value.

  A ring structure-containing (meth) acrylic resin is obtained as described above. After preparing a ring structure-containing (meth) acrylic resin from a (meth) acrylic resin and isolating the ring structure-containing (meth) acrylic resin as necessary, the obtained ring structure-containing (meth) acrylic resin When imidized, an imide structure can be efficiently produced in a ring structure-containing (meth) acrylic resin. This method is effective when, for example, aniline having a smaller basicity than an alkylamine such as methylamine is used as an imidizing agent.

  Next, an imide structure-containing (meth) acrylic resin can be obtained by imidizing the ring structure-containing (meth) acrylic resin with an imidizing agent.

Examples of a method for imidizing a ring structure-containing (meth) acrylic resin with an imidizing agent include a known imidizing method. As a specific method for imidizing a ring structure-containing (meth) acrylic resin with an imidizing agent, for example,
(1) The ring structure-containing (meth) acrylic resin can be dissolved, the ring structure-containing (meth) acrylic resin is dissolved in a solvent inert to imidization, and the resulting ring structure-containing ( Imidizing a ring structure-containing (meth) acrylic resin with an imidizing agent by adding an imidizing agent to the (meth) acrylic resin solution and reacting the ring structure-containing (meth) acrylic resin with the imidizing agent Method (batch reaction method),
(2) Using an extruder or the like, an imidizing agent is added to the ring structure-containing (meth) acrylic resin in a molten state, and the ring structure-containing (meth) acrylic resin and the imidizing agent are reacted to form a ring. Method of imidizing structure-containing (meth) acrylic resin (melt kneading method)
However, the present invention is not limited to such examples.

  For the batch reaction method, a batch reaction tank (pressure vessel) can be used. The batch-type reaction vessel (pressure vessel) has a structure in which a solution obtained by dissolving a ring structure-containing (meth) acrylic resin in a solvent can be heated and stirred, and an imidizing agent can be added. Preferably, the viscosity of the solution may increase with the progress of the imidization reaction, and thus it is more preferable that the stirring efficiency is excellent. Examples of the batch-type reaction vessel (pressure vessel) include a Max blend (registered trademark) agitation vessel manufactured by Sumitomo Heavy Industries, Ltd., but the present invention is not limited to such examples. Absent.

  In the batch reaction method, examples of the solvent inert to imidization include aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; benzene, toluene, xylene, and chlorobenzene. And aromatic compounds such as chlorotoluene; ether compounds and the like, but the present invention is not limited to such examples. These solvents may be used alone or in combination of two or more. Among these solvents, toluene and a mixed solvent of toluene and methanol are preferable.

  In the batch reaction method, the reaction temperature for reacting the ring structure-containing (meth) acrylic resin with the imidizing agent is such that the ring structure-containing (meth) acrylic resin is efficiently imidized with the imidizing agent. From the viewpoint of suppressing decomposition, coloring, etc. of the (meth) acrylic resin due to excessive heat history, it is preferably 160 to 400 ° C, more preferably 180 to 350 ° C, and further preferably 200 to 300 ° C.

  In the melt-kneading method, an extruder can be used. Examples of the extruder include a single-screw extruder, a twin-screw extruder, and a multi-screw extruder, but the present invention is not limited to such examples. Among these extruders, a twin-screw extruder is preferable because the ring structure-containing (meth) acrylic resin and the imidizing agent can be efficiently mixed. Examples of the twin screw extruder include, for example, a non-meshing type co-rotating twin screw extruder, a meshing type co-rotating twin screw extruder, a non-meshing different direction rotating twin screw extruder, and a meshing type. Although a different direction rotation type twin screw extruder etc. are mentioned, this invention is not limited only to this illustration. These extruders may be used singly or two or more may be connected in series. Among the twin screw extruders, the meshing type co-rotating twin screw extruder can rotate at high speed and can efficiently mix the ring structure-containing (meth) acrylic resin and the imidizing agent. Therefore, it is preferable.

  In the melt-kneading method, imidation of the ring structure-containing (meth) acrylic resin is performed, for example, by introducing the ring structure-containing (meth) acrylic resin from the raw material charging portion of the extruder, and the ring structure-containing (meth) acrylic. After melting the system resin and filling the cylinder, an imidizing agent is injected into the extruder with an addition pump.

  In the melt-kneading method, the temperature (resin temperature) of the reaction zone in the extruder is a viewpoint that efficiently advances the imidization reaction of the ring structure-containing (meth) acrylic resin and improves chemical resistance and heat resistance. Therefore, it is preferably 180 ° C. or higher, more preferably 220 ° C. or higher, preferably from the viewpoint of suppressing the decomposition of the ring structure-containing (meth) acrylic resin and improving the bending resistance of films such as optical films. Is 380 ° C. or lower, more preferably 350 ° C. or lower, and further preferably 300 ° C. or lower. In addition, the reaction zone in the said extruder means the area | region from the injection position of an imidizing agent to the resin discharge port (die part) in the cylinder of an extruder.

  In the melt-kneading method, the ring structure-containing (meth) acrylic resin is imidized by increasing the reaction time of the ring structure-containing (meth) acrylic resin and the imidizing agent in the reaction zone in the extruder. Can be promoted. The time required for imidation of the ring structure-containing (meth) acrylic resin in the reaction zone in the extruder is preferably 10 seconds or more from the viewpoint of sufficiently imidating the ring structure-containing (meth) acrylic resin. More preferably, it is 30 seconds or more. From the viewpoint of improving the solubility of the imidizing agent, the pressure of the ring structure-containing (meth) acrylic resin in the extruder is preferably at least atmospheric pressure, more preferably at least 1 MPa, considering the pressure resistance of the extruder. Thus, it is preferably 50 MPa or less, more preferably 30 MPa or less.

  In order to remove unreacted imidizing agent and by-products, the extruder is preferably provided with a vent that can be depressurized below atmospheric pressure. The number of vents may be only one or plural.

  When the (meth) acrylic resin is imidized by the melt-kneading method, instead of an extruder, for example, a horizontal biaxial reactor (manufactured by Sumitomo Heavy Industries, Ltd., trade name: Vivolak), vertical concentricity A reaction apparatus capable of dealing with high viscosity such as a biaxial stirring tank (manufactured by Sumitomo Heavy Industries, Ltd., trade name: Super Blend) can be used.

Examples of the imidizing agent include amine compounds represented by the formula: NH ₂ R ³ (wherein R ³ is the same as described above). Specific examples of the amine compound include, for example, an aliphatic hydrocarbon group-containing amine such as methylamine, ethylamine, and n-butylamine, a cycloalkylamine having 3 to 12 carbon atoms such as cyclohexylamine, aniline, and benzyl. Examples include arylamines having an aryl group having 6 to 10 carbon atoms such as amine, toluidine, and trichloroaniline, but the present invention is not limited to such examples. These imidizing agents may be used alone or in combination of two or more. Among the imidizing agents, cyclohexylamine, aniline and toluidine are preferable, and aniline is more preferable from the viewpoint of obtaining an optical film having excellent heat resistance and low birefringence.

  The amount of the imidizing agent cannot be generally determined, and it is usually preferable to adjust the ring structure-containing (meth) acrylic resin so as to have a desired imidization ratio.

  By imidating the ring structure-containing (meth) acrylic resin with an imidizing agent as described above, an imide structure-containing (meth) acrylic resin can be obtained.

