CN114341210A - Copolymer and method for producing same, copolymer mixture, doped resin composition, and resin molded article and method for producing same - Google Patents

Abstract

Disclosed is a method for producing a copolymer containing a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms. The method for producing the copolymer comprises a step of polymerizing monomers including alpha-methylene lactone and alkyl (meth) acrylate in the presence of a solvent. The solvent satisfies either condition (A) (at least one solvent selected from the group consisting of cyclic amides and cyclic esters) or condition (B) (a mixed solvent containing a first solvent having a boiling point of less than 100 ℃ and a second solvent having a boiling point of 100 ℃ or higher, wherein the first solvent is at least one solvent selected from the group consisting of ketones and chlorinated alkanes, the second solvent is at least one solvent selected from the group consisting of cyclic ketones, cyclic esters, amides, and sulfoxides, and the mixed solvent has a boiling point of 70-120 ℃).

Description

Copolymer and method for producing same, copolymer mixture, doped resin composition, and resin molded article and method for producing same

Technical Field

The present invention relates to a copolymer and a method for producing the same, a copolymer mixture, a dope resin composition, and a resin molded article and a method for producing the same.

Background

Copolymers containing structural units derived from α -methylene lactone are excellent in transparency, heat resistance and optical isotropy, and are expected to be applied to optical applications. For example, patent document 1 describes that the film is suitable for use as an optical member, such as a film as a molded article of a copolymer (resin) containing a predetermined structural unit derived from α -methylene lactone.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2008-179813

Disclosure of Invention

Problems to be solved by the invention

However, since a copolymer containing a structural unit derived from α -methylene lactone generally tends to have low solubility in a solvent, polymerization is carried out in the absence of a solvent or in a dimethyl sulfoxide (DMSO) solvent. However, in the polymerization in the absence of a solvent, the heat of polymerization cannot be removed, and in the polymerization in a DMSO solvent, the solvent itself is decomposed by heating to generate a harmful substance, and is explosive under a specific condition, so that there is a problem in safety, and it is not suitable for industrialization. Further, according to the study by the present inventors, it was found that when polymerization is performed in a DMSO solvent, the obtained copolymer containing a structural unit derived from α -methylene lactone tends to be colored and the transparency tends to be lowered.

Accordingly, a main object of the present invention is to provide a method for producing a copolymer containing a structural unit derived from α -methylene lactone by polymerization using a solvent, which method can improve the transparency of the resulting copolymer.

Means for solving the problems

The present invention provides a method for producing a copolymer described in the following [1] to [8], a copolymer described in the following [9] to [11], a copolymer mixture described in the following [12] to [14], a dope resin composition described in the following [15], a resin molded article described in the following [16], and a method for producing a resin molded article described in the following [17] and [18 ].

[1] A method for producing a copolymer comprising a structural unit derived from alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms, which comprises a step of polymerizing a monomer comprising alpha-methylene lactone and an alkyl (meth) acrylate in the presence of a solvent, wherein the solvent satisfies either of the following condition (A) or the following condition (B).

Condition (a): at least one solvent selected from the group consisting of cyclic amides and cyclic esters.

Condition (B): the solvent composition comprises a mixed solvent containing a first solvent having a boiling point lower than 100 ℃ and a second solvent having a boiling point higher than 100 ℃, wherein the first solvent is at least one selected from the group consisting of ketones and chloroalkanes, the second solvent is at least one selected from the group consisting of cyclic ketones, cyclic esters, amides and sulfoxides, and the boiling point of the mixed solvent is 70-120 ℃.

[2] The process for producing a copolymer according to [1], wherein the solvent satisfies the condition (A).

[3] The process for producing a copolymer according to [1], wherein the solvent satisfies the condition (B).

[4] The method for producing a copolymer according to [3], wherein the first solvent is acetone.

[5] The method for producing a copolymer according to [3] or [4], wherein the second solvent is a cyclic ketone.

[6] The process for producing a copolymer according to [5], wherein the cyclic ketone is cyclohexanone.

[7] The method for producing a copolymer according to [3] or [4], wherein the second solvent is at least one selected from the group consisting of cyclic esters, amides, and sulfoxides.

[8] The process for producing a copolymer according to [7], wherein the second solvent is at least one selected from the group consisting of γ -butyrolactone, γ -valerolactone, δ -valerolactone, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, N' -dimethylimidazolidinone, and dimethyl sulfoxide.

[9] A copolymer comprising a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms, wherein the internal haze per 100 [ mu ] m thickness when the copolymer is produced into a film is less than 2.5%.

[10] A copolymer which comprises a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms and has a weight-average molecular weight of 200000 or more and 1000000 or less.

[11] The copolymer according to [9] or [10], which is produced as a film having an internal b value per 100 μm thickness of the Lab system of less than 1.6.

[12] A copolymer mixture comprising the copolymer according to any one of [9] to [11] and at least one compound selected from the group consisting of cyclic amides, cyclic esters, and cyclic ketones.

[13] A copolymer mixture containing a copolymer comprising a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms and at least one compound selected from the group consisting of cyclic amides, cyclic esters, and cyclic ketones.

[14] The copolymer mixture according to [12] or [13], wherein the content of the compound is 10 to 3000 ppm by mass based on the total amount of the copolymer.

[15] A dope resin composition comprising the copolymer according to any one of [9] to [11] and a dispersion medium, wherein the content of the copolymer is 5% by mass or more based on the total amount of the dope resin composition.

[16] A molded resin product comprising the copolymer according to any one of [9] to [11] or the copolymer mixture according to any one of [12] to [14 ].

[17] A method for producing a resin molded article, comprising a step of molding a resin composition containing the copolymer according to any one of [9] to [11] or the copolymer mixture according to any one of [12] to [14] to obtain a resin molded article.

[18] A method for producing a resin molded body, comprising: a step of applying the dope resin composition according to [15 ]; and a step of removing the dispersion medium from the applied dope resin composition to obtain a resin molded article.

Effects of the invention

According to the present invention, there is provided a method for producing a copolymer containing a structural unit derived from α -methylene lactone by polymerization using a solvent, the method being capable of improving the transparency of the obtained copolymer. Several methods of manufacturing copolymers are easy to polymerize under reflux. Further, the present invention provides a copolymer obtained by such a production method and a copolymer mixture containing the copolymer. The copolymer mixture of the several modes tends to be excellent in terms of reduction in processing load on a formed film, strength of the formed film, and the like. Further, the present invention provides a dope resin composition and a resin molded article using the copolymer or the copolymer mixture, and a method for producing the resin molded article.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

In the present specification, "resin (composition)" is a broader concept than "polymer (copolymer)". The resin may be composed of one or two or more kinds of polymers (copolymers), and may contain additives such as antioxidants other than the polymers (copolymers) as needed.

[ method for producing copolymer ]

A method for producing a copolymer according to one embodiment is a method for producing a copolymer containing a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms.

The structural unit derived from α -methylenelactone is formed by polymerization of α -methylenelactone having a methylene group bonded to the carbon at the α -position. The specific structure of the structural unit derived from α -methylene lactone is not particularly limited. The number of ring members of the lactone is not particularly limited, and a five-membered ring (γ -lactone) or a six-membered ring (δ -lactone) is preferable because the stability of the ring structure is high and a higher surface strength is obtained based on the high stability.

Specific examples of α -methylenelactones as five-or six-membered rings are α -methylene- γ -butyrolactone, α -methylene- δ -valerolactone. They may have a substituent.

The structural unit derived from α -methylenelactone is preferably a structural unit having a structure represented by the following formula (1).

R in the formula (1)¹～R⁴Independently represents a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

The structural unit having the structure represented by formula (1) can be formed by polymerization of a monomer containing α -methylene- γ -butyrolactone represented by formula (2) below.

R in the formula (2)¹～R⁴Independently represents a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

The hydrocarbon group is an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group is, for example, an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 10, more preferably 1 to 8. The alkyl group may be linear, branched or cyclic. Examples of the alkyl group include: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl and the like.

The aromatic hydrocarbon group is not particularly limited, and may include a heterocyclic structure, for example. Examples of the aromatic hydrocarbon group include: phenyl, tolyl, benzyl, and the like.

R¹～R⁴The hydrogen atoms or alkyl groups having 1 to 10 carbon atoms are preferably independent of each other, and all of the hydrogen atoms are more preferably used.

The content of the α -methylenelactone-derived structural unit in the copolymer is preferably 5 to 40% by mass, more preferably 7.5 to 35% by mass, and still more preferably 10 to 30% by mass, from the viewpoint of further improving heat resistance and the like. The content of each structural unit in the copolymer can be measured by dissolving the copolymer in a deuterated solvent¹H-NMR was calculated and the area ratio of peaks corresponding to the respective structural units was determined.

The structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms is formed by polymerization of the alkyl (meth) acrylate. Examples of the alkyl group having 1 to 6 carbon atoms in the alkyl (meth) acrylate include: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl and the like. These may be used alone or in combination of two or more.

The number of carbon atoms of the alkyl group in the alkyl (meth) acrylate is preferably 1 to 3, more preferably 1 or 2, and still more preferably 1.

The number of carbon atoms of the alkyl group in the alkyl methacrylate is preferably 1 to 3, more preferably 1 or 2, and still more preferably 1.

The content of the structural unit derived from the alkyl (meth) acrylate in the copolymer is preferably 95 to 60% by mass, more preferably 92.5 to 65% by mass, and still more preferably 90 to 70% by mass, from the viewpoint of further improving heat resistance, transparency, and the like.

The copolymer may contain a structural unit derived from a monomer other than a structural unit derived from α -methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms. Specific examples thereof include structural units derived from monomers such as benzyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, styrene, vinyltoluene, α -methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate. These may be used alone or in combination of two or more.

