JP2008050512A - Polysulfone resin, film, optical film, liquid crystal cell and liquid crystal-displaying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film having excellent heat resistance, optical characteristics and dynamic characteristics. <P>SOLUTION: This film consists of a polysulfone resin containing a recurring unit expressed by general formula (1) [wherein, R<SP>1</SP>to R<SP>4</SP>are each H or a substituent; R<SP>5</SP>, R<SP>6</SP>are each a substituent; (m), (n) are each 0 to 4; and at least one of the R<SP>1</SP>, R<SP>2</SP>and at least one of the R<SP>3</SP>, R<SP>4</SP>are each the substituent] in its main chain. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polysulfone resin and an optical film excellent in optical properties. The polysulfone resin of the present invention has good transparency and heat resistance, and has low birefringence. Moreover, it has low thermal expansibility.

  Inorganic glass materials are widely used as transparent materials because they are excellent in transparency and heat resistance and have small optical anisotropy. However, since inorganic glass has a large specific gravity and is brittle, a molded glass product is heavy and has a defect such as being easily damaged. Due to such drawbacks, in recent years, development of plastic materials that replace inorganic glass materials has been actively conducted.

  As plastic materials for the purpose of replacing such inorganic glass materials, for example, polymethyl methacrylate, polycarbonate, polyethylene terephthalate and the like are known. Since these plastic materials are lightweight, excellent in mechanical properties, and excellent in processability, these plastic materials are recently used in various applications such as lenses and films.

  On the other hand, in the field of flat panel displays such as liquid crystal display elements, there is an increasing need for improvement in breakage resistance, weight reduction, and thickness reduction, and replacement of glass substrates with plastic film substrates is being studied. Since a plastic film substrate can be a flexible substrate, it can be used as a substrate for a mobile information communication device display device such as a portable information terminal such as a mobile phone, an electronic notebook, or a laptop personal computer. As a substrate of a display device, a functional material such as a transparent conductive film or a switching element is formed on a film. At that time, processing at a high temperature is required to improve the performance of the formed functional material. Therefore, it is required to provide a plastic substrate having heat resistance and a low coefficient of thermal expansion.

  As heat-resistant plastics used for the above purpose, heat-resistant amorphous polymers such as modified polycarbonate (modified PC), polyethersulfone (PES), and cycloolefin copolymer have been known so far. However, there is a problem that sufficient heat resistance as a plastic film substrate cannot be obtained even if these heat-resistant plastics are used.

  Furthermore, conventional plastics generate birefringence due to molecular orientation when formed into a film shape from the film forming conditions and the optical elasticity coefficient peculiar to the resin. There was a problem that the display quality was remarkably lowered and the optical properties were inferior to those of glass. For this reason, the plastic film substrate is required to have both higher optical isotropy and heat resistance.

Low birefringence polysulfone resins using biphenols substituted at least at the 3,3′-position have been developed as a technique for solving the above-mentioned problems in the optical properties of plastics (see, for example, Patent Document 1). . However, this polysulfone resin has a problem that it has high heat resistance but a large coefficient of thermal expansion. Further, as a polysulfone resin having a reduced coefficient of thermal expansion, a polysulfone resin copolymerized with an unsubstituted biphenol (for example, Non-Patent Document 1) is known, but this has a problem that optical anisotropy tends to occur. Had. Therefore, it has been strongly desired to develop a plastic material that solves the problems of the plastic materials that have been proposed so far, has high heat resistance, and sufficiently satisfies mechanical characteristics and optical characteristics.
JP-A-2-233728 Journal of Polymer Science, Polymer Chemistry Edition (1967), 5 (9), 2375-98

  The present invention has been made to solve the problems of conventional plastic materials, and a first object of the present invention is to provide a resin having excellent heat resistance, optical properties and mechanical properties. . The second object of the present invention is a transparent conductive film substrate, a color filter substrate, a TFT substrate, a liquid crystal display substrate, an organic EL display substrate, an electronic paper substrate, a solar cell substrate, an optical disk substrate, a touch panel, etc. It is providing the optical film using the said suitable resin composition.

  As a result of intensive investigations regarding the solution of the above-mentioned problems, the present inventors have solved these problems with a polysulfone resin containing a biphenyl having a substituent at a specific position in the main chain of the polymer, and have excellent heat resistance. The present invention has been completed by finding that a film having a property, an optical property, and a mechanical property can be provided.