  The glass transition temperature of the imide structure-containing (meth) acrylic resin of the present invention is 150 ° C. or higher from the viewpoint of improving the heat resistance of the film. Further, the glass transition temperature of the imide structure-containing (meth) acrylic resin is preferably 250 ° C. or lower, more preferably 230 ° C. or lower, more preferably 210 ° C. or lower, from the viewpoint of improving the moldability to a film. More preferably, it is 200 degrees C or less.

  In addition, in this specification, the glass transition temperature of imide structure containing (meth) acrylic-type resin is a value when calculated | required based on prescription | regulation of JISK7121. More specifically, a differential scanning calorimeter [trade name: Thermo plus EVO DSC-8230, manufactured by Rigaku Corporation] was used, and α-alumina was used as a reference, and an imide structure-containing (meth) acrylic system in a nitrogen gas atmosphere. It is the temperature when about 10 mg of the resin is heated from room temperature to 200 ° C. at a rate of temperature increase of 20 ° C./min and determined from the obtained DSC curve by the starting point method.

  The imide structure-containing (meth) acrylic resin of the present invention has improved heat resistance, reduced birefringence, increased surface hardness, reduced photoelastic coefficient, reduced water absorption, thickness From the viewpoint of reducing the change value of the directional phase difference Rth and further improving the dimensional stability, the formula (I):

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ³ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or an alkyl group having 3 to 12 carbon atoms. A cycloalkyl group or an aryl group having 6 to 10 carbon atoms)
Repeating units represented by the formula (II):

(Wherein R ⁴ and R ⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 2 to 6 carbon atoms)
It is preferable to have a repeating unit represented by:

In the repeating unit represented by the formula (I), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, n- Examples include a hexyl group, an isohexyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, and a 2-ethylhexyl group, but the present invention is not limited to such examples. Among R ¹ and R ² , a hydrogen atom or an alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of obtaining an optical film having excellent heat resistance and low birefringence.

In the repeating unit represented by the formula (I), R ³ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms. Among R ³ , heat resistance is improved, birefringence is decreased, surface hardness is increased, photoelastic coefficient is decreased, water absorption is decreased, and thickness direction retardation Rth is changed. From the viewpoint of reducing the size and further improving the dimensional stability, a cycloalkyl group having 3 to 12 carbon atoms or an aryl group having 6 to 10 carbon atoms is preferable. Examples of the cycloalkyl group having 3 to 12 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and the like, but the present invention is not limited to such examples. Among these cycloalkyl groups, a cycloalkyl group having 3 to 6 carbon atoms is preferable, and a cyclohexyl group is more preferable from the viewpoint of obtaining an optical film having excellent heat resistance and low birefringence. Examples of the aryl group having 6 to 10 carbon atoms include phenyl, benzyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl, 2,4-xylyl, 2,5- Examples include xylyl group, 2,6-xylyl group, 3,4-xylyl group, 3,5-xylyl group, 1-naphthyl group, 2-naphthyl group, binaphthyl group, anthryl group, and the like. It is not limited to illustration only. Among these aryl groups, a phenyl group and a tolyl group are preferable from the viewpoint of obtaining an optical film having excellent heat resistance and low birefringence. Among R ³ , a cycloalkyl group having 3 to 6 carbon atoms, a phenyl group and a tolyl group are preferable, and a cyclohexyl group and a phenyl group are more preferable from the viewpoint of obtaining an optical film having excellent heat resistance and low birefringence. preferable.

In the repeating unit represented by the formula (I), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms from the viewpoint of obtaining an optical film having excellent heat resistance and low birefringence. , Preferably a hydrogen atom or a methyl group, and it is desirable that R ³ is a cyclohexyl group or a phenyl group, preferably a phenyl group.

  The imide structure-containing (meth) acrylic resin may contain two or more repeating units represented by the formula (I).

In the repeating unit represented by the formula (II), R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, n- Examples include a hexyl group, an isohexyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, and a 2-ethylhexyl group, but the present invention is not limited to such examples. Among these alkyl groups, an alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient.

In the repeating unit represented by the formula (II), R ⁶ is an alkyl group having 2 to 6 carbon atoms. Examples of the alkyl group having 2 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, and hexyl group. The present invention is not limited to such examples. Among the alkyl groups having 2 to 6 carbon atoms, an alkyl group having 2 to 4 carbon atoms is preferable from the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient. An ethyl group and an n-butyl group are more preferable.

In the repeating unit represented by the formula (II), R ⁴ and R ⁵ are each independently from the viewpoint of obtaining an optical film having excellent heat resistance, low birefringence, high surface hardness, and low photoelastic coefficient. A hydrogen atom or an alkyl group having 1 to 8 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or a methyl group, and R ⁶ is an alkyl group having 2 to 6 carbon atoms, Preferably it is a C2-C4 alkyl group, More preferably, it is an ethyl group or n-butyl group.

  The imide structure-containing (meth) acrylic resin may contain two or more repeating units represented by the formula (II).

  The content of the repeating unit represented by the formula (I) in the imide structure-containing (meth) acrylic resin improves the heat resistance and transparency of the imide structure-containing (meth) acrylic resin, and has a small birefringence. Is preferably 5 wt% or more, more preferably 10 wt% or more, and even more preferably 15 wt% or more, improving the moldability to the film, increasing the mechanical strength, and reducing the birefringence. From the viewpoint of obtaining an optical film, it is preferably 85% by weight or less, more preferably 80% by weight or less, and further preferably 75% by weight or less.

  Further, the content of the repeating unit represented by the formula (II) in the imide structure-containing (meth) acrylic resin improves the moldability to the film, increases the mechanical strength, and obtains an optical film having a small birefringence. From the viewpoint, it is preferably 15% by weight or more, more preferably 20% by weight or more, and further preferably 25% by weight or more, improving the heat resistance and transparency of the imide structure-containing (meth) acrylic resin, and birefringence. Is preferably 95% by weight or less, more preferably 90% by weight or less, and still more preferably 85% by weight or less, from the viewpoint of obtaining an optical film having a small thickness.

  In addition, the imide structure-containing (meth) acrylic resin includes, for example, a repeating unit represented by the formula (I) such as a styrene unit and a repeating unit represented by the formula (II) within a range in which the object of the present invention is not hindered. Repeating units other than may be included. For example, when the repeating unit represented by the formula (I) and the repeating unit other than the repeating unit represented by the formula (II) are styrene units, the content of styrene units in all the repeating units is preferably 10% by weight or less. More preferably, it is 5% by weight or less, more preferably 2% by weight or less, and still more preferably 1% by weight or less.

  The weight average molecular weight of the imide structure-containing (meth) acrylic resin is preferably 10,000 or more, more preferably 30000 or more from the viewpoint of increasing the mechanical strength of the film, and preferably from the viewpoint of improving moldability to the film. Is 500,000 or less, more preferably 300,000 or less.

  In the present specification, the weight average molecular weight of the (meth) acrylic resin, the ring structure-containing (meth) acrylic resin and the imide structure-containing (meth) acrylic resin is determined by gel permeation chromatography (GPC) as follows. This is the value obtained when the condition is obtained.

