JP5308891B2 - Acrylic polymer, method for producing the same, acrylic resin composition, retardation film, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic polymer that has a low content of foreign substances while having a structural unit represented by formula (1) or (2) and a ring structure. <P>SOLUTION: The acrylic polymer has the structural unit represented by formula (1) or (2) and the ring structure in a main chain. The acrylic polymer has a Tg of 110&deg;C or higher and has measured solution turbidity of 2% or less when made into a chloroform solution with concentration of 15 wt.% and contained and measured in a measuring cell of which a transmission distance of measuring light is 1 cm. In the formula (1) and (2), R<SP>1</SP>through R<SP>4</SP>is hydrogen or an organic residue, R<SP>5</SP>is an organic residue of which carbon linked to O<SP>1</SP>is secondary or tertiary, and Ar is an aryl group. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an acrylic polymer and a method for producing the same. The present invention also relates to an acrylic resin composition and a retardation film containing the polymer, and an image display device including the retardation film.

  Acrylic polymers are suitable as optical materials because they have high transparency, surface gloss, and weather resistance, and are excellent in the balance of various properties such as mechanical strength, molding processability, and surface hardness. However, taking a typical polymethyl methacrylate (PMMA) as an acrylic polymer as an example, its glass transition temperature is around 100 ° C., which is not necessarily excellent in heat resistance. Moreover, even if it tries to use the stretched film for a phase difference film, since the expression property of the phase difference by extending | stretching is low, coexistence with thinness and phase difference is difficult.

  One method for improving the retardation and heat resistance of an acrylic polymer is to introduce a ring structure into the main chain. In JP 2008-189886 A, at least one ring structure selected from a lactone ring structure, a glutaric anhydride structure, and a glutarimide structure is introduced into the main chain of the acrylic polymer. For example, introduction of a lactone ring structure into the main chain raises the glass transition temperature of the acrylic polymer and improves its heat resistance. Moreover, although it depends on the amount of introduction, a retardation film showing a large positive retardation can be realized. These ring structures, including lactone ring structures, are dealcoholized to precursors (acrylic polymers) having (meth) acrylic acid ester units and / or (meth) acrylic acid units as constituent units. It can be formed by advancing the condensation reaction. The dealcoholization cyclocondensation reaction is a reaction between a carboxyl group or a hydroxy group and an ester group (carboxylic acid ester group) in the precursor structural unit, or two ester groups (carboxylic acid ester) in the precursor structural unit. Group) and an imidizing agent added to the reaction system. The structural unit of the precursor may be selected so that the above-described ring structure is formed by this reaction and according to the composition desired as the acrylic polymer. As described in JP 2008-189886 A, an organophosphorus compound is mainly used as a catalyst for the dealcoholization cyclocondensation reaction.

  By the way, the introduction of the ring structure into the main chain improves the heat resistance and retardation of the acrylic polymer, while the molecular chain becomes rigid so that the moldability and flexibility of the film can be improved. Sex is reduced. In JP 2008-189886 A, a structural unit having a specific structure such as a benzyl methacrylate (BzMA) unit is further introduced, thereby maintaining an acrylic heavy polymer having a ring structure in the main chain while maintaining retardation performance. It is described that the formability of coalescence is improved.

  Apart from this, the addition of elastic organic fine particles to acrylic polymers has been widely carried out in order to improve the flexibility of the film. JP 2008-242421 describes the addition of elastic organic fine particles to an acrylic polymer, and the transparency of the film may decrease due to the difference in refractive index between the two, BzMA By introducing a structural unit having a specific structure such as a unit into an acrylic polymer, the difference in refractive index between the two is reduced while maintaining retardation performance, and a decrease in transparency as a film is suppressed. Have been described.

JP 2008-189886 JP 2008-242421 A

  However, when an acrylic polymer having a ring structure in the main chain and having a BzMA unit is used, foreign matter may be observed in a molded product produced from the polymer. The foreign matter is an optical defect when an acrylic polymer is used as an optical material, particularly when it is used as an optical film.

  As a result of studies by the present inventors, this foreign material is an acrylic polymer having a ring structure in the main chain, and is not limited to the BzMA unit, but has structural units represented by the following formulas (1) and (2). It was found to be characteristic of acrylic polymers. Focusing on this point, the present inventors have further studied and found that the catalyst used in the dealcoholization cyclocondensation reaction for introducing a ring structure into the main chain is the key.

In the formulas (1) and (2), R ^{1 to} R ⁴ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms, and R ⁵ is a carbon atom bonded to the oxygen atom O ^1. Is a secondary or tertiary organic residue having 1 to 20 carbon atoms, and Ar is an aryl group.

  The acrylic polymer having a cyclic structure in the main chain and having the structural units represented by the formulas (1) and (2) is usually a (meth) acrylic acid ester unit and / or ( The above-described dealcoholization cyclocondensation reaction is allowed to proceed on a copolymer (acrylic polymer that is a precursor) having a (meth) acrylic acid unit and a structural unit represented by formula (1) or (2). Form. It is considered that the catalyst (mainly organophosphorus compound) used at that time is the reason for the formation of foreign matter. The present inventors have estimated the following reaction mechanism for the formation of foreign matter.

The structural unit represented by the formula (1) or (2) is a carboxylic acid ester unit, and when the dealcoholization cyclocondensation reaction proceeds with respect to the acrylic polymer as a precursor having the structural unit, An alcohol represented by the formula ArCR ² (R ³ ) OH or the formula R ⁵ OH is generated by causing a part of the unit to undergo a dealcoholization cyclization condensation reaction. For example, when the acrylic polymer has a benzyl methacrylate (BzMA) unit represented by the following formula (3) as a structural unit represented by the formula (1), benzyl alcohol represented by the following formula (4) is generated.

  Next, the produced benzyl alcohol undergoes a reaction shown in the following formula (5) by phosphoric acid derived from an organophosphorus compound that is a catalyst for the dealcoholization cyclocondensation reaction and heat applied to the reaction system, It becomes benzyl cation which is a kind of carbocation.

The produced benzyl cation attacks benzyl alcohol that has not yet undergone the reaction shown in formula (5), and by an electrophilic substitution reaction, an benzyl group (C ₆ (H ₅ —CH ₂ group) is added. The formation of the benzyl cation and the electrophilic substitution reaction to the aromatic ring by the generated benzyl cation are considered to be a modification of the Friedel-Crafts alkylation reaction using phosphoric acid as the Lewis acid.

  Next, also with respect to the produced | generated alcohol shown to Formula (6), reaction shown to the following formula | equation (7) by phosphoric acid and a heat | fever will arise again, and a new carbocation will arise. Since the produced carbocation also attacks benzyl alcohol, the addition of the benzyl group to benzyl alcohol proceeds in a chain manner. As a result, a compound in which a benzyl group is added in a chain is generated, and when the molecular weight of the compound exceeds a certain level, the above-mentioned foreign matter is formed.

