JP5475367B2 - N-vinylcarbazole copolymer retardation film and method for producing N-vinylcarbazole copolymer retardation film - Google Patents

Description

  The present invention relates to a retardation film composed of a copolymer using at least N-vinylcarbazole as a raw material, and a method for producing an N-vinylcarbazole copolymer retardation film.

  In recent years, the application range of liquid crystal displays has expanded from display boards such as calculators and digital clocks to computer displays and liquid crystal televisions, and is becoming indispensable for our lives. A liquid crystal display generally has a configuration in which a liquid crystal cell is sandwiched between two polarizing plates. Polarized light that has passed through an incident-side polarizing plate is twisted by the liquid crystal cell and passed through an outgoing-side polarizing plate. At this time, light control is performed depending on the presence or absence of voltage load on the liquid crystal cell.

  Here, in a liquid crystal cell of a liquid crystal display, a phenomenon called wavelength dispersion occurs in which the phase of incident light is shifted depending on the wavelength. As display methods for liquid crystal displays, STN, TN, VA, IPS, OCB, and the like are known. In particular, STN liquid crystal displays have a large twist angle of 180 to 270 ° in the liquid crystal cell. Therefore, the phase shift is large. As a result, there is a problem that the liquid crystal display is colored.

  In order to solve the above problem, a phase difference film exhibiting wavelength dispersion, that is, reverse wavelength dispersion, in which birefringence becomes smaller as the wavelength of light is shorter, is combined with a liquid crystal cell. In addition to the optical compensation described above, a retardation film exhibiting reverse wavelength dispersion is also used for improving the contrast in the oblique direction of a VA liquid crystal display. It is also applied to an antireflection 1 / 4λ plate of an organic EL display.

  As the resin material constituting the retardation film, a copolymer containing an N-vinylcarbazole unit is used because it has a high glass transition temperature and excellent heat resistance and a high refractive index.

  For example, Patent Document 1 discloses an optical resin composition containing a polymer containing N-vinylcarbazole as a main monomer component, which has excellent moldability and small birefringence.

  Patent Document 2 describes an electroluminescent device in which N-vinylcarbazole is copolymerized as a charge transporting compound.

  Further, Patent Documents 3 to 4 disclose an optical film made of a copolymer of N-vinylcarbazole, particularly a retardation plate.

  However, the conventional N-vinylcarbazole copolymer is colored light yellow to light brown. Furthermore, since the casting method is costly when forming into a film shape, generally, heat forming such as melt extrusion forming or hot press forming is performed, and this heating increases the degree of coloring. As a result, there is a problem that light absorption occurs in the visible light region and the light transmittance is lowered.

  In addition, since N-vinylcarbazole is generally isolated and purified from coal tar, a compound having a similar chemical structure is mixed therein. Some of these similar compounds emit a unique odor and remain after the copolymerization, which causes a problem that a unique odor remains in the N-vinylcarbazole copolymer film.

JP 58-162617 A JP-A-7-188340 JP 2009-102625 A JP 2009-138069 A

  As described above, the N-vinylcarbazole copolymer film has been conventionally used as a retardation film or the like, but there is a problem that light transmittance in the visible light region is reduced due to coloring. Further, the N-vinylcarbazole copolymer has a problem that it has a unique odor.

  Accordingly, the present invention relates to a method for producing an N-vinylcarbazole copolymer retardation film in which coloring and odor are remarkably suppressed, and an N-vinylcarbazole copolymer retardation in which coloring and odor are remarkably suppressed. The object is to provide a film.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, it was found that if a high-purity carbazole which is a raw material compound of N-vinylcarbazole is used, an N-vinylcarbazole copolymer retardation film in which coloring and odor are remarkably suppressed can be produced. Was completed.

  In more detail, the present inventors first considered the purification of N-vinylcarbazole to increase the purity of the copolymer. However, it is extremely difficult to remove impurities contained in the layered N-vinylcarbazole. Thus, the coloration and odor of the copolymer could not be reduced. Therefore, an attempt was made to identify a compound that causes coloring and odor, and to examine means for reducing the compound, but the cause compound was not identified. That is, carbazole, which is a raw material of N-vinylcarbazole, is isolated and purified from crude oil, but tends to be contaminated with impurities derived from crude oil. For example, the purity of a commercially available carbazole product is about 95%, It can be said that there are relatively many types and quantities. In addition, it was not possible to determine whether the coloring-causing compound was a trace amount and caused coloring and odor. However, the present inventors thoroughly refined carbazole as a raw material compound, synthesized N-vinylcarbazole from the obtained high-purity carbazole, and copolymerized it. As a result, coloring and odor were significantly suppressed. We succeeded in obtaining the phase difference film.