System: Made by Tosoh Corporation, trade name: GPC system HLC-8220
・ Developing solvent: Tetrahydrofuran [Wako Pure Chemical Industries, Ltd., special grade]
・ Solvent flow rate: 0.6 mL / min
Standard sample: TSK standard polystyrene [trade name: PS-oligomer kit, manufactured by Tosoh Corporation]
Measurement side column configuration: guard column [manufactured by Tosoh Corporation, trade name: TSK-GEL super HZM-M 6.0 × 150 in series, two manufactured by Tosoh Corporation, trade name: TSK-GEL super HZ -L is used-Reference column configuration: Reference column [manufactured by Tosoh Corporation, trade name: TSK-GEL SuperH-RC 6.0 × 150, two in series]
-Column temperature: 40 ° C

The absolute value of the stress optical coefficient (Cr) of the imide structure-containing (meth) acrylic resin of the present invention suppresses the anisotropy of the refractive index of an optical film made of the resin, for example, a stretched film, and reduces the birefringence. ^Therefore , it is 0.3 × 10 ⁻⁹ Pa ⁻¹ or less, preferably 0.2 × 10 ⁻⁹ Pa ⁻¹ or less, more preferably 0.1 × 10 ⁻⁹ Pa ⁻¹ or less. The stress optical coefficient (Cr) of the imide structure-containing (meth) acrylic resin is a value when measured based on the method described in the following examples.

In addition, by controlling the absolute value of the stress optical coefficient (Cr) of the imide structure-containing (meth) acrylic resin of the present invention to 0.3 × 10 ⁻⁹ Pa ⁻¹ or less, the optical film after biaxial stretching The absolute value of the thickness direction retardation Rth can be 20 nm or less.

  Further, the acid value of the imide structure-containing (meth) acrylic resin of the present invention is 1.4 mmol / g or less, preferably 1.2 mmol / g or less, more preferably from the viewpoint of improving molding processability such as film formation. Is 1.0 mmol / g or less. The acid value of the imide structure-containing (meth) acrylic resin of the present invention is a value when measured based on the method described in the following examples.

  The imide structure-containing (meth) acrylic resin of the present invention may contain other thermoplastic resins as long as the object of the present invention is not impaired. Other thermoplastic resins include, for example, olefin-based polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; (Meth) acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; polyethylene terephthalate, poly Polyesters such as butylene terephthalate and polyethylene naphthalate; biodegradable polyesters such as polylactic acid and polybutylene succinate; polyamides such as nylon 6, nylon 66, nylon 610; polyaceter Polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyether ether ketone, polyether nitrile, polysulfone, polyether sulfone, polyoxybenzylene, polyamideimide, and rubbers such as polybutadiene rubber and acrylic rubber. The invention is not limited to such examples.

  In addition, the imide structure-containing (meth) acrylic resin of the present invention includes, for example, a hindered phenol antioxidant, a phosphorus antioxidant, a sulfur antioxidant, and the like within a range in which the object of the present invention is not inhibited. Antioxidants; stabilizers such as light stabilizers, weather stabilizers and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; near infrared absorbers; tris (dibromopropyl) phosphate, triallyl phosphate Flame retardants such as antimony oxide; antistatic agents such as anionic surfactants, cationic surfactants and nonionic surfactants; colorants such as inorganic pigments, organic pigments and dyes; organic fillers and inorganic fillers Fillers such as materials; resin modifiers; plasticizers; lubricants and the like may be included.

  The optical film of the present invention can be produced by using the imide structure-containing (meth) acrylic resin of the present invention, for example, by a melt extrusion molding method such as a T-die method or an inflation method, a cast molding method, a press molding method, or the like. it can. When the optical film is produced by a melt extrusion method, for example, a single screw extruder, a twin screw extruder, or the like can be used.

  As described above, the optical film of the present invention can be obtained. From the viewpoint of increasing the mechanical strength, the optical film of the present invention is preferably uniaxially stretched or biaxially stretched, and biaxially stretched. Is more preferable. Examples of the method for biaxially stretching the optical film of the present invention include a sequential biaxial stretching method and a simultaneous biaxial stretching method. However, the present invention is not limited to such examples.

  The stretching temperature for stretching the optical film of the present invention is preferably an imide structure-containing (meth) acrylic resin from the viewpoint of stretching the optical film without causing breakage of the optical film and sufficiently aligning the molecules. From a temperature range from a temperature 20 ° C. lower than the glass transition temperature to 50 ° C. higher than the glass transition temperature, more preferably 10 ° C. lower than the glass transition temperature of the imide structure-containing (meth) acrylic resin. It is a temperature range up to a temperature 30 ° C. higher than the glass transition temperature.

  The stretching ratio of the optical film is preferably about 1.5 to 3 times from the viewpoint of increasing mechanical strength in both the longitudinal direction and the transverse direction orthogonal to the longitudinal direction. More preferably, it is about 5 to 2.5 times.

  The dimensional change rate of the stretched optical film is preferably 1.0% or less, more preferably 0.7% or less, from the viewpoint of improving the durability of a film subjected to secondary processing such as an ITO film. More preferably, it is 0.5% or less, and still more preferably 0.2% or less.

  Since the thickness of the optical film of the present invention varies depending on its use and the like, it cannot be determined unconditionally. For example, when the optical film of the present invention is used for a liquid crystal display device, a protective film used for an image display device such as an organic EL display device, an antireflection film, a polarizing film, the thickness of the optical film is Preferably it is 1-250 micrometers, More preferably, it is 10-100 micrometers, More preferably, it is 20-80 micrometers. In addition, for example, when the optical film of the present invention is used for a transparent conductive film used for an ITO vapor-deposited film, a silver nanowire film, a metal mesh film, or the like, the thickness of the optical film is preferably 20 It is -400 micrometers, More preferably, it is 30-350 micrometers, More preferably, it is 40-300 micrometers.

  In addition, in this specification, the thickness of an optical film is a thickness when it measures using a Digimatic micrometer [product made from Mitutoyo Corporation], for example.

  The in-plane retardation Re of the optical film with respect to light having a wavelength of 590 nm of the present invention is preferably 20 nm or less, more preferably 10 nm or less, from the viewpoint of suppressing the refractive index anisotropy of the optical film and reducing birefringence. More preferably, it is 5 nm or less, More preferably, it is 3 nm or less. Further, the absolute value of the thickness direction retardation Rth of the optical film with respect to light having a wavelength of 590 nm of the present invention, like the in-plane retardation Re, suppresses the anisotropy of the refractive index of the optical film and reduces the birefringence. Therefore, the thickness is preferably 20 nm or less, more preferably 10 nm or less, further preferably 5 nm or less, and still more preferably 3 nm or less.

  In this specification, the in-plane retardation Re and the thickness direction retardation Rth of the optical film with respect to light having a wavelength of 590 nm are obtained by using a retardation film / optical material inspection apparatus [manufactured by Otsuka Electronics Co., Ltd., product number: RETS-100]. It is a value when used and measured under the condition of an incident angle of 40 °.

The in-plane retardation Re of the optical film is expressed by the formula:
[In-plane phase difference Re] = (nx−ny) × d
[Where nx is the refractive index in the slow axis direction (the direction showing the maximum refractive index in the plane of the optical film) for light having a wavelength of 590 nm, and ny is the fast axis direction (perpendicular to nx in the plane of the optical film) The refractive index in the azimuth direction), ny is the refractive index in the fast axis direction in the plane of the film, and d is the thickness (nm) of the optical film.
Based on.