The content of the other structural unit in the copolymer is preferably 30% by mass or less, more preferably 20% by mass or less, and further preferably 10% by mass or less.

The method for producing a copolymer of the present embodiment includes a step of polymerizing monomers including an α -methylene lactone and an alkyl (meth) acrylate in the presence of a solvent. The solvent is a solvent satisfying either the following condition (a) or the following condition (B).

Condition (a): at least one solvent selected from the group consisting of cyclic amides and cyclic esters.

Condition (B): the solvent composition comprises a mixed solvent containing a first solvent having a boiling point lower than 100 ℃ and a second solvent having a boiling point higher than 100 ℃, wherein the first solvent is at least one selected from the group consisting of ketones and chloroalkanes, the second solvent is at least one selected from the group consisting of cyclic ketones, cyclic esters, amides and sulfoxides, and the boiling point of the mixed solvent is 70-120 ℃.

According to the method for producing a copolymer of the present embodiment, the transparency of the obtained copolymer can be improved. The reason for such an effect is not necessarily clear, but the present inventors believe that the cause of coloring (reduction in transparency) is the formation of a homopolymer of α -methylene lactone (homopolymer). The homopolymer tends to be soluble in a DMSO solvent alone, but is not soluble or hardly soluble in a solvent satisfying the condition (a) or a solvent satisfying the condition (B). Therefore, it is considered that the formation of a homopolymer of α -methylene lactone is suppressed by polymerizing the monomer containing α -methylene lactone using a solvent satisfying the condition (a) or a solvent satisfying the condition (B), whereby the coloration of the copolymer can be reduced and the transparency can be improved.

In addition, by using a solvent satisfying the condition (B), the method for producing a copolymer of the present embodiment can easily perform a polymerization reaction under reflux in producing a copolymer containing a structural unit derived from α -methylene lactone, and can perform polymerization under reflux at a normal polymerization temperature (for example, 70 to 120 ℃). When the polymerization is carried out in a reflux state, the polymerization heat can be reduced during the polymerization, and the polymerization temperature can be controlled to be near the boiling point, so that the polymerization can be carried out safely and stably. When the boiling point of the mixed solvent is 120 ℃ or lower, it is advantageous in that the polymerization rate can be easily controlled, the by-products can be suppressed, and the polymerization temperature is not excessively higher than the boiling point of the alkyl (meth) acrylate monomer. Further, when the boiling point of the mixed solvent is 70 ℃ or higher, it is advantageous in terms of productivity such as viscosity of the polymerization solution and polymerization rate.

The solvent shown in the condition (a) is at least one solvent selected from the group consisting of cyclic amides and cyclic esters, and may be one single solvent or a mixed solvent in which two or more kinds are combined, and preferably is one single solvent. From the viewpoint of easy control of the content of the solvent (compound) in the copolymer mixture, the boiling point of the solvent (the boiling point of the solvent alone or the boiling point of the mixed solvent) is preferably more than 200 ℃ and 300 ℃ or less.

Examples of the cyclic amide include: n-methylpyrrolidone (NMP), N' -Dimethylimidazolidinone (DMI), and the like. Among them, NMP is preferable as the cyclic amide because of its high versatility.

Examples of the cyclic ester include: gamma-butyrolactone (GBL), gamma-valerolactone, delta-valerolactone, and the like. Among them, GBL is preferable from the viewpoint of high versatility.

In the case of using the solvent shown in the condition (a), the polymerization temperature and the polymerization time are different depending on the kind of the monomer used, the use ratio, and the like, and the polymerization temperature is preferably 0 to 150 ℃, more preferably 50 to 150 ℃, and further preferably 60 to 140 ℃. The polymerization time is preferably 0.5 to 20 hours, more preferably 1 to 10 hours.

The solvent represented by the condition (B) is a mixed solvent including a first solvent having a boiling point of less than 100 ℃ and a second solvent having a boiling point of 100 ℃ or higher, wherein the first solvent is at least one selected from the group consisting of ketones and chloroalkanes, and the second solvent is at least one selected from the group consisting of cyclic ketones, cyclic esters, amides, and sulfoxides, and the boiling point of the mixed solvent is 70 to 120 ℃.

The first solvent is a solvent having a boiling point of less than 100 ℃ and is at least one solvent selected from the group consisting of ketones and chlorinated alkanes. Examples of such a first solvent include: ketones such as Acetone (ACE) and Methyl Ethyl Ketone (MEK), and chloroalkanes such as dichloromethane, chloroform, 1, 2-dichloroethane and 1, 1-dichloroethane. The first solvent may be used alone or two or more kinds may be used in combination. Among them, the first solvent is preferably acetone.

The second solvent is a solvent having a boiling point of 100 ℃ or higher, and is at least one solvent selected from the group consisting of cyclic ketones, cyclic esters, amides, and sulfoxides. Examples of such a second solvent include: cyclic ketones such as cyclohexanone (Anone) and cyclopentanone, cyclic esters such as γ -butyrolactone (GBL), γ -valerolactone and δ -valerolactone, amides such as N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone (NMP) and N, N' -Dimethylimidazolidinone (DMI), and sulfoxides such as dimethyl sulfoxide. The second solvent may be used alone or two or more kinds may be used in combination. One embodiment of the second solvent is preferably a cyclic ketone, more preferably cyclohexanone. Another mode of the second solvent is preferably at least one selected from the group consisting of cyclic esters, amides, and sulfoxides, and more preferably at least one selected from the group consisting of γ -butyrolactone, γ -valerolactone, δ -valerolactone, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, N' -dimethylimidazolidinone, and dimethylsulfoxide.

The combination of the first solvent and the second solvent may be a combination of acetone and cyclohexanone. According to the studies of the present inventors, it was found that acetone and cyclohexanone each alone have a tendency to dissolve the copolymer with difficulty, but become extremely easy to dissolve the above copolymer. Therefore, by using such a mixed solvent, the polymerization reaction can be easily performed under reflux, and the transparency of the obtained copolymer can be improved.

The copolymer has a tendency to be easily dissolved in a chlorinated alkane having a boiling point of less than 100 ℃ as a first solvent and at least one solvent selected from the group consisting of cyclic esters, amides and sulfoxides having a boiling point of 100 ℃ or higher as a second solvent. Therefore, the combination of the first solvent and the second solvent may be a combination of a chlorinated alkane having a boiling point lower than 100 ℃ and a solvent having a boiling point of 100 ℃ or higher (i.e., at least one solvent selected from the group consisting of cyclic ketones, cyclic esters, amides, and sulfoxides), or a combination of a solvent having a boiling point lower than 100 ℃ (i.e., at least one solvent selected from the group consisting of ketones and chlorinated alkanes) and at least one solvent selected from the group consisting of cyclic esters, amides, and sulfoxides.

The boiling point of the mixed solvent is 70 to 120 ℃, preferably 75 to 115 ℃, and more preferably 80 to 110 ℃. When the boiling point of the mixed solvent is in such a range, the polymerization reaction can be easily performed under reflux. In the present specification, the boiling point of the mixed solvent is a value measured by the method described in examples.

The mixing ratio of the first solvent and the second solvent is not particularly limited as long as the boiling point of the mixed solvent is 70 to 120 ℃, and may be adjusted at any ratio. By adjusting the first solvent and the second solvent at an arbitrary ratio to adjust the boiling point of the mixed solvent to a range of 70 to 120 ℃, the polymerization reaction can be easily performed under reflux, and the transparency of the obtained copolymer can be improved. For example, the mass ratio of the first solvent to the second solvent (mass of the first solvent/mass of the second solvent) is preferably 1/9 or more, more preferably 2/8 or more, preferably 9/1 or less, more preferably 8/2 or less, further preferably 7/3 or less, particularly preferably 6/4 or less, and most preferably 5/5 or less.

In the case of using the solvent shown in condition (B), the polymerization temperature and polymerization time vary depending on the kind of the monomer used, the ratio of the monomer used, etc., and the polymerization temperature is preferably 120 ℃ or less from the viewpoint of easy control of the polymerization rate, suppression of by-products, and prevention of the polymerization temperature from becoming excessively higher than the boiling point of the alkyl (meth) acrylate monomer, and is preferably 70 ℃ or more from the viewpoint of productivity such as the viscosity of the polymerization solution and the polymerization rate. The polymerization temperature is more preferably 75 to 115 ℃ and still more preferably 80 to 110 ℃. The polymerization time is preferably 0.5 to 20 hours, more preferably 1 to 10 hours.

In the polymerization step, the method of charging the monomer components (α -methylene lactone, alkyl (meth) acrylate, other monomers, and the like) into the reactor is not particularly limited, and examples thereof include: a method of charging all monomers before charging the polymerization initiator; a method of continuously dropping all monomers while feeding a polymerization initiator; a method of adding a part of the monomers first and dropping the remaining monomers after the polymerization is started; and a method of changing the content ratio of α -methylenelactone in the monomer composition to be charged first and the content ratio of α -methylenelactone in the monomer composition to be charged after the start of polymerization.

When the monomer is polymerized, a polymerization initiator may be added as needed. Examples of the polymerization initiator include: organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butyl peroxyisopropylcarbonate, t-amyl peroxy (2-ethylhexanoate), t-butyl peroxy (2-ethylhexanoate), and the like; azo compounds such as 2,2 '-azobisisobutyronitrile, 1' -azobis (cyclohexanecarbonitrile), 2 '-azobis (2, 4-dimethylvaleronitrile), and dimethyl 2, 2' -azobis (2-methylpropionate). The content ratio of the polymerization initiator may be appropriately set depending on the combination of monomers used, reaction conditions, and the like, and is not particularly limited, but is preferably 10 to 10000 ppm by mass, more preferably 100 to 3000 ppm by mass, and still more preferably 300 to 2000 ppm by mass, based on the total monomers.