  The method for producing an N-vinylcarbazole copolymer retardation film according to the present invention completed by the above-described research is a step of synthesizing N-vinylcarbazole from carbazole having a purity of 99.0% by mass or more; 1% by mass or more, 15% by mass. % Of N-vinyl carbazole and a monomer group containing 85% by mass or more and 99% by mass or less of a (meth) acrylic acid monomer; and the obtained copolymer is thermoformed into a film. Including a process.

  As the (meth) acrylic acid monomer, at least methyl methacrylate and 2- (hydroxymethyl) methyl acrylate are used, and the adjacent methyl methacrylate unit and 2- (hydroxymethyl) methyl acrylate unit are dealcoholated. It is preferable to carry out a step of forming a lactone ring structure by polycondensation. The N-vinylcarbazole copolymer phase difference film introduced with such a ring structure is extremely excellent in heat resistance.

  The N-vinylcarbazole copolymer phase difference film according to the present invention is remarkably suppressed in coloration, and the rate of change in YI value before and after heating at 280 ° C. for 20 minutes is 3.5 times or less. It is characterized by being.

  As the N-vinylcarbazole copolymer retardation film according to the present invention, those showing reverse wavelength dispersion are suitable.

  According to the method of the present invention, it is possible to produce an N-vinylcarbazole copolymer retardation film in which coloring and odor are remarkably suppressed as compared with the prior art.

  In addition, the conventional N-vinylcarbazole copolymer containing a relatively large amount of coloring substances increases the degree of coloration by heating when melt-molded, whereas the N-vinylcarbazole copolymer retardation according to the present invention is increased. Even if the film undergoes thermoforming, an increase in the degree of coloring can be suppressed.

  Therefore, the N-vinylcarbazole copolymer retardation film according to the present invention is very practical as light absorption in the visible light region is suppressed and odor is also suppressed.

It is a chart presumed to be a thing of N-methyl carbazole among the mass spectrum charts obtained by GS-MS analysis of the odor emitted from a N-vinyl carbazole polymer. It is a chart presumed to be a thing of dihydroacridine among the mass spectrum charts obtained by GS-MS analysis of the odor emitted from an N-vinyl carbazole polymer. It is a chart presumed to be azafluorene among the mass spectrum charts obtained by GS-MS analysis of the odor emitted from an N-vinylcarbazole polymer. It is a chart presumed to be a thing of methyl acridine among the mass spectrum charts obtained by GS-MS analysis of the odor emitted from a N-vinyl carbazole polymer. It is a chart presumed to be an ethyl acridine thing among the mass spectrum charts obtained by GS-MS analysis of the odor emitted from a N-vinyl carbazole polymer.

  Hereinafter, the method of the present invention will be described in the order of execution.

1. Step of synthesizing N-vinylcarbazole In the method of the present invention, carbazole having a purity of 99.0% by mass or more is used as a raw material. Since carbazole is generally isolated and refined from crude oil, it is an impurity derived from crude oil, and in particular, those having a structure and physical properties similar to carbazole are mixed therein, so that the purity of commercially available products is relatively low.

  If the purity of the carbazole as a raw material is 99.0% by mass or more, even if N-vinylcarbazole is synthesized from carbazole and further copolymerized, coloring and odor of the resulting N-vinylcarbazole copolymer are suppressed. Moreover, even if the copolymer is melt-molded, an increase in the degree of coloring is suppressed. Since this effect becomes more excellent as the purity of carbazole is higher, the purity is more preferably 99.1% by mass or more, and further preferably 99.2% by mass or more.

Examples of the carbazole purification method include distillation, azeotropic distillation, extraction and recrystallization. More specifically, since the boiling point of carbazole is 355 ° C., a fraction showing such boiling point is collected in a general distillation. As azeotropic agents used for azeotropic distillation of carbazole, monohydric alcohols, polyalkylene glycols and the like are known. As a solvent used for extraction, toluene, benzene, chlorotoluene, or the like is used. As a solvent used for recrystallization, C _1-6 alcohol or the like is used in addition to the extraction solvent.

  In the present invention, purification is repeated until the purity of the carbazole as a raw material becomes 99.0% by mass or more. For this purity, for example, carbazole cannot be completely purified by general distillation alone, so different purification methods are combined or the same purification is repeated until the desired purity is achieved.

  Next, N-vinylcarbazole is synthesized using the obtained high-purity carbazole as a raw material. As a method for synthesizing N-vinylcarbazole from carbazole, there are mainly a Reppe method and an intramolecular dehydration method.