The thickness direction retardation Rth of the optical film is expressed by the formula:
[Thickness direction retardation Rth] = {(nx + ny) / 2−nz} × d
[Where nx is the refractive index in the slow axis direction for light of wavelength 590 nm, ny is the refractive index in the fast axis direction, nz is the refractive index in the film thickness direction, and d is the film thickness (nm)].
Based on.

The absolute value of the photoelastic coefficient for light having a wavelength of 590 nm of the optical film of the present invention is preferably 10 × 10 ⁻¹² Pa ⁻¹ or less from the viewpoint of suppressing light leakage, particularly light leakage in a high temperature and high humidity environment. More preferably, it is 6 × 10 ⁻¹² Pa ⁻¹ or less.

  In this specification, the photoelastic coefficient of the optical film with respect to light with a wavelength of 590 nm is cut into 20 mm × 50 mm with the stretching direction of the optical film as the long side, and a sample is prepared. This sample is an ellipsometer [manufactured by JASCO Corporation] , Product number: M-150], and birefringence is measured at three points while applying a stress load of 5 to 25 N in parallel with the stretching direction. It is a value when the inclination of refraction is obtained as a photoelastic coefficient.

  The change value of the thickness direction retardation Rth (590) of the optical film of the present invention is preferably 10 nm or less, more preferably 5 nm, from the viewpoint of suppressing light leakage, particularly light leakage in a high temperature and high humidity environment. It is. In addition, the change value of thickness direction phase difference Rth (590) of an optical film is a value when it measures based on the method as described in a following example.

The linear expansion coefficient in the temperature range of 60 to 100 ° C. of the optical film of the present invention is preferably 80 × 10 ⁻⁶ K ⁻¹ or less, more preferably 70 × 10 ⁻ from the viewpoint of suppressing dimensional change in a high temperature environment. ⁶ K ^-1 or less.

In this specification, the linear expansion coefficient at 60 to 100 ° C. of the optical film is from 60 ° C. to 100 ° C. under the following measurement conditions using a thermomechanical measuring device [manufactured by Shimadzu Corporation, product number: TMA-60]. It was calculated as the slope at.
〔Measurement condition〕
・ Sample size: 5 mm × 20 mm (the long side is the stretching direction)
Sample pretreatment: After pretreatment at 60 ° C. for 15 hours, cooling to room temperature Measurement weight: 5 g
・ Raising rate: 5 ° C / min

  The water absorption of the optical film of the present invention is preferably 3.0% or less, more preferably 2.5% or less, and even more preferably 2.0% or less, from the viewpoint of improving the molding processability to an ITO film, for example. It is. The water absorption rate of the optical film is a value when measured based on the method described in the following examples.

  If necessary, a coating layer may be formed on at least one surface of the optical film of the present invention. Examples of the coating layer include an antistatic layer, an adhesive layer, an adhesive layer, an easy-adhesion layer, an antiglare layer (non-glare) layer, a photocatalyst layer, an antifouling layer, an antireflection layer, a hard coat layer, an ultraviolet shielding layer, and a heat ray. Although a shielding layer, an electromagnetic wave shielding layer, a gas barrier layer, etc. are mentioned, this invention is not limited only to this illustration.

As described above, the optical film of the present invention is weakly positive based on the repeating unit represented by the formula (I) in which R ³ is a cycloalkyl group having 3 to 12 carbon atoms or an aryl group having 6 to 10 carbon atoms. It has birefringence and weak negative birefringence based on the repeating unit represented by the formula (II), but the birefringence of both cancels each other, so that it has low birefringence as a whole. Further, since the optical film of the present invention has a repeating unit represented by the formula (I), it has excellent heat resistance, and has substantially no repeating unit based on an aromatic vinyl monomer typified by styrene. In some cases, it has excellent properties of having a hard surface hardness and a low photoelastic coefficient, which are characteristics based on the repeating unit represented by the formula (II).

  The optical film of the present invention is, for example, a protective film for an optical disc, a polarizer protective film used for a polarizing plate of an image display device such as a liquid crystal display device, a retardation film, a viewing angle compensation film, a light diffusion film, a reflective film, a reflective film. It is expected to be used for applications such as a prevention film, an antiglare film, a brightness enhancement film, a conductive film for a touch panel, a diffusion plate, a light guide, and a prism sheet. Therefore, the optical film of the present invention is expected to be suitably used for applications such as image display devices such as liquid crystal display devices and capacitive touch panels.

  Moreover, for example, a transparent conductive layer, an optical adjustment layer, a transparent hard coat layer, an antiglare layer, an antireflection layer and the like may be formed on at least one surface of the optical film of the present invention.

  The optical film having a transparent conductive layer formed on at least one surface of the optical film of the present invention can be used as a transparent conductive film. Examples of the transparent conductive layer include an inorganic compound layer having a property of reflecting infrared rays, such as an indium-tin oxide (ITO) layer, and a metal mesh layer made of a metal such as silver, copper, nickel, and tungsten. However, the present invention is not limited to such examples.

  When the transparent conductive layer is an inorganic compound layer, the thickness of the transparent conductive layer is preferably 0.001 to 10 μm, more preferably 0.005 to 1 μm, from the viewpoint of improving conductivity and light transmittance. Preferably it is 0.01-0.5 micrometer. When the transparent conductive layer is a metal mesh layer, the thickness of the transparent conductive layer is preferably 0.1 to 30 μm, more preferably 0.1 to 10 μm from the viewpoint of improving conductivity and light transmittance. More preferably, it is 1-5 micrometers.

  The optical adjustment layer is a layer for appropriately adjusting the transmittance or reflectance of incident light. As described in, for example, Japanese Patent Application Laid-Open No. 2006-201450, the optical adjustment layer is formed by alternately arranging a low refractive index layer having a relatively low refractive index and a high refractive index layer having a relatively high refractive index. It can be formed by laminating.

  EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to this Example.

Example 1
In a reaction kettle equipped with a stirrer, temperature sensor, cooling pipe and nitrogen gas introduction pipe, 70 parts by weight of ethyl methacrylate, 30 parts by weight of methacrylic acid, 78.8 parts by weight of toluene as a polymerization solvent and 33.8 parts by weight of methanol A mixed solvent and an antioxidant (manufactured by ADEKA, trade name: ADK STAB 2112) were added in an amount of 0.05 part by weight, and the temperature was raised to 73 ° C. while passing nitrogen gas through the reaction kettle. At the time when the reflux accompanying the temperature rise starts, dimethyl-2,2′-azobis (2-methylpropionate) [manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-601] as a polymerization initiator. 25 parts by weight was added to the reaction kettle, and dimethyl-2,2′-azobis (2-methylpropionate) [Wako Pure Chemical Industries, Ltd.] was added to a mixed solvent of 6.4 parts by weight of toluene and 2.7 parts by weight of methanol. Kogyo Co., Ltd., trade name: V-601] Performing solution polymerization under reflux at about 71 to 76 ° C. while dropping 0.35 parts by weight of the solution in which the solution was dissolved in the reaction kettle over 2 hours. After completion of the dropwise addition of dimethyl-2,2′-azobis (2-methylpropionate), aging was performed for another 4 hours.

  The content of repeating units derived from methacrylic acid in the (meth) acrylic resin contained in the polymer solution obtained above was 30.2% by weight. Moreover, the weight average molecular weight of the (meth) acrylic resin was 122,000.

  Next, a solution prepared by dissolving 0.1 part by weight of sodium methoxide as a cyclization catalyst in 9.9 parts by weight of methanol is dropped into the polymerization solution in the reaction kettle at a temperature of about 65 to 70 ° C. over 20 minutes. A uniform polymerization solution was obtained.