By the way, in order for the electrophilic substitution reaction to the aromatic ring by the carbocation to proceed, the chemical stability of the cation is very important. Carbocations formed from alcohols of the formula ArCR ² (R ³ ) OH or formula R ⁵ OH have carbon atoms (because of the presence of ArC groups (eg benzyl groups) or as carbocations in the group R ⁵ ( In the state of the alcohol molecule before becoming a cation, the carbon atom bonded to the oxygen atom of the hydroxy group is secondary or tertiary, so that chemical stability is high. For this reason, when the acrylic polymer which is a precursor has the structural unit shown to Formula (1) or (2), it is thought that the said foreign material arises characteristically. On the other hand, as disclosed in JP-A-2008-189886, a copolymer of methyl methacrylate (MMA) and 2- (hydroxymethyl) methyl acrylate (MHMA) (this copolymer is represented by the formula (1) or Acrylic polymer having a ring structure in the main chain is formed by the progress of dealcoholization cyclocondensation reaction with respect to (without the structural unit shown in (2)), but the alcohol (with the heat from the MMA unit and MHMA unit) R ⁶ OH) is generated, and even if a carbocation is formed by Lewis acid and heat, the carbon atom which is the carbocation in the group R ⁶ is primary, so that the chemical stability of the cation is low, It is considered that the electrophilic substitution reaction to the aromatic ring hardly occurs, that is, the foreign matter is not generated.

The acrylic polymer of the present invention realized for the first time on the basis of such studies by the inventors, is a structural unit that is a factor causing the generation of foreign substances characteristically during the dealcoholization cyclocondensation reaction, that is, the following formula ( Despite having the structural unit shown in 1 ), the amount of foreign matter contained is small. Specifically, it has a structural unit represented by the following formula (1 ), has a ring structure in the main chain, and has a glass transition temperature of 110 ° C. or higher measured according to ASTM-D-3418. When a chloroform solution having a concentration of 15% by weight is used, the turbidity of the solution measured in a measuring cell having a transmission distance of measuring light of 1 cm is 2% or less.

R ¹ to R ³ which in formula (1) are each independently a hydrogen atom or an organic residue having a carbon number of 1 to 20, A r is an aryl group.

The acrylic resin composition of the present invention comprises by the acrylic polymer of the present invention as a main component, may further including Ndei elastic organic fine particles with 5% by weight or more content.

The retardation film of the present invention contains the acrylic polymer of the present invention as a main component . The polarizer protective film of the present invention contains the acrylic polymer of the present invention as a main component.

The image display device of the present invention includes the retardation film of the present invention. Or the image display apparatus of this invention is equipped with the polarizer protective film of this invention.

The method for producing an acrylic polymer of the present invention is a method for producing an acrylic polymer having a structural unit represented by the following formula (1 ) and having a ring structure in the main chain, wherein (I) the acrylic polymer The acrylic polymer having the structural unit shown in (1 ) , which is a polymer precursor, and having a carboxyl group or a hydroxy group and an ester group in a molecular chain, the carboxyl group or the hydroxy group and the Or (II) having the structural unit shown in (1 ) above, which is a precursor of the acrylic polymer, and having the ester group as a molecular chain. By proceeding a dealcoholization cyclocondensation reaction between the two ester groups and the imidizing agent added to the reaction system for the acrylic polymer having And the polymer to form the ring structure in the main chain of the child, the catalyst used in the progress of the reaction is a zinc compound.

R ¹ to R ³ which in formula (1) are each independently a hydrogen atom or an organic residue having a carbon number of 1 to 20, A r is an aryl group.

  Since the acrylic polymer of the present invention has a ring structure in the main chain, it has a high glass transition temperature of 110 ° C. or higher and is excellent in heat resistance. In addition, the acrylic polymer of the present invention has the structural unit represented by the formula (1) or (2), and thus has such a structural unit such as excellent moldability and flexibility when used as a film. It is possible to improve the characteristics of an acrylic polymer that is not present. The structural unit represented by the formula (1) or (2) causes the generation of foreign substances characteristically during the dealcoholization cyclocondensation reaction for introducing a ring structure into the main chain, but the acrylic polymer of the present invention Despite having such a structural unit, the amount of foreign matter contained is small.

  In the method for producing an acrylic polymer of the present invention, a zinc compound is used as a catalyst for a dealcoholization cyclocondensation reaction for forming an acrylic polymer by forming a ring structure in the main chain of an acrylic polymer as a precursor. Is used. Thereby, the acrylic polymer of this invention which has the said characteristic is obtained.

[Acrylic polymer]
The acrylic polymer of the present invention has a structural unit represented by the following formula (1) or (2).

The structural unit represented by the formula (1) or (2) improves the characteristics (for example, moldability, flexibility when used as a film, etc.) of an acrylic polymer that does not have the structural unit. . As an example, the acrylic polymer of the present invention has a benzyl methacrylate (BzMA) unit (a structural unit in which R ¹ is a methyl group, R ² and R ³ are hydrogen atoms, and Ar is a phenyl group in Formula (1)). When it has, the moldability and flexibility when it is used as a film are improved while maintaining the retardation development as an acrylic polymer. In this case, since the refractive index of the acrylic polymer increases, an acrylic resin composition in which elastic organic fine particles are added to the polymer is used, and this composition is a molded body (typically a film). In addition, since the refractive index difference between the matrix made of the acrylic polymer and the elastic organic fine particles is reduced, the transparency can be secured while obtaining the benefit of the flexibility improvement by the elastic organic fine particles.

  An acrylic polymer is a polymer having a (meth) acrylic acid ester unit and / or a (meth) acrylic acid unit as a constituent unit, and is derived from a (meth) acrylic acid ester or a derivative of (meth) acrylic acid. You may have a structural unit, for example, the cyclic structure mentioned later. The total of the proportions of the structural units derived from the (meth) acrylic acid ester unit, the (meth) acrylic acid unit and the above derivatives in all the structural units of the acrylic polymer is usually 50% by weight or more, preferably 60 % By weight or more, more preferably 70% by weight or more. The acrylic polymer of the present invention is obtained by allowing a dealcoholization cyclocondensation reaction to proceed with an acrylic polymer as a precursor. In this specification, the acrylic polymer as a precursor is In order to distinguish it from the acrylic polymer of the present invention, it is called “acrylic polymer”.

R ^{1 to} R ³ in the structural unit represented by the formula (1) are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue is, for example, an alkyl group such as a methyl group, an ethyl group, or a propyl group; an unsaturated aliphatic hydrocarbon group such as an ethenyl group or a propenyl group; an aromatic hydrocarbon group such as a phenyl group or a naphthyl group; A group, one or more of hydrogen atoms in the unsaturated aliphatic hydrocarbon group or the aromatic hydrocarbon group substituted by at least one group selected from a hydroxy group, a carboxyl group, an ether group and an ester group ;

R ¹ is typically a hydrogen atom or a methyl group. When R ¹ is a hydrogen atom, the structural unit represented by formula (1) is a kind of acrylate unit, and when R ¹ is a methyl group, the structural unit represented by formula (1) is a kind of methacrylic ester unit. .

R ² and R ³ are preferably hydrogen atoms, and such a structural unit is chemically stable.

  Ar in the structural unit represented by the formula (1) is an aryl group. The aryl group is, for example, a phenyl group, an alkylphenyl group, a methoxyphenyl group, a biphenyl group, or a naphthyl group, and a phenyl group or a methylphenyl group is preferable.

Specific examples of the structural unit represented by the formula (1) are a benzyl methacrylate unit, a methylbenzyl methacrylate unit, a 1-phenylethyl methacrylate unit, and a 2-phenylpropan-2-yl methacrylate unit. A benzyl methacrylate unit is preferable because an acrylic polymer having excellent flexibility is obtained. In the benzyl methacrylate unit, R ¹ is a methyl group, R ² and R ³ are hydrogen atoms, and Ar is a phenyl group.