  The Reppe method is a method in which acetylene is reacted with carbazole in a solvent. The reaction conditions are not particularly limited. For example, carbazole is dissolved in a solvent such as dimethylformamide or dimethylacetamide, and acetylene is added. A strong base such as sodium hydroxide or potassium carbazole may be added as a catalyst. The reaction temperature can be about 100 ° C. or higher and 200 ° C. or lower. Further, the reaction is carried out in a closed system so that acetylene does not evaporate, and the reaction is preferably carried out under pressure. More specifically, Japanese Patent Laid-Open No. 48-68564 may be referred to.

  The intramolecular dehydration method is a method for obtaining N- (2-hydroxyethyl) carbazole from carbazole and further obtaining N-vinylcarbazole by intramolecular dehydration. The conditions for the intramolecular dehydration reaction are not particularly limited. For example, N- (2-hydroxyethyl) carbazole is dissolved in an aromatic hydrocarbon solvent such as toluene, vaporized and passed through the catalyst packed bed, and the intramolecular dehydration is performed. Can be made. Examples of the dehydration catalyst include those containing silica and an alkali metal element. The dehydration temperature may be about 300 ° C. or more and 1000 ° C. or less. More specifically, for example, the pamphlet of International Publication No. 2006/046540 may be referred to.

2. Copolymerization Step In the method of the present invention, a monomer group containing 1% by mass or more and 15% by mass or less of N-vinylcarbazole and 85% by mass or more and 99% by mass or less of a (meth) acrylic acid monomer is copolymerized.

  Since the N-vinylcarbazole unit in the copolymer is widely known to exhibit a large refractive index and a high glass transition temperature, N-vinylcarbazole as a monomer is a synthetic intermediate of a dye or a photoconductive material, Or it is very useful as a raw material for manufacturing a thermoplastic resin material. In particular, in thermoplastic resin materials, heat resistance is improved by the N-vinylcarbazole unit, which is suitable for thermoforming.

  The proportion of N-vinylcarbazole in the monomer group is preferably 1% by mass or more and 15% by mass or less. If the said ratio is 1 mass% or more, the heat resistant improvement effect and favorable refractive property of a copolymer will be acquired. On the other hand, if the ratio is too high, the retardation film may show a negative retardation, and therefore the ratio is preferably 15% by mass or less. As the said ratio, 2 mass% or more and 12 mass% or less are more preferable, and 3 mass% or more and 10 mass% or less are more preferable.

  In the present invention, a (meth) acrylic acid monomer is used in addition to N-vinylcarbazole. The (meth) acrylic acid monomer unit in the copolymer shows not only transparency, but also surface gloss and weather resistance, and has a good balance of mechanical strength, molding processability, and surface hardness. Widely used in However, since the glass transition temperature of the (meth) acrylic acid polymer is around 100 ° C. and the heat resistance is not sufficient, in the present invention, it is a copolymer with N-vinylcarbazole.

  The proportion of the (meth) acrylic acid monomer in the monomer group is preferably 85% by mass or more and 99% by mass or less. If the said ratio is 85 mass% or more, the outstanding characteristic of the (meth) acrylic-acid type monomer unit mentioned above can fully be provided to a copolymer. On the other hand, if the ratio is too high, heat resistance may not be sufficiently obtained, and therefore the ratio is preferably 99% by mass or less. As the said ratio, 87 mass% or more and 95 mass% or less are further more preferable.

  Examples of (meth) acrylic acid monomers include (meth) acrylic acid such as acrylic acid, methacrylic acid, and crotonic acid; methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, Acrylic acid esters such as t-butyl acrylate, cyclohexyl acrylate, benzyl acrylate, carbazoyl ethyl acrylate, phenyl acrylate, naphthyl acrylate, anthracenyl acrylate, isobornyl acrylate; methyl methacrylate, ethyl methacrylate, methacryl Propyl acid, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, carbazoyl ethyl methacrylate, phenyl methacrylate, methacrylate Methacrylic acid esters such as naphthyl acid, anthracenyl methacrylate, isobornyl methacrylate; methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, 2- (hydroxy Examples thereof include 2-substituted (meth) acrylic acid alkyl esters such as methyl) normal butyl acrylate and t-butyl 2- (hydroxymethyl) acrylate.

  In the present invention, in addition to N-vinylcarbazole and (meth) acrylic acid monomers, N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam, N-vinyl-2-piperidone, N-vinyl-4- Vinyl lactam monomers such as methyl-2-pyrrolidone, N-methyl-5-methyl-2-pyrrolidone, N-vinyl-ω-heptalactam, styrene, vinyl naphthalene, vinyl toluene, α-methyl styrene, acrylonitrile, One or more monomers such as methyl vinyl ketone, ethylene, propylene, and vinyl acetate may be used.