  Vent type screw twin screw extruder having a barrel temperature of 290 ° C., a rotation speed of 160 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1, and a forevent number of 2 (Pore diameter: 15 mm, L / D: 45) Introduced at a processing speed of 420 g / h in terms of resin amount, devolatilized in this extruder, and extruded with an on-axis residence time of about 3.6 minutes A transparent ring structure-containing (meth) acrylic resin pellet was obtained.

  The weight average molecular weight of the ring structure-containing (meth) acrylic resin obtained above was 113,000, and the glass transition temperature was 109 ° C.

  Next, the pellet obtained above was a barrel type screw twin screw extruder (hole diameter: 15 mm) with a barrel temperature of 290 ° C., a rotation speed of 300 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), and a single vent number. L / D: 45) was introduced from the hopper at a processing rate of 420 g / h in terms of resin amount, and aniline was injected from the hopper after the hopper at a charging rate of 202 g / h. By extruding in about 2 minutes, transparent imide structure-containing (meth) acrylic resin pellets were obtained.

The weight average molecular weight of the imide structure-containing (meth) acrylic resin obtained above was 10.11,000. The imide structure-containing (meth) acrylic resin obtained above has the formula (I) in which R ¹ is a methyl group, R ² is a hydrogen atom, and R ³ is a phenyl group, In (II), an imide structure-containing (meth) acrylic resin having a repeating unit in which R ⁴ is a hydrogen atom, R ⁵ is a methyl group, R ⁶ is an ethyl group, and has a glass transition temperature of 168 ° C. Met.

The imidization ratio of the imide structure-containing (meth) acrylic resin obtained above was 54.6%, the content of the repeating unit represented by the formula (II) was 26.0% by weight, and the stress optical coefficient (Cr) was 0. 0.02 × 10 ⁻⁹ Pa ⁻¹ . The acid value of the imide structure-containing (meth) acrylic resin was 0.88 mmol / g.

  In this specification, the imidization ratio of the imide structure-containing (meth) acrylic resin, the content of repeating units represented by the formula (II) and the stress optical coefficient (Cr), and the imide structure-containing (meth) acrylic resin The acid value of the resin was examined based on the following method.

[Imidation rate]
Imide structure-containing (meth) imidization ratio of the acrylic resin, the absorption derived from a carboxylic acid anhydride group in the vicinity of 1803cm ^-1, and the absorption derived from the ester carbonyl group in the vicinity of 1720 cm ^-1, 1680 cm ^-1 vicinity of The imidization rate was determined from the intensity ratio with the absorption derived from the imidocarbonyl group. Here, the imidization rate is a ratio of imide carbonyl groups in all carbonyl groups.

[Content of repeating unit represented by formula (II)]
In the imide structure-containing (meth) acrylic resin, the content of the repeating unit represented by the formula (II) is determined by measuring a ¹ H-NMR spectrum using an NMR measuring apparatus (manufactured by Varian, trade name: Unity Plus 400). Was determined by

More specifically, heavy acetone contains an imide structure-containing (meth) acrylic resin (weight: a) and 1,1,2,2-tetrachloroethane (molecular weight: 167.85, weight: b) as an internal standard. The area ratio of the peak derived from the internal standard (5.9 ppm, 2 protons) and the R ⁶ proton adjacent to the ester carbonyl group [the peak area A derived from the R ⁶ proton adjacent to the ester carbonyl group and The ratio of the repeating unit represented by the formula (II) was calculated from the ratio (peak area A / peak area B) to the peak area B derived from the internal standard proton.

For example, when R ^{4 of the} repeating unit represented by the formula (II) is a hydrogen atom, R ⁵ is a methyl group, and R ⁶ is a methyl group (the molecular weight of the repeating unit is 100.12), the formula (II The content (% by weight) of the repeating unit represented by
[Content of repeating unit represented by formula (II) (% by weight)]
= [(Peak area A / Peak area B) × (2/3) × (b / 167.85) × (1 / 100.12)] × (100 / a)
Can be determined based on

[Stress optical coefficient (Cr)]
For the stress optical coefficient (Cr) of the imide structure-containing (meth) acrylic resin, the unstretched film is cut into a 60 mm × 20 mm rectangle, and the weight is selected so that the stress is 1 N / mm ² or less. Attached to the lower end.

  This unstretched film was set at a temperature of 3 ° C higher than the glass transition temperature of the imide structure-containing (meth) acrylic resin at a constant temperature dryer (manufactured by ASONE, product number: DOV-450A) with a chuck distance of 40 mm. After stretching by holding at that temperature for about 30 minutes, the heating is stopped, and the cooling rate is about 1 ° C./min until the temperature becomes 40 ° C. lower than the glass transition temperature of the imide structure-containing (meth) acrylic resin. Cooled with. Then, the obtained stretched film was taken out from the constant temperature dryer, and the length, thickness and weight of the stretched film were measured, and the in-plane retardation Re of the stretched film was measured.

Further, the length, thickness and weight of the stretched film were measured in the same manner as described above using four kinds of weights so that the stress was 1 N / mm ² or less, and the film was stretched. In-plane retardation Re was measured.

Based on the above results, based on the measurement method described in Polymer Science Society, “Frontier of Transparent Plastics (Polymer Frontier 21 Series)”, NTS, October 2006, pages 37-44. The stress optical coefficient (Cr) was calculated. More specifically, Δn (nx−ny) is plotted on the y-axis, σ is plotted on the x-axis, the slope of the straight line obtained by the least square method is obtained, and the value of the slope is expressed as the stress optical coefficient (Cr). did. Note that nx is the refractive index in the slow axis direction in the plane of the film (direction showing the maximum refractive index in the film plane), and ny is the fast axis direction in the plane of the film (perpendicular to nx in the film plane). (Direction) is a refractive index, σ, is a stress (N / m ² ) on stretching.

[Method for measuring the amount of acid component (acid value) remaining in the imide structure-containing (meth) acrylic resin]
In 24.94 g of methylene chloride was dissolved 0.15 g of an imide structure-containing (meth) acrylic resin, and 14.85 g of methanol was added to the resulting solution, and the mixture was stirred for 3 hours. Then, 2 drops of 1 wt% phenolphthalein ethanol solution was added to this solution, 0.1N sodium hydroxide aqueous solution was added with stirring, and stirring was continued for 1 hour at room temperature. The amount was Aml. 0.1N hydrochloric acid was added dropwise to this solution, and the amount of 0.1N hydrochloric acid added until the reddish purple color of the solution disappeared (Bml) was measured.

  Next, 2 drops of a 1% by weight phenolphthalein ethanol solution are added to a mixed solution of 24.94 g of methylene chloride and 14.85 g of methanol, a 0.1N aqueous sodium hydroxide solution is added with stirring, and the mixture is stirred at room temperature for 1 hour. Stirring was continued and the amount of 0.1N sodium hydroxide aqueous solution was Cml. 0.1N hydrochloric acid was added dropwise to this solution, and the amount of 0.1N hydrochloric acid added (Dml) required until the reddish purple color of the solution disappeared was measured.

The amount of the acid component remaining in the imide structure-containing (meth) acrylic resin (total amount of carboxyl group and acid anhydride group) (mmol / g) is expressed by the formula:
[Amount of acid component remaining in imide structure-containing (meth) acrylic resin (total amount of carboxyl group and acid anhydride group) (mmol / g)]
= 0.1 × [(A−B) − (C−D)] / 0.15
Based on.