That is, the said subject of this invention is achieved by the following means.
[1] A polysulfone resin comprising a repeating structural unit represented by the following general formula (1) in the main chain.

（式中、Ｒ¹〜Ｒ⁴はそれぞれ独立に水素原子または置換基を表し、Ｒ⁵、Ｒ⁶はそれぞれ独立に置換基を表し、ｍおよびｎはそれぞれ独立に０〜４の整数である。Ｒ¹とＲ²のうち少なくとも一つは置換基であり、Ｒ³とＲ⁴のうち少なくとも一つは置換基である。）
［２］ 一般式（１）中のＲ¹〜Ｒ⁴で表される置換基がそれぞれ独立にアルキル基またはハロゲン原子であることを特徴とする［１］に記載のポリスルホン樹脂。
［３］ 一般式（１）中、エーテル結合の位置がビフェニル骨格の４位と４’位であることを特徴とする［１］または［２］に記載のポリスルホン樹脂。
［４］ 一般式（１）中のｍ、ｎがいずれも０であることを特徴とする［１］〜［３］のいずれか一項に記載のポリスルホン樹脂。
［５］ ［１］〜［４］のいずれか一項に記載のポリスルホン樹脂からなることを特徴とするフィルム。
［６］ ［１］〜［４］のいずれか一項に記載のポリスルホン樹脂からなることを特徴とする光学フィルム。
［７］ ［５］に記載のフィルムを使用してなることを特徴とする液晶セル。
［８］ ［７］に記載の液晶セルを使用してなることを特徴とする液晶表示装置。

(Wherein R ^{1 to} R ⁴ each independently represent a hydrogen atom or a substituent, R ⁵ and R ⁶ each independently represent a substituent, and m and n are each independently an integer of 0 to 4). (At least one of R ¹ and R ² is a substituent, and at least one of R ³ and R ⁴ is a substituent.)
[2] The polysulfone resin according to [1], wherein the substituents represented by R ^{1 to} R ⁴ in the general formula (1) are each independently an alkyl group or a halogen atom.
[3] The polysulfone resin according to [1] or [2], wherein, in the general formula (1), the positions of the ether bonds are the 4th and 4 ′ positions of the biphenyl skeleton.
[4] The polysulfone resin according to any one of [1] to [3], wherein m and n in the general formula (1) are both 0.
[5] A film comprising the polysulfone resin according to any one of [1] to [4].
[6] An optical film comprising the polysulfone resin according to any one of [1] to [4].
[7] A liquid crystal cell comprising the film according to [5].
[8] A liquid crystal display device using the liquid crystal cell according to [7].

  If the polysulfone resin of the present invention is used, a film having excellent heat resistance and mechanical properties, low birefringence and transparency, and excellent optical properties can be provided. The film made of the polysulfone resin of the present invention has both low thermal expansibility and low birefringence, which are in a trade-off relationship with the conventional film made of polysulfone resin. By using such a film of the present invention, a liquid crystal cell and a liquid crystal display device excellent in display quality can be provided.

  Hereinafter, the resin and optical film of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Polysulfone resin]
The polysulfone resin of the present invention is characterized by containing a repeating structural unit represented by the following general formula (1) in the main chain.

一般式（１）中、Ｒ¹〜Ｒ⁴はそれぞれ独立に水素原子または置換基を表し、Ｒ⁵、Ｒ⁶はそれぞれ独立に置換基を表し、ｍおよびｎはそれぞれ独立に０〜４の整数である。Ｒ¹とＲ²のうち少なくとも一つは置換基であり、Ｒ³とＲ⁴のうち少なくとも一つは置換基である。
ビフェニル骨格の上記の位置に置換基を有することにより、適度な分子間相互作用を付与することが可能となり、特に熱膨張率の低下に効果がある。

In general formula (1), R ^{1 to} R ⁴ each independently represents a hydrogen atom or a substituent, R ⁵ and R ⁶ each independently represent a substituent, and m and n are each independently an integer of 0 to 4 It is. At least one of R ¹ and R ² is a substituent, and at least one of R ³ and R ⁴ is a substituent.
By having a substituent at the above-mentioned position of the biphenyl skeleton, it becomes possible to impart an appropriate intermolecular interaction, and in particular, it is effective in reducing the thermal expansion coefficient.