R ⁴ in the structural unit represented by the formula (2) is a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue is, for example, the same group as the organic residue in formula (1). R ⁴ is typically a hydrogen atom or a methyl group.

R ⁵ in the structural unit represented by the formula (2) is an organic residue having 1 to 20 carbon atoms in which the carbon atom bonded to the oxygen atom O ¹ is secondary or tertiary. Such an organic residue is, for example, a sec-butyl group, a cyclohexyl group, a t-butyl group, a norbornyl group, an adamantyl group, a 1-phenylpropan-2-yl group, or a 4-phenylbutan-2-yl group.

By the way, as described above, it is presumed that the formation of a carbocation during the dealcoholization cyclocondensation reaction of an acrylic polymer is the reason for the formation of foreign matter. At that time, it is considered that more foreign substances are formed as the chemical stability of the carbocation is higher. The chemical stability of the carbocation formed from the structural unit represented by the formula (1) or (2) is the highest in the carbocation formed from the structural unit represented by the formula (1) (the carbon atom serving as the carbocation is If the carbon atom bonded to the oxygen atom O ¹ in the structural unit shown in the formula (2) is tertiary, then the last In the case where the carbon atom bonded to the oxygen atom O ¹ in the structural unit represented by the formula (2) is secondary. In addition, when the said carbon atom is primary, the chemical stability of the carbocation formed is very low, and as already described, the electrophilic substitution reaction does not proceed as much as foreign substances are formed.

  Therefore, the effect of the present invention is that when the acrylic polymer as a precursor has a structural unit represented by the formula (1) (since many of the structural units represented by the formula (1) remain after the cyclization condensation, That is, this is particularly noticeable when the acrylic polymer has a structural unit represented by the formula (1).

  In the acrylic polymer of the present invention, the proportion of the structural unit represented by the formula (1) or (2) in all the structural units (content of the structural unit represented by the formula (1) or (2) in the acrylic polymer) Is not particularly limited, and may be adjusted according to the desired properties of the acrylic polymer, for example, 5 to 50% by weight, and preferably 10 to 30% by weight.

  The acrylic polymer of the present invention has a ring structure in the main chain. Thereby, the acrylic polymer of the present invention has a high glass transition temperature (Tg), specifically, a Tg of 110 ° C. or higher when measured in accordance with ASTM-D-3418, and is heat resistant. Excellent. A film obtained by molding such an acrylic polymer having high heat resistance can be placed close to a heat generating part such as a light source in an image display device such as a liquid crystal display device.

  The Tg of the acrylic polymer of the present invention is 115 ° C. or higher, 120 ° C. or higher, and 130 ° C. or higher, depending on the type of ring structure and the ring structure content in the acrylic polymer.

  In addition, the acrylic polymer of the present invention has a ring structure in the main chain, so that depending on the type of ring structure and the content thereof, the optical properties when formed into a molded body compared to the case without the ring structure. The characteristics are improved.

  The ring structure is typically a ring structure formed through a dealcoholization cyclocondensation reaction in an acrylic polymer that is a precursor of an acrylic polymer. At this time, the acrylic polymer as a precursor has a structural unit represented by the above formula (1) or (2).

  The dealcoholization cyclocondensation reaction is, for example, (i) a reaction between the carboxyl group or hydroxy group and the ester group in an acrylic polymer having a carboxyl group or hydroxy group and an ester group in the molecular chain, or (ii) This is a reaction between two ester groups and an imidizing agent added to the reaction system in an acrylic polymer having an ester group in the molecular chain. The hydroxy group, carboxyl group, and ester group may be bonded to the main chain of the acrylic polymer directly or via some atoms.

  Specific examples of the reaction (i) include (i-1) an ester group of a (meth) acrylic acid ester unit that the acrylic polymer has as a structural unit, and a carboxyl group of a (meth) acrylic acid unit that also has as a structural unit. Or (i-2) the ester group of the (meth) acrylic acid ester unit that the acrylic polymer has as a structural unit, and the hydroxy group-containing (meth) acrylic acid ester unit that also has the structural unit Reaction between hydroxy groups. A specific example of the reaction (ii) is a reaction between two ester groups of a (meth) acrylic acid ester unit that an acrylic polymer has as a structural unit and an imidizing agent. Note that these reactions usually occur between constituent units adjacent on the main chain.

  A specific example of the ring structure is at least one selected from a lactone ring structure, a glutaric anhydride structure, and a glutarimide structure. The ring structure is preferably at least one selected from a lactone ring structure and a glutaric anhydride structure, and more preferably a lactone ring structure, because a molded article having a high degree of freedom in controlling optical properties such as wavelength dispersion can be obtained. .

  The lactone ring structure is not particularly limited, and for example, is a structure represented by the following formula (8).

R ⁷ , R ⁸ and R ⁹ in formula (8) are independently of each other a hydrogen atom or a group similar to the organic residue in formula (1).

The lactone ring structure represented by the formula (8) is, for example, dealcoholization cyclocondensation with respect to an acrylic polymer having a methyl methacrylate (MMA) unit and a 2- (hydroxymethyl) methyl acrylate (MHMA) unit. It can be formed by advancing the reaction. The cyclization condensation reaction at this time is the reaction of (i-2) above, and R ⁷ of the formed lactone ring structure is H, R ⁸ is CH ₃ , and R ⁹ is CH ₃ . In addition, the dealcoholization cyclocondensation reaction proceeds also between a part of the structural unit represented by the formula (1) or (2) of the acrylic polymer as a precursor and the MHMA unit, and the formula (8) The lactone ring structure shown is formed.

  When the lactone ring structure represented by the formula (8) is present in the main chain of the polymer, the intrinsic birefringence of the polymer is positively increased as compared with the case where the lactone ring structure is not present. The acrylic polymer of the present invention having a lactone ring structure represented by the formula (8) in the main chain is suitable for, for example, a positive retardation film, although it depends on the type of other structural units and the content thereof. It is.

  The following formula (9) shows a glutarimide structure and a glutaric anhydride structure.

In the formula (9), R ¹⁰ and R ¹¹ are each independently a hydrogen atom or a methyl group, and X ¹ is an oxygen atom or a nitrogen atom. When X ¹ is an oxygen atom, R ¹² does not exist, and when X ¹ is a nitrogen atom, R ¹² is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. .

When X ¹ is an oxygen atom, the ring structure shown in Formula (9) is a glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by proceeding a dealcoholization cyclocondensation reaction on an acrylic polymer having a (meth) acrylic acid ester unit and a (meth) acrylic acid unit. The cyclization condensation reaction at this time is the reaction (i-1). Note that the dealcoholization cyclocondensation reaction also proceeds between a part of the structural units represented by the formula (1) or (2) of the acrylic polymer and the (meth) acrylic acid unit, so that the glutaric anhydride structure is formed. It is formed.