  Next, the pellet obtained above is put into a single screw extruder (hole diameter: 20 mm, L / D: 25), the T die temperature is adjusted to 290 ° C., and melt extrusion is performed from a coat hanger type T die (width 150 mm). And was discharged onto a cooling roll having a roll temperature of 163 ° C. to produce an unstretched film having a thickness of 160 μm.

  Next, the unstretched film obtained above was cut out to 96 mm × 96 mm, and successively 240 mm / min at a temperature of 188 ° C. using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, product number: X-6S). Biaxial stretching was performed sequentially so that the stretching ratio was doubled in the order of the machine direction (MD direction) and the transverse direction (TD direction) at the stretching speed of. The stretched film obtained above was quickly taken out from the test apparatus and cooled to obtain an optical film having a thickness of 40 μm.

  The in-plane retardation and thickness direction retardation of the optical film obtained above were 0.4 nm and 1.4 nm, respectively.

  The water absorption rate, thickness direction retardation value and dimensional change rate of the optical film obtained above were examined based on the following methods. The results are shown in Table 1. Also in the following examples and comparative examples, the water absorption rate, the change value of the thickness direction retardation and the dimensional change rate of the optical film were examined based on the following method.

[Water absorption rate]
Using a manual heating press (manufactured by Imoto Seisakusho Co., Ltd., model IMC-180C), resin pellets were melt-pressed at a pressure of 20 MPa at a temperature of 250 ° C. for 2 minutes to form an unstretched film having a thickness of 200 μm Produced. The obtained unstretched film was dried at 80 ° C. for 24 hours, and then its mass (X) was measured.

  Next, the unstretched film obtained above is absorbed in water by storing it in a thermostatic bath at 85 ° C. and a relative humidity of 85%, taken out from the thermostatic bath after 250 hours, and the mass of the unstretched film after water absorption (Y ) Was measured.

The water absorption of the unstretched film is expressed by the formula:
[Water absorption (%)] = [(Y−X) / X] × 100
Based on.

[Change in thickness direction retardation]
After measuring the thickness direction retardation Rth ₁ (590) of the optical film, the optical film is stored in a thermostatic bath having a temperature of 85 ° C. and a relative humidity of 85%, and is taken out from the thermostatic bath after 250 hours. Again, the thickness direction retardation Rth ₂ (590) of the optical film was measured.

Next, the change value of the thickness direction retardation of the optical film is expressed by the formula:
[Change in thickness direction retardation]
= | Thickness direction retardation Rth ₁ (590) −Thickness direction retardation Rth ₂ (590) |
Based on.

[Dimensional change rate]
By cutting the optical film, three square samples having a length of 40 mm and a width of 40 mm were produced. The length of each side of the sample (La1, La2, La3, La4) was measured with a digital caliper.

  Next, the sample is stored in a thermostatic chamber having a temperature of 85 ° C. and a relative humidity of 85%, taken out from the thermostatic chamber after 250 hours, and the length of the four pieces of the sample (Lb1, Lb2, Lb3, Lb4) ) Was measured again.

Next, the dimensional change rate at each side of the three samples is expressed by the formula:
[Dimensional change rate (%)] = | (Lb−La) / La | × 100
(In the formula, La represents the length of one side before the test, and Lb represents the length of one piece after the test)
After obtaining the average value of the dimensional change rate of each side of the three obtained samples, and obtaining the sum of the average value of each side, dividing the sum by 4 The dimensional change rate was used.

Example 2
In a reaction kettle equipped with a stirrer, temperature sensor, cooling pipe and nitrogen gas introduction pipe, 60 parts by weight of n-butyl methacrylate, 40 parts by weight of methacrylic acid, 67.5 parts by weight of toluene as a polymerization solvent and 45 parts by weight of methanol A mixed solvent and an antioxidant (manufactured by ADEKA, trade name: ADK STAB 2112) were added in an amount of 0.05 part by weight, and the temperature was raised to 73 ° C. while passing nitrogen gas through the reaction kettle. At the time when the reflux accompanying the temperature rise starts, dimethyl-2,2′-azobis (2-methylpropionate) [manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-601] as a polymerization initiator. 25 parts by weight was added to the reaction kettle, and dimethyl-2,2′-azobis (2-methylpropionate) [Wako Pure Chemical Industries, Ltd.] was added to a mixed solvent of 5.5 parts by weight of toluene and 3.6 parts by weight of methanol. Kogyo Co., Ltd., trade name: V-601] Performing solution polymerization under reflux at about 71 to 76 ° C. while dropping 0.35 parts by weight of the solution in which the solution was dissolved in the reaction kettle over 2 hours. After completion of the dropwise addition of dimethyl-2,2′-azobis (2-methylpropionate), aging was further performed for 5 hours.

  The content of repeating units derived from methacrylic acid in the (meth) acrylic resin contained in the polymer solution obtained above was 40.1% by weight. Moreover, the weight average molecular weight of the (meth) acrylic resin was 145,000.

  Next, a solution prepared by dissolving 0.1 part by weight of sodium methoxide as a cyclization catalyst in 9.9 parts by weight of methanol is dropped into the polymerization solution in the reaction kettle at a temperature of about 65 to 70 ° C. over 20 minutes. A uniform polymerization solution was obtained.

  Next, the polymer solution obtained above was subjected to a vent type screw having a barrel temperature of 290 ° C., a rotation speed of 70 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1, and a forevent number of 2. It was introduced into a shaft extruder (hole diameter: 15 mm, L / D: 45) at a processing rate of 420 g / h in terms of resin amount, devolatilized in this extruder, and pushed in a shaft residence time of about 3.6 minutes. As a result, a transparent ring structure-containing (meth) acrylic resin pellet was obtained.

  The weight average molecular weight of the ring structure-containing (meth) acrylic resin obtained above was 1280,000, and the glass transition temperature was 98 ° C.

  Next, the pellet obtained above was a barrel type screw twin screw extruder (hole diameter: 15 mm) with a barrel temperature of 290 ° C., a rotation speed of 300 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), and a single vent number. L / D: 45) is introduced from the hopper at a processing speed of 456 g / h in terms of resin amount, and aniline is injected from the hopper after the hopper at a charging speed of 219 g / h. By extruding in about 2 minutes, transparent imide structure-containing (meth) acrylic resin pellets were obtained.

The weight average molecular weight of the imide structure-containing (meth) acrylic resin obtained above was 101,000. The (meth) acrylic resin obtained above has a repeating unit in the formula (I) wherein R ¹ is a methyl group, R ² is a hydrogen atom, and R ³ is a phenyl group. , An imide structure-containing (meth) acrylic resin having a repeating unit in which R ⁴ is a hydrogen atom, R ⁵ is a methyl group, R ⁶ is an n-butyl group, and a glass transition temperature is 161 ° C. there were.

The imidization ratio of the imide structure-containing (meth) acrylic resin obtained above was 61.0%, the content of the repeating unit represented by the formula (II) was 22.9% by weight, and the stress optical coefficient (Cr) was 0. 0.08 × 10 ⁻⁹ Pa ⁻¹ . The acid value of the imide structure-containing (meth) acrylic resin was 1.08 mmol / g.

