Resin molded body, its use, and flexible display

Abstract

To provide a production method of a copolymer including a constitutional unit derived from α-methylene lactone by polymerization with use of solvent, capable of improving transparency of the resulting copolymer.SOLUTION: Provided is a resin molding that contains a copolymer including a constitutional unit derived from α- methylene lactone and a constitutional unit derived from an alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms. The copolymer has a weight average molecular weight of 220000 or more and 1000000 or less. The copolymer has a glass transition temperature of 110°C or more and 160°C or less. The resin molding is a stretched film. A test piece of the resin molding having cut-out sizes of 15 mm by 80 mm satisfies conditions that no fracture occurs in 100000 repetitions of bending by a predetermined method.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a copolymer, a method for producing the same, a copolymer mixture, a dope resin composition, and a resin molded body and a method for producing the same.

Background Art

[0002] 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 a film or the like, which is a molded body of a copolymer (resin) containing structural units derived from a predetermined α-methylene lactone, is suitable for use as an optical member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, generally, copolymers containing structural units derived from α-methylene lactone tend to have low solubility in solvents, so polymerization is carried out in a solvent-free or dimethyl sulfoxide (DMSO) solvent. However, in solvent-free polymerization, the heat of polymerization cannot be removed, and in polymerization with a DMSO solvent, the solvent itself decomposes upon heating to generate harmful substances and has explosiveness under specific conditions, so there are problems in terms of safety and it is not suitable for industrialization. Further, according to the studies of the present inventors, it has been found that when polymerization is carried out in a DMSO solvent, the resulting copolymer containing structural units derived from α-methylene lactone tends to be colored and the transparency tends to decrease.

[0005] Therefore, the 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 can improve the transparency of the resulting copolymer.

Means for Solving the Problems

[0006] The present invention provides a method for producing a copolymer described in the following [1] to [8], a copolymer described in [9] to

[11] , a copolymer mixture described in

[12] to

[14] , a dope resin composition described in

[15] , a resin molded body described in

[16] , and a method for producing the resin molded body described in

[17] and

[18] . [1] A method for producing a copolymer containing 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, comprising a step of polymerizing a monomer containing α-methylene lactone and an alkyl (meth)acrylate in the presence of a solvent, wherein 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 a cyclic amide and a cyclic ester. Condition (B): A mixed solvent composed of a first solvent having a boiling point of less than 100°C and a second solvent having a boiling point of 100°C or higher, wherein the first solvent is at least one selected from the group consisting of a ketone and an alkyl chloride, the second solvent is at least one selected from the group consisting of a cyclic ketone, a cyclic ester, an amide, and a sulfoxide, and the boiling point is 70 to 120°C. [2] The method for producing a copolymer according to [1], wherein the solvent satisfies condition (A). [3] The method for producing a copolymer according to [1], wherein the solvent satisfies 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 method 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 method 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,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N,N'-dimethylimidazolidinone, and dimethyl sulfoxide. [9] A copolymer containing 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, and having an internal haze of less than 2.5% per 100 μm thickness when formed into a film.

[10] A copolymer containing 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, and having a weight average molecular weight of 200,000 or more and 1,000,000 or less.

[11] L when formed into a film * a * b * The internal b value per 100 μm thickness in the color system * is less than 1.6, the copolymer according to [9] or

[10] .

[12] A copolymer mixture containing 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 containing 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 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 mass ppm based on the total amount of the copolymer. A dope resin composition containing the copolymer according to any one of

[15] [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. A resin molded article containing the copolymer according to any one of

[16] [9] to

[11] or the copolymer mixture according to any one of

[12] to

[14] . A method for producing a resin molded article, comprising a step of molding a resin composition containing the copolymer according to any one of

[17] [9] to

[11] or the copolymer mixture according to any one of

[12] to

[14] to obtain a resin molded article. A method for producing a resin molded article, comprising a step of coating the dope resin composition according to

[18]

[15] , and a step of removing the dispersion medium from the coated dope resin composition to obtain a resin molded article.

Advantages of the Invention

[0007] 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, which can improve the transparency of the obtained copolymer. The method for producing a copolymer according to some embodiments enables the polymerization reaction to be easily carried out under reflux. Further, according to the present invention, there are provided a copolymer obtained by such a production method and a copolymer mixture containing the copolymer. The copolymer mixture according to some embodiments tends to be excellent in reducing the processing load on the formed film and the strength of the formed film. Furthermore, according to the present invention, there are provided a dope resin composition using the copolymer or the copolymer mixture, a resin molded article, and a method for producing the same.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[0009] In this specification, "resin (composition)" is a broader concept than "(co)polymer". The resin may be composed of, for example, one or more (co)polymers, and may contain additives such as antioxidants other than the (co)polymer as required.

[0010] [Method for producing copolymer] The method for producing a copolymer according to one embodiment is a method for producing a copolymer containing 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.

[0011] The structural unit derived from α-methylene lactone is formed by the polymerization of α-methylene lactone in which a methylene group is 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, but is preferably a 5-membered ring (γ-lactone) or a 6-membered ring (δ-lactone) because of the high stability of the ring structure and the higher surface strength obtained based on this high stability.

[0012] Specific examples of α-methylene lactone that is a 5-membered ring or a 6-membered ring are α-methylene-γ-butyrolactone and α-methylene-δ-valerolactone. These may have substituents.

[0013] The structural unit derived from α-methylene lactone is preferably a structural unit having the structure shown in the following formula (1).

[0014] [Chemical formula]

[0015] R in formula (1) 1 ~R 4 are each independently a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

[0016] The structural unit having the structure shown in the formula (1) can be formed by polymerization of a monomer containing α-methylene-γ-butyrolactone shown in the following formula (2).

[0017]

Chemical formula

[0018] R in the formula (2) 1 ~R 4 are, independently of each other, a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

[0019] 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 a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, a cyclohexyl group and the like.

[0020] The aromatic hydrocarbon group is not particularly limited and may contain, for example, a heterocyclic structure. Examples of the aromatic hydrocarbon group include a phenyl group, a tolyl group, a benzyl group and the like.

[0021] R 1 ~R 4 are preferably, independently of each other, a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably all hydrogen atoms.

[0022] From the viewpoint of further improving heat resistance and the like, the content of the structural unit derived from α-methylene lactone in the copolymer is preferably 5 to 40% by mass, more preferably 7.5 to 35% by mass, still more preferably 10 to 30% by mass. The content of each structural unit in the copolymer can be determined by dissolving the copolymer in a heavy solvent, 1 measuring 1H-NMR and calculating the area ratio of the peaks corresponding to each structural unit.

[0023] The structural unit derived from an alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms is formed by polymerization of an alkyl (meth)acrylate. Examples of the alkyl group with 1 to 6 carbon atoms in the alkyl (meth)acrylate include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, a cyclohexyl group, etc. These may be used alone or in combination of two or more.

[0024] 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.

[0025] 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.

[0026] From the viewpoint of further improving heat resistance, transparency, etc., the content of the structural unit derived from an 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.

[0027] The copolymer may contain a structural unit derived from an α-methylene lactone and a structural unit of other monomers other than the 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, methyl vinyl ketone, ethylene, propylene, vinyl acetate, etc. These may be used alone or in combination of two or more.

[0028] The content of other structural units in the copolymer is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less.

[0029] The method for producing a copolymer according to this embodiment includes a step of polymerizing monomers including α-methylene lactone and an alkyl (meth)acrylate in the presence of a solvent. The solvent is a solvent that satisfies either the following condition (A) or the following condition (B). Condition (A): It is at least one solvent selected from the group consisting of a cyclic amide and a cyclic ester. Condition (B): It is a mixed solvent composed of a first solvent having a boiling point of less than 100°C and a second solvent having a boiling point of 100°C or higher, where the first solvent is at least one selected from the group consisting of a ketone and an alkyl chloride, the second solvent is at least one selected from the group consisting of a cyclic ketone, a cyclic ester, an amide, and a sulfoxide, and the boiling point is 70 to 120°C.

[0030] According to the method for producing a copolymer according to this embodiment, it becomes possible to improve the transparency of the obtained copolymer. Although the reason for such an effect is not necessarily clear, the inventors believe that the cause of coloring (decrease in transparency) lies in the formation of a homopolymer of α-methylene lactone. The homopolymer dissolves in DMSO solvent alone, but tends not to dissolve or to be hardly soluble in a solvent that satisfies condition (A) or a solvent that satisfies condition (B). Therefore, by polymerizing monomers containing α-methylene lactone using a solvent that satisfies condition (A) or a solvent that satisfies condition (B), the formation of the homopolymer of α-methylene lactone can be suppressed, thereby reducing the coloring of the copolymer and improving the transparency.