When the monomer is polymerized, a chain transfer agent may be added as necessary. Examples of the chain transfer agent include: monofunctional thiol compounds such as n-dodecyl mercaptan and β -mercaptopropionic acid; bifunctional thiol compounds such as both-terminal mercapto-modified polysiloxanes; side chain polyfunctional mercapto-modified polysiloxanes whose side chains are modified with mercapto groups, and the like. The content ratio of the chain transfer agent is not particularly limited as long as it is appropriately set according to the combination of monomers to be used, reaction conditions, and the like, and is preferably 10 to 10000 ppm by mass, more preferably 100 to 3000 ppm by mass, based on the total monomers.

In the polymerization of the monomer, the concentration of the copolymer in the polymerization reaction mixture is preferably controlled to 90% by mass or less, more preferably 70% by mass or less, and still more preferably 50% by mass or less, in order to suppress the viscosity of the reaction solution from increasing. Further, when the concentration of the copolymer in the polymerization reaction mixture is too low, productivity is lowered, and therefore, the concentration of the polymer in the polymerization reaction mixture is preferably controlled to 10% by mass or more, more preferably 20% by mass or more.

The polymerization reaction mixture obtained through the polymerization step usually contains a solvent in addition to the target copolymer. The method for separating the copolymer from the solvent is not particularly limited, and examples thereof include: a reprecipitation method is used; a method of removing the solvent using a devolatilization apparatus comprising a heat exchanger and a devolatilization vessel, an extruder with an exhaust port, and the like.

[ copolymer ]

The copolymer of one embodiment comprises a structural unit derived from alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms, and has an internal haze per 100 [ mu ] m thickness of less than 2.5% when formed into a film. The copolymer of the present embodiment may be a copolymer obtained by the above-described production method. The above-mentioned production method can improve the transparency of the resulting copolymer, and therefore, by using this production method, the internal haze per 100 μm thickness at the time of producing a film, the internal b value per 100 μm thickness of the laab coloring system at the time of producing a film, and the like can be made to be in predetermined ranges.

The internal haze per 100 μm thickness of the film made of the copolymer is less than 2.5%. The internal haze is preferably 2.0% or less, more preferably 1.5% or less, further preferably 1.0% or less, and particularly preferably 0.8% or less. The internal haze per 100 μm thickness of the copolymer when formed into a film can be measured by the method described in examples. The temperature at which the copolymer is hot-press molded may be, for example, 200 to 270 ℃, and more specifically, 240 ℃.

The copolymer of another embodiment comprises a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms, and has a weight average molecular weight (Mw) of 200000 or more and 1000000 or less. By using the copolymer of the present embodiment, a film excellent in transparency, heat resistance and flexibility can be formed.

The copolymer is substantially free from the solvent used in the above-mentioned production method. Here, "substantially not contained" means that the content of the solvent may be less than 10 mass ppm based on the total amount of the copolymer. The content of the solvent can be measured using a film formed of the copolymer or the copolymer mixture, for example, by the method described in examples.

The internal b value per 100 μm thickness of the chromophoric system when the copolymer is made into a film is preferably less than 1.6. The inner part b^*The value is more preferably 1.2 or less, still more preferably 0.8 or less, particularly preferably 0.6 or less, and most preferably 0.4 or less. The internal b value per 100 μm thickness of the colorimetric system in the case of producing a film from a copolymer can be measured, for example, by the method described in examples. Further, the copolymer is subjected to hot press moldingThe temperature may be set to, for example, 200 to 270 ℃, and more specifically, 240 ℃.

The weight average molecular weight (Mw) of the copolymer is preferably 100000 or more, more preferably 150000 or more, further preferably 200000 or more, particularly preferably 220000 or more, and most preferably 240000 or more. The weight average molecular weight (Mw) of the copolymer is preferably 1000000 or less, more preferably 750000 or less, and still more preferably 500000 or less. When the Mw of the copolymer is within the above-specified range, the flexibility of the film can be further improved. The Mw of the copolymer can be measured, for example, by the method described in examples.

The number average molecular weight (Mn) of the copolymer is preferably 20000 or more, more preferably 50000 or more, and further preferably 100000 or more. The number average molecular weight (Mn) of the copolymer is preferably 500000 or less, more preferably 400000 or less, and further preferably 300000 or less. The Mn of the copolymer can be measured, for example, by the method described in examples. The dispersity (Mw/Mn) of the copolymer is preferably 3.0 or less, more preferably 2.8 or less, and still more preferably 2.5 or less.

The Yellowness (YI) of the copolymer, measured according to the provisions of JIS Z8729 when prepared as a 15% chloroform solution of the copolymer, is preferably 5 or less, more preferably 3 or less, and still more preferably 1 or less. When the YI of the copolymer is in such a range, a resin molded article with low coloring can be obtained.

From the viewpoint of further improving heat resistance and the like, the glass transition temperature (Tg) of the copolymer measured according to the regulations of JIS K7121 is preferably 110 ℃ or higher, more preferably 115 ℃ or higher, and still more preferably 120 ℃ or higher. The upper limit of the glass transition temperature of the copolymer is not particularly limited, and may be set to, for example, 160 ℃ or lower.

From the viewpoint of further improving the heat resistance and the like, the 5% weight loss temperature of the copolymer is preferably 280 ℃ or more, more preferably 290 ℃ or more, and still more preferably 300 ℃ or more. The upper limit of the 5% weight loss temperature of the copolymer is not particularly limited, and may be set to 400 ℃ or lower, for example. The 5% weight loss temperature can be measured, for example, by the method described in examples.

[ copolymer mixture ]

The copolymer mixture of one embodiment contains a copolymer including a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms, and at least one compound selected from the group consisting of cyclic amides, cyclic esters, and cyclic ketones. One embodiment of the copolymer mixture contains the above copolymer and at least one compound selected from the group consisting of cyclic amides, cyclic esters, and cyclic ketones.

At least one compound selected from the group consisting of cyclic amides, cyclic esters, and cyclic ketones can be used as the compound exemplified as the solvent in the above-mentioned method for producing a copolymer. The content of the compound is preferably 10 to 3000 ppm by mass based on the total amount of the copolymer. The content of the compound is more preferably 200 mass ppm or more, further preferably 300 mass ppm or more, more preferably 2500 mass ppm or less, further preferably 2000 mass ppm or less, based on the total amount of the copolymer. When the content of the compound is in such a range, the processability of the resin, the reduction in processing load on the formed film, the strength of the formed film, and the like tend to be excellent. The content of the compound can be measured using a film formed of the copolymer or the copolymer mixture, for example, by the method described in examples.

The copolymer mixture can be obtained by leaving the solvent (compound) so that the content of the compound becomes a predetermined range when the copolymer is separated from the solvent in the above-mentioned method for producing a copolymer, or can be obtained by adding the compound to the separated copolymer so that the content of the compound becomes a predetermined range.

[ doped resin composition ]

One embodiment of the dope resin composition contains the above copolymer and a dispersion medium. The dope resin composition can be suitably used for the production of a resin molded article.

One embodiment of the dispersion medium is exemplified bySuch as: chlorinated alkane solvents such as chloroform and methylene chloride; aromatic solvents such as toluene, xylene, and benzene; alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, and 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and dioxane

Alkane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone, ethyl acetate, diethyl ether, NMP, GBL, and the like. These may be used alone or in combination of two or more. However, when two or more kinds are used in combination, the solvent shown in the above condition (B) is not included.

Another embodiment of the dispersion medium is the solvent described in the above condition (B). The boiling point of the mixed solvent (the solvent shown in the condition (B)) is preferably 70 to 120 ℃. The combination of the first solvent and the second solvent, the boiling point of the mixed solvent, the mixing ratio of the first solvent and the second solvent, and the like of the mixed solvent are the same as those of the combination of the first solvent and the second solvent, the boiling point of the mixed solvent, the mixing ratio of the first solvent and the second solvent, and the like described above. Therefore, a repetitive description will be omitted here. The first solvent may be further added to the mixed solvent. The boiling point of the dispersion medium when the first solvent is further added to the mixed solvent is preferably 30 to 110 ℃, and more preferably 40 to 100 ℃.

From the viewpoint of efficiently producing the resin molded article, the content of the copolymer in the dope resin composition is 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more, based on the total amount of the dope resin composition. From the viewpoint of ensuring fluidity and stable production by a production facility, the content of the copolymer is preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less, based on the total amount of the dope resin composition.

The dope resin composition may contain another polymer in a resin molded article described later. The content of the other polymer is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, even more preferably 0 to 30% by mass, particularly preferably 0 to 20% by mass, most preferably 0 to 10% by mass, based on the total amount of the dope resin composition.

The dope resin composition may contain other additives in the resin molded body described later. The doped resin composition may contain one or more other additives. The content of the other additives is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, and further preferably 0 to 0.5% by mass, based on the total amount of the dope resin composition.

The Yellowness (YI) of the doped resin composition measured according to the provisions of JIS Z8729 is preferably 5 or less, more preferably 3 or less, and even more preferably 1 or less, from the viewpoint of obtaining a low-colored resin molded article.

From the viewpoint of improving productivity of the resin molded article, the doped resin composition preferably has a viscosity of 0.001Pa · s or more, more preferably 0.01Pa · s or more, further preferably 0.1Pa · s or more, preferably 10Pa · s or less, more preferably 5Pa · s or less, further preferably 1Pa · s or less at 25 ℃. The viscosity at 25 ℃ can be measured, for example, by the method described in examples.

From the viewpoint of obtaining a highly transparent resin molded article, the haze of the dope resin composition measured according to the specification of JIS K7136 is preferably 5 or less, more preferably 3 or less, and further preferably 1 or less.

[ resin molded article and method for producing the same ]

The resin molded article of one embodiment contains the above copolymer or the above copolymer mixture as a main component. The resin molded article of the present embodiment can be produced using a resin composition containing the copolymer or the copolymer mixture, or a doped resin composition containing the copolymer or the copolymer mixture.

The content of the copolymer or the copolymer mixture is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, even more preferably 70 to 100% by mass, particularly preferably 80 to 100% by mass, and most preferably 90 to 100% by mass, based on the total amount of the resin molded product. When the content of the copolymer or the copolymer mixture in the resin molded article is 50% by mass or more, a resin molded article having more excellent transparency can be obtained.

The resin molded article may contain a polymer (other polymer) other than the above-mentioned copolymer. Examples of other polymers include: olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymers, and poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and vinyl chloride resins; acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymers, styrene-acrylonitrile copolymers, and acrylonitrile-butadiene-styrene block copolymers; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyamides such as nylon 6, nylon 66, and nylon 610; a polyacetal; a polycarbonate; polyphenylene ether; polyphenylene sulfide; polyether ether ketone; polysulfones; polyether sulfone; polyoxybenzyl ester; a polyamide-imide; elastic organic fine particles such as polybutadiene-based rubber and acrylic rubber; and rubbery polymers such as ABS resins and ASA resins containing polybutadiene rubber and acrylic rubber. The content of the other polymer is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, even more preferably 0 to 30% by mass, particularly preferably 0 to 20% by mass, and most preferably 0 to 10% by mass, based on the total amount of the resin molded article (resin composition).

The resin molded article may contain other additives. Examples of other additives include: antioxidants such as hindered phenols, phosphorus-based antioxidants and sulfur-based antioxidants; stabilizers such as light-resistant stabilizers, weather-resistant stabilizers and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; ultraviolet absorbers such as phenyl salicylate, (2, 2' -hydroxy-5-methylphenyl) benzotriazole, and 2-hydroxybenzophenone; a near infrared ray absorber; flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; an organic filler or an inorganic filler; a resin modifier; organic or inorganic fillers; a plasticizer; a lubricant; an antistatic agent; a flame retardant; a fluidizing agent; solubilizers, and the like. The resin molded article may contain one or two or more other additives. The content of the other additives is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, and further preferably 0 to 0.5% by mass, based on the total amount of the resin molded article.

The resin molded article is preferably a film-shaped resin molded article or a sheet-shaped resin molded article. In the present specification, a film-shaped resin molded body (film) means a resin molded body having a film thickness of less than 350 μm, and a sheet-shaped resin molded body (sheet) means a resin molded body having a film thickness of 350 μm or more.

One embodiment of the method for producing a resin molded article includes a step of molding a resin composition containing the copolymer or the copolymer mixture to obtain a resin molded article. The method for molding the resin composition is not particularly limited, and examples thereof include: a conventionally known method such as a melt extrusion method, a rolling method, a compression molding method, or the like. Among them, the method of molding the resin composition is preferably a melt extrusion method.

The resin composition may contain the above-mentioned other polymer, the above-mentioned other additive, and the like in addition to the above-mentioned copolymer or the above-mentioned copolymer mixture, depending on the desired resin molded article. The content of the copolymer or the copolymer mixture, other polymer, other additive, and the like in the resin composition may be the same as the content of each component exemplified in the resin molded article.

Specific examples of the melt extrusion method include: t-die, blow molding, and the like. The molding temperature of the resin molded article is preferably 150 to 350 ℃, and more preferably 200 to 300 ℃.

Another embodiment of the method for producing a resin molded article includes: a step of applying the dope resin composition; and a step of removing the dispersion medium from the applied dope resin composition to obtain a resin molded article. The method for applying the dope resin composition is not particularly limited, and examples thereof include conventionally known methods such as a solution casting method (solution casting method). In the solution casting method (solution casting method), for example, a roll caster, a band caster, a spin coater, or the like can be used.

The method for removing the dispersion medium from the dope resin composition is not particularly limited, and examples thereof include a method of heating the dope resin composition to volatilize the dispersion medium. The heating temperature may be appropriately set according to the dispersion medium used.

The film-shaped resin molded product (film) can be stretched to form a stretched film. The film is preferably a stretched film because it has excellent flexibility and can impart a retardation in some cases.

As a method for stretching the film, a conventionally known stretching method can be applied, and examples thereof include: uniaxial stretching such as free width uniaxial stretching, fixed width uniaxial stretching, and the like; and biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching. The method of stretching the film is preferably biaxial stretching in view of improving the folding resistance in two directions orthogonal to each other in the film plane.

The stretching temperature at the time of stretching the film is preferably close to the glass transition temperature of the copolymer. More specifically, it is preferably (glass transition temperature-30) DEG C to (glass transition temperature +100) DEG C, more preferably (glass transition temperature-20) DEG C to (glass transition temperature +50) DEG C, and still more preferably (glass transition temperature-10) DEG C to (glass transition temperature +30) DEG C.

The stretch ratio in stretching the film may be, for example, in the range of 1.05 to 10 times in the longitudinal and transverse directions.

The film thickness of the film-shaped resin molded article (film) is preferably 1 μm or more and less than 350 μm, more preferably 10 μm or more and 300 μm or less. The film thickness of the sheet-like resin molded article (sheet) is preferably 350 μm or more and 10mm or less, more preferably 350 μm or more and 5mm or less.

When the resin molded article is a film, the total light transmittance of the film measured by the method according to JIS K7136 is preferably 85% or more, more preferably 88% or more, further preferably 90% or more, and particularly preferably 92% or more. The total light transmittance is a criterion of transparency, and when it is 85% or more, a film having sufficient transparency can be formed.

When the resin molded article is a film, the elastic modulus of the film is preferably 4GPa or more, more preferably 4.5GPa or more, and even more preferably 5GPa or more, from the viewpoint of further improving the strength of the film. The upper limit of the elastic modulus of the film is not particularly limited, and may be set to 15GPa or less, for example. The elastic modulus of the film can be measured, for example, by the method described in examples.

When the resin molded article is a film, the young's modulus of the film is preferably 4GPa or more, more preferably 4.5GPa or more, and even more preferably 5GPa or more, from the viewpoint of further improving the strength of the film. The upper limit of the Young's modulus of the film is not particularly limited, and may be set to, for example, 15GPa or less. The young's modulus of the film can be measured, for example, by the method described in examples.

When the resin molded article is a film, the pencil hardness of the film is preferably H or more, more preferably 2H or more, and further preferably 3H or more, from the viewpoint of further improving the strength of the film.

When the resin molded article is a film, it is preferable that the film is not broken at the bent portion even if the number of bending times exceeds 100000 times in a bending test (folding test) in which the film is bent into a U-shape and restored under predetermined conditions. The predetermined conditions may be, for example, the conditions described in the examples.

The resin molded article of the present embodiment can be applied to various applications, and can be suitably used for optical applications, for example. Specific examples of the use include: light guide members, films, lenses (optical lenses, etc.), covers, foams (for example, cushioning materials, heat insulating/heat insulating materials, vibration absorbing materials, sound insulating materials, sealing materials, and fillers).

The resin molded article (particularly, film-shaped resin molded article) of the present embodiment can be suitably used for optical applications. The resin molded article (particularly, film-shaped resin molded article) of the present embodiment is excellent in transparency, heat resistance, flexibility, and surface hardness, and therefore can be suitably used for flexible display applications, and particularly can be suitably used as an outermost cover window. Specific examples of the flexible display include: a thin and bendable flexible type organic EL display, a smart phone capable of being folded or rolled, and the like. Further, since the film-shaped resin molded article has a low phase difference, it can be used as a protective film for each layer of a flexible display. Further, a polarizing plate or a touch panel can be manufactured using a film-shaped resin molded product.

When a film-shaped resin molded product (film) is used as a cover window for a flexible display, it can be used as a laminate having another layer such as a hard coat layer, for example. The cover window for a flexible display formed of a film may be disposed on the surface of the flexible display via an adhesive layer or the like, for example.

Examples

The present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. In the following, unless otherwise specified, "part" means "part by mass". In addition, various physical properties were measured and evaluated as follows.

< example A >

[ polymerization reaction Rate and Polymer composition analysis ]

The reaction rate during the polymerization reaction and the content of the specific monomer unit in the copolymer were determined by measuring the amount of unreacted monomer in the obtained polymerization reaction liquid by using a gas chromatograph (GC-2014, manufactured by Shimadzu corporation).

[ weight average molecular weight and number average molecular weight ]

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the copolymer were determined by polystyrene conversion using Gel Permeation Chromatography (GPC). The apparatus and measurement conditions used for the measurement are as follows.

The system comprises the following steps: GPC System HLC-8220 manufactured by Tosoh

Measurement side column configuration:

guard column (TSKguardcolumn SuperHZ-L, manufactured by Tosoh)

Two separation columns (TSKgel SuperHZM-M, manufactured by Tosoh) were connected in series

The reference side column comprises:

reference column (TSKgel SuperH-RC, manufactured by Tosoh)

Developing solvent: chloroform (Heguang pure drug industry, special grade)

Flow rate of developing solvent: 0.6 mL/min

Standard sample: TSK Standard polystyrene (PS- オリゴマーキット, made by Tosoh)

Column temperature: 40 deg.C

[ ML content in copolymer ]

ML content (content of structural units derived from. alpha. -methylenelactone) in the copolymer is determined by¹H-NMR was obtained. Specifically, the reaction was carried out using deuterated DMSO or deuterated chloroform as a deuterated solvent and a nuclear magnetic resonance spectrometer (AV 300M, manufactured by BRUKER)¹H-NMR measurement of the resulting¹The ML content in the copolymer was determined from the area ratio of the H-NMR spectrum.

[ glass transition temperature (Tg) ]

The glass transition temperature of the copolymer was determined in accordance with JIS K7121. Specifically, a DSC curve was obtained by heating about 10mg of a sample from room temperature to 200 ℃ (the heating rate was 20 ℃/min) in a nitrogen atmosphere using a differential scanning calorimeter (Thermo plus EVO DSC-8230, manufactured by Rigaku), and the DSC curve was evaluated by the start point method. Alpha-alumina was used as reference.

[ 5% weight loss temperature ]

The 5% weight loss temperature of the copolymer was determined in accordance with JIS K7120. Specifically, about 10mg of the sample was heated from room temperature to 400 ℃ at 10 ℃ per minute under a nitrogen atmosphere using a differential type differential thermal balance apparatus (manufactured by Rigaku, Thermo plus2 Tg-8120). At this time, the temperature was determined by measuring the temperature at the time when the mass of the sample decreased 5% during the temperature rise.

[ thickness of film ]

The thickness of the film was determined by デジマチックマイクロメーター (digital micrometer, manufactured by Sanfeng).

[ Total light transmittance of film ]

The total light transmittance of the film was determined in accordance with JIS K7361. Specifically, the measurement was carried out using a haze meter (NDH-1001 DP, manufactured by Nippon Denshoku industries Co., Ltd.).

[ tensile test (elastic modulus measurement) of film ]

The stretched film was cut into a size of 90mm × 20mm to prepare a test piece, and a tensile test was performed according to JIS K7127 using an automatic plotter (manufactured by Shimadzu corporation: AG-X) at a temperature of 25 ℃ under an atmosphere of a relative humidity of 50%. The conditions were as follows: the tensile rate was set to 0.25 mm/min to 0.5% deformation, then set to 1 mm/min, the distance between chucks was set to 55mm, the interval between the graticules measured by a displacement gauge was set to 25mm, three tests were performed at 25 ℃, and the average value was taken as the measured value. The displacement was measured using a non-contact extensometer (manufactured by Shimadzu corporation: TRViewX), and the modulus of elasticity was evaluated as the slope of the deformation from 0.05% to 0.25%.

[ Young's modulus of film ]

The Young's modulus of the film was evaluated on a stretched film (thickness 4 μm) by a method in accordance with ISO-14577-1 using an ultramicro durometer (manufactured by フィッシャーインストルメンツ, フィッシャースコープ HM-2000). The evaluation was performed in a state where the unstretched film was fixed to the glass substrate. The measurement conditions were as follows: using a four-pyramid vickers indenter (a facing angle a of 136 °), a maximum test load of 3 mN; the application time when the load was applied was 20 seconds; creep time 5 seconds; application time 20 seconds when the load was reduced; the measurement temperature was set at room temperature (25 ℃), and the Young's modulus of the film was determined by averaging the three measurement values.

[ Pencil hardness of film ]

The pencil hardness of the film was evaluated by using a test pencil specified in JIS-S-6006, a pencil scratch hardness tester No.533 manufactured by Antian Seiko Seiki machine under a load of 750g in accordance with JIS K5600-5-4(1999), and the highest pencil hardness without damage was defined as the pencil hardness.

[ folding test of film ]

The stretched film was cut into a size of 15mm × 80mm to prepare a test piece, and the test piece was fixed to a Tension-FreeFoldering Clamshell-type (manufactured by ユアサシステム, DMLHP-CS) by means of an adhesive tape. The test piece was folded at a half position of the long side, and the test piece was set to be folded such that the distance between both ends of the long side of the folded test piece was 5mm and the radius of curvature of the folded portion of the test piece was 2.5 mm. Then, under an environment of 25 ℃, bending was repeated 10 ten thousand times at 1 minute and 30 times of bending, with 1 bend as a bend from a state of being opened flatly to a state of being folded. The folded portion after the test was evaluated as "good" when the film did not break and as "poor" when the film broke.

(example A1)

To a reactor equipped with a stirrer, a temperature sensor, a condenser and a nitrogen gas inlet tube, 9 parts of Methyl Methacrylate (MMA), 0.75 parts of α -methylene- γ -butyrolactone (ML) and 10 parts of N-methylpyrrolidone (NMP) as a solvent were charged, and nitrogen gas was introduced thereinto while the temperature was raised to 105 ℃. Then, 0.003 part of t-amyl peroxyisononanoate (manufactured by アルケマ JIFU, Luperox (registered trademark) 570, hereinafter also referred to as "initiator 570") as a polymerization initiator was added thereto, and while 0.005 part of initiator 570 and 0.25 part of ML diluted with 0.2 part of NMP were added dropwise at a constant rate over 2 hours, solution polymerization was carried out at 105 ℃ and 115 ℃ for 6 hours. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction mixture, were 98.8% and 99.3%, respectively. Subsequently, the obtained polymerization reaction liquid was vacuum-dried at 240 ℃ for 2 hours (1mmHg), thereby obtaining a white copolymer. The physical properties of the obtained copolymer are shown in table 1. Subsequently, the obtained copolymer was subjected to hot press molding at 240 ℃ to obtain an unstretched cast film having a thickness of about 160 μm, and then the obtained unstretched cast film was cut into a size of 96mm × 96mm, subjected to successive biaxial stretching at a stretching temperature of 140 ℃ (Tg +18 ℃) at a stretching speed of 300%/min at a stretching ratio of 2.0 times in the order of the longitudinal direction (MD direction) and the transverse direction (TD direction) using a successive biaxial stretcher (X6-S, manufactured by toyo seiki seiko corporation), and cooled to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 1.

[ Table 1]

< test example B, and comparative example B >

[ polymerization reaction Rate in static polymerization ]

The polymerization reaction rate in the static polymerization was determined as follows: the polymerization solution was diluted with chloroform and then dropped into methanol to extract a copolymer by reprecipitation, and after drying the copolymer at 240 ℃ for 1 hour, the polymerization reaction rate in the standing polymerization was simply determined from the amount of the obtained copolymer.

[ polymerization reaction Rate in agitation polymerization and composition analysis of copolymer ]

The reaction rate at the time of polymerization in the agitation polymerization and the content of the specific monomer unit in the copolymer were determined by measuring the amount of unreacted monomer in the obtained polymerization reaction liquid by using a gas chromatograph (GC-2014, manufactured by Shimadzu corporation).

[ weight average molecular weight and number average molecular weight of copolymer ]

The weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer were determined in the same manner as those of the copolymer of < example a >.

[ ML content in copolymer ]

The ML content (content of a structural unit derived from α -methylene lactone) in the copolymer was determined in the same manner as in the copolymer of < example a >.

[ glass transition temperature (Tg) of copolymer ]

The glass transition temperature of the copolymer was determined in the same manner as that of the copolymer of < example a >.

[ 5% weight loss temperature of copolymer ]

The 5% weight loss temperature of the copolymer was determined in the same manner as the 5% weight loss temperature of the copolymer of < example a >.

[ internal haze of copolymer ]

The internal haze of the copolymer was determined in accordance with the JIS K7136. Specifically, an unstretched film obtained by hot press molding a copolymer at 240 ℃ under 40MPa for 10 minutes was prepared, and 1,2,3, 4-tetrahydronaphthalene (tetrahydronaphthalene) was filled in a quartz cell having an optical path length of 10mm by a haze meter (NDH-1001 DP, manufactured by Nippon Denshoku industries Co., Ltd.), and the film was immersed in the solution and measured, whereby the internal haze of the copolymer was calculated as an internal haze value per 100 μm.

[ interior b of copolymer^*Value of]

An unstretched film obtained by hot press molding a copolymer at 240 ℃ under 40MPa for 10 minutes was prepared, and measured by immersing the film in 1,2,3, 4-tetrahydronaphthalene (tetrahydronaphthalene) filled in a quartz cell having an optical path length of 10mm using a spectrophotometer (Colrometer ZE6000), and b of the thickness of 100 μm of the L.a.b.color system^*Calculation of internal b of the copolymer in the form of values^*The value is obtained.

[ content of solvent (Compound) in copolymer or copolymer mixture ]

The content of the solvent (compound) in the copolymer or the copolymer mixture was determined by dissolving the copolymer or the copolymer mixture in dimethylacetamide and measuring the solution by a gas chromatograph (GC-2014, manufactured by Shimadzu corporation).

[ viscosity of dope resin composition ]

The viscosity of the dope resin composition was measured at 25 ℃ with a BHII type viscometer (manufactured by Toyobo industries).

[ Yellowness (YI) of the dope resin composition ]

The Yellowness (YI) of the dope resin composition was determined in accordance with JIS Z8729. Specifically, the measurement was carried out using a quartz cell having an optical path length of 10mm in a transmission mode of a spectrocolorimeter (manufactured by Nippon Denshoku industries Co., Ltd.: Colrometer ZE 6000).

[ haze of doped resin composition ]

The haze of the dope resin composition was determined in accordance with the specification of JIS K7136. Specifically, the measurement was carried out by a haze meter (NDH-1001 DP, manufactured by Nippon Denshoku industries Co., Ltd.) using a quartz cell having an optical path length of 10 mm.

[ thickness of film ]

The thickness of the film was determined in the same manner as that of the film of < example a >.

[ Total light transmittance of film ]

The total light transmittance of the film was determined in the same manner as that of the film of < example a >.

[ tensile test (elastic modulus measurement) of film ]

The tensile test (elastic modulus measurement) of the film was performed in the same manner as the tensile test of the film of < example a >, and the elastic modulus was measured.

[ Pencil hardness of film ]

The pencil hardness of the film was determined in the same manner as that of the film of < example a >.

[ folding test of film ]

The film folding test was performed in the same manner as the film folding test of < example a >, and the presence or absence of film breakage at the folded portion after the test was evaluated in the same manner as < example a >.

[ phase difference of film ]

The in-plane retardation Re and the thickness direction retardation Rth of the stretched film with respect to light having a wavelength of 589nm were measured using a full-automatic birefringence meter ("KOBRA-WR" manufactured by Oji scientific instruments) at an incident angle of 40 ℃. Specifically, the in-plane retardation Re and the thickness direction retardation Rth are obtained from the following expressions, where nx is a refractive index in the slow axis direction of the film, ny is a refractive index in the fast axis direction of the film, nz is a refractive index in the thickness direction of the film, and d is a thickness of the film. In the following examples, the in-plane retardation Re and the thickness direction retardation Rth were obtained with the film thickness d set to 40 μm.

In-plane retardation Re ═ nx-ny) × d

Thickness direction retardation Rth ═ [ (nx + ny)/2-nz ] × d

< Synthesis of copolymer by static polymerization >

(test example B1)

In a reaction vessel capable of being sealed, 7 parts of Methyl Methacrylate (MMA), 3 parts of α -methylene- γ -butyrolactone (ML), 10 parts of N-methylpyrrolidone (NMP) as a solvent, and 0.03 part of Azobisisobutyronitrile (AIBN) as an initiator were charged, and after 2 minutes of nitrogen gas bubbling, the vessel was purged with nitrogen gas, and then, the lid was tightened to seal the vessel. Then, the reaction vessel was immersed in an oil bath at 75 ℃ for 2 hours to conduct polymerization. After the polymerization, the resulting solution was diluted with chloroform and then added to methanol to reprecipitate, and a white solid was taken out. Vacuum drying was then carried out at 240 ℃ for 1 hour to obtain about 6 parts of a white copolymer. The physical properties of the obtained copolymer are shown in table 2.

(test example B2)

Polymerization, reprecipitation and drying were carried out in the same manner as in test example B1 except that the solvent was changed from NMP to γ -butyrolactone (GBL), to obtain 6.5 parts of a white copolymer. The physical properties of the obtained copolymer are shown in table 2.

(test example B3)

Polymerization, reprecipitation, and drying were performed in the same manner as in test example B1 except that the solvent was changed from NMP to dimethyl sulfoxide (DMSO), to obtain 6 parts of a white copolymer. The physical properties of the obtained copolymer are shown in table 2.

(test example B4)

Polymerization was carried out in the same manner as in test example B1 except that the solvent was changed from NMP to toluene. However, the polymerization is completed because a solid precipitates and solidifies during the polymerization.

(test example B5)

Polymerization was carried out in the same manner as in test example B1 except that a solvent such as NMP was not used. However, the polymerization is completed because a solid precipitates and solidifies during the polymerization.

According to test examples B1 to B5, NMP, GBL and DMSO having a polymerization reaction rate of 50% or more were judged to be good, and the following stirring polymerization was performed using these solvents.

< Synthesis of copolymer and production of film by agitation polymerization >

(example B1-1)

To a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen introduction tube, 8 parts of Methyl Methacrylate (MMA), 1.5 parts of α -methylene- γ -butyrolactone (ML), 0.005 part of N-dodecylmercaptan (nDM) as a chain transfer agent and 10 parts of N-methylpyrrolidone (NMP) as a solvent were charged, and nitrogen was introduced thereinto while the temperature was raised to 105 ℃. Then, 0.003 part of tert-amyl peroxyisononanoate (manufactured by アルケマ Jifu, Luperox (registered trademark) 570, hereinafter also referred to as "initiator 570") as a polymerization initiator was added thereto, and 0.005 part of initiator 570 and 0.5 part of ML diluted with 0.2 part of NMP were added dropwise at 105 to 115 ℃ at a constant rate over 2 hours. After the dropwise addition, 4 parts of NMP was added, and further solution stirring polymerization was carried out at 105 to 115 ℃ for 4 hours. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction liquid, were 99.1% and 99.5%, respectively. The obtained polymerization reaction liquid was vacuum-dried at 240 ℃ for 2 hours (133Pa (1mmHg)), whereby a white copolymer was obtained. The physical properties of the obtained copolymer are shown in table 3.

The resulting copolymer of example B1-1 was then hot-pressed at 240 ℃ to give an unstretched pressed film having a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96mm × 96mm, sequentially biaxially stretched at a stretching temperature of Tg +18 ℃ (146 ℃) of 300%/min at a stretching ratio of 2.0 times in the longitudinal direction (MD direction) and transverse direction (TD direction) in this order by a sequential biaxial stretcher (X6-S, manufactured by tokyo Seiki Seisaku-sho Ltd.), and cooled to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 3.

(example B1-2)

A copolymer and a stretched film having a thickness of 40 μm were obtained in the same manner as in example B1-1 except that the solvent was changed from NMP to gamma-butyrolactone (GBL). The conversion rates of MMA and ML calculated from the amounts of unreacted monomers in the polymerization reaction mixture were 98.5% and 99.0%, respectively. The physical properties of the obtained copolymer and the physical properties of the stretched film are shown in table 3.

(example B1-3)

To a reactor equipped with a stirrer, a temperature sensor, a condenser and a nitrogen inlet tube, 9 parts of MMA, 0.75 part of ML, 0.005 part of nDM and 10 parts of GBL as a solvent were charged, and the temperature was raised to 105 ℃ while introducing nitrogen. Then, 0.003 part of the initiator 570 was added, and 0.005 part of the initiator 570 and 0.25 part of ML diluted with 0.2 part of GBL were added dropwise at 105 to 115 ℃ over 2 hours at a constant rate. After dropwise addition, 4 parts of GBL was added, and further solution polymerization was carried out at 105 to 115 ℃ for 4 hours with stirring. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction mixture, were 98.4% and 99.2%, respectively. The obtained polymerization reaction liquid was subjected to the same operation as in example B1-1 to obtain a copolymer and a stretched film having a thickness of 40 μm. The physical properties of the obtained copolymer and the physical properties of the stretched film are shown in table 3.

(example B1-4)

A copolymer and a stretched film having a thickness of 40 μm were obtained in the same manner as in example B1-3, except that nDM was changed from 0.005 parts to 0.03 parts, GBL as a solvent was changed from 10 parts to 15 parts, and 4 parts of GBL added after dropwise addition was not added. The conversion rates of MMA and ML calculated from the amounts of unreacted monomers in the polymerization reaction mixture were 98.0% and 98.5%, respectively. The physical properties of the obtained copolymer and the physical properties of the stretched film are shown in table 3.

(example B1-5)

In a reactor equipped with a stirrer, a temperature sensor, a condenser and a nitrogen inlet tube, 7 parts of MMA, 2.2 parts of ML and 10 parts of GBL as a solvent were charged, and nitrogen was introduced thereinto while the temperature was raised to 105 ℃. Then, 0.003 part of the initiator 570 was added, and 0.005 part of the initiator 570 diluted with 0.2 part of GBL and 0.8 part of ML were added dropwise at 105 to 115 ℃ over 2 hours at a constant rate. After dropwise addition, 4 parts of GBL was added, and further solution polymerization was carried out at 105 to 115 ℃ for 4 hours with stirring. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction liquid, were 99.1% and 99.2%, respectively. The obtained polymerization reaction liquid was subjected to the same operation as in example B1-1 to obtain a copolymer and a stretched film having a thickness of 40 μm. The physical properties of the obtained copolymer and the physical properties of the stretched film are shown in table 3.

Comparative example B1-1

In a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen introduction tube, 7 parts of MMA, 3 parts of ML and 10 parts of DMSO as a solvent were charged, and nitrogen was introduced thereinto while the temperature was raised to 105 ℃. Then, 0.02 part of an initiator 570 was added thereto, and solution stirring polymerization was carried out at 105 to 115 ℃ for 6 hours. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction liquid, were 99.1% and 99.5%, respectively. The obtained polymerization reaction liquid was subjected to the same operation as in example B1-1 to obtain a copolymer and a stretched film having a thickness of 40 μm. The physical properties of the obtained copolymer and the physical properties of the stretched film are shown in table 3.

< preparation of dope resin composition and production of film >

(example B2-1)

1 part of the copolymer obtained in example B1-2 and 7 parts of methylene chloride as a dispersion medium were mixed, shaken for 1 minute, and then stirred and mixed for 60 minutes to prepare a dope resin composition having a solid content of 12.5 mass%. The dope resin composition had a viscosity of 0.3 pas, YI of 0.9, and a haze of 0.3%. As a result of visually confirming the doped resin composition, the dispersion was uniform, and even after standing, no change was observed in the appearance of the doped resin composition.

Next, the dope resin composition was dropped onto the PET film, and the film was spread to a thickness of 800 μm by using a coater. Then, each PET film was put into a dryer, dried at 40 ℃ for 30 minutes, and dried at 60 ℃ for 30 minutes, and after that, the coated film was peeled off from the PET. After mounting wide-width mountain-shaped jigs on the upper and lower sides so that the obtained film was not curled, and hanging the jig in a dryer, the resultant film was dried at 100 ℃ for 12 hours to obtain an unstretched cast film having a thickness of 160 μm. The cast unstretched film thus obtained was stretched by a sequential biaxial stretcher in the same manner as in example B1-1 to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 3.

[ Table 2]

< test example C, example C and comparative example C >

[ measurement of boiling Point of Mixed solvent ]

500ml of a mixed solvent was added to a 1L separable flask equipped with a stirrer, a temperature sensor, a condenser and a nitrogen gas inlet pipe, and the temperature was raised while stirring while introducing nitrogen gas, and the internal temperature at the time of reflux from the condenser was measured as the boiling point of the mixed solvent.

[ polymerization reaction Rate in static polymerization ]

The polymerization reaction rate in the static polymerization was determined in the same manner as in the static polymerization of < test example B, example B and comparative example B >.

[ polymerization reaction Rate in agitation polymerization and composition analysis of copolymer ]

The reaction rate at the time of polymerization in the agitation polymerization and the content of the specific monomer unit in the copolymer were determined in the same manner as the reaction rate at the time of polymerization in the agitation polymerization and the content of the specific monomer unit in the copolymer in < test example B, and comparative example B >.

[ weight average molecular weight and number average molecular weight of copolymer ]

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the copolymer were determined in the same manner as those of the copolymer of < example a >.

[ ML content in copolymer ]

The ML content (content of a structural unit derived from α -methylene lactone) in the copolymer was determined in the same manner as in the copolymer of < example a >.

[ glass transition temperature (Tg) of copolymer ]

The glass transition temperature of the copolymer was determined in the same manner as that of the copolymer of < example a >.

[ 5% weight loss temperature of copolymer ]

The 5% weight loss temperature of the copolymer was determined in the same manner as the 5% weight loss temperature of the copolymer of < example a >.

[ internal haze of copolymer ]

The internal haze of the copolymer was determined in the same manner as in < test example B, and comparative example B >.

[ interior b of copolymer^*Value of]

Interior b of the copolymer^*Value and<test example B, example B and comparative example B>Interior b of the copolymer^*The values were similarly determined.

[ content of solvent (Compound) in copolymer ]

The content of the solvent (compound) in the copolymer was determined in the same manner as in the copolymer of < test example B, example B and comparative example B >.

[ viscosity of dope resin composition ]

The viscosity of the dope resin composition was determined in the same manner as in < test example B, and comparative example B >.

[ Yellowness (YI) of the dope resin composition ]

The Yellowness (YI) of the dope resin composition was determined in the same manner as in < test example B, and comparative example B >.

[ haze of doped resin composition ]

The haze of the dope resin composition was determined in the same manner as in < test example B, and comparative example B >.

[ thickness of film ]

The thickness of the film was determined in the same manner as that of the film of < example a >.

[ Total light transmittance of film ]

The total light transmittance of the film was determined in the same manner as that of the film of < example a >.

[ tensile test (elastic modulus measurement) of film ]

The tensile test (elastic modulus measurement) of the film was performed in the same manner as the tensile test of the film of < example a >, and the elastic modulus was measured.

[ Pencil hardness of film ]

The pencil hardness of the film was determined in the same manner as that of the film of < example a >.

[ folding test of film ]

The film folding test was performed in the same manner as the film folding test of < example a >, and the presence or absence of film breakage at the folded portion after the test was evaluated in the same manner as < example a >.

[ phase difference of film ]

The retardation of the film was determined in the same manner as the retardation of the film of < test example B, example B and comparative example B >.

< Synthesis of copolymer by static polymerization >

(test C1)

In a reaction vessel capable of being sealed, 7 parts of Methyl Methacrylate (MMA), 3 parts of α -methylene- γ -butyrolactone (ML), 10 parts of toluene (tol) as a solvent, and 0.03 parts of Azobisisobutyronitrile (AIBN) as an initiator were charged, and the vessel was purged with nitrogen for 2 minutes, and then, the cap was tightened to seal the vessel. Then, the reaction vessel was immersed in an oil bath at 75 ℃ for 2 hours to conduct polymerization. However, the polymerization is completed because a solid precipitates and solidifies during the polymerization. After the polymerization, the resulting solution was diluted with chloroform and reprecipitated by adding it to methanol, and a white solid was taken out.

(test C2)

Polymerization was carried out in the same manner as in test example C1, except that the solvent was changed from toluene to Acetone (ACE). However, the polymerization is completed because a solid precipitates and solidifies during the polymerization.

(test C3)

Polymerization was carried out in the same manner as in test example C1, except that the solvent was changed from toluene to cyclohexanone (Anone). However, the polymerization is completed because a solid precipitates and solidifies during the polymerization.

(test C4)

Polymerization was carried out in the same manner as in test example C1 except that the solvent was changed from toluene to a mixed solvent (1: 1 (mass ratio)) of Acetone (ACE) and cyclohexanone (Anone). After the polymerization, the resulting solution was diluted with chloroform and reprecipitated by adding it to methanol, and a white solid was taken out. Then, vacuum drying was performed at 240 ℃ for 1 hour to obtain about 6 parts of a white copolymer. The physical properties of the obtained copolymer are shown in table 4.

The mixed solvent of test example C4, in which no solid precipitated during the polymerization, was judged to be good according to test examples C1 to C4, and the following studies of stirred polymerization were conducted, centering on such a mixed solvent.

< Synthesis of copolymer and production of film by agitation polymerization >

(example C1-1)

In a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen introduction tube, 7.5 parts of Methyl Methacrylate (MMA), 2 parts of α -methylene- γ -butyrolactone (ML), 0.005 part of n-dodecylmercaptan (nDM) as a chain transfer agent, and 10 parts of Acetone (ACE) and cyclohexanone (Anone) as solvents were charged at a ratio of 1: 1 (mass ratio), introducing nitrogen gas, and simultaneously heating to 70 ℃. Then, 0.004 parts of AIBN as a polymerization initiator was added, and 0.2 parts of ACE and Anone were added dropwise at a constant rate at 70 to 75 ℃ over 3 hours with a rate of 1: 1 (mass ratio), 0.011 part of initiator AIBN and 0.5 part of ML after dilution. After dropwise addition, 4 parts of ACE and Anone were added at a rate of 1: 1 (mass ratio), and further carrying out solution stirring polymerization at 70-75 ℃ for 4 hours. The conversions of MMA and ML were 92.1% and 95.5%, respectively, as calculated from the amounts of unreacted monomers in the polymerization reaction mixture. The obtained polymerization reaction liquid was vacuum-dried at 240 ℃ for 2 hours (133Pa (1mmHg)), whereby a white copolymer was obtained. The physical properties of the obtained copolymer are shown in table 5.

The resulting copolymer of example C1-1 was then hot-pressed at 240 ℃ to give an unstretched pressed film having a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96mm × 96mm, subjected to successive biaxial stretching at a stretching temperature of Tg +18 ℃ (146 ℃) at a stretching speed of 300%/min at a stretching magnification of 2.0 times in the longitudinal direction (MD direction) and transverse direction (TD direction) in this order using a successive biaxial stretcher (X6-S, manufactured by tokyo Seiki Seisaku-sho Ltd.), and cooled to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 5.

(example C1-2)

To a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen introduction tube, 6 parts of Methyl Methacrylate (MMA), 3 parts of α -methylene- γ -butyrolactone (ML), 0.005 part of n-dodecylmercaptan (nDM) as a chain transfer agent, and 10 parts of Acetone (ACE) and cyclohexanone (Anone) as solvents were charged in a ratio of 3: 7 (mass ratio), introducing nitrogen gas, and heating to 85 ℃. Then, 0.004 parts of t-amyl peroxy 2-ethylhexanoate (manufactured by アルケマ gifh, Luperox (registered trademark) 575, hereinafter also referred to as "initiator 575") was added, and ACE and Anone were added dropwise at a constant rate of 3: 7 (mass ratio) and 0.009 parts of initiator 575 and 1 part of ML diluted mixed solvent. After dropwise addition, 4 parts of ACE and Anone were added at a rate of 3: 7 (mass ratio) and further carrying out solution stirring polymerization at 85-90 ℃ for 4 hours. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction mixture, were 93.1% and 95.5%, respectively. The obtained polymerization reaction liquid was vacuum-dried at 240 ℃ for 2 hours (133Pa (1mmHg)), whereby a white copolymer was obtained. The physical properties of the obtained copolymer are shown in table 5.

The resulting copolymer of example C1-2 was then hot-pressed at 240 ℃ to give an unstretched pressed film having a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96mm × 96mm, subjected to successive biaxial stretching at a stretching temperature of Tg +18 ℃ (146 ℃) at a stretching speed of 300%/min at a stretching magnification of 2.0 times in the longitudinal direction (MD direction) and transverse direction (TD direction) in this order using a successive biaxial stretcher (X6-S, manufactured by tokyo Seiki Seisaku-sho Ltd.), and cooled to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 5.

(example C1-3)

To a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen gas introduction tube, 6 parts of Methyl Methacrylate (MMA), 3 parts of α -methylene- γ -butyrolactone (ML) and 10 parts of Acetone (ACE) and γ -butyrolactone (GBL) as solvents were charged at a ratio of 2: 8 (mass ratio), introducing nitrogen gas, and heating to 100 ℃. Then, 0.004 parts of tert-amyl peroxyisononanoate (manufactured by アルケマ gifh, Luperox (registered trademark) 570, hereinafter also referred to as "initiator 570") as a polymerization initiator was added, and 0.2 parts of ACE and GBL were added dropwise at 100 to 110 ℃ at a constant rate over 3 hours with 2: 0.009 parts of initiator 570 and 1 part of ML diluted in 8 parts by mass of a mixed solvent. After dropwise addition, 4 parts of ACE and GBL were added at 2: 8 (mass ratio) and further carrying out solution stirring polymerization at 100-110 ℃ for 4 hours. The conversions of MMA and ML were 92.2% and 96.5%, respectively, as calculated from the amounts of unreacted monomers in the polymerization reaction mixture. The obtained polymerization reaction liquid was vacuum-dried at 240 ℃ for 2 hours (133Pa (1mmHg)), whereby a white copolymer was obtained. The physical properties of the obtained copolymer are shown in table 5.

The resulting copolymer of example C1-3 was then hot-pressed at 240 ℃ to give an unstretched pressed film having a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96mm × 96mm, subjected to successive biaxial stretching at a stretching temperature of Tg +18 ℃ (146 ℃) at a stretching speed of 300%/min at a stretching magnification of 2.0 times in the longitudinal direction (MD direction) and transverse direction (TD direction) in this order using a successive biaxial stretcher (X6-S, manufactured by tokyo Seiki Seisaku-sho Ltd.), and cooled to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 5.

(example C1-4)

In a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen gas introduction tube, 5 parts of Methyl Methacrylate (MMA), 3.2 parts of α -methylene- γ -butyrolactone (ML) and 10 parts of Acetone (ACE) and N, N-dimethylacetamide (DMAc) as solvents were charged at a ratio of 3: 7 (mass ratio), introducing nitrogen gas, and heating to 85 ℃. Then, 0.004 part of initiator 575 was added, and 0.2 part of ACE and DMAc was added dropwise at 85 to 90 ℃ over 3 hours at a constant rate in a ratio of 3: 7 (mass ratio) and 0.009 parts of initiator 575 and 1.8 parts of ML diluted mixed solvent. After dropwise addition, 4 parts of ACE and DMAc were added in a ratio of 3: 7 (mass ratio) and further carrying out solution stirring polymerization at 85-90 ℃ for 4 hours. The conversions of MMA and ML were 90.2% and 95.5%, respectively, as calculated from the amounts of unreacted monomers in the polymerization reaction mixture. The obtained polymerization reaction liquid was vacuum-dried at 240 ℃ for 2 hours (133Pa (1mmHg)), whereby a white copolymer was obtained. The physical properties of the obtained copolymer are shown in table 5.

The resulting copolymer of example C1-4 was then hot-pressed at 240 ℃ to give an unstretched pressed film having a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96mm × 96mm, subjected to successive biaxial stretching at a stretching temperature of Tg +18 ℃ (146 ℃) at a stretching speed of 300%/min at a stretching magnification of 2.0 times in the longitudinal direction (MD direction) and transverse direction (TD direction) in this order using a successive biaxial stretcher (X6-S, manufactured by tokyo Seiki Seisaku-sho Ltd.), and cooled to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 5.

Comparative example 1-1

In a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen introduction tube, 7 parts of MMA, 3 parts of ML and 10 parts of DMSO as a solvent were charged, and nitrogen was introduced thereinto while the temperature was raised to 105 ℃. Then, 0.02 part of an initiator 570 was added thereto, and solution polymerization was carried out at 105 to 110 ℃ for 6 hours with stirring. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction liquid, were 99.1% and 99.5%, respectively. The obtained polymerization reaction liquid was subjected to the same operation as in example C1-1 to obtain a copolymer and a stretched film having a thickness of 40 μm. The physical properties of the obtained copolymer and the physical properties of the stretched film are shown in table 5.

< preparation of dope resin composition and production of film >

(example C2-1)

In a reactor equipped with a stirring device, a temperature sensor, a condenser tube and a nitrogen introduction tube, 7.5 parts of Methyl Methacrylate (MMA), 2 parts of α -methylene- γ -butyrolactone (ML), 0.005 part of n-dodecylmercaptan (nDM) as a chain transfer agent, and 10 parts of Acetone (ACE) and cyclohexanone (Anone) as solvents were charged at a ratio of 3: 7 (mass ratio), introducing nitrogen gas, and heating to 85 ℃. Then, 0.004 part of initiator 575 was added, and 0.2 part of ACE and Anone was added dropwise at 85 to 90 ℃ over 3 hours at a constant rate in a ratio of 3: 7 (mass ratio) and 0.009 parts of initiator 575 and 0.5 parts of ML after dilution with a mixed solvent. After dropwise addition, 4 parts of ACE and Anone were added at a rate of 3: 7 (mass ratio) and further carrying out solution stirring polymerization at 85-90 ℃ for 4 hours. The conversions of MMA and ML, which were calculated from the amounts of unreacted monomers in the polymerization reaction liquid, were 93.1% and 97.5%, respectively. ACE and Anone were mixed with 55 parts in a ratio of 3: 7 (mass ratio) the obtained polymerization reaction solution was diluted with a mixed solvent to prepare a dope resin composition having a copolymer content of 12.5 mass%. The dope resin composition was subjected to pressure filtration using a 3 μm membrane filter. The physical properties of the dope resin composition are shown in table 5. As a result of visually confirming the doped resin composition, the dispersion was uniform, and even after standing, no change was observed in the appearance of the doped resin composition.

Next, the dope resin composition of example C2-1 was coated on a glass substrate, and vacuum-dried at 150 ℃ for 2 hours to obtain an unstretched cast film having a thickness of 120 μm. The cast unstretched film thus obtained was stretched by a sequential biaxial stretcher in the same manner as in example C1-1 to obtain a stretched film having a thickness of 30 μm. The physical properties of the obtained stretched film are shown in table 5.

(example C2-2)

1 part of the copolymer obtained in example C1-2 and 7 parts of methylene chloride as a dispersion medium were mixed, shaken for 1 minute, and then stirred and mixed for 60 minutes to prepare a dope resin composition having a solid content of 12.5 mass%. The physical properties of the dope resin composition are shown in table 5. As a result of visually confirming the doped resin composition, the dispersion was uniform, and even after standing, no change was observed in the appearance of the doped resin composition.

Next, the dope resin composition of example C2-2 was dropped onto the PET film, and the film was spread to a film thickness of 800 μm by using a coater. Then, each PET film was put into a dryer, dried at 40 ℃ for 30 minutes, and dried at 60 ℃ for 30 minutes, and after that, the coated film was peeled off from the PET. After mounting wide-width mountain-shaped jigs on the upper and lower sides so that the obtained film was not curled, and hanging the jig in a dryer, the resultant film was dried at 100 ℃ for 12 hours to obtain an unstretched cast film having a thickness of 160 μm. The cast unstretched film thus obtained was stretched by a sequential biaxial stretcher in the same manner as in example C1-1 to obtain a stretched film having a thickness of 40 μm. The physical properties of the obtained stretched film are shown in table 5.

[ Table 4]

Claims (18)

1. A method for producing a copolymer comprising a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms,

which comprises a step of polymerizing a monomer comprising the alpha-methylene lactone and the alkyl (meth) acrylate in the presence of a solvent,

the solvent is a solvent satisfying either the following condition (A) or the following condition (B),

condition (a): at least one solvent selected from the group consisting of cyclic amides and cyclic esters;

condition (B): the solvent composition comprises a mixed solvent containing a first solvent having a boiling point lower than 100 ℃ and a second solvent having a boiling point of 100 ℃ or higher, wherein the first solvent is at least one selected from the group consisting of ketones and chloroalkanes, the second solvent is at least one selected from the group consisting of cyclic ketones, cyclic esters, amides, and sulfoxides, and the mixed solvent has a boiling point of 70-120 ℃.

2. The method for producing a copolymer according to claim 1, wherein the solvent is a solvent that satisfies the condition (A).

3. The method for producing a copolymer according to claim 1, wherein the solvent is a solvent that satisfies the condition (B).

4. The method for producing a copolymer according to claim 3, wherein the first solvent is acetone.

5. The method for producing a copolymer according to claim 3 or 4, wherein the second solvent is a cyclic ketone.

6. The method for producing a copolymer according to claim 5, wherein the cyclic ketone is cyclohexanone.

7. The method for producing a copolymer according to claim 3 or 4, wherein the second solvent is at least one selected from the group consisting of cyclic esters, amides, and sulfoxides.

8. The method for producing a copolymer according to claim 7, wherein the second solvent is at least one selected from the group consisting of γ -butyrolactone, γ -valerolactone, δ -valerolactone, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, N' -dimethylimidazolidinone, and dimethyl sulfoxide.

9. A copolymer comprising a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms,

the internal haze per 100 μm thickness when made into a film is less than 2.5%.

10. A copolymer which comprises a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1-6 carbon atoms and has a weight-average molecular weight of 200000 or more and 1000000 or less.

11. Copolymer according to claim 9 or 10, which, when produced as a film, has an internal b value per 100 μm thickness of the colorimetric system of less than 1.6.

12. A copolymer mixture comprising the copolymer according to any one of claims 9 to 11 and at least one compound selected from the group consisting of cyclic amides, cyclic esters and cyclic ketones.

13. A copolymer mixture containing a copolymer comprising a structural unit derived from an alpha-methylene lactone and a structural unit derived from an alkyl (meth) acrylate having an alkyl group with 1 to 6 carbon atoms and at least one compound selected from the group consisting of cyclic amides, cyclic esters, and cyclic ketones.

14. The copolymer mixture according to claim 12 or 13, wherein the content of the compound is 10 to 3000 ppm by mass based on the total amount of the copolymer.

15. A dope resin composition comprising the copolymer according to any one of claims 9 to 11 and a dispersion medium, wherein the content of the copolymer is 5% by mass or more based on the total amount of the dope resin composition.

16. A resin molded article comprising the copolymer according to any one of claims 9 to 11 or the copolymer mixture according to any one of claims 12 to 14.

17. A method for producing a resin molded article, comprising a step of molding a resin composition containing the copolymer according to any one of claims 9 to 11 or the copolymer mixture according to any one of claims 12 to 14 to obtain a resin molded article.

18. A method for producing a resin molded body, comprising:

a step of applying the dope resin composition according to claim 15; and

and a step of removing the dispersion medium from the applied dope resin composition to obtain a resin molded article.