  Next, the pellet obtained above is put into a single screw extruder (hole diameter: 20 mm, L / D: 25), the T die temperature is adjusted to 285 ° C., and melt extrusion is performed from a coat hanger type T die (width 150 mm). And was discharged onto a cooling roll having a roll temperature of 155 ° C. to produce an unstretched film having a thickness of 160 μm.

  Next, the unstretched film obtained above was cut out to 96 mm × 96 mm, and sequentially 240 mm / min at a temperature of 182 ° C. using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, product number: X-6S). Biaxial stretching was performed sequentially so that the stretching ratio was doubled in the order of the machine direction (MD direction) and the transverse direction (TD direction) at the stretching speed of. The stretched film obtained above was quickly taken out from the test apparatus and cooled to obtain an optical film having a thickness of 40 μm.

  The in-plane retardation and thickness direction retardation of the optical film obtained above were 2.5 nm and 4.8 nm, respectively.

  In the same manner as in Example 1, the water absorption, the change value of the thickness direction retardation and the dimensional change rate of the optical film obtained above were examined. The results are shown in Table 1.

Example 3
In a reaction kettle equipped with a stirrer, temperature sensor, cooling pipe and nitrogen gas introduction pipe, 60 parts by weight of n-butyl methacrylate, 40 parts by weight of methacrylic acid, 67.5 parts by weight of toluene as a polymerization solvent and 45 parts by weight of methanol A mixed solvent and an antioxidant (manufactured by ADEKA, trade name: ADK STAB 2112) were added in an amount of 0.05 part by weight, and the temperature was raised to 73 ° C. while passing nitrogen gas through the reaction kettle. At the time when the reflux accompanying the temperature rise starts, dimethyl-2,2′-azobis (2-methylpropionate) [manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-601] as a polymerization initiator. 25 parts by weight was added to the reaction kettle, and dimethyl-2,2′-azobis (2-methylpropionate) [Wako Pure Chemical Industries, Ltd.] was added to a mixed solvent of 5.5 parts by weight of toluene and 3.6 parts by weight of methanol. Kogyo Co., Ltd., trade name: V-601] Performing solution polymerization under reflux at about 71 to 76 ° C. while dropping 0.35 parts by weight of the solution in which the solution was dissolved in the reaction kettle over 2 hours. After completion of the dropwise addition of dimethyl-2,2′-azobis (2-methylpropionate), aging was further performed for 5 hours.

  The content of repeating units derived from methacrylic acid in the (meth) acrylic resin contained in the polymer solution obtained above was 40.1% by weight. Moreover, the weight average molecular weight of the (meth) acrylic resin was 145,000.

  Next, a solution prepared by dissolving 0.1 part by weight of sodium methoxide as a cyclization catalyst in 9.9 parts by weight of methanol is dropped into the polymerization solution in the reaction kettle at a temperature of about 65 to 70 ° C. over 20 minutes. A uniform polymerization solution was obtained.

  Next, the polymer solution obtained above was subjected to a vent type screw having a barrel temperature of 290 ° C., a rotation speed of 70 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1, and a forevent number of 2. It was introduced into a shaft extruder (hole diameter: 15 mm, L / D: 45) at a processing rate of 420 g / h in terms of resin amount, devolatilized in this extruder, and pushed in a shaft residence time of about 3.6 minutes. As a result, a transparent ring structure-containing (meth) acrylic resin pellet was obtained.

  The weight average molecular weight of the ring structure-containing (meth) acrylic resin obtained above was 1280,000, and the glass transition temperature was 98 ° C.

  Next, the pellet obtained above was a barrel type screw twin screw extruder (hole diameter: 15 mm) with a barrel temperature of 290 ° C., a rotation speed of 300 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), and a single vent number. L / D: 45) is introduced from the hopper at a processing rate of 456 g / h in terms of resin amount, and aniline is injected from the hopper after the hopper at a feed rate of 378 g / h, and the residence time in the shaft is 5 By extruding in about 2 minutes, transparent imide structure-containing (meth) acrylic resin pellets were obtained.

The weight average molecular weight of the imide structure-containing (meth) acrylic resin obtained above was 107,000. The (meth) acrylic resin obtained above has a repeating unit in the formula (I) wherein R ¹ is a methyl group, R ² is a hydrogen atom, and R ³ is a phenyl group. , An imide structure-containing (meth) acrylic resin having a repeating unit in which R ⁴ is a hydrogen atom, R ⁵ is a methyl group, R ⁶ is an n-butyl group, and a glass transition temperature is 162 ° C. there were.

The imidization ratio of the imide structure-containing (meth) acrylic resin obtained above was 61.8%, the content of the repeating unit represented by the formula (II) was 22.6% by weight, and the stress optical coefficient (Cr) was 0. 0.09 × 10 ⁻⁹ Pa ⁻¹ . The acid value of the imide structure-containing (meth) acrylic resin was 0.92 mmol / g.

  Next, the pellet obtained above is put into a single screw extruder (hole diameter: 20 mm, L / D: 25), the T die temperature is adjusted to 285 ° C., and melt extrusion is performed from a coat hanger type T die (width 150 mm). And was discharged onto a cooling roll having a roll temperature of 155 ° C. to produce an unstretched film having a thickness of 160 μm.

  Next, the unstretched film obtained above was cut out to 96 mm × 96 mm, and sequentially 240 mm / min at a temperature of 182 ° C. using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, product number: X-6S). Biaxial stretching was performed sequentially so that the stretching ratio was doubled in the order of the machine direction (MD direction) and the transverse direction (TD direction) at the stretching speed of. The stretched film obtained above was quickly taken out from the test apparatus and cooled to obtain an optical film having a thickness of 40 μm.

  The in-plane retardation and thickness direction retardation of the optical film obtained above were 1.2 nm and 6.1 nm, respectively.

  In the same manner as in Example 1, the water absorption, the change value of the thickness direction retardation and the dimensional change rate of the optical film obtained above were examined. The results are shown in Table 1.

Comparative Example 1
In a reaction kettle equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen gas introduction pipe, 79.4 parts by weight of methyl methacrylate, 20.6 parts by weight of methacrylic acid, 90.0 parts by weight of toluene as a polymerization solvent and 22. A mixed solvent with 5 parts by weight and 0.05 parts by weight of an antioxidant (manufactured by ADEKA, trade name: ADK STAB 2112) were charged, and the temperature was raised to 73 ° C. while passing nitrogen gas into the reaction kettle. At the time when the reflux accompanying the temperature rise starts, dimethyl-2,2′-azobis (2-methylpropionate) [manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-601] as a polymerization initiator. 25 parts by weight was added to the reaction kettle, and dimethyl-2,2′-azobis (2-methylpropionate) [Wako Pure Chemical Industries, Ltd.] was added to a mixed solvent of 7.3 parts by weight of toluene and 1.8 parts by weight of methanol. Kogyo Co., Ltd., trade name: V-601] Performing solution polymerization under reflux at about 71 to 76 ° C. while dropping 0.35 parts by weight of the solution in which the solution was dissolved in the reaction kettle over 2 hours. After completion of the dropwise addition of dimethyl-2,2′-azobis (2-methylpropionate), aging was performed for another 4 hours.

  The content of the repeating unit derived from methacrylic acid in the (meth) acrylic resin contained in the polymer solution obtained above was 20.6% by weight. Moreover, the weight average molecular weight of the (meth) acrylic resin was 110,000.