When X ¹ is a nitrogen atom, the ring structure shown in Formula (9) is a glutarimide structure. The glutarimide structure can be formed, for example, by advancing a dealcoholization cyclocondensation reaction on an acrylic polymer having a (meth) acrylic acid ester unit in the presence of an imidizing agent. The cyclization condensation reaction at this time is the reaction (ii) above. Note that a dealcoholization cyclocondensation reaction involving a part of the structural unit represented by the formula (1) or (2) of the acrylic polymer also proceeds to form a glutarimide structure. The imidizing agent includes, for example, an amine containing an aliphatic hydrocarbon group such as methylamine, ethylamine, n-propylamine, i-propylamine, n-butylamine, i-butylamine, tert-butylamine, n-hexylamine; aniline, An aromatic hydrocarbon group-containing amine such as toluidine or trichloroaniline; an alicyclic hydrocarbon-containing amine such as cyclohexylamine; ammonia. In addition, urea compounds such as urea, 1,3-dimethylurea, 1,3-diethylurea, and 1,3-dipropylurea that generate these amines by heating may be used as an imidizing agent.

When the glutaric anhydride structure is present in the main chain of the polymer, the intrinsic birefringence of the polymer is positively increased as compared with the case where it is not present. When the glutarimide structure is present in the main chain of the polymer, the intrinsic birefringence of the polymer is positively increased depending on the type of R ¹² as compared to the case where the structure is not present.

  The content of the ring structure in the main chain of the acrylic polymer of the present invention is not particularly limited, and may be adjusted according to the desired properties as the acrylic polymer, for example, 5 to 90% by weight, 80 weight% is preferable and 20 to 60 weight% is more preferable.

  The content of the lactone ring structure can be determined by the dynamic TG method as follows. First, a dynamic TG measurement is performed on an acrylic polymer having a lactone ring structure, a weight loss rate between 150 ° C. and 300 ° C. is measured, and the obtained value is an actual weight loss rate (X). And 150 ° C. is a temperature at which a hydroxy group and an ester group remaining in the polymer start a cyclization condensation reaction, and 300 ° C. is a temperature at which thermal decomposition of the acrylic polymer starts. Separately, assuming that all hydroxy groups contained in the precursor acrylic polymer have undergone dealcoholization cyclocondensation reaction to form a lactone ring, the weight loss rate by the reaction (ie, precursor The weight reduction rate assuming that the dealcoholization cyclocondensation reaction rate of the body was 100%) was calculated and used as the theoretical weight reduction rate (Y). Specifically, the theoretical weight reduction rate (Y) can be determined from the content of the structural unit having a hydroxy group involved in the dealcoholization cyclocondensation reaction in the precursor. The composition of the precursor can be derived from the composition of the acrylic polymer. Next, the dealcoholization reaction rate of the acrylic polymer is determined by the formula [1- (actually measured weight reduction rate (X) / theoretical weight reduction rate (Y))] × 100 (%). In the acrylic polymer, it is considered that a lactone ring structure is formed for the determined dealcoholization reaction rate. Therefore, the acrylic polymer is obtained by multiplying the content of the structural unit having a hydroxy group involved in the dealcoholization cyclocondensation reaction in the precursor by the obtained dealcoholization reaction rate and converting it to the weight of the lactone ring structure. The content of the lactone ring structure in can be determined.

The content of the glutaric anhydride structure and the glutarimide structure can be determined by a known method, for example, ¹ H nuclear magnetic resonance ( ¹ H-NMR) or infrared spectroscopic analysis (IR).

  The (meth) acrylic acid ester unit other than the structural unit represented by the formula (1) or (2) that the acrylic polymer of the present invention may have as a structural unit is, for example, methyl acrylate or ethyl acrylate. Acrylate monomers such as acrylate, n-propyl acrylate, n-butyl acrylate, phenyl acrylate, naphthyl acrylate, anthracenyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n methacrylate -A structural unit formed by polymerization of methacrylic acid ester monomers such as butyl, phenyl methacrylate, naphthyl methacrylate, anthracenyl methacrylate.

  The hydroxy group-containing (meth) acrylic acid ester unit that the acrylic polymer of the present invention may have as a structural unit is, for example, methyl 2- (hydroxymethyl) acrylate, 2- (hydroxymethyl) acrylic acid Ethyl, isopropyl 2- (hydroxymethyl) acrylate, n-butyl 2- (hydroxymethyl) acrylate, t-butyl 2- (hydroxymethyl) acrylate, 2- (hydroxymethyl) methyl methacrylate, 2- (hydroxy Methyl) ethyl methacrylate, 2- (hydroxymethyl) isopropyl methacrylate, 2- (hydroxymethyl) n-butyl methacrylate and 2- (hydroxymethyl) t-butyl methacrylate are formed by polymerization. It is a structural unit.

  Since an acrylic polymer having high heat resistance and transparency is obtained, the acrylic polymer of the present invention preferably has a methyl methacrylate (MMA) unit. When the main chain has a lactone ring structure, it preferably has a 2- (hydroxymethyl) methyl acrylate (MHMA) unit together with the MMA unit.

  The acrylic polymer of the present invention has a structural unit represented by the formula (1) or (2) and is formed through a ring structure in the main chain, typically a dealcoholization cyclocondensation reaction in an acrylic polymer. Despite having a ring structure, the content of foreign matter is small. When the acrylic polymer of the present invention is a chloroform solution having a concentration of 15% by weight, the turbidity of the solution measured in a measurement cell having a measurement light transmission distance of 1 cm is 2% or less. The turbidity is 1.5% or less, 1% or less, and further 0.5% or less depending on the type and content of the structural unit of the acrylic polymer and the production conditions of the acrylic polymer. .

  As long as the effects of the present invention are obtained, the acrylic polymer of the present invention is a structural unit derived from (meth) acrylic acid ester units, (meth) acrylic acid units and derivatives of these units (rings such as lactone ring structures). Including structural units) and structural units other than the structural units represented by formula (1) or (2). Such a structural unit is, for example, a structural unit formed by polymerization of each monomer of styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate.

  The acrylic polymer of the present invention can be produced, for example, by the method for producing an acrylic polymer of the present invention.

[Method for producing acrylic polymer]
<Acrylic polymer>
In the production method of the present invention, (I) dealcoholization cyclization between a hydroxy group or a carboxyl group in the molecular chain of the acrylic polymer as a precursor and an ester group in the molecular chain of the acrylic polymer Either proceed with the condensation reaction or (II) proceed with the dealcoholization cyclocondensation reaction between the two ester groups in the molecular chain of the acrylic polymer that is the precursor and the imidizing agent added to the reaction system By doing so, a ring structure is formed in the main chain of the acrylic polymer to form the acrylic polymer of the present invention. Here, the cyclization catalyst used for the progress of the dealcoholization cyclization condensation reaction is a zinc compound.

  The acrylic polymer as a precursor satisfies the above-described conditions for the content of constituent units derived from (meth) acrylic acid ester units, (meth) acrylic acid units, and derivatives of these units, and the formula (1) or As long as it has the structural unit shown in (2) and a ring structure is formed in the main chain by the dealcoholization cyclocondensation reaction shown in the above (I) or (II), it is not particularly limited. The hydroxy group, carboxyl group, and ester group involved in the reaction may be bonded to the main chain of the acrylic polymer directly or via some atoms. Specific examples of the dealcoholization cyclocondensation reaction and specific examples of the ring structure formed by the reaction are as described in the description of the acrylic polymer of the present invention.