[0031] Also, by using a solvent that satisfies condition (B), the method for producing a copolymer according to the present embodiment can easily perform a polymerization reaction under reflux when producing a copolymer containing a structural unit derived from α-methylene lactone. For example, at a general polymerization temperature (e.g., 70 to 120°C), it is possible to carry out the polymerization in a reflux state. When the polymerization is carried out in a reflux state, the heat of polymerization during polymerization can be gradually heated, and the polymerization temperature can be controlled near the boiling point. Therefore, the polymerization can proceed safely and stably. When the boiling point of the mixed solvent is 120°C or lower, it is advantageous in that it is easy to control the polymerization rate, suppress by-products, and the polymerization temperature does not become too high compared to the boiling point of the (meth)acrylic acid alkyl monomer. Also, when the boiling point of the mixed solvent is 70°C or higher, it is advantageous in terms of productivity such as the viscosity of the polymerization solution and the polymerization rate.

[0032] The solvent represented by condition (A) is at least one solvent selected from the group consisting of cyclic amides and cyclic esters, and may be a single solvent of one kind, or a mixed solvent of two or more kinds combined, but preferably a single solvent of one kind. The boiling point of the solvent (the boiling point of the single solvent or the boiling point of the mixed solvent) is preferably above 200°C and below 300°C because it is easy to control the content of the solvent (compound) in the copolymer mixture.

[0033] Examples of the cyclic amide include N-methylpyrrolidone (NMP), N,N'-dimethylimidazolidinone (DMI), and the like. Among these, the cyclic amide is preferably NMP because of its high versatility.

[0034] Examples of the cyclic ester include γ-butyrolactone (GBL), γ-valerolactone, δ-valerolactone, and the like. Among these, the cyclic ester is preferably GBL from the viewpoint of high versatility.

[0035] When using the solvent represented by condition (A), the polymerization temperature and polymerization time vary depending on the type and usage ratio of the monomers used. However, the polymerization temperature is preferably 0 to 150 °C, more preferably 50 to 150 °C, and even more preferably 60 to 140 °C. Also, the polymerization time is preferably 0.5 to 20 hours, more preferably 1 to 10 hours.

[0036] The solvent represented by condition (B) is a mixed solvent composed of a first solvent having a boiling point of less than 100 °C and a second solvent having a boiling point of 100 °C or higher, where the first solvent is at least one selected from the group consisting of ketones and alkyl chlorides, 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 °C.

[0037] The first solvent is a solvent having a boiling point of less than 100 °C and is at least one solvent selected from the group consisting of ketones and alkyl chlorides. Examples of such a first solvent include ketones such as acetone (ACE) and methyl ethyl ketone (MEK), and alkyl chlorides such as dichloromethane, chloroform, 1,2 - dichloroethane, and 1,1 - dichloroethane. The first solvent may be used alone or in combination of two or more. Among these, the first solvent is preferably acetone.

[0038] The second solvent is a solvent having a boiling point of 100°C 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,N-dimethylacetamide, N-methylpyrrolidone (NMP), and N,N'-dimethylimidazolidinone (DMI), and sulfoxides such as dimethyl sulfoxide. The second solvent may be used alone or in combination of two or more. One embodiment of the second solvent is preferably a cyclic ketone, more preferably cyclohexanone. Another embodiment of the second solvent is preferably at least one selected from the group consisting of cyclic esters, amides, and sulfoxides, more preferably at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, δ-valerolactone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N,N'-dimethylimidazolidinone, and dimethyl sulfoxide.

[0039] 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, acetone and cyclohexanone each tend to be difficult to dissolve the copolymer alone, but it has been found that they become extremely specifically easy to dissolve the above-mentioned copolymer. Therefore, by using such a mixed solvent, it becomes easy to carry out the polymerization reaction under reflux, and it becomes possible to improve the transparency of the obtained copolymer.

[0040] The above copolymer tends to be easily dissolved in an alkyl chloride having a boiling point of less than 100°C as the first solvent and at least one solvent selected from the group consisting of a cyclic ester, an amide, and a sulfoxide having a boiling point of 100°C or higher as the second solvent. Therefore, the combination of the first solvent and the second solvent may be a combination of an alkyl chloride having a boiling point of less than 100°C and a solvent having a boiling point of 100°C or higher, which is at least one solvent selected from the group consisting of a cyclic ketone, a cyclic ester, an amide, and a sulfoxide, or may be a combination of at least one solvent selected from the group consisting of a ketone and an alkyl chloride having a boiling point of less than 100°C and at least one solvent selected from the group consisting of a cyclic ester, an amide, and a sulfoxide.

[0041] The boiling point of the mixed solvent is 70 to 120°C, preferably 75 to 115°C, more preferably 80 to 110°C. When the boiling point of the mixed solvent is within such a range, it becomes easy to carry out the polymerization reaction under reflux. In the present specification, the boiling point of the mixed solvent means the value measured by the method described in the examples.

[0042] 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°C, and can be adjusted at any ratio. By adjusting the first solvent and the second solvent at any ratio so that the boiling point of the mixed solvent is in the range of 70 to 120°C, it becomes easy to carry out the polymerization reaction under reflux, and it becomes possible to improve the transparency of the resulting copolymer. 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, still more preferably 7 / 3 or less, particularly preferably 6 / 4 or less, and most preferably 5 / 5 or less.

[0043] When using the solvent represented by condition (B), the polymerization temperature and polymerization time vary depending on the type and usage ratio of the monomers used. However, from the perspective of easily controlling the polymerization rate, suppressing by-products, and ensuring that the polymerization temperature does not exceed the boiling point of the alkyl (meth)acrylate monomer, the polymerization temperature is preferably 120°C or lower, and preferably 70°C or higher from the perspective of productivity such as polymerization solution viscosity and polymerization rate. The polymerization temperature is more preferably 75 - 115°C, and even more preferably 80 - 110°C. Also, the polymerization time is preferably 0.5 - 20 hours, and more preferably 1 - 10 hours.

[0044] In the polymerization step, the method of introducing each monomer component (α-methylene lactone, alkyl (meth)acrylate, other monomers, etc.) into the reactor is not particularly limited, and examples include a method of introducing the total amount of monomers before introducing the polymerization initiator, a method of continuously dropping and introducing the total amount of monomers simultaneously with the introduction of the polymerization initiator, a method of first introducing a part of the monomers and then dropping and introducing the remaining monomers after the start of polymerization, and a method of changing the content ratio of α-methylene lactone in the monomer composition introduced first and the content ratio of α-methylene lactone in the monomer composition introduced after the start of polymerization and then introducing them.

[0045] When polymerizing the monomer, a polymerization initiator may be added as necessary. Examples of the polymerization initiator include organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-amyl peroxy-2-ethylhexanoate, and t-butyl peroxy-2-ethylhexanoate; and azo compounds such as 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and dimethyl-2,2'-azobis(2-methylpropionate). The content ratio of the polymerization initiator may be appropriately set according to the combination of monomers used, reaction conditions, etc., and is not particularly limited. However, it is preferably 10 to 10,000 mass ppm, more preferably 100 to 3,000 mass ppm, and still more preferably 300 to 2,000 mass ppm based on the total monomers.

[0046] When polymerizing the monomer, 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 polysiloxane; and side-chain polyfunctional mercapto-modified polysiloxane with a mercapto-modified side chain. The content ratio of the chain transfer agent may be appropriately set according to the combination of monomers used, reaction conditions, etc., and is not particularly limited. However, it is preferably 10 to 10,000 mass ppm, more preferably 100 to 3,000 mass ppm based on the total monomers.

[0047] When polymerizing the monomer, in order to suppress the increase in viscosity of the reaction solution, it is preferable to control the concentration of the copolymer in the polymerization reaction mixture to be 90% by mass or less, more preferably 70% by mass or less, and still more preferably 50% by mass or less. Also, if the concentration of the copolymer in the polymerization reaction mixture is too low, the productivity will decrease. Therefore, it is preferable to control the concentration of the polymer in the polymerization reaction mixture to be 10% by mass or more, more preferably 20% by mass or more.

[0048] In the polymerization reaction mixture obtained through the polymerization process, usually, in addition to the target copolymer, a solvent is contained. The method for separating the copolymer from the solvent is not particularly limited, and examples include a method by reprecipitation, a devolatilization apparatus composed of a heat exchanger and a devolatilization tank, a method of removing the solvent using an extruder with a vent, and the like.