  Although the usage-amount in the case of using monomers other than N-vinyl carbazole and a (meth) acrylic-acid type monomer should just be adjusted suitably, it is preferable to set it as 0.5 mass% or more and 10 mass% or less. Of course, when only N-vinylcarbazole and (meth) acrylic acid monomer are used, the total of N-vinylcarbazole and (meth) acrylic acid monomer in the monomer group is 100% by mass. When other monomers are used, the total amount of N-vinylcarbazole, (meth) acrylic acid monomers and other monomers is 100% by mass.

  In the method of the present invention, a monomer group including N-vinylcarbazole and a (meth) acrylic acid-based monomer and other optional monomers is copolymerized.

  As the solvent used in the polymerization reaction, any solvent can be used without particular limitation as long as it can appropriately dissolve monomers and does not inhibit the polymerization reaction. For example, aromatic hydrocarbon solvents such as toluene; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; and mixed solvents thereof can be used. Moreover, when performing photopolymerization, you may use reactive solvents, such as N-vinyl pyrrolidone. What is necessary is just to adjust the usage-amount of a solvent suitably according to the solubility with respect to a monomer.

  As a polymerization initiator used in the polymerization reaction, an organic peroxide, an azo compound, a mixture of hydrogen peroxide and a metal salt, or the like can be used.

  Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 1,1′-di-t-butylperoxy-3,3. , 5-trimethylenecyclohexane, 1,3-di- (t-butylperoxy) -diisopropylbenzene, di-t-butyl peroxide, t-butyl hydroperoxide, t-butylperoxy-2-ethylhexanoate, t- Mention may be made of butyl peroxypivalate, t-amyl peroxy-2-ethylhexanoate, t-amyl hydroperoxide. Among these organic peroxides, t-butyl hydroperoxide and t-amylperoxy-2-ethylhexanoate are preferable, and t-amylperoxy-2-ethylhexanoate is particularly preferable. Only one organic peroxide may be selected and used, or two or more organic peroxides may be selected and used in combination.

  Examples of the azo compound include 2,2′-azobis (isobutyronitrile), 2,2′-azobis (2-methylbutyronitrile), and 2,2′-azobis (2,4-dimethylvaleronitrile). 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (isobutyric acid) dimethyl, 4,4′-azobis (4-cyanovaleric acid), 2,2 '-Azobis (2-methylpropionamidine) dihydrochloride, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] hydrate, 2,2'-azobis [2- ( 2-Imidazolin-2-yl) propane] dihydrate, 1,1′-azobis (cyclohexane-1-carbonitrile). Among these azo compounds, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (isobutyric acid) dimethyl, 2,2′-azobis (2-methylpropionamidine) dihydrochloride Is preferred. Only one azo compound may be selected and used, or two or more azo compounds may be selected and used in combination.

  As the polymerization reaction, a so-called photopolymerization reaction may be performed. Examples of the polymerization initiator for the photopolymerization reaction include benzophenone, hydroxybenzophenone, bis-N, N-dimethylaminobenzophenone, bis-N, N-diethylaminobenzophenone, 4-methoxy-4′-dimethylaminobenzophenone, and the like. Benzophenones and salts thereof; thioxanthones such as thioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, chlorothioxanthone and isopropoxycyclothioxanthone and salts thereof; anthraquinones such as ethyl anthraquinone, benzanthraquinone, aminoanthraquinone and chloroanthraquinone; acetophenone Benzoin ethers such as benzoin methyl ether; benzoin ethers such as benzoin methyl ether; 2,4 6-trihalomethyltriazines; 1-hydroxycyclohexyl phenyl ketone, 2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di (m-methoxyphenyl) ) Imidazole dimer, 2- (o-methoxyphenyl) -4,5-diphenylimidazole dimer, 2- (p-methoxyphenyl) -4,5-diphenylimidazole dimer, 2- (p-methoxy) Imidazoles such as phenyl) -5-phenylimidazole dimer, 2- (2,4-dimethoxyphenyl) -4,5-diphenylimidazole dimer, 2,4,5-triarylimidazole dimer; benzyl Dimethyl ketal, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) butan-1-o 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- [4- (2-hydroxy Ethoxy) phenyl] -2-hydroxy-2-methyl-1-propan-1-one, phenanthrenequinone, 9,10-phenanthrenequinone, methylbenzoin, ethylbenzoin, and other benzoins; 9-phenylacridine, 1,7- Acridine derivatives such as bis (9,9′-acridinyl) heptane; phosphine oxides such as bisacylphosphine oxide, bisphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide; 4 -(2-Hydroxyethoxy) phenyl- (2-hydride) Roxy-2-propyl) ketone and its ethylene oxides.