  Next, a solution prepared by dissolving 0.1 part by weight of sodium methoxide as a cyclization catalyst in 9.9 parts by weight of methanol is dropped into the polymerization solution in the reaction kettle at a temperature of about 65 to 70 ° C. over 20 minutes. A uniform polymerization solution was obtained.

  Next, the polymer solution obtained above was subjected to a vent type screw having a barrel temperature of 290 ° C., a rotation speed of 238 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1, and a forevent number of 2. It is introduced into a shaft extruder (hole diameter: 15 mm, L / D: 45) at a processing rate of 300 g / h in terms of resin amount, devolatilized in this extruder, and pushed in a shaft residence time of about 0.9 minutes. As a result, a transparent ring structure-containing (meth) acrylic resin pellet was obtained.

  The ring structure-containing (meth) acrylic resin obtained above had a weight average molecular weight of 100,000 and a glass transition temperature of 131 ° C.

  Next, the pellet obtained above was a barrel type screw twin screw extruder (hole diameter: 15 mm) with a barrel temperature of 290 ° C., a rotation speed of 300 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), and a single vent number. L / D: 45) is introduced from the hopper at a processing rate of 420 g / h in terms of resin amount, and aniline is injected from the hopper after the hopper at a feeding rate of 101 g / h. By extruding in about 2 minutes, transparent imide structure-containing (meth) acrylic resin pellets were obtained.

The weight average molecular weight of the imide structure-containing (meth) acrylic resin obtained above was 94,000. The (meth) acrylic resin obtained above has a repeating unit in the formula (I) wherein R ¹ is a methyl group, R ² is a hydrogen atom, and R ³ is a phenyl group. , An imide structure-containing (meth) acrylic resin having a repeating unit in which R ⁴ is a hydrogen atom, R ⁵ is a methyl group, R ⁶ is a methyl group, and a glass transition temperature is 169 ° C. .

The imidization ratio of the imide structure-containing (meth) acrylic resin obtained above was 40.8%, the content of the repeating unit represented by the formula (II) was 38.3% by weight, and the stress optical coefficient (Cr) was 0. It was 15 × 10 ⁻⁹ Pa ⁻¹ . The acid value of the imide structure-containing (meth) acrylic resin was 1.42 mmol / g.

  Next, the pellet obtained above is put into a single screw extruder (hole diameter: 20 mm, L / D: 25), the T die temperature is adjusted to 290 ° C., and melt extrusion is performed from a coat hanger type T die (width 150 mm). And was discharged onto a cooling roll having a roll temperature of 165 ° C. to produce an unstretched film having a thickness of 160 μm.

Next, the unstretched film obtained above was cut out into 96 mm × 96 mm, and successively 240 mm / min at a temperature of 189 ° C. using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, product number: X-6S). Biaxial stretching was performed sequentially so that the stretching ratio was doubled in the order of the machine direction (MD direction) and the transverse direction (TD direction) at the stretching speed of. The stretched film obtained above was quickly taken out from the test apparatus and cooled to obtain an optical film having a thickness of 40 μm.
Then, the film was taken out from the test apparatus and cooled to obtain an optical film having a thickness of 40 μm.

  The in-plane retardation and thickness direction retardation of the optical film obtained above were 1.5 nm and 7.2 nm, respectively.

  In the same manner as in Example 1, the water absorption, the change value of the thickness direction retardation and the dimensional change rate of the optical film obtained above were examined. The results are shown in Table 1.

  From the results shown in Table 1, each of the optical films obtained in each example has a low water absorption rate of the unstretched film compared to the optical film obtained in Comparative Example 1, and the thickness of the stretched film. It turns out that it has the outstanding property that a length direction phase difference change value and a dimensional change rate are small.

  Next, the in-plane retardation, thickness direction retardation, photoelastic coefficient, and linear expansion coefficient of the optical film obtained in each Example and Comparative Example 1 were examined. The results are shown in Table 2. Further, as physical properties of these optical films, haze, total light transmittance, number of MIT folding resistance tests, film impact strength, and pencil hardness were examined according to the following methods. The results are shown in Table 2. Table 2 shows the glass transition temperature of the imide structure-containing (meth) acrylic resin as an index of heat resistance of the optical film.

(1) Haze and total light transmittance Haze and total light transmittance were measured using a turbidimeter [Nippon Denshoku Industries Co., Ltd., product number: NDH 5000].

(2) MIT fold resistance test number The MIT fold resistance test number was determined by cutting an optical film into 15 mm length and 90 mm length according to JIS P8115, and using the obtained test piece, an MIT fold resistance test machine [ Tester Sangyo Co., Ltd., product number: BE-201], and a load of 200 g was applied in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50%.

(3) Film impact strength The film impact strength was measured according to ASTM D3420 in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% using a film impact tester [Tester Sangyo Co., Ltd., product number: BU-302]. .

(4) Pencil Hardness According to JIS K5600-5-4 (1999), a pencil scratch hardness tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) was used and measured at a load of 750 g.

From the results shown in Tables 1 and 2, all of the optical films obtained in each Example have a low water absorption, a small change in thickness direction retardation under wet heat, and a dimensional change under wet heat. It can be seen that it has excellent properties such as a low rate, excellent heat resistance, and a small photoelastic coefficient.

Claims (9)

  An imide structure-containing (meth) acrylic resin using a (meth) acrylic resin obtained by polymerizing a monomer component containing a (meth) acrylic monomer as a raw material, wherein the (meth) acrylic monomer is an alkyl (Meth) acrylic acid alkyl ester having 2 to 6 carbon atoms and (meth) acrylic monomer containing (meth) acrylic acid and having a glass transition temperature of 150 ° C. or higher Structure-containing (meth) acrylic resin. Imide structure-containing (meth) acrylic resin is represented by the formula (I):

(In the formula, R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R ³ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or an alkyl group having 3 to 12 carbon atoms. A cycloalkyl group or an aryl group having 6 to 10 carbon atoms)
Repeating units represented by the formula (II):

(Wherein R ⁴ and R ⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 2 to 6 carbon atoms)
The imide structure containing (meth) acrylic resin of Claim 1 which has a repeating unit represented by these. The imide structure-containing (meth) acrylic resin according to claim 2, wherein R ³ in formula (I) is a cycloalkyl group having 3 to 12 carbon atoms or an aryl group having 6 to 10 carbon atoms.   The imide according to any one of claims 1 to 3, wherein the (meth) acrylic resin has 5 to 85% by weight of the repeating unit represented by the formula (I) and 15 to 95% by weight of the repeating unit represented by the formula (II). Structure-containing (meth) acrylic resin. 5. The imide structure-containing (meth) acrylic resin according to claim 1, wherein the absolute value of the stress optical coefficient (Cr) is 0.3 × 10 ⁻⁹ Pa ⁻¹ or less.   A method for producing an imide structure-containing (meth) acrylic resin using a (meth) acrylic resin obtained by polymerizing a monomer component containing a (meth) acrylic monomer as a raw material, wherein the monomer component is an alkyl ester A method for producing an imide structure-containing (meth) acrylic resin, comprising using a monomer component containing (meth) acrylic acid alkyl ester having 2 to 6 carbon atoms and (meth) acrylic acid.   An optical film comprising the imide structure-containing (meth) acrylic resin according to claim 1.   The optical film according to claim 7, wherein a transparent conductive layer is formed on at least one surface. An image display device comprising the optical film according to claim 7.