[0049] [Copolymer] The copolymer according to one embodiment contains 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, and the internal haze per 100 μm of thickness when formed into a film is less than 2.5%. The copolymer of this embodiment can be the copolymer obtained by the above production method. Since the above production method can improve the transparency of the obtained copolymer, by using the production method, the internal haze per 100 μm of thickness when formed into a film, the L * a * b * Internal b per 100 μm of thickness in the color system * values and the like can be made to fall within a predetermined range.

[0050] The copolymer has an internal haze per 100 μm of thickness when formed into a film of less than 2.5%. The internal haze is preferably 2.0% or less, more preferably 1.5% or less, still more preferably 1.0% or less, and particularly preferably 0.8% or less. The internal haze per 100 μm of thickness when the copolymer is formed into a film can be measured, for example, by the method described in the examples. Also, the temperature when thermally press-molding the copolymer can be, for example, 200 to 270 °C, and more specifically, it can be 240 °C.

[0051] The copolymer according to another embodiment includes 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, and has a weight average molecular weight (Mw) of 200,000 or more and 1,000,000 or less. By using the copolymer of this embodiment, it becomes possible to form a film excellent in transparency, heat resistance, and flexibility.

[0052] The copolymer is in a state that substantially does not contain the solvent used in the above production method. Here, "substantially does not contain" 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, for example, by the method described in the examples using a film formed from the copolymer or the copolymer mixture.

[0053] The copolymer has an internal b * a * b * value per 100 μm thickness in the L*a*b* color system preferably less than 1.6. The internal b * 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 when the copolymer is formed into a film can be measured, for example, by the method described in the examples. Also, the temperature when the copolymer is hot press molded can be, for example, 200 to 270 °C, and more specifically, 240 °C. * a * b * value per 100 μm thickness in the L*a*b* color system * The temperature when hot press molding the copolymer can be, for example, 200 to 270 °C, and more specifically, it can be 240 °C.

[0054] The weight average molecular weight (Mw) of the copolymer is preferably 100,000 or more, more preferably 150,000 or more, still more preferably 200,000 or more, particularly preferably 220,000 or more, and most preferably 240,000 or more. The weight average molecular weight (Mw) of the copolymer is preferably 1,000,000 or less, more preferably 750,000 or less, still more preferably 500,000 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 the examples.

[0055] The number average molecular weight (Mn) of the copolymer is preferably 20,000 or more, more preferably 50,000 or more, still more preferably 100,000 or more. The number average molecular weight (Mn) of the copolymer is preferably 500,000 or less, more preferably 400,000 or less, still more preferably 300,000 or less. The Mn of the copolymer can be measured, for example, by the method described in the examples. Also, the dispersity (Mw / Mn) of the copolymer is preferably 3.0 or less, more preferably 2.8 or less, still more preferably 2.5 or less.

[0056] The yellowness index (YI) of the copolymer measured in accordance with the provisions of JIS Z 8729 when it is a 15% chloroform solution of the copolymer is preferably 5 or less, more preferably 3 or less, still more preferably 1 or less. When the YI of the copolymer is within such a range, a resin molded article with low coloring can be obtained.

[0057] The glass transition temperature (Tg) of the copolymer measured in accordance with the provisions of JIS K 7121 is preferably 110°C or more, more preferably 115°C or more, still more preferably 120°C or more from the viewpoint of further improving heat resistance and the like. The upper limit of the glass transition temperature of the copolymer is not particularly limited, but can be, for example, 160°C or less.

[0058] The 5% weight loss temperature of the copolymer is preferably 280 °C or higher, more preferably 290 °C or higher, and still more preferably 300 °C or higher from the viewpoint of further improving heat resistance and the like. The upper limit of the 5% weight loss temperature of the copolymer is not particularly limited, but can be, for example, 400 °C or lower. The 5% weight loss temperature can be measured, for example, by the method described in the examples.

[0059] [Copolymer mixture] The copolymer mixture according to one embodiment contains a copolymer containing 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, and at least one compound selected from the group consisting of a cyclic amide, a cyclic ester, and a cyclic ketone. One aspect of the copolymer mixture contains the above-mentioned copolymer and at least one compound selected from the group consisting of a cyclic amide, a cyclic ester, and a cyclic ketone.

[0060] As the at least one compound selected from the group consisting of a cyclic amide, a cyclic ester, and a cyclic ketone, those exemplified as the solvent in the above-mentioned method for producing the copolymer can be used. The content of the compound is preferably 10 to 3000 mass ppm based on the total amount of the copolymer. The content of the compound is more preferably 200 mass ppm or more, still more preferably 300 mass ppm or more, more preferably 2500 mass ppm or less, and still more 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, reduction of the processing load on the formed film, and strength of the formed film tend to be excellent. The content of the compound can be measured, for example, by the method described in the examples using a film formed from the copolymer or the copolymer mixture.

[0061] The copolymer mixture can be obtained by leaving the solvent (compound) when separating the copolymer from the solvent so that the content of the compound is within a predetermined range in the method for producing the copolymer described above, and can also be obtained by adding the compound so that the content of the compound is within a predetermined range in the copolymer after isolation.

[0062] [Dope resin composition] The dope resin composition according to one embodiment contains the copolymer described above and a dispersion medium. The dope resin composition can be suitably used for producing a resin molded body.

[0063] As one aspect of the dispersion medium, for example, alkyl chloride solvents such as chloroform and dichloromethane; 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, dioxane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone, ethyl acetate, diethyl ether, NMP, GBL, etc. can be mentioned. These may be used alone or in combination of two or more. However, when using a combination of two or more, those other than the solvent represented by the above condition (B) shall be used.

[0064] Another aspect of the dispersion medium is the solvent represented by the above condition (B). The boiling point of the mixed solvent (the solvent represented by condition (B)) is preferably 70 to 120°C. The combination of the first solvent and the second solvent of the mixed solvent, the boiling point of the mixed solvent, the mixing ratio of the first solvent and the second solvent, etc. are the same as 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, etc. described above. Therefore, the overlapping explanations are omitted here. Note that the first solvent may be further added to the above mixed solvent. The boiling point of the dispersion medium when the first solvent is further added to the above mixed solvent is preferably 30 to 110°C, more preferably 40 to 100°C.

[0065] From the perspective of efficiently manufacturing a resin molded body, 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, still more preferably 20% by mass or more, based on the total amount of the dope resin composition. From the perspective of ensuring fluidity for stable production in manufacturing equipment, the content of the copolymer is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, based on the total amount of the dope resin composition.

[0066] The dope resin composition may contain other polymers in the resin molded body described below. The content of the other polymers is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, still more preferably 0 to 30% by weight, particularly preferably 0 to 20% by mass, most preferably 0 to 10% by mass, based on the total amount of the dope resin composition.

[0067] The dope resin composition may contain other additives in the resin molded body described below. The dope resin composition can 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, still more preferably 0 to 0.5% by mass, based on the total amount of the dope resin composition.

[0068] The yellowness index (YI) of the dope resin composition measured in accordance with the provisions of JIS Z 8729 is preferably 5 or less, more preferably 3 or less, still more preferably 1 or less, from the perspective of obtaining a resin molded body with low coloring.

[0069] The viscosity of the dope resin composition at 25°C is preferably 0.001 Pa·s or more, more preferably 0.01 Pa·s or more, still more preferably 0.1 Pa·s or more, and preferably 10 Pa·s or less, more preferably 5 Pa·s or less, still more preferably 1 Pa·s or less, from the perspective of improving the productivity of the resin molded body. The viscosity at 25°C can be measured, for example, by the method described in the examples.

[0070] The haze measured in accordance with JIS K7136 of the doped resin composition is preferably 5 or less, more preferably 3 or less, still more preferably 1 or less from the viewpoint of obtaining a highly transparent resin molded article.

[0071] [Resin Molded Article and Method for Producing the Same] The resin molded article according to one embodiment contains the above copolymer or the above copolymer mixture as a main component. The resin molded article according to this embodiment can be produced using a resin composition containing the above copolymer or the above copolymer mixture, or a doped resin composition containing the above copolymer or the above copolymer mixture.

[0072] The content of the copolymer or copolymer mixture is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, still more preferably 70 to 100% by weight, particularly preferably 80 to 100% by mass, and most preferably 90 to 100% by mass based on the total amount of the resin molded article. In the resin molded article, when the content of the copolymer or copolymer mixture is 50% by mass or more, a resin molded article with more excellent transparency can be obtained.

[0073] The resin molded body may contain polymers other than the above-mentioned copolymer (other polymers). Examples of other polymers include olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, and poly(4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resin; acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene block copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyamides such as nylon 6, nylon 66, and nylon 610; polyacetal; polycarbonate; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polysulfone; polyether sulfone; polyoxybenzylene; polyamideimide; elastic organic fine particles such as polybutadiene-based rubber and acrylic rubber; rubbery polymers such as ABS resin and ASA resin blended with polybutadiene-based rubber and acrylic rubber. The content of other polymers is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, still more preferably 0 to 30% by weight, particularly preferably 0 to 20% by mass, and most preferably 0 to 10% by mass based on the total amount of the resin molded body (resin composition).

[0074] The resin molded article may contain other additives. Examples of other additives include antioxidants such as hindered phenol-based, phosphorus-based, and sulfur-based antioxidants; stabilizers such as light stabilizers, weather 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; near-infrared absorbers; 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; organic fillers or inorganic fillers; resin modifiers; organic fillers or inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; fluidizing agents; compatibilizers, and the like. The resin molded article can 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 still more preferably 0 to 0.5% by mass based on the total amount of the resin molded article.

[0075] The resin molded article is preferably a sheet-like resin molded article such as a film-like resin molded article or a sheet-like resin molded article. In the present specification, a film-like resin molded article (film) means one having a film thickness of less than 350 μm, and a sheet-like resin molded article (sheet) means one having a film thickness of 350 μm or more.

[0076] One aspect of the method for producing a resin molded article includes a step of molding a resin composition containing the above copolymer or the above copolymer mixture to obtain a resin molded article. The method for molding the resin composition is not particularly limited, and examples thereof include conventionally known methods such as a melt extrusion method, a calender method, and a compression molding method. Among these, the method for molding the resin composition is preferably a melt extrusion method.

[0077] The resin composition may contain, in addition to the above-mentioned copolymer or the above-mentioned copolymer mixture, the above-mentioned other polymers, the above-mentioned other additives, etc., according to the desired resin molded article. The content of the copolymer or copolymer mixture, other polymers, other additives, etc. in the resin composition may be the same as the content of each component exemplified in the resin molded article.

[0078] Specific examples of the melt extrusion method include, for example, the T-die method, the inflation method, etc. The molding temperature of the resin molded article is preferably 150 to 350°C, more preferably 200 to 300°C.

[0079] Another aspect of the method for producing a resin molded article includes a step of coating the above-mentioned dope resin composition and a step of removing the dispersion medium from the coated dope resin composition to obtain a resin molded article. The method for coating the dope resin composition is not particularly limited, and examples include conventionally known methods such as the solution casting method (solution casting method). For the solution casting method (solution casting method), for example, apparatuses such as a drum casting machine, a band casting machine, and a spin coater can be used.

[0080] The method for removing the dispersion medium from the dope resin composition is not particularly limited, and examples include a method of heating the dope resin composition to volatilize the dispersion medium. The heating temperature can be appropriately set according to the dispersion medium used.

[0081] The film-shaped resin molded article (film) can be made into a stretched film by stretching. The film is preferably a stretched film in terms of excellent flexibility and, in some cases, the ability to impart a retardation.

[0082] As a method for stretching the film, conventionally known stretching methods can be applied. Examples include uniaxial stretching such as free-width uniaxial stretching and fixed-width uniaxial stretching; biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching. The method for stretching the film is preferably biaxial stretching in terms of improving the fold resistance in any two orthogonal directions within the film plane.

[0083] When stretching the film, the stretching temperature is preferably near the glass transition temperature of the above-mentioned copolymer. More specifically, it is preferably (glass transition temperature - 30) °C to (glass transition temperature + 100) °C, more preferably (glass transition temperature - 20) °C to (glass transition temperature + 50) °C, and still more preferably (glass transition temperature - 10) °C to (glass transition temperature + 30) °C.

[0084] When stretching the film, the stretching ratio may be, for example, in the range of 1.05 to 10 times in both the longitudinal and lateral directions.

[0085] The film thickness of the film-shaped resin molded body (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-shaped resin molded body (sheet) is preferably 350 μm or more and 10 mm or less, more preferably 350 μm or more and 5 mm or less.

[0086] When the resin molded body is a film, the total light transmittance measured by the method according to JIS K7136 of the film is preferably 85% or more, more preferably 88% or more, still more preferably 90% or more, and particularly preferably 92% or more. The total light transmittance is a measure of transparency, and when it is 85% or more, the transparency of the film can be sufficient.

[0087] When the resin molded body is a film, the elastic modulus of the film is preferably 4 GPa or more, more preferably 4.5 GPa or more, and still more preferably 5 GPa 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, but it can be, for example, 15 GPa or less. The elastic modulus of the film can be measured, for example, by the method described in the examples.

[0088] When the resin molded body is a film, the Young's modulus of the film is preferably 4 GPa or more, more preferably 4.5 GPa or more, and still more preferably 5 GPa 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, but for example, it can be 15 GPa or less. The Young's modulus of the film can be measured by, for example, the method described in the examples.

[0089] When the resin molded body is a film, the pencil hardness of the film is preferably H or more, more preferably 2H or more, and still more preferably 3H or more from the viewpoint of further improving the strength of the film.

[0090] When the resin molded body is a film, it is preferable that in a bending test (foldable test) in which the film is repeatedly bent into a U shape and returned under predetermined conditions, no breakage occurs in the bent portion even when the number of bends exceeds 100,000 times. The predetermined conditions can be, for example, the conditions described in the examples.

[0091] The resin molded body of this embodiment can be applied to various uses, and for example, it can be suitably applied to optical uses. Examples of specific uses include, for example, various uses such as light guide members, film uses, lenses (such as optical lenses), covers, and foam uses (such as cushioning materials, heat insulating materials, vibration damping materials, sound insulating materials, sealing materials, packing materials, etc.).

[0092] The resin molded body (particularly, a film-shaped resin molded body) of the present embodiment can be suitably used for optical applications. Further, since the resin molded body (particularly, a film-shaped resin molded body) of the present embodiment is excellent in transparency, heat resistance, flexibility, and surface hardness, it can be suitably used for flexible display applications, and in particular, it can be more suitably used as the outermost cover window. Specific examples of flexible displays include flexible organic EL displays that are thin and bendable, smartphones that can be folded or rolled up, and the like. Further, since the film-shaped resin molded body has a low retardation, it can also be used as a protective film for each layer of a flexible display. Furthermore, it is possible to produce a polarizing plate or a touch panel using the film-shaped resin molded body.

[0093] When applying the film-shaped resin molded body (film) as a cover window for a flexible display, for example, it may be used as a laminate having other layers such as a hard coat layer. Further, the cover window for a flexible display formed from the film can be disposed on the surface of the flexible display via, for example, an adhesive layer.

Examples

[0094] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by the examples. In the following, unless otherwise specified, "parts" means "parts by mass". Further, various physical properties were measured and evaluated as follows.

[0095] <Example A> [Polymerization reaction rate and polymer composition analysis] The reaction rate during the polymerization reaction and the content of specific monomer units in the copolymer were determined by measuring the amount of unreacted monomers in the obtained polymerization reaction solution using gas chromatography (manufactured by Shimadzu Corporation, apparatus name: GC-2014).

[0096] [Weight average molecular weight and number average molecular weight] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer were determined in terms of polystyrene using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement were as follows. System: Tosoh GPC system HLC-8220 Measurement side column configuration: · Guard column (manufactured by Tosoh, TSKguardcolumn SuperHZ-L) · Two separation columns (manufactured by Tosoh, TSKgel SuperHZM-M) connected in series Reference side column configuration: · Reference column (manufactured by Tosoh, TSKgel SuperH-RC) Developing solvent: chloroform (manufactured by Wako Pure Chemical Industries, special grade) Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit) Column temperature: 40 °C

[0097] [ML content in copolymer] The ML content in the copolymer (content of structural units derived from α-methylene lactone) was 1 determined by 1H-NMR. Specifically, deuterated DMSO or deuterated chloroform was used as the heavy solvent, and 1H-NMR measurement was performed using a nuclear magnetic resonance spectrometer (manufactured by BRUKER, AV300M). 1 The 1H-NMR measurement was carried out, and it was determined from the area ratio of the obtained 1 1H-NMR profile.

[0098] [Glass transition temperature (Tg)] The glass transition temperature of the copolymer was determined in accordance with the provisions of JIS K 7121. Specifically, using a differential scanning calorimeter (manufactured by Rigaku, Thermo plus EVO DSC-8230), in a nitrogen gas atmosphere, a sample of about 10 mg was heated from room temperature to 200 °C (heating rate 20 °C / min), and it was evaluated by the starting point method from the obtained DSC curve. α-alumina was used as the reference.

[0099] [5% weight loss temperature] The 5% weight loss temperature of the copolymer was determined in accordance with the provisions of JIS K 7120. Specifically, using a differential scanning calorimeter (manufactured by Rigaku, Thermo plus2 Tg-8120), about 10 mg of the sample was heated from room temperature to 400 °C at a rate of 10 °C / min under a nitrogen gas atmosphere. At this time, it was determined by measuring the temperature at the point when the mass of the sample during heating decreased by 5%.

[0100] [Thickness of the film] The thickness of the film was determined using a digital micrometer (manufactured by Mitutoyo).

[0101] [Total light transmittance of the film] The total light transmittance of the film was determined in accordance with the provisions of JIS K7361. Specifically, it was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-1001DP).

[0102] [Tensile test of the film (measurement of elastic modulus)] The stretched film was cut into a size of 90 mm × 20 mm as a test piece, and a tensile test was carried out in accordance with JIS K7127 using an autograph (manufactured by Shimadzu Corporation: AG-X) under an atmosphere of a temperature of 25 °C and a relative humidity of 50%. The conditions were a tensile speed of 0.25 mm / min up to a strain of 0.5%, and 1 mm / min thereafter, a chuck distance of 55 mm, and a gauge length for measurement with a displacement meter of 25 mm. Three tests were carried out at 25 °C, and the average value was taken as the measured value. The displacement was measured using a non-contact elongation width meter (manufactured by Shimadzu Corporation: TRViewX), and the elastic modulus was evaluated as the slope between a strain of 0.05% and 0.25%.

[0103] [Young's modulus of the film] The Young's modulus of the film was evaluated for the drawn film (thickness 4 μm) by a method compliant with ISO-14577-1 using a ultra-micro hardness tester (Fisher Instruments, Fisher Scope HM-2000). The evaluation was performed with the undrawn film fixed to a glass substrate. The measurement conditions were as follows: a square pyramid type Vickers indenter (opposite face angle a = 136°) was used, the maximum test load was 3 mN; the application time during load application was 20 seconds; the creep time was 5 seconds; the application time during load reduction was 20 seconds; the measurement temperature was room temperature (25°C), and the values measured three times were averaged to obtain the result.

[0104] [Pencil hardness of the film] The pencil hardness of the film was evaluated under a load of 750 g in accordance with JIS K5600-5-4 (1999) using a test pencil specified in JIS-S-6006 and a pencil scratch hardness tester No. 533 manufactured by Yasuda Seiki Seisakusho. The hardness of the hardest pencil that did not cause scratches was defined as the pencil hardness.

[0105] [Foldability test of the film] The drawn film was cut into a size of 15 mm × 80 mm to obtain a test piece, which was fixed with tape to a Tension-Free Folding Clamshell-type (manufactured by Yuasa System Devices, DMLHP-CS). Also, the test piece was bent at the midpoint of the long side, and a folded state was set such that the distance between both ends of the long side of the folded test piece was 5 mm and the radius of curvature of the bent portion of the test piece was 2.5 mm. Then, in an environment at 25°C, changing from the flat-open state to the folded state was defined as one flexion, and flexion was repeated 100,000 times at a flexion frequency of 30 times per minute. When the film at the folded portion after the test was not broken, it was evaluated as "good", and when it was broken, it was evaluated as "bad".

[0106] (Example A1) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 9 parts of methyl methacrylate (MMA), 0.75 part of α-methylene-γ-butyrolactone (ML), and 10 parts of N-methylpyrrolidone (NMP) as a solvent were charged, and the temperature was raised to 105 °C while passing nitrogen through it. Then, 0.003 part of t-amyl peroxyisooctanoate (manufactured by Arkema Kichijo, Lupersol (registered trademark) 570, hereinafter also referred to as "initiator 570") was added as a polymerization initiator, and while dropping 0.005 part of initiator 570 diluted with 0.2 part of NMP and 0.25 part of ML at a constant rate over 2 hours, solution polymerization was carried out at 105 - 115 °C for 6 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomer in the polymerization reaction solution were 98.8% and 99.3%, respectively. Next, the obtained polymerization reaction solution was vacuum dried at 240 °C for 2 hours (1 mmHg) to obtain a white copolymer. The physical properties of the obtained copolymer are shown in Table 1. Next, the obtained copolymer was hot press molded at 240 °C to obtain an unstretched press film with a thickness of about 160 μm. After that, the obtained unstretched cast film was cut into a size of 96 mm × 96 mm, and using a sequential biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X6-S), sequential biaxial stretching was carried out at a stretching temperature of 140 °C (Tg + 18 °C) at a stretching rate of 300% / min so that the stretching ratio in the longitudinal direction (MD direction) and the transverse direction (TD direction) was 2.0 times in order, and then cooled to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 1.

[0107]

Table 1

[0108] <Test Example B, Example B, and Comparative Example B> [Polymerization reaction rate in static polymerization] The polymerization reaction rate in static polymerization was simply determined by the amount of copolymer obtained after diluting the polymerization solution with chloroform, dropping it into methanol for reprecipitation to take out the copolymer, and drying the copolymer at 240 °C for 1 hour.

[0109] [Polymerization reaction rate and copolymer composition analysis in stirring polymerization] The reaction rate during the polymerization reaction in the stirring polymerization and the content of specific monomer units in the copolymer were determined by measuring the amount of unreacted monomers in the obtained polymerization reaction solution using gas chromatography (manufactured by Shimadzu Corporation, apparatus name: GC-2014).

[0110] [Weight-average molecular weight and number-average molecular weight of the copolymer] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the copolymer were determined in the same manner as the weight-average molecular weight and number-average molecular weight of the copolymer in <Example A>.

[0111] [ML content in the copolymer] The ML content (content of structural units derived from α-methylene lactone) in the copolymer was determined in the same manner as the ML content in the copolymer in <Example A>.

[0112] [Glass transition temperature (Tg) of the copolymer] The glass transition temperature of the copolymer was determined in the same manner as the glass transition temperature of the copolymer in <Example A>.

[0113] [5% weight loss temperature of the copolymer] The 5% weight loss temperature of the copolymer was determined in the same manner as the 5% weight loss temperature of the copolymer in <Example A>.

[0114] [Internal haze of the copolymer] The internal haze of the copolymer was determined in accordance with the provisions of JIS K7136. Specifically, an unstretched film obtained by thermally pressing the copolymer at 240 °C and 40 MPa for 10 minutes was prepared. Using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-1001DP), 1,2,3,4-tetrahydronaphthalene (tetralin) was filled in a quartz cell with an optical path length of 10 mm, and the film was immersed therein for measurement, and it was calculated as the internal haze value per 100 μm.

[0115] [Internal b * value] An unstretched film obtained by hot press molding a copolymer at 240 °C and 40 MPa for 10 minutes was prepared. Using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., Colormeter ZE6000), 1,2,3,4-tetrahydronaphthalene (tetralin) was filled in a quartz cell with an optical path length of 10 mm, and the film was immersed therein for measurement, and L * a * b * b per 100 μm thickness of the color system * was calculated as the value.

[0116] [Solvent (compound) content in the copolymer or copolymer mixture] The solvent (compound) content in the copolymer or copolymer mixture was determined by dissolving the copolymer or copolymer mixture in dimethylacetamide and then measuring it using gas chromatography (manufactured by Shimadzu Corporation, apparatus name: GC-2014).

[0117] [Viscosity of the dope resin composition] The viscosity of the dope resin composition was measured at 25 °C using a BHII type viscometer (manufactured by Toki Sangyo Co., Ltd.).

[0118] [Yellowness index (YI) of the dope resin composition] The yellowness index (YI) of the dope resin composition was determined in accordance with the provisions of JIS Z 8729. Specifically, it was measured in the transmission mode of a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.: Colormeter ZE6000) using a quartz cell with an optical path length of 10 mm.

[0119] [Haze of the dope resin composition] The haze of the dope resin composition was determined in accordance with the provisions of JIS K7136. Specifically, it was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-1001DP) using a quartz cell with an optical path length of 10 mm.

[0120] [Film thickness] The film thickness was determined in the same manner as the film thickness of <Example A>.

[0121] [Total light transmittance of the film] The total light transmittance of the film was determined in the same manner as that of the film of <Example A>.

[0122] [Tensile test of film (measurement of elastic modulus)] A tensile test (measurement of elastic modulus) of the film was carried out in the same manner as the tensile test of the film of <Example A>, and the elastic modulus was measured.

[0123] [Pencil hardness of film] The pencil hardness of the film was determined in the same manner as the pencil hardness of the film of <Example A>.

[0124] [Foldability test of film] A foldability test of the film was carried out in the same manner as the foldability test of the film of <Example A>. Similar to <Example A>, the presence or absence of breakage of the folded part of the film after the test was evaluated.

[0125] [Birefringence of film] The in-plane birefringence Re and the thickness-direction birefringence Rth of the stretched film with respect to light of wavelength 589 nm were measured using a fully automatic birefringence meter ("KOBRA-WR" manufactured by Oji Scientific Instruments) under the condition of an incident angle of 40°. Specifically, with the refractive index in the slow axis direction in the plane of the film being nx, the refractive index in the fast axis direction in the plane of the film being ny, the refractive index in the thickness direction of the film being nz, and the thickness of the film being d, the in-plane birefringence Re and the thickness-direction birefringence Rth were respectively determined from the following formulas. In the following examples, with the thickness d of the film being 40 μm, the in-plane birefringence Re and the thickness-direction birefringence Rth were determined. In-plane birefringence Re = (nx - ny) × d Thickness-direction birefringence Rth = [(nx + ny) / 2 - nz] × d

[0126] [Synthesis of copolymer by static polymerization] (Test Example B1) Into a sealable reaction vessel, 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. Nitrogen was bubbled through this mixture for 2 minutes to replace the air in the vessel with nitrogen, and then the lid was tightened to seal the vessel. Subsequently, the reaction vessel was immersed in an oil bath at 75 °C for 2 hours to carry out the polymerization. After dilution with chloroform after polymerization, it was added to methanol for reprecipitation, and a white solid was taken out. Then, vacuum drying was carried out at 240 °C for 1 hour to obtain about 6 parts of a white copolymer. The physical properties of the obtained copolymer are shown in Table 2.

[0127] (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), and 6.5 parts of a white copolymer were obtained. The physical properties of the obtained copolymer are shown in Table 2.

[0128] (Test Example B3) 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 dimethyl sulfoxide (DMSO), and 6 parts of a white copolymer were obtained. The physical properties of the obtained copolymer are shown in Table 2.

[0129] (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, since solids precipitated and solidified during the polymerization, the polymerization was terminated.

[0130] (Test Example B5) Polymerization was carried out in the same manner as in Test Example B1, except that no solvent such as NMP was used. However, since solids precipitated and solidified during the polymerization, the polymerization was terminated.

[0131] From Test Examples B1 to B5, NMP, GBL, and DMSO with a polymerization reaction rate of 50% or more were judged to be good, and the following stirring polymerization was carried out using these solvents.

[0132] <Synthesis of Copolymer and Preparation of Film by Stirring Polymerization> (Example B1-1) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 8 parts of methyl methacrylate (MMA), 1.5 parts of α-methylene-γ-butyrolactone (ML), 0.005 part of n-dodecyl mercaptan (nDM) as a chain transfer agent, and 10 parts of N-methylpyrrolidone (NMP) as a solvent were charged, and the temperature was raised to 105 °C while passing nitrogen through it. Then, 0.003 part of t-amyl peroxyisooctanoate (manufactured by Arkema Kishima, Lupersol (registered trademark) 570, hereinafter also referred to as "initiator 570") was added as a polymerization initiator, and 0.005 part of initiator 570 diluted with 0.2 part of NMP and 0.5 part of ML were added dropwise at a constant rate over 2 hours at 105 to 115 °C. After the dropwise addition, 4 parts of NMP were added, and solution stirring polymerization was further carried out at 105 to 115 °C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution were 99.1% and 99.5%, respectively. The obtained polymerization reaction solution was vacuum dried at 240 °C for 2 hours (133 Pa (1 mmHg)) to obtain a white copolymer. The physical properties of the obtained copolymer are shown in Table 3.

[0133] Next, the copolymer obtained in Example B1-1 was hot press molded at 240 °C to obtain an unstretched press film with a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96 mm × 96 mm, and using a sequential biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X6-S), sequential biaxial stretching was carried out in the longitudinal direction (MD direction) and the transverse direction (TD direction) in this order at a stretching temperature of Tg + 18 °C (146 °C) and a stretching rate of 300% / min so that the stretching ratio in each direction was 2.0 times, and then cooled to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 3.

[0134] (Example B1-2) A copolymer and a stretched film with 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 γ-butyrolactone (GBL). The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution 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.

[0135] (Example B1-3) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 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 °C while passing nitrogen through it. Then, 0.003 part of initiator 570 was added, and 0.005 part of initiator 570 diluted with 0.2 part of GBL and 0.25 part of ML were added dropwise at a constant rate over 2 hours at 105 - 115 °C. After the dropwise addition, 4 parts of GBL were added, and solution stirring polymerization was carried out at 105 - 115 °C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomer in the polymerization reaction solution were 98.4% and 99.2% respectively. The obtained polymerization reaction solution was treated in the same manner as in Example B1-1 to obtain a copolymer and a stretched film with 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.

[0136] (Example B1-4) nDM was changed from 0.005 part to 0.03 part, and GBL as a solvent was changed from 10 parts to 15 parts. A copolymer and a stretched film with a thickness of 40 μm were obtained in the same manner as in Example B1-3, except that the 4 parts of GBL added after the dropwise addition were not added. The conversion rates of MMA and ML calculated from the amount of unreacted monomer in the polymerization reaction solution 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.

[0137] (Example B1-5) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 7 parts of MMA, 2.2 parts of ML, and 10 parts of GBL as a solvent were charged, and the temperature was raised to 105 °C while passing nitrogen through it. Then, 0.003 part of initiator 570 was added, and 0.005 part of initiator 570 diluted with 0.2 part of GBL and 0.8 part of ML were added dropwise at a constant rate over 2 hours at 105 - 115 °C. After the dropwise addition, 4 parts of GBL were added, and solution stirring polymerization was carried out at 105 - 115 °C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomer in the polymerization reaction solution were 99.1% and 99.2% respectively. The obtained polymerization reaction solution was treated in the same manner as in Example B1-1 to obtain a copolymer and a stretched film with 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.

[0138] (Comparative Example B1-1) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 7 parts of MMA, 3 parts of ML, and 10 parts of DMSO as a solvent were charged, and the temperature was raised to 105 °C while passing nitrogen through it. Then, 0.02 part of initiator 570 was added, and solution stirring polymerization was carried out at 105 - 115 °C for 6 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomer in the polymerization reaction solution were 99.1% and 99.5% respectively. The obtained polymerization reaction solution was treated in the same manner as in Example B1-1 to obtain a copolymer and a stretched film with 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.

[0139] <Preparation of Dope Resin Composition and Fabrication of Film> (Example B2-1) 1 part of the copolymer obtained in Example B1-2 and 7 parts of dichloromethane as a dispersion medium were mixed, shaken by hand for 1 minute, and then stirred and mixed for 60 minutes to prepare a dope resin composition with a solid content of 12.5% by mass. The viscosity of the dope resin composition was 0.3 Pa·s, the YI was 0.9, and the haze was 0.3%. When the dope resin composition was visually confirmed, it was uniformly dispersed, and no change was observed in the appearance of the dope resin composition even after standing overnight.

[0140] Next, the dope resin composition was dropped onto the PET film and spread to a film thickness of 800 μm using an applicator. Then, the PET film was placed in a dryer and dried at 40°C for 30 minutes and at 60°C for 30 minutes. After that, the applied film was peeled off from the PET. Wide mountain-shaped clips were attached to the top and bottom so that the obtained film would not curl, and it was hung in the dryer and dried at 100°C for 12 hours to obtain an unstretched cast film with a thickness of 160 μm. The obtained unstretched cast film was stretched using a sequential biaxial stretching machine in the same manner as in Example B1-1 to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 3.

[0141] [Table 2]

[0142] [Table 3]

[0143] [Test Example C, Example C, and Comparative Example C] [Measurement of Boiling Point of Mixed Solvent] 500 ml of the mixed solvent was added to a 1 L separable flask equipped with a stirring device, a temperature sensor, a condenser, and a nitrogen inlet tube. While passing nitrogen through it, the temperature was raised with stirring, and the internal temperature when reflux occurred from the condenser was measured as the boiling point of the mixed solvent.

[0144] [Polymerization Reaction Rate in Static Polymerization] The polymerization reaction rate in static polymerization was simply determined in the same manner as the polymerization reaction rate in the static polymerization of [Test Example B, Example B, and Comparative Example B].

[0145] [Polymerization Reaction Rate and Composition Analysis of Copolymer in Stirred Polymerization] The reaction rate during the polymerization reaction and the content of specific monomer units in the copolymer in stirred polymerization were determined in the same manner as the reaction rate during the polymerization reaction and the content of specific monomer units in the copolymer in the stirred polymerization of [Test Example B, Example B, and Comparative Example B].

[0146] [Weight-average molecular weight and number-average molecular weight of the copolymer] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the copolymer were determined in the same manner as the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the copolymer in <Example A>.

[0147] [ML content in the copolymer] The ML content (content of structural units derived from α-methylene lactone) in the copolymer was determined in the same manner as the ML content in the copolymer in <Example A>.

[0148] [Glass transition temperature (Tg) of the copolymer] The glass transition temperature of the copolymer was determined in the same manner as the glass transition temperature of the copolymer in <Example A>.

[0149] [5% weight loss temperature of the copolymer] The 5% weight loss temperature of the copolymer was determined in the same manner as the 5% weight loss temperature of the copolymer in <Example A>.

[0150] [Internal haze of the copolymer] The internal haze of the copolymer was determined in the same manner as the internal haze of the copolymers in <Test Example B, Example B, and Comparative Example B>.

[0151] [Internal b * value] The internal b * value of the copolymer was determined in the same manner as the internal b * value of the copolymers in <Test Example B, Example B, and Comparative Example B>.

[0152] [Solvent (compound) content in the copolymer] The solvent (compound) content in the copolymer was determined in the same manner as the solvent (compound) content in the copolymers in <Test Example B, Example B, and Comparative Example B>.

[0153] [Viscosity of the dope resin composition] The viscosity of the dope resin composition was determined in the same manner as the viscosities of the dope resin compositions of <Test Example B, Example B, and Comparative Example B>.

[0154] [Yellowness index (YI) of the dope resin composition] The yellowness index (YI) of the dope resin composition was determined in the same manner as the yellowness indices (YI) of the dope resin compositions of <Test Example B, Example B, and Comparative Example B>.

[0155] [Haze of the dope resin composition] The haze of the dope resin composition was determined in the same manner as the haze of the dope resin compositions of <Test Example B, Example B, and Comparative Example B>.

[0156] [Thickness of the film] The thickness of the film was determined in the same manner as the thickness of the film of <Example A>.

[0157] [Total light transmittance of the film] The total light transmittance of the film was determined in the same manner as the total light transmittance of the film of <Example A>.

[0158] [Tensile test of the film (measurement of elastic modulus)] A tensile test (measurement of elastic modulus) of the film was carried out in the same manner as the tensile test of the film of <Example A>, and the elastic modulus was measured.

[0159] [Pencil hardness of the film] The pencil hardness of the film was determined in the same manner as the pencil hardness of the film of <Example A>.

[0160] [Foldability test of the film] A foldability test of the film was carried out in the same manner as the foldability test of the film of <Example A>, and the presence or absence of breakage of the film at the folded portion after the test was evaluated in the same manner as <Example A>.

[0161] [Birefringence of the film] The birefringence of the film was determined in the same manner as the birefringence of the films of <Test Example B, Example B, and Comparative Example B>.

[0162] <Synthesis of Copolymer by Static Polymerization> (Test Example C1) Into a sealable reaction vessel, 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 part of azobisisobutyronitrile (AIBN) as an initiator were charged. Nitrogen was bubbled through this mixture for 2 minutes to replace the air in the vessel with nitrogen, and then the lid was tightened to seal the vessel. Subsequently, the reaction vessel was immersed in an oil bath at 75 °C for 2 hours to carry out the polymerization. However, since solids precipitated and solidified during the polymerization, the polymerization was terminated. After dilution with chloroform after polymerization, it was added to methanol for reprecipitation, and a white solid was taken out.

[0163] (Test Example 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, since solids precipitated and solidified during the polymerization, the polymerization was terminated.

[0164] (Test Example 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, since solids precipitated and solidified during the polymerization, the polymerization was terminated.

[0165] (Test Example 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 of acetone (ACE) and cyclohexanone (anone) (1:1 (mass ratio)). After dilution with chloroform after polymerization, it was added to methanol for reprecipitation, and a white solid was taken out. Then, it was vacuum dried at 240 °C for 1 hour to obtain about 6 parts of a white copolymer. The physical properties of the obtained copolymer are shown in Table 4.

[0166] From Test Examples C1 to C4, the mixed solvent of Test Example C4 in which no solids precipitated during the polymerization was judged to be good, and based on such a mixed solvent, the following stirring polymerization was studied.

[0167] <Synthesis of Copolymer and Preparation of Film by Stirring Polymerization> (Example C1-1) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 7.5 parts of methyl methacrylate (MMA), 2 parts of α-methylene-γ-butyrolactone (ML), 0.005 part of n-dodecyl mercaptan (nDM) as a chain transfer agent, and 10 parts of a mixed solvent obtained by mixing acetone (ACE) and cyclohexanone (anone) at a mass ratio of 1:1 were charged. While passing nitrogen through it, the temperature was raised to 70°C. Then, 0.004 part of AIBN was added as a polymerization initiator, and 0.011 part of the initiator AIBN diluted with a mixed solvent obtained by mixing 0.2 part of ACE and anone at a mass ratio of 1:1 and 0.5 part of ML were added dropwise at a constant rate over 3 hours at 70 - 75°C. After the addition, a mixed solvent obtained by mixing 4 parts of ACE and anone at a mass ratio of 1:1 was added, and solution stirring polymerization was further carried out at 70 - 75°C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomer in the polymerization reaction solution were 92.1% and 95.5% respectively. The obtained polymerization reaction solution was vacuum dried at 240°C for 2 hours (133 Pa (1 mmHg)) to obtain a white copolymer. The physical properties of the obtained copolymer are shown in Table 5.

[0168] Next, the copolymer obtained in Example C1-1 was hot press-molded at 240°C to obtain an unstretched press film with a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96 mm × 96 mm, and using a sequential biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X6-S), sequential biaxial stretching was carried out in the longitudinal direction (MD direction) and the transverse direction (TD direction) in this order at a stretching temperature of Tg + 18°C (146°C) and a stretching rate of 300% / min so that the stretching ratio in each direction was 2.0 times, and then cooled to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 5.

[0169] (Example C1-2) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 6 parts of methyl methacrylate (MMA), 3 parts of α-methylene-γ-butyrolactone (ML), 0.005 part of n-dodecyl mercaptan (nDM) as a chain transfer agent, and 10 parts of a mixed solvent obtained by mixing acetone (ACE) and cyclohexanone (anone) at a mass ratio of 3:7 were charged. While passing nitrogen through it, the temperature was raised to 85°C. Then, 0.004 part of t-amyl peroxy 2-ethylhexanoate (manufactured by Arkema Kishima, Lupersol (registered trademark) 575, hereinafter also referred to as "initiator 575") was added, and 0.009 part of initiator 575 diluted with a mixed solvent of 0.2 part of ACE and anone at a mass ratio of 3:7 and 1 part of ML were added dropwise at a constant rate over 3 hours at 85 - 90°C. After the addition, a mixed solvent of 4 parts of ACE and anone at a mass ratio of 3:7 was added, and solution stirring polymerization was further carried out at 85 - 90°C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution were 93.1% and 95.5% respectively. The obtained polymerization reaction solution was vacuum dried at 240°C for 2 hours (133 Pa (1 mmHg)) to obtain a white copolymer. The physical properties of the obtained copolymer are shown in Table 5.

[0170] Next, the copolymer obtained in Example C1-2 was hot press molded at 240°C to obtain an unstretched press film with a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96 mm × 96 mm, and using a sequential biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X6-S), sequential biaxial stretching was performed in the longitudinal direction (MD direction) and the transverse direction (TD direction) in order at a stretching temperature of Tg + 18°C (146°C) at a stretching speed of 300% / min so that the stretching ratio in each direction was 2.0 times, and then cooled to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 5.

[0171] (Example C1-3) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 6 parts of methyl methacrylate (MMA), 3 parts of α-methylene-γ-butyrolactone (ML), and 10 parts of a mixed solvent obtained by mixing acetone (ACE) and γ-butyrolactone (GBL) at a mass ratio of 2:8 were charged. While passing nitrogen through it, the temperature was raised to 100 °C. Then, 0.004 part of t-amyl peroxyisooctanoate (manufactured by Arkema Kogyo, Lupersol (registered trademark) 570, hereinafter also referred to as "initiator 570") was added as a polymerization initiator, and 0.009 part of initiator 570 diluted with a mixed solvent of 0.2 part of ACE and GBL mixed at a mass ratio of 2:8 and 1 part of ML were added dropwise at a constant rate over 3 hours at 100 to 110 °C. After the addition, a mixed solvent of 4 parts of ACE and GBL mixed at a mass ratio of 2:8 was added, and solution stirring polymerization was further carried out at 100 to 110 °C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution were 92.2% and 96.5%, respectively. The obtained polymerization reaction solution was vacuum dried at 240 °C for 2 hours (133 Pa (1 mmHg)) to obtain a white copolymer. The physical properties of the obtained copolymer are shown in Table 5.

[0172] Next, the copolymer obtained in Example C1-3 was hot press molded at 240 °C to obtain an unstretched press film with a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96 mm × 96 mm, and using a sequential biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X6-S), sequential biaxial stretching was carried out in the longitudinal direction (MD direction) and the transverse direction (TD direction) in this order at a stretching temperature of Tg + 18 °C (146 °C) and a stretching rate of 300% / min so that the stretching ratio in each direction was 2.0 times, and then cooled to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 5.

[0173] (Example C1-4) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 5 parts of methyl methacrylate (MMA), 3.2 parts of α-methylene-γ-butyrolactone (ML), and 10 parts of a mixed solvent obtained by mixing acetone (ACE) and N,N-dimethylacetamide (DMAc) at a mass ratio of 3:7 were charged. While passing nitrogen through it, the temperature was raised to 85°C. Then, 0.004 part of initiator 575 was added, and 0.009 part of initiator 575 diluted with a mixed solvent of 0.2 part of ACE and DMAc mixed at a mass ratio of 3:7 and 1.8 parts of ML were added dropwise at a constant rate over 3 hours at 85 - 90°C. After the addition, a mixed solvent of 4 parts of ACE and DMAc mixed at a mass ratio of 3:7 was added, and solution stirring polymerization was further carried out at 85 - 90°C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution were 90.2% and 95.5% respectively. The obtained polymerization reaction solution was vacuum dried at 240°C for 2 hours (133 Pa (1 mmHg)) to obtain a white copolymer. The physical properties of the obtained copolymer are shown in Table 5.

[0174] Next, the copolymer obtained in Example C1-4 was hot press molded at 240°C to obtain an unstretched press film with a thickness of about 160 μm. The obtained unstretched film was cut into a size of 96 mm × 96 mm, and using a sequential biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, X6-S), sequential biaxial stretching was carried out in the longitudinal direction (MD direction) and the transverse direction (TD direction) in this order at a stretching temperature of Tg + 18°C (146°C) at a stretching rate of 300% / min so that the stretching ratio in each direction was 2.0 times, and then cooled to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 5.

[0175] (Comparative Example 1-1) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen inlet pipe, 7 parts of MMA, 3 parts of ML, and 10 parts of DMSO as a solvent were charged, and the temperature was raised to 105 °C while passing nitrogen through it. Then, 0.02 part of initiator 570 was added, and solution stirring polymerization was carried out at 105 - 110 °C for 6 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution were 99.1% and 99.5% respectively. The obtained polymerization reaction solution was treated in the same manner as in Example C1-1 to obtain a copolymer and a stretched film with 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.

[0176] <Preparation of Dope Resin Composition and Fabrication of Film> (Example C2-1) Into a reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen inlet pipe, 7.5 parts of methyl methacrylate (MMA), 2 parts of α-methylene-γ-butyrolactone (ML), 0.005 part of n-dodecyl mercaptan (nDM) as a chain transfer agent, and 10 parts of a mixed solvent of acetone (ACE) and cyclohexanone (anone) mixed at a mass ratio of 3:7 were charged, and the temperature was raised to 85 °C while passing nitrogen through it. Then, 0.004 part of initiator 575 was added, and 0.009 part of initiator 575 diluted with a mixed solvent of 0.2 part of ACE and anone mixed at a mass ratio of 3:7 and 0.5 part of ML were added dropwise at a constant rate over 3 hours at 85 - 90 °C. After the dropwise addition, a mixed solvent of 4 parts of ACE and anone mixed at a mass ratio of 3:7 was added, and solution stirring polymerization was further carried out at 85 - 90 °C for 4 hours. The conversion rates of MMA and ML calculated from the amount of unreacted monomers in the polymerization reaction solution were 93.1% and 97.5% respectively. The obtained polymerization reaction solution was diluted with 55 parts of a mixed solvent of ACE and anone mixed at a mass ratio of 3:7 to prepare a dope resin composition with a copolymer content of 12.5% by mass. The dope resin composition was pressure-filtered through a 3-μm membrane filter. The physical properties of the dope resin composition are shown in Table 5. When the dope resin composition was visually confirmed, it was uniformly dispersed, and no change was observed in the appearance of the dope resin composition even after standing overnight.

[0177] Next, the doped resin composition of Example C2-1 was applied to a glass substrate and vacuum dried at 150 °C for 2 hours to obtain an unstretched cast film with a thickness of 120 μm. The obtained unstretched cast film was stretched using a sequential biaxial stretching machine in the same manner as in Example C1-1 to obtain a stretched film with a thickness of 30 μm. The physical properties of the obtained stretched film are shown in Table 5.

[0178] (Example C2-2) 1 part of the copolymer obtained in Example C1-2 and 7 parts of dichloromethane as a dispersion medium were mixed, shaken by hand for 1 minute, and then stirred and mixed for 60 minutes to prepare a doped resin composition with a solid content of 12.5% by mass. The physical properties of the doped resin composition are shown in Table 5. When the doped resin composition was visually confirmed, it was uniformly dispersed, and no change was observed in the appearance of the doped resin composition even after standing overnight.

[0179] Next, the doped resin composition of Example C2-2 was dropped onto a PET film and spread to a film thickness of 800 μm using an applicator. Then, the PET film together with the film was placed in a dryer and dried at 40 °C for 30 minutes and at 60 °C for 30 minutes. After that, the applied film was peeled off from the PET. Wide mountain-shaped clips were attached vertically to prevent the obtained film from curling, and then it was hung in a dryer and dried at 100 °C for 12 hours to obtain an unstretched cast film with a thickness of 160 μm. The obtained unstretched cast film was stretched using a sequential biaxial stretching machine in the same manner as in Example C1-1 to obtain a stretched film with a thickness of 40 μm. The physical properties of the obtained stretched film are shown in Table 5.

[0180]

Table 4

[0181]

Table 5

Claims

1. A resin molded product containing a copolymer including a structural unit derived from α-methylene lactone and a structural unit derived from an alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, The weight average molecular weight of the copolymer is 220,000 or more and 1,000,000 or less, The copolymer has a glass transition temperature of 110° C. or more and 160° C. or less, A resin molded body that is a film for flexible displays.

2. 2. The resin molded article according to claim 1, having an internal haze of less than 2.5% per 100 μm of thickness.

3. L ＊ a ＊ b ＊ Color system internal b per 100 μm thickness ＊ The resin molded article according to claim 1 , wherein the value is less than 1.

6.

4. A flexible display comprising the resin molded article according to claim 1.

5. Use of the resin molding according to claim 1 as a film constituting a flexible display.

6. A flexible display including a resin molded body, the resin molded product contains a copolymer including a structural unit derived from α-methylene lactone and a structural unit derived from an alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, The weight average molecular weight of the copolymer is 220,000 or more and 1,000,000 or less, The copolymer has a glass transition temperature of 110° C. or more and 160° C. or less, The resin molded body is a stretched film, A flexible display, wherein a test piece measuring 15 mm x 80 mm is cut from the resin molding and satisfies the following conditions: <Conditions> The test piece is folded at a position halfway along its long side, and the test piece is folded so that the distance between both ends of the long side of the test piece in the folded state is 5 mm and the radius of curvature of the folded portion of the test piece is 2.5 mm; The sheet will not break even if it is repeatedly bent 100,000 times at a rate of 30 bends per minute in an environment of 25° C., where one bend is defined as a change from a flat open state to the folded state.

7. A flexible display as described in claim 6, wherein the internal haze per 100 μm thickness of the resin molding is less than 2.5%.

8. A flexible display as described in claim 6, wherein the internal b* value per 100 μm thickness in the L*a*b* color system of the resin molding is less than 1.6.

Images