In the general formula (1), as a preferable substituent represented by R ^{1 to} R ⁴ , an alkyl group (preferably having 1 to 10 carbon atoms, for example, methyl group, ethyl group, isopropyl group, tert-butyl group, etc.) ), Halogen atoms (for example, chlorine atom, bromine atom, iodine atom and the like), aryl groups (preferably having 6 to 20 carbon atoms, for example, phenyl group, biphenyl group, naphthyl group and the like), alkoxy groups (having 1 to 10 carbon atoms). For example, methoxy group, ethoxy group, isopropoxy group and the like), acyl group (preferably having 2 to 10 carbon atoms, for example, acetyl group, propionyl group, butyryl group and the like), acylamino group (having 1 to 10 carbon atoms). Preferable examples include formylamino group and acetylamino group), nitro group, cyano group and the like. More preferred are an alkyl group, a halogen atom, an aryl group, an alkoxy group, and a nitro group, and particularly preferred are an alkyl group and a halogen atom.
When some or all of R ^{1 to} R ⁴ represent a substituent, the substituents may be the same or different. Preferred is an embodiment in which the substituents are the same.

In the general formula (1), preferred substituents represented by R ⁵ and R ⁶ are alkyl groups (preferably having 1 to 10 carbon atoms, such as methyl group, ethyl group, isopropyl group, tert-butyl group, etc. ), Halogen atoms (for example, chlorine atom, bromine atom, iodine atom and the like), aryl groups (preferably having 6 to 20 carbon atoms, for example, phenyl group, biphenyl group, naphthyl group and the like), alkoxy groups (having 1 to 10 carbon atoms). For example, methoxy group, ethoxy group, isopropoxy group and the like), acyl group (preferably having 2 to 10 carbon atoms, for example, acetyl group, propionyl group, butyryl group and the like), acylamino group (having 1 to 10 carbon atoms). Preferable examples include formylamino group and acetylamino group), sulfo group, nitro group, cyano group and the like. More preferred are an alkyl group, a halogen atom, an aryl group, an alkoxy group and a nitro group, and particularly preferred are an alkyl group, an alkoxy group and a halogen atom.

  In the general formula (1), the positions of two ether bonds linked from the biphenyl skeleton are preferably the 4-position and the 4'-position. Having an ether bond at the above position is advantageous in terms of synthesis and can improve intermolecular interaction.

  In the general formula (1), m and n each represents an integer of 0 to 4, but an integer of 0 to 2 is preferable, and 0 is particularly preferable. When m and n are each 0, it is advantageous in terms of synthesis cost, and the intermolecular interaction can be improved.

When m is an integer of 2 or more, m R ^{5 s} may be the same or different. Preferred in terms of synthesis is an embodiment in which m R ⁵ are the same. Similarly, when n is an integer of 2 or more, n R ^{6 s} may be the same or different. Preferred in terms of synthesis is an embodiment in which n R ⁶ are the same.

  Specific examples (P-1 to P-20) of the structural unit of the general formula (1) are shown below, but the structural unit of the general formula (1) that can be used in the present invention is not limited to these. . In the following structural formulas, Et represents an ethyl group, iPr represents an isopropyl group, and Ph represents a phenyl group.

  In the polysulfone resin of the present invention, the content of the general formula (1) is preferably 10 to 100 mol%, more preferably 25 to 100 mol%, and particularly preferably 50 to 100 mol%. When the content of the general formula (1) is in the above range, the effect of lowering optical isotropy and thermal expansion coefficient can be easily obtained.

  The molecular weight of the polysulfone resin of the present invention is usually 10,000 or more in terms of weight average molecular weight, more preferably 20,000 to 300,000, and particularly preferably 30,000 to 200,000. When the molecular weight is 10,000 or more, film forming becomes easy, and preferable mechanical properties are easily obtained after forming. Further, if the molecular weight is 300,000 or less, the molecular weight can be easily controlled in the synthesis, and the viscosity of the solution is too high so that the handling is not difficult. The viscosity corresponding to the molecular weight can be used as a guide.

  The heat-resistant temperature of the polysulfone resin of the present invention is preferably high, and the glass transition temperature (Tg) by DSC measurement can be used as a guide. In this case, a preferable glass transition temperature is 200 ° C. or higher, more preferably 220 ° C. or higher, and particularly preferably 230 ° C. or higher. Further, the case where the glass transition temperature is not substantially observed within the measurement range (for example, 400 ° C. or lower) is also included in the polysulfone resin of the present invention.

  The production method of the polysulfone resin of the present invention is not particularly limited, and a known method such as a nucleophilic substitution polycondensation method can be applied. Specifically, (1) a method in which an alkali metal salt of a diol and a dihalide having a sulfonyl group are heated in a polar solvent for polycondensation, or (2) a diol in a polar solvent in the presence of an alkali metal or metal salt. And a method of polycondensing by heating a dihalide having a sulfonyl group.

  Examples of polar solvents used in these polycondensation reactions include dimethyl sulfoxide, sulfolane, diphenyl sulfone, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2. -Amide solvents such as imidazolidinone are used. These may be used alone or in combination of two or more. In each method, an azeotropic dehydration solvent such as toluene, benzene, chlorobenzene, monochloroethane, dichloroethane, trichloroethane, tetrachloroethane, dichlorobenzene or the like may be added as necessary.

  Further, a preferred specific example of the alkali metal salt used in the method (1) is a sodium salt or a potassium salt. The alkali metal salt used in the method (2) is not particularly limited. For example, sodium carbonate, potassium carbonate, rubidium carbonate, sodium oxalate, potassium oxalate and the like are preferable, and sodium carbonate and potassium carbonate are particularly preferable. . The amount used is preferably an excess mole relative to the molar amount of diphenol in order to obtain a high molecular weight polymer. When producing a polysulfone by the above method (1) or (2), the polymerization temperature is usually in the range of 100 to 400 ° C, more preferably 150 to 280 ° C.

  The reaction is preferably free of oxygen in the reaction atmosphere, and is desirably performed in nitrogen or another inert gas. When the polysulfone is produced by the above method (1) or (2), the reaction mixture is usually cooled to stop the polymerization reaction. Furthermore, in order to stabilize the phenoxide group that may be present at the end of the polymer and stop the polymerization reaction, an aliphatic halide, an aromatic halide, etc. are added and reacted in the latter stage of the reaction. This is also carried out as necessary.

  When a polysulfone resin is produced by the method (1) or (2), a known method can be applied as a method for separating and purifying the produced polymer. For example, after the salt (and excess alkali metal salt) precipitated in the reaction solvent is filtered, the polymer solution which is the filtrate is usually dropped into the poor solvent of the polymer, or conversely, the poor polymer solvent is added to the polymer solution. By adding in, the target polymer can be precipitated. Typical examples of the poor solvent for the polymer include methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, water, and the like. These may be used alone or as a mixture of two or more. . Further, the salt may be removed by washing with water after the polymer is precipitated by the above method without separating the precipitate.

  The amount of residual alkali metal and halogen in the resin of the present invention is preferably 50 ppm or less, particularly preferably 10 ppm or less. If the residual alkali metal content and halogen content are 50 ppm or less, the electrical characteristics are unlikely to deteriorate, and excellent surface characteristics can be easily obtained. In addition, an excellent functional film can be provided even when a conductive film, a semiconductor film, or the like is provided. The amount of residual alkali metal and the amount of halogen can be quantified using known methods such as ion chromatography analysis, atomic absorption spectrometry, and plasma emission spectroscopy.

  The amount of monomer remaining in the polysulfone resin is preferably 3000 ppm or less, more preferably 500 ppm or less, and even more preferably 100 ppm or less. If the amount of residual monomer is 3000 ppm or less, the electrical characteristics and heat resistance are unlikely to decrease, and excellent film surface characteristics can be easily obtained. Also, an excellent functional film can be provided when a barrier film, a conductive film, a semiconductor film, or the like is provided. The amount of residual monomer can be analyzed by a known method such as HPLC or nuclear magnetic resonance.

[the film]
The film of the present invention contains the above-described polysulfone resin of the present invention. The film of the present invention includes those having a shape generally regarded as a sheet. As a method for forming the polysulfone resin of the present invention into a film or sheet, known methods such as a melt film forming method and a solution casting method can be used.

  The melt casting method has features such as low film production costs and excellent optical isotropy of the film. However, a polymer with a high glass transition temperature (as a guideline, 250 ° C or higher) requires a high melting temperature. There is a problem that the polymer is likely to be thermally decomposed. The solution casting method is suitable for forming a polymer with a high glass transition temperature or a polymer with a high molecular weight and a high melt viscosity, and has excellent film surface properties, but it uses a solvent and has a large environmental impact. There is a problem.

  The film of the present invention may be stretched. By stretching, mechanical strength such as folding strength is improved, and there is an advantage that handling property is improved. In particular, those having an orientation release stress in the stretching direction (ASTMD 1504, hereinafter abbreviated as “ORS”) of 0.3 to 3 GPa are preferable because the mechanical strength is improved. ORS is an internal stress generated by stretching inherent in a stretched optical film. For the stretching, a known method can be used. However, when the glass transition temperature of the polysulfone resin is 250 ° C. or higher, the stretching may be difficult only by simple heating. Therefore, it is desirable to perform the stretching in a state containing a solvent. . In this case, it is preferable to perform stretching in the course of drying, for example, a roll uniaxial stretching method or a tenter uniaxial stretching at a temperature between 10 ° C. and 50 ° C. higher than the glass transition temperature in a state containing a solvent. The film can be stretched by a method, a simultaneous biaxial stretching method, a sequential biaxial stretching method, or an inflation method. The draw ratio is preferably 1.1 to 3.5 times, and more preferably 1.2 to 2.5 times.

  The polysulfone resin forming the film of the present invention may be one kind or a mixture of two or more kinds. Moreover, polymers and additives other than polysulfone resin may be included within the range not impairing the effects of the present invention. Content of components other than the polysulfone resin contained in the film of this invention becomes like this. Preferably it is 0-40 weight%, More preferably, it is 0-20 weight%, More preferably, it is 0-10 weight%. Furthermore, a crosslinked resin may be added from the viewpoint of solvent resistance, heat resistance, mechanical strength, and the like. As the kind of the cross-linked resin, various known ones can be used without any particular limitation as the thermosetting resin and the radiation curable resin.

  Examples of the thermosetting resin include phenol resin, urea resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, diallyl phthalate resin, furan resin, bismaleimide resin, cyanate resin and the like. In addition, the crosslinking method can be used without particular limitation as long as it is a reaction that forms a covalent bond, and there is a system in which the reaction proceeds at room temperature using a polyalcohol compound and a polyisocyanate compound to form a urethane bond. Can be used without any particular restrictions. However, such a system often has a problem of pot life before film formation, and is usually used as a two-component mixed type in which a polyisocyanate compound is added immediately before film formation.

  On the other hand, when used as a one-component type, it is effective to protect the functional group involved in the crosslinking reaction, and it is also commercially available as a block type curing agent. As commercially available block type curing agents, B-882N manufactured by Mitsui Takeda Chemical Co., Ltd., Coronate 2513 manufactured by Nippon Polyurethane Industry Co., Ltd. (above block polyisocyanate), Cymel 303 manufactured by Mitsui Cytec Co., Ltd. (methylated melamine resin) ) Etc. are known.

  Radiation curable resins are roughly classified into radical curable resins and cationic curable resins. As the curable component of the radical curable resin, a compound having a plurality of radical polymerizable groups in the molecule is used. As a typical example, a polyfunctional acrylate monomer having 2 to 6 acrylate groups in the molecule And compounds having a plurality of acrylate groups in the molecule called urethane acrylate, polyester acrylate, and epoxy acrylate. As a typical curing method of the radical curable resin, there are a method of irradiating an electron beam and a method of irradiating ultraviolet rays. Usually, in the method of irradiating with ultraviolet rays, a polymerization initiator that generates radicals upon irradiation with ultraviolet rays is added. In addition, if the polymerization initiator which generate | occur | produces a radical by heating is added, it can also be used as a thermosetting resin. As the curable component of the cationic curable resin, a compound having a plurality of cationic polymerizable groups in the molecule is used. As a typical curing method, a photoacid generator that generates an acid upon irradiation with ultraviolet rays is added, and ultraviolet rays are added. And a method of curing by irradiation. Examples of the cationically polymerizable compound include a compound containing a ring-opening polymerizable group such as an epoxy group and a compound containing a vinyl ether group.

  In the film of the present invention, a plurality of thermosetting resins and radiation curable resins mentioned above may be mixed and used, or a thermosetting resin and a radiation curable resin may be used in combination. Moreover, you may mix and use a crosslinkable resin and the polymer which does not have a crosslinkable group.

  Furthermore, in the film of the present invention, it is possible to introduce a crosslinkable group into the polysulfone resin of the present invention used at the time of film formation. You may have. In this case, it can bridge | crosslink without using the general purpose crosslinkable resin mentioned above together.

  The film of the present invention can contain a metal oxide and / or a metal composite oxide, and a metal oxide obtained by a sol-gel reaction. In this case, heat resistance and solvent resistance can be imparted in the same manner as the above-mentioned crosslinked resins. Furthermore, resin modifiers such as plasticizers, dyes / pigments, antistatic agents, ultraviolet absorbers, antioxidants, inorganic fine particles, peeling accelerators, leveling agents, and lubricants as long as the effects of the present invention are not impaired as necessary. May be added.

  The thickness of the film of the present invention is not particularly defined, but is preferably 30 to 700 μm, more preferably 40 to 200 μm, and further preferably 50 to 150 μm. In any case, the haze is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. Further, the total light transmittance is preferably 70% or more, more preferably 80% or more, and further preferably 85% or more.

  The heat resistant temperature of the optical film of the present invention is preferably higher, and the glass transition temperature by DSC measurement can be used as a guide. In this case, a preferable glass transition temperature is 180 ° C. or higher, more preferably 200 ° C. or higher. In addition, when the optical film of the present invention is produced by the solution casting method using only the polysulfone resin of the present invention, the glass transition temperature of the polysulfone resin used and the glass transition of the optical film of the present invention are sufficient if drying is sufficient. It almost coincides with temperature.

The film surface of the present invention may be treated by a method such as saponification, corona treatment, flame treatment, glow discharge treatment, etc., in order to enhance the adhesion with other layers or components depending on the application. it can. Furthermore, an adhesive layer and an anchor layer may be provided on at least one side of the optical film.
In addition, various known functional layers such as a smoothing layer, a hard coat layer, an ultraviolet absorbing layer, a surface roughening layer, a transparent conductive layer, a gas barrier layer, and a solvent resistant layer are provided on the surface of the optical film. It can also be provided.

The optical film of the present invention can reduce the retardation.
In this specification, Re (λ) represents in-plane retardation at the wavelength λ. Re (λ) is measured by making light with a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, materials, usage amounts, ratios, processing contents, processing procedures, and the like shown in the following examples are appropriately changed without departing from the gist of the present invention. be able to. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

1. Synthesis of polysulfone resin [polysulfone resin P-1 of the present invention]
75 ml of dimethylacetamide, 8.6 g of potassium carbonate, 10.71 g of 2,2′-dimethyl-4,4′-dihydroxylbiphenyl and 14.4 g of 4-chlorophenylsulfone were put into a reaction vessel equipped with a stirrer, and nitrogen was added. The mixture was stirred at 160 ° C. and a stirring speed of 100 rpm for 15 hours under an air stream. 100 ml of dimethylacetamide was added to the reaction solution and filtered to remove inorganic salts. The resulting solution was poured into 3 liters of vigorously stirred methanol. The white precipitate obtained in methanol was collected by filtration, dried by heating at 40 ° C. for 12 hours, and then dried under reduced pressure at 70 ° C. for 3 hours to obtain 20 g of P-1 as a white powder.

[Comparison Polysulfone Resin H-1]
The same method as P-1 except that 2,2′-dimethyl-4,4′-dihydroxylbiphenyl is changed to the same molar amount of 4,4′-biphenol (ie, 4,4′-dihydroxylbiphenyl). H-1 having the following structure was synthesized.

[Comparison Polysulfone Resin H-2]
The same method as P-1 except that 2,2′-dimethyl-4,4′-dihydroxylbiphenyl is changed to 3,3 ′, 5,5′-tetramethyl-4,4′-dihydroxylbiphenyl H-2 having the following structure was synthesized.

2. Preparation of Optical Film Sample Polysulfone resin P-1 of the present invention and comparative polysulfone resins H-1 and H-2 are dissolved in chloroform, and the solution viscosity after dissolution is adjusted to a concentration in the range of 800 to 1500 mPa · s. It was adjusted. The solution was filtered through a 5 μm filter and cast on a glass substrate using a doctor blade. After casting, heat dry at 45 ° C for 2 hours, 80 ° C for 2 hours, 120 ° C for 4 hours, peel off the film from the glass substrate, fix to a metal frame, and vacuum dry at 100 ° C for 3 hours Thus, film samples 1 to 3 were obtained.

3. Measuring method of characteristic value (1) Measuring method of characteristic value of polysulfone resin The weight average molecular weight and glass transition temperature (Tg) of each synthesized polysulfone resin were measured by the following measuring method.
[Weight average molecular weight]
Using HLC-8120GPC manufactured by Tosoh Corporation, it was obtained by polystyrene conversion GPC measurement using chloroform as a solvent in comparison with a molecular weight standard product of polystyrene.
[Glass transition temperature (Tg)]
It measured by DSC (in nitrogen, temperature rising temperature 10 degree-C / min) using DSC6200 by Seiko Co., Ltd.

(2) Measuring method of characteristic value of film sample The film thickness, retardation, linear thermal expansion coefficient, total light transmittance, and tensile elastic modulus of each obtained film sample were measured by the following measuring methods.
[Film thickness]
Measurement was performed with a dial thickness gauge using K402B manufactured by Anritsu Corporation.
[Retardation]
A value at a wavelength of 589.3 nm was measured with a phase difference measuring device (manufactured by Oji Scientific Instruments, KOBRA-WR) from the direction perpendicular to the film plane.
[Linear thermal expansion coefficient]
A film sample (19 mm × 5 mm) was prepared and measured using TMA (manufactured by Rigaku Corporation, TMA8310). The measurement speed was 3 ° C./min. Three samples were measured and the average value was used. The measurement was performed in a temperature range of 25 ° C. to 300 ° C., and the linear thermal expansion coefficient was calculated in the range of 25 ° C. to 150 ° C. at the time of temperature increase. However, about the comparative example sample whose glass transition is 200 degrees C or less, it computed in the temperature range of 25 degreeC-150 degreeC.
[Total light transmittance]
It measured with the JASCO-made haze meter.
[Tensile modulus]
A film sample (1.0 cm × 5.0 cm piece) was prepared, and the tensile elastic modulus was measured using Tensilon (manufactured by Toyo Baldwin Co., Ltd., Tensilon RTM-25) at 25 ° C. and a tensile speed of 3 mm / min. did. Three samples were measured and evaluated by calculating the average value (the sample was used after standing overnight at 25 ° C. and a relative humidity of 60%. The distance between chucks was 3 cm).

4). Measurement results and evaluation Each of the resin and the film sample characteristic values, showing the results of measurement of the characteristic values in the measuring method described above in Table 1 below.

  From Table 1, it can be seen that the optical film of the present invention is excellent in heat resistance and excellent in optical properties from the results of total light transmittance and retardation. The optical film of the present invention has a small coefficient of linear thermal expansion, good dimensional stability, and excellent mechanical properties.

  If the polysulfone resin of this invention is used, the film excellent in heat resistance, transparency, a mechanical characteristic, and an optical characteristic can be provided. Therefore, the film of the present invention is suitable for transparent conductive film substrates, color filter substrates, TFT substrates, liquid crystal cell substrates, organic EL display substrates, electronic paper substrates, solar cell substrates, optical disk substrates, touch panels, and the like. Can be used. Moreover, the liquid crystal display device which has the outstanding function is producible by using the liquid crystal cell using the optical film of this invention. Therefore, the present invention has high industrial applicability.

Claims (8)

A polysulfone resin comprising a repeating structural unit represented by the following general formula (1) in a main chain.

(Wherein R ^{1 to} R ⁴ each independently represent a hydrogen atom or a substituent, R ⁵ and R ⁶ each independently represent a substituent, and m and n are each independently an integer of 0 to 4). (At least one of R ¹ and R ² is a substituent, and at least one of R ³ and R ⁴ is a substituent.) The polysulfone resin according to claim 1, wherein the substituents represented by R ^{1 to} R ⁴ in the general formula (1) are each independently an alkyl group or a halogen atom.   The polysulfone resin according to claim 1 or 2, wherein the position of the ether bond in the general formula (1) is at the 4-position and the 4'-position of the biphenyl skeleton.   The polysulfone resin according to any one of claims 1 to 3, wherein both m and n in the general formula (1) are 0.   A film comprising the polysulfone resin according to any one of claims 1 to 4.   An optical film comprising the polysulfone resin according to any one of claims 1 to 4.   A liquid crystal cell comprising the film according to claim 5.   A liquid crystal display device comprising the liquid crystal cell according to claim 7.