  The amount of the polymerization initiator used is not particularly limited as long as it is appropriately adjusted according to the type and concentration of the monomer. For example, it is 0.001 part by mass or more and 3 parts by mass or less with respect to 100 parts by mass of the monomer. 0.005 mass part or more and 2 mass parts or less are preferable.

  A chain transfer agent, a pH adjuster, a buffering agent, and the like can be added to the reaction mixture for polymerization as necessary.

  The polymerization reaction can be started by raising the temperature of the reaction solution or irradiating with ultraviolet rays or electron beams. Usually, the temperature of the reaction solution is raised to about 100 ° C. in order to start the polymerization reaction. What is necessary is just to maintain the reaction temperature after reaction start at about 60 degreeC or more and 200 degrees C or less. When the reaction temperature exceeds the boiling point of the reaction solution, pressure may be applied.

  The reaction time is not particularly limited, and the progress of the reaction may be confirmed by chromatography, or may be appropriately determined by preliminary experiments, etc., but can usually be about 1 hour or more and 20 hours or less.

  After completion of the reaction, the copolymer may be separated by a conventional method. For example, the solvent may be distilled off from the reaction solution under reduced pressure, and further heated and dried under normal pressure or reduced pressure.

3. Intramolecular cyclization step In order to further improve the heat resistance of the copolymer, an intramolecular cyclization reaction may be carried out to form a ring structure. Examples of such a ring structure include a lactone ring structure, an imide ring structure, a lactam ring structure, a cyclic acid anhydride structure, and an aliphatic hydrocarbon ring structure. Hereinafter, the lactone ring structure, glutarimide structure, glutaric anhydride structure, N-substituted maleimide structure and maleic anhydride structure will be described as examples.

(1) Lactone ring structure Examples of the lactone ring structure include the following structures.

[In the above formula, R ^{1 to} R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom]

Examples of the organic residue include C _1-20 alkyl groups such as a methyl group, an ethyl group, and a propyl group; C _1-20 unsaturated aliphatic hydrocarbon groups such as an ethenyl group and a propenyl group; a phenyl group and a naphthyl group And C _6-20 aromatic hydrocarbon groups. In the above group, one or more hydrogen atoms may be substituted with one or more groups selected from the group consisting of a hydroxyl group, a carboxy group, an ether group and an ester group.

The lactone ring structure is adjacent to the obtained copolymer after copolymerization of a monomer group including, for example, methyl methacrylate (MMA) and methyl 2- (hydroxymethyl) acrylate (MHMA). It can be formed by dealcoholization cyclocondensation of MMA units and MHMA units. In this case, R ¹ is a hydrogen atom, and R ² and R ³ are methyl groups.

(2) Glutarimide structure and glutaric anhydride structure Examples of the glutarimide structure and glutaric anhydride structure include the following structures.

[Wherein, R ⁴ and R ⁵ each independently represent a hydrogen atom or a methyl group, and X ¹ represents an oxygen atom or a nitrogen atom. However, when X ¹ is an oxygen atom, R ⁶ is not present, and when X ¹ is a nitrogen atom, R ⁶ is a hydrogen atom, a C _1-6 linear alkyl group, a C _3-8 cycloalkyl group or C _{6-10 represents an} aromatic hydrocarbon group. ]

_{Examples of the} C _3-8 cycloalkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. _{Examples of the} C _1-6 linear alkyl group include those that are linear and have 1 to 6 carbon atoms among the aforementioned C _1-20 alkyl groups. Examples of the C _6-10 aromatic hydrocarbon group include those having 6 to 10 carbon atoms among the aforementioned C _6-20 aromatic hydrocarbon groups.

In the above formula, when X ¹ is a nitrogen atom, the structure is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

In the above formula, when X ¹ is an oxygen atom, the above structure becomes a glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by subjecting a copolymer of (meth) acrylic acid ester and (meth) acrylic acid to dealcoholization cyclocondensation in the molecule.

(3) N-substituted maleimide structure and maleic anhydride structure Examples of the N-substituted maleimide structure and maleic anhydride structure include the following structures.

[Wherein, R ⁷ and R ⁸ each independently represent a hydrogen atom or a methyl group, and X ² represents an oxygen atom or a nitrogen atom. However, when X ² is an oxygen atom, R ⁹ does not exist, and when X ² is a nitrogen atom, R ⁹ is a hydrogen atom, a C _1-6 linear alkyl group, a C _3-8 cycloalkyl group or C _{6-10 represents an} aromatic hydrocarbon group. ]

Examples of the C _1-6 linear alkyl group, the C _3-8 cycloalkyl group, and the C _6-10 aromatic hydrocarbon group include the same ones as described above.

In the above formula, when X ² is a nitrogen atom, the structure is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

In the above formula, when X ² is an oxygen atom, the structure is a maleic anhydride structure. The maleic anhydride structure can be formed, for example, by copolymerizing maleic anhydride and (meth) acrylic acid ester.

4). Thermoforming process In the method of the present invention, the obtained copolymer is thermoformed to form a film.

  The conditions for the heat molding may be ordinary ones known to those skilled in the art. For example, in the case of hot press molding, the heating temperature is preferably not less than the glass transition temperature and not less than the glass transition temperature + 20 ° C., and in the case of melt extrusion molding, it is preferably not less than the melting point and not more than the melting point + 20 ° C.

5-1. Stretching process Next, if necessary, the obtained film may be stretched. By such stretching, a reverse wavelength dispersion type retardation film can be obtained.

  The film may be uniaxially stretched or biaxially stretched. The draw ratio may be adjusted as appropriate, but can usually be about 1.1 to 5 times. Moreover, when biaxially stretching, it may be sequentially stretched in two directions or simultaneously.

5-2. Lamination process In addition to before or after the stretching process, or in place of the stretching process, another film may be optionally laminated. For example, when the film obtained by the above method exhibits a negative intrinsic birefringence, it is possible to impart reverse wavelength dispersion by laminating films exhibiting a positive intrinsic birefringence. In that case, the orientation direction (optical axis) of both films is made orthogonal. Moreover, as a bonding method of both films, a method using an adhesive or a pressure-sensitive adhesive, and a method of stretching a coextruded film can be mentioned.

  The N-vinylcarbazole copolymer retardation film produced by the method of the present invention is suppressed in coloring, and has a low YI value indicating yellowing and a b value indicating yellowishness. In addition, the degree of coloring is remarkably suppressed even when subjected to a thermal history in a melt molding process or the like. More specifically, the change rate of the YI value before and after heating at 280 ° C. for 20 minutes is 3.5 times or less. The rate of change is preferably 3.0 times or less. Moreover, the change rate of b value before and behind the heat processing is 2.5 times or less. The change rate is preferably 2.0 times or less.

  In general, when the polymer contains a substance that causes coloring, the degree of coloring increases due to the thermal history. Therefore, since the YI value after the heat treatment is larger than the YI value before the heat treatment, the change rate of the YI value before and after heating at 280 ° C. for 20 minutes, that is, the YI value after the heat treatment is the YI value before the heat treatment. The value divided by is 1.0 times or more. The same applies to the b value.

  In the conventional N-vinylcarbazole copolymer, the copolymer itself is colored, and the degree of coloring is further increased by heat treatment. Therefore, the retardation film of N-vinylcarbazole copolymer formed by heating is colored from yellow to brown, and light absorption in the visible light region becomes a problem. On the other hand, the N-vinylcarbazole copolymer retardation film according to the present invention is probably due to the high purity of the raw material carbazole and the reduced amount of the color-causing substance. Even if it exists, coloring is suppressed notably. Therefore, the N-vinylcarbazole copolymer retardation film according to the present invention is extremely useful as a constituent member of a display, etc., compared to conventional films.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  In addition, evaluation of the copolymer was implemented on condition of the following.

Test Example 1 Measurement of Weight Average Molecular Weight The weight average molecular weight of the copolymer was determined by polystyrene conversion using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement are as follows.
Column: TSK-GEL superHZM-M 6.0 × 150 2 in series
TSK-GEL superHZ-L 4.6 × 35 1 column Reference column: TSK-GEL superH-RC 6.0 × 150
Two in series Eluent: Chloroform, Flow rate: 0.6 mL / min Column temperature: 40 ° C

Test Example 2 Measurement of Glass Transition Temperature The glass transition temperature (Tg) of the copolymer was determined according to JIS K7121. Specifically, a differential scanning calorimeter (manufactured by Rigaku Corporation, DSC-8230) was used, and a sample of about 10 mg was heated from room temperature to 200 ° C. at a heating rate of 20 ° C./min in a nitrogen gas atmosphere. The glass transition temperature was determined from the DSC curve by the starting point method. Α-alumina was used as a reference.

Test Example 3 Measurement of 5% Weight Reduction Temperature The 5% weight reduction temperature of the copolymer, that is, the temperature at which the weight decreased by 5% when the copolymer was heated at a constant rate was measured. Specifically, using a differential calorimetric balance (manufactured by Rigaku Corporation, TG-8120), a 10 mg sample was heated at a heating rate of 10 ° C./min and measured in a nitrogen atmosphere.

Test Example 4 Measurement of Hue (YI Value) The copolymer was dissolved in chloroform to obtain a 15% by mass solution. The hue (YI value) of the obtained solution was measured with a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., ZE6000).

  Moreover, after heating a copolymer at 280 degreeC for 20 minute (s), YI value was measured similarly and the rate of change of YI value before and behind heating was computed.

Test Example 5 Odor Measurement A copolymer is dissolved in acetone to prepare a 5% by mass solution, and the autosampler is used to split the solution into an inlet of a gas chromatograph mass spectrometer (manufactured by ThermoQuest, PolarisQ). 1 μL was injected and the solution was analyzed under the following conditions.
Measurement mass range: M / c = 30 to 600
Fragment ion generation method: EI method Constant temperature bath temperature: 40 ° C. for 5 minutes → 5 ° C./minute temperature increase → 320 ° C. for 20 minutes Carrier gas: He
Gas flow rate: 1 mL / min Inlet temperature: 250 ° C
Send ratio to column by split method: 1/49
Column: InertCap-1MS, nonpolar, inner diameter 0.25 mm × 30 m, film thickness 0.25 μm

Test Example 6 Measurement of Hue (b Value) The b value of the copolymer film was measured with a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., ZE6000).

  Moreover, after heating a copolymer at 280 degreeC for 20 minute (s), b value was measured similarly.

Example 1 Production of Copolymer Film According to the Present Invention (1) Purification of carbazole A commercially available carbazole having a purity of 95% was added to acetone and stirred, and the mixture was heated to 50 ° C. to completely remove carbazole. Dissolved. The solution was allowed to stand, and the precipitated crystals were separated by filtration and washed with methanol. By repeating this operation, carbazole having a purity of 99.2% by mass was obtained. The purity of carbazole was analyzed using gas chromatography (Shimadzu Corporation, GC-2010, column: ULBON-HR1, 0.25 mmφ × 50 m, 0.25 μm, manufactured by Shinwa Kako).

(2) Synthesis of N-vinylcarbazole The carbazole having a purity of 99.2% by mass obtained in the above (1) and potassium hydroxide were added to a mixed solvent of xylene and dimethyl sulfoxide. Further, acetylene gas was added to seal the reaction vessel, and the reaction was performed at 120 ° C. or higher in an autoclave. The reaction solution was analyzed by thin layer chromatography in a timely manner to confirm the residual state of the raw material carbazole, and when the raw material carbazole could not be confirmed, the reaction was terminated. After completion of the reaction, the reaction solution was concentrated under reduced pressure to remove the low boiling fraction, and further distilled under reduced pressure to obtain crude N-vinylcarbazole. The obtained crude N-vinylcarbazole was dissolved in methanol, and insoluble matters were filtered off. The solution was cooled, and the precipitated crystals were filtered. By repeating this recrystallization operation, N-vinylcarbazole having a purity of 99.9% by mass was obtained. The purity was measured by the same method as in (1) above.

(3) Copolymerization reaction A reactor equipped with a stirrer, a temperature sensor, a cooling tube and a nitrogen introduction tube was added to 25 parts by mass of methyl 2- (hydroxymethyl) acrylate, 58 parts by mass of methyl methacrylate, and n-butyl methacrylate. 10 parts by mass, 7 parts by mass of N-vinylcarbazole synthesized in the above (2), and 90 parts by mass of toluene were charged. The temperature of the reaction mixture was raised to 105 ° C. while introducing nitrogen gas into the reaction vessel. When the refluxing was started, 0.04 parts by mass of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator. Further, a copolymerization reaction was carried out at reflux at about 105 to 110 ° C. for 4 hours while dropping a solution prepared by dissolving 0.08 parts by mass of t-amylperoxyisononanoate in 10 parts by mass of toluene over 3 hours. .

  After completion of the reaction, 0.9 part by mass of an octyl phosphate / dioctyl mixture was added to the obtained copolymer solution, and the mixture was refluxed at 80 to 105 ° C. for 2 hours to carry out a cyclization condensation reaction. Furthermore, it heated at 240 degreeC for 90 minute (s) in the autoclave. The obtained copolymer solution was concentrated at 240 ° C. under reduced pressure for 1 hour to obtain a transparent copolymer having a lactone ring structure in the main chain.

(4) Heat molding The copolymer obtained in (3) above was press-molded at 250 ° C with a press molding machine to obtain a film having a thickness of about 140 µm. Next, the film was uniaxially stretched at a free end at Tg + 5 ° C. so that the stretch ratio was doubled to obtain a stretched film having a thickness of 100 μm.

  The in-plane retardation of the obtained film was measured at a measurement wavelength of 590 nm, 447 nm and 750 nm with a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR). The ratio (R / R0) between the phase differences R and R0 at other measurement wavelengths was calculated using the in-plane phase difference when the measurement wavelength was 590 nm as a reference (R0).

Comparative Example 1 Production of Film Consisting of Copolymer from Crude Carbazole (1) Synthesis of N-Vinylcarbazole Purity in the same manner as in Example 1 (2) except that commercial carbazole having a purity of 95% was used. 98.7% by mass of N-vinylcarbazole was obtained. Although the recrystallization operation was repeated, the purity of N-vinylcarbazole did not exceed 98.7% by mass.

(2) Copolymerization reaction and film formation A copolymer having a lactone ring structure in the main chain was obtained in the same manner as in Example 1 (3) except that the N-vinylcarbazole obtained in (1) above was used. It was. Moreover, it carried out similarly to the said Example 1 (4), the stretched film was obtained from the said copolymer, and the in-plane phase difference was measured.

  Table 1 shows the physical properties and the like of the copolymers obtained in Example 1 and Comparative Example 1.

  As described above, when 95.0% carbazole was used as the raw material, the N-vinylcarbazole polymer itself before the heat treatment was already colored, and the coloration further progressed after the heat treatment. Almost brown. Moreover, the rate of change of the YI value before and after the heat treatment was 4.25, which was very large.

  On the other hand, when 99.2% by mass of carbazole was used as a raw material, it was only slightly colored after heat treatment, and the rate of change was significantly reduced to 1.92. .

  Further, the polymer of Example 1 according to the present invention has a glass transition temperature (Tg) of 3 ° C. higher than that of the polymer of Comparative Example 1, and the 5% weight loss temperature is 6 ° C. higher. It was. Although the difference of 3 ° C. in the glass transition temperature is large, usually 3 ° C. does not change unless the composition ratio of the resin is changed. Thus, it has been clarified that the difference in purity of carbazole as a raw material affects the heat resistance of the polymer.

  Furthermore, the compounds considered as odor-causing substances emitted from the polymers obtained in Example 1 and Comparative Example 1, the retention time and peak intensity of the gas chromatography chart, and the chemical structure are shown below. Moreover, the mass spectrum chart of obtained GC-MS is shown in FIGS.

  As can be seen from the above results, the polymer of Example 1 according to the present invention is significantly reduced in the content of the compound considered to be the cause of odor compared to the polymer of Comparative Example 1. It was.

  Table 3 shows the measurement results of the in-plane retardation and hue (b value) of the copolymer films obtained in Example 1 and Comparative Example 1.

  As shown in the above results, compared to the film of Comparative Example 1 consisting of a copolymer of N-vinylcarbazole synthesized from ordinary carbazole, the implementation consisting of a copolymer of N-vinylcarbazole synthesized from high-purity carbazole. It was found that the film of Example 1 tends to have a phase difference. The reason for this is not clear, but it is considered that the film of the present invention has a low impurity content, so that the stress during stretching is sufficiently applied to the film and the polymer is sufficiently oriented.

  Also, the b value representing the yellowish hue is high even before the heat treatment in the copolymer film synthesized from carbazole having a purity of 95.0% by mass, and increases to about 2.8 times after the heat treatment. . On the other hand, in the copolymer film synthesized from carbazole having a purity of 99.2% by mass, not only the b value before the heat treatment was clearly low, but also only about 1.9 times after the heat treatment. .

  Therefore, according to the present invention, it was demonstrated that an N-methylcarbazole copolymer retardation film in which coloring and odor are remarkably suppressed can be obtained.

Claims (5)

A method for producing an N-vinylcarbazole copolymer retardation film having a YI value change rate of 3.5 times or less before and after heating at 280 ° C. for 20 minutes,
Synthesizing N-vinylcarbazole from carbazole having a purity of 99.0% by mass or more;
Copolymerizing a monomer group containing 1% by mass or more and 15% by mass or less N-vinylcarbazole and 85% by mass or more and 99% by mass or less (meth) acrylic acid monomer; and the obtained copolymer A step of thermoforming into a film;
A process for producing an N-vinylcarbazole copolymer retardation film, comprising:   The production method according to claim 1, wherein at least methyl methacrylate and methyl 2- (hydroxymethyl) acrylate are used as the (meth) acrylic acid monomer.   Furthermore, the manufacturing method of Claim 2 including the process of carrying out dealcohol cyclization condensation of the adjacent methyl methacrylate unit and 2- (hydroxymethyl) acrylate unit, and forming a lactone ring structure. A N-vinylcarbazole copolymer obtained from the production method according to any one of claims 1 to 3, wherein the rate of change in the YI value before and after heating at 280 ° C for 20 minutes is 3.5 times or less. Body retardation film.   The N-vinylcarbazole copolymer retardation film according to claim 4, which exhibits reverse wavelength dispersion.