  As an example, in the production method of the present invention, a dealcoholization cyclocondensation reaction is allowed to proceed on an acrylic polymer that is a precursor, so that the main chain of the polymer has a lactone ring structure, anhydrous glutarite as a ring structure. You may form at least 1 sort (s) chosen from an acid structure and a glutarimide structure. As a more specific example, for an acrylic polymer having a hydroxy group and an ester group in the molecular chain, a ring structure is obtained by allowing a dealcoholization cyclocondensation reaction to proceed between the hydroxy group and the ester group. A lactone ring structure may be formed.

  In the production method of the present invention, a reaction system comprising at least a part of a hydroxy group and an ester group, at least a part of a carboxyl group and an ester group, or an ester group by a dealcoholization cyclocondensation reaction on an acrylic polymer as a precursor. At least a part of the imidizing agent added to is condensed and cyclized to form a ring structure in the main chain.

  In the acrylic polymer for proceeding the reaction of (I), it is preferable that the hydroxy group or the carboxyl group and the ester group exist in close proximity to each other. In this case, the progress of the dealcoholization cyclization condensation reaction is promoted, A ring structure is easily formed.

  The acrylic polymer that advances the reaction (I) may have both a hydroxy group and a carboxyl group.

  In the acrylic polymer that promotes the reaction of (II), it is preferable that ester groups involved in the reaction are present close to each other. In this case, the progress of the dealcoholization cyclocondensation reaction is promoted, and the ring structure Is easily formed.

  An acrylic polymer having a hydroxy group and an ester group in the molecular chain is, for example, a monomer that becomes a structural unit represented by the formula (1) or (2) by polymerization and both the hydroxy group and the ester group in the molecular chain. It can form by polymerizing with the monomer which has. Instead of a monomer having both a hydroxy group and an ester group, a monomer having a hydroxy group in the molecular chain and a monomer having an ester group in the molecular chain may be used. In addition, the acrylic polymer has a hydroxy group added to the polymer having the structural unit represented by the formula (1) or (2), the polymer having an ester group in the molecular chain is hydrolyzed, a carboxyl group or It can also be formed by esterifying the polymer having an acid anhydride group in the molecular chain. That is, a hydroxy group or an ester group may be introduced into the polymer later to form an acrylic polymer.

  Similarly, the acrylic polymer having a carboxyl group and an ester group in the molecular chain is, for example, a monomer that becomes a structural unit represented by the formula (1) or (2) by polymerization, and both the carboxyl group and the ester group. Can be formed by polymerizing with a monomer having in the molecular chain. Instead of a monomer having both a carboxyl group and an ester group in the molecular chain, a monomer having a carboxyl group in the molecular chain and a monomer having an ester group in the molecular chain may be used.

  An acrylic polymer having an ester group in a molecular chain and undergoing condensation cyclization by a dealcoholization cyclocondensation reaction between an imidizing agent added to the reaction system and the two ester groups is represented by, for example, a formula ( It can be formed by polymerizing a monomer as a constituent unit shown in 1) or (2) and a monomer having an ester group in the molecular chain.

  The (meth) acrylic acid ester unit possessed by the acrylic polymer is, for example, the (meth) acrylic acid ester unit described above in the description of the acrylic polymer of the present invention.

  As long as the acrylic polymer of the present invention is obtained, the acrylic polymer is a structural unit derived from a (meth) acrylic acid ester unit, a (meth) acrylic acid unit and a derivative of these units, and the formula (1) or ( You may have structural units other than the structural unit shown in 2). Such a structural unit is, for example, a structural unit formed by polymerization of each monomer of styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate.

  A specific polymerization method for obtaining the acrylic polymer is not particularly limited, but solution polymerization is preferable. In this case, after obtaining an acrylic polymer by polymerization, it is possible to subsequently carry out a dealcoholization cyclocondensation reaction of the polymer.

  When an acrylic polymer is formed by solution polymerization, in addition to the acrylic polymer, the polymerization solvent used for the polymerization is included in the polymerization product, but the solvent is not necessarily removed and the acrylic polymer is taken out as a solid. It does not have to be. As described above, the polymerization product can be introduced into the dealcoholization cyclocondensation step while containing the solvent. Of course, after the acrylic polymer is taken out as a solid, a solvent more suitable than the solvent used in the polymerization may be added again to allow the dealcoholization cyclocondensation reaction to proceed.

  When forming an acrylic polymer by solution polymerization, the polymerization solvent used is, for example, aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as methyl ethyl ketone and methyl isobutyl ketone; chloroform, dimethyl sulfoxide (DMSO) , Tetrahydrofuran and the like. Of these, aromatic hydrocarbons and ketones are preferably used as the polymerization solvent, and in particular, toluene and methyl isobutyl ketone are preferably used.

  When the acrylic polymer is polymerized, a polymerization initiator can be used as necessary. The polymerization initiator is not particularly limited, and examples thereof include cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropyl carbonate, and t-amyl peroxide. Organic peroxides such as oxy-2-ethylhexanoate; 2,2′-azobis (isobutyronitrile), 1,1′-azobis (cyclohexanecarbonitrile), 2,2′-azobis (2-methyl) Azo compounds such as isobutyronitrile) and 2,2′-azobis (2,4-dimethylvaleronitrile); Two or more polymerization initiators may be used in combination. What is necessary is just to set the usage-amount of a polymerization initiator suitably according to the combination of the monomer used for superposition | polymerization, or polymerization conditions.

  In the production method of the present invention, depending on the structure of the acrylic polymer (specifically, the conditions for polymerizing and forming the acrylic polymer overlap with the conditions for the dealcoholization cyclocondensation of the formed acrylic polymer. The acrylic polymer formed can be condensed and cyclized at the same time as the polymerization of the acrylic polymer proceeds.

<Dealcoholization cyclocondensation reaction>
In the dealcoholization cyclocondensation reaction in the production method of the present invention, heating causes at least a part of the hydroxy group or carboxyl group present in the molecular chain of the acrylic polymer and at least a part of the ester group to undergo condensation cyclization ( The reaction (I)), or at least a part of the ester group present in the molecular chain of the acrylic polymer and at least a part of the imidizing agent added to the reaction system are condensed and cyclized (the reaction (II) ), A reaction in which a ring structure such as a lactone ring structure, a glutaric anhydride structure, or a glutarimide structure is formed in the main chain of the polymer. This reaction is a kind of transesterification reaction, and as its name suggests, alcohol is by-produced.

  In the production method of the present invention, a zinc compound is used as a catalyst for this reaction. Thereby, the quantity of the foreign material contained in the acrylic polymer formed by the reaction is reduced. The reason why the amount of foreign matter is reduced is that the alcohol generated from the structural unit represented by the formula (1) or (2), which is found when an organic phosphorus compound, which is a conventional catalyst, is used by using a zinc compound as a catalyst. This is presumably because the addition reaction of does not proceed in a chain.

  Further, the use of a zinc compound is expected to improve the speed of dealcoholization cyclization condensation reaction and to suppress the condensation cyclization reaction between acrylic polymers, that is, the occurrence of cross-linking between polymers.

  Examples of the zinc compound include organic zinc compounds such as zinc acetate, zinc propionate, and zinc octylate; inorganic zinc compounds such as zinc oxide, zinc chloride, and zinc sulfate; organic zinc compounds containing fluorine such as zinc trifluoromethanesulfonate; It is.

  The amount of the zinc compound used as a catalyst for the dealcoholization cyclocondensation reaction is not particularly limited, but is preferably 0.005 to 0.5% by weight based on the weight of the acrylic polymer as the precursor, and 0 0.01 to 0.3 wt% is more preferable, and 0.02 to 0.1 wt% is more preferable. When the amount of the zinc compound used is less than 0.005% by weight, the cyclization reaction rate is not sufficiently improved. On the other hand, when the amount of the zinc compound used exceeds 0.5% by weight, the obtained acrylic polymer may be colored or the obtained acrylic polymer may contain a gel.

  The dealcoholization cyclocondensation reaction of the acrylic polymer can be initiated by heating. For this reason, the timing at which the catalyst is added is not particularly limited. For example, the catalyst may be added before the reaction or at the initial stage of the reaction, or may be added at any time after the reaction starts.

  Although reaction conditions are not specifically limited, 80 degreeC or more is preferable and reaction temperature is preferable 80-150 degreeC. If the reaction temperature is excessively high, the resulting acrylic polymer may be colored or gelled.

  Other specific methods and conditions other than those described above for advancing the dealcoholization cyclocondensation reaction on the acrylic polymer are the methods disclosed in Japanese Patent Application Laid-Open No. 2008-189886 (Patent Document 1). For example, a known method may be applied.

[Acrylic resin composition]
The acrylic resin composition of the present invention contains the acrylic polymer of the present invention as a main component. Since the acrylic resin composition of the present invention contains the acrylic polymer of the present invention as a main component, the amount of foreign matter contained is small. Moreover, when the acrylic polymer has a ring structure in the main chain, the resin composition is excellent in heat resistance. Depending on the type and content of the ring structure, the resin composition is excellent in optical properties when formed into a molded body, typically as an optical film. In addition, a main component is a component with the largest content rate in a composition, The content rate is 50 weight% or more normally, Preferably it is 60 weight% or more, More preferably, it is 70 weight% or more.

  As long as the effect of this invention is acquired, the acrylic resin composition of this invention can contain arbitrary materials other than the acrylic polymer of this invention. Such materials are, for example, other polymers, elastic organic fine particles, and additives.

  Other polymers include, for example, olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; Styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; polyamides such as nylon 6, nylon 66, nylon 610; Polyacetal; Polycarbonate; Polyphenylene oxide; Polyphenylene sulfide; Polyetheretherketone; Polysulfone; Polyethersulfone; Polyoxybenzylene; Polyamideimide.

  Additives include, for example, hindered phenol-based, phosphorus-based, sulfur-based antioxidants; light-resistant stabilizers, weather-resistant stabilizers, thermal stabilizers, and other stabilizers; reinforcing materials such as glass fibers and carbon fibers; UV absorbers such as tyrates, (2,2′-hydroxy-5-methylphenyl) benzotriazole, 2-hydroxybenzophenone; near infrared absorbers; difficulties such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide Antistatic agents such as anionic, cationic and nonionic surfactants; colorants such as inorganic pigments, organic pigments and dyes; organic fillers, inorganic fillers; resin modifiers; organic fillers, inorganic fillers; Plasticizer; a lubricant.

  For example, the acrylic resin composition of the present invention may further contain elastic organic fine particles at a content of 5% by weight or more. By further containing the elastic organic fine particles, the flexibility of the film is further improved.

  The elastic organic fine particles are, for example, elastic organic fine particles having a structural unit (for example, a butadiene unit or an isoprene unit) formed by polymerization of a conjugated diene monomer. As the elastic organic fine particles, the elastic organic fine particles disclosed in JP 2008-242421 A (Patent Document 2) can be used. The method for producing elastic organic fine particles is disclosed in the publication.

  When the acrylic resin composition of the present invention contains elastic organic fine particles, the content of elastic organic fine particles in the resin composition is, for example, 5 to 50% by weight, preferably 5 to 30% by weight, and 10 to 20% by weight. Is more preferable.

  The acrylic resin composition of the present invention can be produced by a known method using the acrylic polymer of the present invention.

  The acrylic resin composition of this invention can be shape | molded in arbitrary shapes, and can be used for arbitrary uses. The acrylic resin composition of the present invention is suitable for use as an optical member because of the small amount of foreign matter contained. The optical member is, for example, an optical protective film (sheet), specifically, a protective film for various optical disk (VD, CD, DVD, MD, LD, etc.) substrates, or an image display device such as a liquid crystal display (LCD). It is a polarizer protective film used for the polarizing plate with which is provided. Also, for example, retardation films, viewing angle compensation films, light diffusion films, reflection films, antireflection films, antiglare films, brightness enhancement films, optical films such as touch panel conductive films, diffusion plates, light guides, retardations An optical sheet such as a plate or a prism sheet.

[Phase difference film]
The retardation film of the present invention contains the acrylic polymer of the present invention as a main component. Thereby, the amount of foreign matter contained is small, and the retardation film has few optical defects. In addition, since the acrylic polymer has a ring structure in the main chain, the heat resistance is excellent, and depending on the type and content of the ring structure, the optical characteristics are also excellent. Furthermore, since the acrylic polymer has the structural unit represented by the above formula (1) or (2), the flexibility is excellent.

  The retardation film of the present invention can be formed by forming a resin composition containing the acrylic polymer of the present invention as a main component into a film by a technique such as extrusion, and stretching the obtained film. A known method may be applied to a method for forming the film and a method for stretching the obtained film.

  The content of the acrylic polymer of the present invention in the retardation film of the present invention is more preferably 60% by weight or more, and even more preferably 70% by weight or more in order to obtain the above-described effects more reliably.

  When the acrylic polymer of the present invention has the lactone ring structure represented by the formula (8) in the main chain, the retardation film of the present invention includes the content of the lactone ring structure in the polymer and the retardation film of the present invention. Although it depends on the content of the acrylic polymer, it is typically a positive retardation film.

  The use of the retardation film of the present invention is not particularly limited. The retardation film of the present invention is suitable for an image display device such as a liquid crystal display device based on the excellent characteristics described above.

[Image display device]
The structure of the image display device of the present invention is not particularly limited as long as it includes the retardation film of the present invention. The image display device of the present invention is, for example, a liquid crystal display device (LCD), and the image display unit of the LCD device includes the retardation film of the present invention together with members such as a liquid crystal cell, a polarizing plate, and a backlight. The image display device of the present invention typically includes the retardation film of the present invention as an optical compensation film. The retardation film of the present invention may be provided as a polarizer protective film for a polarizing plate.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below.

(Production Example 1: Production of elastic organic fine particles)
In a polymerization vessel equipped with a cooler and a stirrer, 120 parts by weight of deionized water, 50 parts by weight of butadiene-based rubber polymer latex (average particle size 240 nm) (in terms of solid content), 1.5 parts by weight of potassium oleate and soy 0.6 wt part of formaldehyde sulfoxylate (SFS) was added, and the inside of the polymerization vessel was sufficiently replaced with nitrogen gas.

  Next, after raising the temperature in the container to 70 ° C., a mixed monomer solution comprising 36.5 parts by weight of styrene and 13.5 parts by weight of acrylonitrile, 0.27 parts by weight of cumene hydroxyperoxide and 20 deionized water. The polymerization was advanced while continuously dropping dropwise a polymerization initiator solution consisting of 0.0 part by weight over 2 hours. After completion of the dropping, the temperature in the container was set to 80 ° C., and the polymerization was further continued for 2 hours. Next, after the temperature in the container was lowered to 40 ° C., the contents were passed through a 300-mesh wire mesh to obtain an emulsion polymerization liquid of elastic organic fine particles.

  The obtained emulsion polymerization liquid of elastic organic fine particles is salted out and coagulated with calcium chloride, and the solidified product is washed with water and dried to obtain powdered elastic organic fine particles (G1) (average particle size 0.260 μm, soft A refractive index of 1.516) of the polymer layer was obtained. The average particle size of the elastic organic fine particles was evaluated by a particle size distribution measuring device (Submicron Particle Sizer NICOMP380) manufactured by NICOMP.

  The butadiene rubber polymer latex used for the production of the elastic organic fine particles was produced by the following method. In a pressure-resistant reaction vessel, 70 parts by weight of deionized water, 0.5 parts by weight of sodium pyrophosphate, 0.2 parts by weight of potassium oleate, 0.005 parts by weight of ferrous sulfate, 0.2 parts by weight of dextrose, p-menthane A reaction mixture consisting of 0.1 part by weight of hydroperoxide and 28 parts by weight of 1,3-butadiene was added, the temperature in the container was raised to 65 ° C., and polymerization was allowed to proceed for 2 hours. Next, 0.2 parts by weight of p-hydroperoxide was further added to the mixture in the container obtained by this polymerization, and then 72 parts by weight of 1,3-butadiene, 1.33 parts by weight of potassium oleate and desorption were performed. A mixture of 75 parts by weight of ionic water was continuously added dropwise over 2 hours. Thereafter, the polymerization was allowed to proceed until 21 hours had elapsed from the start of polymerization to obtain a butadiene-based rubber polymer latex.

Example 1
In a reaction vessel having an internal volume of 30 L equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 2500 g of methyl 2- (hydroxymethyl) acrylate (MHMA), 5200 g of methyl methacrylate (MMA), benzyl methacrylate (BzMA) ) 2300 g and 10000 g of toluene as a polymerization solvent were charged, and the temperature was raised to 105 ° C. through nitrogen. When refluxing with increasing temperature started, 6.0 g of t-amylperoxyisononanoate (manufactured by Atofina Yoshitomi, trade name: Lupazole 570) was added as a polymerization initiator, and the above t-to 100 g of toluene. While a solution in which 12.0 g of amyl peroxyisononanoate was dissolved was dropped over 6 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by further heating and aging for 2 hours. The reaction rate of the obtained polymer (precursor) is 96.4%, and the proportion of MHMA units (content of MHMA units) in the total constituent units of the precursor is 25.1% by weight, the proportion of BzMA units. (BzMA unit content) was 23.2% by weight.

  Next, 20 g of zinc octylate was added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction, and the cyclization condensation reaction was allowed to proceed for 2 hours under reflux at about 80 to 105 ° C. Next, the mixture was further heated at 240 ° C. for 90 minutes under pressure (maximum gauge pressure of 1.6 MPa) by an autoclave. The obtained polymerization solution was converted into a vent type screw twin screw extruder (φ = four) having a barrel temperature of 250 ° C., a rotation speed of 100 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 4. 29.75 mm, L / D = 30) was introduced at a processing rate of 2.0 kg per hour in terms of resin amount, and further cyclization condensation reaction and devolatilization were performed in the extruder. Thereafter, the contents were extruded from an extruder to obtain transparent pellets (P1) made of an acrylic polymer having a lactone ring structure in the main chain and having MMA units, MHMA units and BzMA units as constituent units.

When dynamic TG was measured for the obtained pellet (P1), a weight loss of 0.15% by weight was detected. The weight average molecular weight of the polymer constituting the pellet (P1) was 135,000, the glass transition temperature (Tg) was 130 ° C., and the melt flow rate (MFR) of the pellet (P1) was 30 g / 10 minutes. It was. The ratio of the BzMA unit in the total constituent units of the polymer constituting the pellet (P1) obtained from ¹ H-NMR measurement was 23.6% by weight (content of BzMA unit). ¹ H-NMR measurement was carried out by using FT-NMR UNITY plus 400 (400 MHz) manufactured by Varian, using deuterated chloroform as a solvent and mesitylene as an internal standard. The refractive index of the polymer measured by producing a press film was 1.517.

The weight average molecular weight of the polymer constituting the pellet (P1) was determined by gel conversion using gel permeation chromatography (GPC). The equipment and measurement conditions used for the measurement are as follows:
System: manufactured by Tosoh Column: TSK-GEL SuperHZM-M 6.0 × 150 2 in series Guard column: TSK-GEL SuperHZ-L 4.6 × 35 1 Reference column: TSK-GEL SuperH-RC 6.0 × 150 2 in series Eluent: Chloroform Flow rate 0.6 mL / min Column temperature: 40 ° C.

  The glass transition temperature (Tg) of the polymer constituting the pellet (P1) was determined in accordance with ASTM-D-3418. Specifically, a differential scanning calorimeter (manufactured by Rigaku Corporation, DSC-8230) was used to raise a temperature of about 10 mg from room temperature to 200 ° C. under a nitrogen flow (50 mL / min). From the DSC curve obtained by the above method, the midpoint method was used for evaluation. Α-alumina was used as a reference.

The measurement of dynamic TG for the pellet (P1) was performed as follows. The prepared pellet (P1) was dissolved in tetrahydrofuran (THF), and then an acrylic polymer was precipitated using excess hexane or methanol. Next, the precipitate is vacuum-dried (pressure 1.33 hPa, 80 ° C., 3 hours or more) to remove volatile components, and the obtained white solid resin is subjected to dynamic TG measurement under the following measurement conditions. did;
Measuring device: Rigaku, Thermo Plus 2 TG-8120 Dynamic TG
Sample weight: 5-10mg
Temperature increase rate: 10 ° C./min Atmosphere: under nitrogen flow (200 ml / min) Measurement method: step-like isothermal control method (controlled at 60 to 500 ° C. with a weight reduction rate value of 0.005% / sec or less) .

  The MFR of the pellet (P1) was measured at a test temperature of 240 ° C. and a test load of 10 kg in accordance with JIS K6874.

  About the characteristic of each pellet produced by subsequent comparative examples 1 and 2, it evaluated by the same method as the evaluation method with respect to a pellet (P1).

(Comparative Example 1)
In the same manner as in Example 1 except that 20 g of an octyl phosphate / dioctyl phosphate mixture (Phoslex A-8, manufactured by Sakai Chemical) was used in place of zinc octylate as a catalyst for the cyclization condensation reaction, Transparent pellets (P2) made of an acrylic polymer having a ring structure and having MMA units, MHMA units, and BzMA units as constituent units were obtained.

When dynamic TG was measured for the obtained pellet (P2), a weight loss of 0.15% by weight was detected. Moreover, the weight average molecular weight of the polymer which comprises a pellet (P2) was 150,000, Tg was 130 degreeC, and MFR of the pellet (P2) was 20 g / 10min. The ratio of BzMA units to the total constituent units of the polymer constituting the pellet (P2) determined from ¹ H-NMR measurement (the content of BzMA units) was 23.6% by weight. The refractive index of the polymer measured by producing a press film was 1.517.

(Comparative Example 2)
MHMA 3000 g, MMA 7000 g and toluene 6667 g as a polymerization solvent were charged in a reaction vessel having an internal volume of 30 L equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, and the temperature was raised to 105 ° C. through nitrogen. When refluxing with a rise in temperature started, 6.0 g of t-amylperoxyisononanoate (manufactured by Atofina Yoshitomi, trade name: Lupazole 570) was added as a polymerization initiator, and the above t- was added to 3315 g of toluene. While a solution in which 12.0 g of amyl peroxyisononanoate was dissolved was added dropwise over 3 hours, solution polymerization was allowed to proceed under reflux at about 95 to 110 ° C., followed by further heating and aging for 4 hours. The reaction rate of the obtained polymer (precursor) was 94.5%, and the proportion of MHMA units (content of MHMA units) in all the constituent units of the precursor was 29.7% by weight.

  Next, 20 g of an octyl phosphate / dioctyl phosphate mixture (Phoslex A-8, manufactured by Sakai Chemical Co., Ltd.) as a catalyst for the cyclization condensation reaction is added to the obtained polymerization solution and refluxed at about 85 to 100 ° C. for 2 hours. The cyclization condensation reaction was allowed to proceed. Next, it was further heated by an autoclave at 240 ° C. for 90 minutes under pressure (maximum gauge pressure of 2 MPa). The obtained polymerization solution was introduced into the same vent type screw twin screw extruder as in Example 1 at a processing rate of 2.0 kg per hour in terms of resin amount, and further cyclization condensation reaction and devolatilization were carried out in the extruder. went. Thereafter, the contents were extruded from an extruder to obtain transparent pellets (P3) made of an acrylic polymer having a lactone ring structure in the main chain and having MMA units and MHMA units as constituent units.

  When dynamic TG was measured for the obtained pellet (P3), a weight loss of 0.25 wt% was detected. Moreover, the weight average molecular weight of the polymer which comprises a pellet (P3) was 127,000, Tg was 140 degreeC, and MFR of the pellet (P3) was 6.5 g / 10min. The refractive index of the polymer measured by preparing a press film was 1.504.

  3 g of each pellet prepared in Example 1 and Comparative Examples 1 and 2 was sufficiently dissolved in 17 g of chloroform to obtain a solution having a concentration of 15% by weight, and the solution was placed in a quartz cell for measurement having a transmission distance of 1 cm for measurement light. The turbidity of the solution in the cell was measured with a haze meter (Nippon Denshoku, NDH5000). The measurement results are shown in Table 1 below.

(Example 2)
The pellet (P1) produced in Example 1 was melt-extruded from a T-type die having a width of 150 mm using a single screw extruder having a 30 mmφ screw to produce a film having a thickness of about 140 μm. The obtained unstretched film was uniaxially stretched using an autograph (manufactured by Shimadzu Corporation, AGS-100D) at a stretching temperature of 130 ° C., a stretching speed of 400% / min, and a stretching ratio of 2 times, and stretched to a thickness of 100 μm. A film (FP1) was obtained.

(Example 3)
While feeding the pellet (P1) produced in Example 1 and the elastic organic fine particles (G1) produced in Production Example 1 using a feeder so that the weight ratio of P1: G1 = 80: 20, the cylinder Using a twin screw extruder with a diameter of 20 mm, the mixture was kneaded at 240 ° C. to obtain pellets (B1) made of a resin composition having a structure in which G1 was dispersed in a P1 matrix. The obtained pellet (B1) was melt extruded in the same manner as in Example 2 to form an unstretched film having a thickness of 140 μm, and then further uniaxially stretched in the same manner as in Example 2 to obtain a stretched film (FB1) having a thickness of 98 μm. Got.

  For the stretched films produced in Examples 2 and 3, the in-plane direction retardation (per 100 μm film thickness) was evaluated by a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR). The stretched film (FP1) produced in Example 2 was 251 nm, and the stretched film (FB1) produced in Example 3 was 254 nm.

  The acrylic polymer of the present invention can be suitably used for an optical member such as a retardation film.

Claims (15)

Having a structural unit represented by the following formula (1 ) and having a ring structure in the main chain;
The glass transition temperature measured in accordance with the provisions of ASTM-D-3418 is 110 ° C. or higher,
An acrylic polymer having a turbidity of 2% or less when measured in a measuring cell having a measurement light transmission distance of 1 cm when a chloroform solution having a concentration of 15% by weight is used.

R ¹ to R ³ which in formula (1) are each independently a hydrogen atom or an organic residue having a carbon number of 1 to 20, A r is an aryl group. The acrylic polymer according to claim 1, wherein R ² and R ³ are hydrogen atoms. The acrylic polymer according to claim 2 , wherein R ¹ is a methyl group, and Ar is a phenyl group. The ring structure is a ring structure formed through a dealcoholization cyclocondensation reaction in an acrylic polymer that is a precursor of the acrylic polymer,
The acrylic polymer according to claim 1, wherein the acrylic polymer has a structural unit represented by the formula (1 ) . The dealcoholization cyclocondensation reaction is
(I) reaction of the carboxyl group or hydroxy group with the ester group in the acrylic polymer having a carboxyl group or hydroxy group and an ester group in the molecular chain; or (ii) the ester group having a molecular chain in the molecular chain. The acrylic polymer according to claim 4 , which is a reaction between the two ester groups in the acrylic polymer and an imidizing agent added to the reaction system of the reaction.   The acrylic polymer according to claim 1, wherein the ring structure is at least one selected from a lactone ring structure, a glutaric anhydride structure, and a glutarimide structure.   The acrylic polymer according to claim 1, wherein the ring structure is a lactone ring structure.   An acrylic resin composition comprising the acrylic polymer according to claim 1 as a main component. The acrylic resin composition according to claim 8 , further comprising elastic organic fine particles at a content of 5% by weight or more.   A retardation film comprising the acrylic polymer according to claim 1 as a main component. A polarizer protective film comprising the acrylic polymer according to claim 1 as a main component. An image display device comprising the retardation film according to claim 10 or the polarizer protective film according to claim 11 . A method for producing an acrylic polymer having a structural unit represented by the following formula (1 ) and having a ring structure in the main chain,
(I) The acrylic polymer having the structural unit shown in (1 ) , which is a precursor of the acrylic polymer, and having a carboxyl group or a hydroxy group and an ester group in a molecular chain. Or (II) having the structural unit shown in the above (1 ) , which is a precursor of the acrylic polymer, or proceeds with a dealcoholization cyclocondensation reaction between a group or a hydroxy group and the ester group, By proceeding a dealcoholization cyclocondensation reaction between two ester groups and an imidizing agent added to the reaction system for an acrylic polymer having an ester group in the molecular chain,
Forming the ring structure in the main chain of the polymer to form the polymer;
A method for producing an acrylic polymer, wherein the catalyst used for the progress of the reaction is a zinc compound.

R ¹ to R ³ which in formula (1) are each independently a hydrogen atom or an organic residue having a carbon number of 1 to 20, A r is an aryl group.   The method for producing an acrylic polymer according to claim 13, wherein the ring structure is at least one selected from a lactone ring structure, a glutaric anhydride structure, and a glutarimide structure.   A lactone ring structure is formed as the ring structure by causing a dealcoholization cyclocondensation reaction between the hydroxy group and the ester group for the acrylic polymer having a hydroxy group and an ester group in the molecular chain. The method for producing an acrylic polymer according to claim 13, wherein: