Copolymer, method for producing the same, method for using the copolymer, dope solution, and film

Abstract

To provide a method for producing a copolymer comprising an α-methylene lactone-derived constitutional unit, enabling the resultant copolymer to have improved transparency, the copolymer also having high solubility in a solvent primarily composed of a ketone solvent, and further having high heat resistance.SOLUTION: The present invention provides a method for producing a copolymer that comprises an α-methylene lactone-derived constitutional unit and an alkylmethacrylate-derived constitutional unit comprising a C1-6 alkyl group. The method comprises a polymerization step for polymerizing, in a water solvent, monomers comprising α-methylene lactone and alkylmethacrylate. In the copolymer, the content of the α-methylene lactone-derived constitutional unit is 10-40 mass%, and the total amount of the monomers is made to exist in a system from the beginning of the polymerization step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a method for producing the copolymer, a dope solution, and a film thereof. [Background technology]

[0002] Copolymers containing structural units derived from α-methylene lactone are excellent in transparency, heat resistance, and optical isotropy, and are expected to be used in optical applications. For example, Patent Document 1 describes that films and the like that are molded articles of copolymers (resins) containing structural units derived from specific α-methylene lactones are suitable for use as optical components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-179813 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, copolymers containing structural units derived from α-methylene lactone tend to have low solubility in solvents, and therefore are polymerized without a solvent or in a dimethyl sulfoxide (DMSO) solvent. However, polymerization without a solvent does not yield copolymers with high transparency. Furthermore, the inventors have found that when polymerization is performed in a DMSO solvent, the resulting copolymer containing structural units derived from α-methylene lactone tends to become discolored and lose transparency. Furthermore, polymerization in a DMSO solvent causes problems such as the DMSO, which functions as a plasticizer, remaining in the copolymer, degrading the physical properties of films formed from the copolymer.

[0005] Furthermore, in terms of solubility, copolymers containing structural units derived from α-methylene lactone that are polymerized without solvent or in a dimethyl sulfoxide (DMSO) solvent are known to dissolve only in halogenated solvents or high-boiling point solvents (such as dimethylacetamide). However, the use of halogenated solvents may be restricted due to their toxicity, and high-boiling point solvents may be difficult to dry due to equipment limitations. Therefore, copolymers containing structural units derived from α-methylene lactone are required to maintain high heat resistance while being soluble in solvents primarily composed of common ketone solvents such as methyl ethyl ketone (for example, solvents containing ketone solvents at a ratio of preferably 50% by mass or more, more preferably 70% by mass or more).

[0006] Therefore, a main object of the present invention is to provide a method for producing a copolymer containing a structural unit derived from α-methylene lactone, which can improve the transparency of the obtained copolymer, and can also provide a copolymer that has excellent solubility in a solvent containing a ketone solvent as a main component and high heat resistance. [Means for solving the problem]

[0007] The present invention provides methods for producing copolymers described in the following items [1] to [4], copolymers described in items [5] to [7], dope solutions described in items [8] and [9], and films described in items

[10] and

[11] . [1] A method for producing a copolymer containing structural units derived from α-methylene lactone and structural units derived from alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, the method comprising a polymerization step of polymerizing monomers containing α-methylene lactone and alkyl (meth)acrylate in an aqueous solvent, wherein the content of the structural units derived from α-methylene lactone in the copolymer is 10 to 40 mass%, and the total amount of the monomers is present in the system from the early stage of the polymerization step. [2] The method for producing a copolymer according to [1], wherein the content of structural units derived from alkyl (meth)acrylate in the copolymer is 90 to 50% by mass. [3] The method for producing a copolymer according to [1] or [2], wherein the polymerization is carried out in the presence of a chain transfer agent. [4] The method for producing a copolymer according to any one of [1] to [3], wherein the polymerization is suspension polymerization. [5] 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 having 1 to 6 carbon atoms, wherein the copolymer has a haze of 40% or less when dissolved in a solvent containing a ketone solvent at 25% by mass to form a solution, and the copolymer has a glass transition temperature of 115°C or higher. [6] The copolymer according to [5], wherein the content of the constitutional unit derived from α-methylene lactone in the copolymer is 10 to 40 mass %. [7] The copolymer according to [5] or [6], wherein the content of structural units derived from alkyl (meth)acrylate in the copolymer is 90 to 50 mass %. [8] A dope solution containing the copolymer according to any one of [5] to [7] and a dispersion medium. [9] The dope solution according to [8], which has a haze of 40% or less.

[10] A film containing the copolymer according to any one of [5] to [7].

[11] The film according to

[10] , having an internal haze of 2.0% or less per 100 μm thickness. [Effects of the Invention]

[0008] According to the present invention, there is provided a method for producing a copolymer containing a structural unit derived from α-methylene lactone, which can improve the transparency of the resulting copolymer and can produce a copolymer having excellent solubility in a solvent mainly composed of a ketone solvent and high heat resistance. The present invention also provides a copolymer obtained by such a production method. Furthermore, the present invention also provides a dope solution and a film using such a copolymer. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0010] [Method of producing copolymer] A method for producing a copolymer in one embodiment is a method for producing a copolymer containing structural units derived from α-methylene lactone and structural units derived from alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms.

[0011] The α-methylene lactone-derived structural unit is formed by polymerization of α-methylene lactone in which a methylene group is bonded to the α-position carbon. The specific structure of the α-methylene lactone-derived structural unit is not particularly limited. The number of ring members in the lactone is not particularly limited, but is preferably a 5-membered ring (γ-lactone) or a 6-membered ring (δ-lactone) because the ring structure is highly stable and, based on this high stability, higher surface strength can be obtained.

[0012] Specific examples of 5- or 6-membered α-methylene lactones include α-methylene-γ-butyrolactone and α-methylene-δ-valerolactone, which may have a substituent.

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

[0014] [ka]

[0015] R in Equation (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 formula (1) can be formed by polymerizing a monomer containing α-methylene-γ-butyrolactone shown in formula (2) below.

[0017] [ka]

[0018] R in Equation (2) 1 ~R 4 are each independently 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 in the alkyl group is preferably 1 to 10, more preferably 1 to 8. The alkyl group may be linear or branched, or may be 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, and a cyclohexyl group.

[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, and a benzyl group.

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

[0022] The content of the α-methylene lactone-derived structural units in the copolymer is 10 to 40% by mass. When the content of the α-methylene lactone-derived structural units in the copolymer is 10% by mass or more, the heat resistance of the copolymer tends to be improved. When the content of the α-methylene lactone-derived structural units in the copolymer is 40% by mass or less, the copolymer tends to have excellent solubility in solvents mainly composed of ketone solvents. From the viewpoint of further improving heat resistance, the content of the α-methylene lactone-derived structural units in the copolymer is preferably 12% by mass or more, more preferably 15% by mass or more, and from the viewpoint of further improving solubility in solvents mainly composed of ketone solvents, it is preferably 35% by mass or less, more preferably 30% by mass or less. The content of each structural unit in the copolymer is determined by dissolving the copolymer in a heavy solvent and 1It can be determined by measuring H-NMR and calculating the area ratio of the peaks corresponding to each structural unit.

[0023] The structural unit derived from alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms is formed by polymerization of alkyl (meth)acrylate. Examples of the alkyl group having 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, and a cyclohexyl group. These may be used alone or in combination of two or more.

[0024] The alkyl group in the alkyl (meth)acrylate preferably has 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms, and even more preferably 1 carbon atom.

[0025] The content of structural units derived from alkyl (meth)acrylate in the copolymer is preferably 90 to 50% by mass. When the content of structural units derived from alkyl (meth)acrylate in the copolymer is 90% by mass or less, the heat resistance of the copolymer tends to be improved. When the content of structural units derived from alkyl (meth)acrylate in the copolymer is 50% by mass or more, the copolymer tends to have excellent solubility in solvents mainly composed of ketone solvents. From the viewpoint of further improving heat resistance, the content of structural units derived from alkyl (meth)acrylate in the copolymer is preferably 88% by mass or less, more preferably 85% by mass or less. From the viewpoint of further improving solubility in solvents mainly composed of ketone solvents, the content is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more.

[0026] The copolymer may contain structural units of other monomers in addition to the structural units derived from α-methylene lactone and the structural units derived from alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms. Specific examples include structural units derived from monomers such as benzyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, styrene, vinyl toluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate. These may be used alone or in combination of two or more.

[0027] The content of other structural units in the copolymer is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0028] The method for producing the copolymer of the present embodiment includes a polymerization step of polymerizing, in an aqueous solvent, monomers containing the α-methylene lactone and the alkyl (meth)acrylate, and is characterized in that the entire amount of the monomers is present in the system from the early stage of the polymerization step.

[0029] According to the method for producing a copolymer of this embodiment, the transparency of the obtained copolymer can be improved. Furthermore, according to the method for producing a copolymer of this embodiment, since an aqueous solvent is used as the solvent, a copolymer that is substantially free of organic solvents such as DMSO can be produced. Furthermore, according to the method for producing a copolymer of this embodiment, it is possible to obtain a copolymer that has excellent solubility in solvents mainly composed of ketone solvents and high heat resistance.

[0030] The aqueous solvent is preferably water alone, but may contain a non-aqueous solvent (particularly a water-soluble organic solvent) within a range that does not impair the effects of the present invention. Examples of the water-soluble organic solvent include alcohol solvents such as methanol, ethanol, propanol, butanol, 2-methylpropyl alcohol, and 2-methyl-2-propanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate; and ether solvents such as dioxane, diethyl ether, and tetrahydrofuran.

[0031] The proportion of the non-aqueous solvent (water-soluble organic solvent) in the aqueous solvent is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0032] The polymerization temperature is preferably 40 to 100° C., more preferably 50 to 90° C., and even more preferably 70 to 90° C. The polymerization time is preferably 0.5 to 20 hours, and more preferably 1 to 10 hours.

[0033] In the polymerization step, in order to have the entire amount of monomers present in the system from the early stage of the polymerization step, it is sufficient that the entire amount of monomers is charged into the reactor substantially before the start of polymerization, and for example, the entire amount of monomers can be charged into the reactor before the temperature of the reactor is raised to the polymerization temperature. When dispersing the monomers in the aqueous solvent, the dispersion may be carried out by stirring with a paddle blade or the like, or may be carried out using an emulsifying and dispersing device such as a high-speed shear turbine type disperser, a high-pressure jet homogenizer, an ultrasonic type emulsifying and dispersing machine, a medium stirring and dispersing machine, or a forced gap passing type disperser.

[0034] When polymerizing the monomers, a polymerization initiator, a chain transfer agent, a dispersant (emulsifier) ​​and / or an additive may be added as needed.

[0035] Examples of the polymerization initiator include organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, and t-butylperoxy-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 of the polymerization initiator is not particularly limited and may be appropriately set depending on the combination of monomers used, reaction conditions, etc., but is preferably 100 to 50,000 ppm by mass, more preferably 500 to 30,000 ppm by mass, and even more preferably 1,000 to 20,000 ppm by mass, based on the total monomers.

[0036] Examples of chain transfer agents include monofunctional thiol compounds such as n-dodecyl mercaptan and β-mercaptopropionic acid; bifunctional thiol compounds such as polysiloxanes modified at both ends with mercapto groups; and side-chain polyfunctional mercapto-modified polysiloxanes in which the side chains are mercapto-modified. The molecular weight of the resulting copolymer can be adjusted by adding or not adding a chain transfer agent, and by adjusting the amount added if added. The content of the chain transfer agent can be appropriately set depending on the combination of monomers used, reaction conditions, etc., and is not particularly limited, but is preferably 10 to 10,000 ppm by mass, more preferably 100 to 3,000 ppm by mass, based on the total monomers.

[0037] Examples of dispersants (emulsifiers) include water-soluble polymer dispersion stabilizers such as polyvinyl alcohol (PVA), polyvinylpyrrolidone, cellulose, gelatin, sodium polyacrylate, and sodium polymethacrylate; anionic surfactants such as sodium lauryl sulfate and polyoxyethylene alkylphenyl ether sulfate salts (e.g., polyoxyethylene distyrylphenyl ether ammonium sulfate); cationic surfactants such as alkylamine salts and quaternary ammonium salts; zwitterionic surfactants such as lauryl dimethylamine oxide; nonionic surfactants such as polyoxyethylene alkyl ethers; and inorganic dispersants such as alginates, zein, and casein; barium sulfate, calcium sulfate, barium carbonate, magnesium carbonate, calcium phosphate, talc, clay, diatomaceous earth, bentonite, titanium hydroxide, thorium hydroxide, and metal oxide powders. The addition of a dispersant can improve the stability of the polymerization reaction. The content of the dispersant is not particularly limited, but is preferably 0.1 to 4 mass%, more preferably 0.2 to 3 mass%, based on the total monomers.

[0038] Examples of additives include antioxidants, light stabilizers, weather stabilizers, ultraviolet absorbers, infrared absorbers, non-water-soluble organic solvents such as alkanes, radical scavengers, etc. The content of the additives is not particularly limited, but is preferably 0.001 to 2% by mass, more preferably 0.005 to 1% by mass, based on the total monomers.

[0039] Examples of the polymerization reaction mode in the production method of this embodiment include suspension polymerization, emulsion polymerization, etc. Among these, suspension polymerization, in which a reaction is carried out by suspending a monomer in an aqueous solvent in the presence of a dispersant, is preferred because it can further improve the transparency of the resulting copolymer.

[0040] In the production method of this embodiment, the copolymer may be recovered by solid-liquid separation after the polymerization step. Examples of solid-liquid separation methods include filtration, centrifugation, and a combination thereof. In particular, the copolymer obtained by suspension polymerization can be easily filtered as a powder and is easy to handle.

[0041] The resulting copolymer is preferably dried at a temperature of, for example, 60 to 120°C.

[0042] Alternatively, water may be removed directly by drying without solid-liquid separation. The copolymer can be directly obtained as a powder by drying using various dryers.

[0043] [Copolymer] The copolymer of one embodiment is a copolymer containing structural units derived from α-methylene lactone and structural units derived from alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms. The copolymer may be a copolymer obtained by the above-mentioned production method. The copolymer of this embodiment has excellent solubility in a solvent containing a ketone solvent as the main component. Although the reason for this is not entirely clear, the inventors believe that it is because the above-mentioned production method was able to suppress the composition distribution. Furthermore, since the copolymer of this embodiment is substantially free of organic solvents such as DMSO, it also has excellent transparency when dissolved in a solvent containing a ketone solvent as the main component to form a solution.

[0044] The haze of a solution obtained by dissolving the copolymer in a ketone solvent at 25% by mass to prepare a solution is 40% or less. The haze is preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less. Examples of the ketone solvent include acetone and methyl ethyl ketone. The ketone solvent can be, for example, methyl ethyl ketone. The ketone solvent-containing solvent used for measuring the haze may be a solvent containing a ketone solvent as its main component. In this specification, a solvent containing a ketone solvent as its main component refers to a solvent containing a ketone solvent in a proportion of preferably 50% by mass or more, more preferably 70% by mass or more. The ketone solvent-containing solvent may be a solvent consisting of a ketone solvent. The haze can be measured, for example, by the method described in the Examples.

[0045] The copolymer has a glass transition temperature (Tg) of 115°C or higher, measured in accordance with the specifications of JIS K 7121, from the viewpoint of improving heat resistance, etc. The glass transition temperature (Tg) is preferably 118°C or higher, and more preferably 120°C or higher. The upper limit of the glass transition temperature of the copolymer is not particularly limited, but can be, for example, 160°C or lower.

[0046] The weight average molecular weight (Mw) of the copolymer is preferably 100,000 or more, more preferably 150,000 or more, even 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, and even more preferably 500,000 or less. When the Mw of the copolymer is within the above-mentioned 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.

[0047] The number average molecular weight (Mn) of the copolymer is preferably 20,000 or more, more preferably 50,000 or more, and even 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, and even more preferably 300,000 or less. The Mn of the copolymer can be measured, for example, by the method described in the Examples. The dispersity (Mw / Mn) of the copolymer is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.5 or less.

[0048] The copolymer has an internal haze of 2.0% or less per 100 μm thickness when made into a film. The internal haze is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less. The internal haze of the copolymer when made into a film of 100 μm thickness can be measured, for example, by the method described in the Examples. The temperature when the copolymer is hot-press molded may be, for example, 200 to 270°C, and more specifically, 240°C.

[0049] The copolymer of this embodiment can be used in various optical applications, such as light guide members, films, and lenses (optical lenses, etc.).

[0050] [Dope liquid] The dope liquid according to one embodiment contains the copolymer and a dispersion medium, and can be suitably used for producing a film, for example.

[0051] Examples of the dispersion medium include ketone solvents such as acetone and methyl ethyl ketone; alkyl chloride solvents such as dichloromethane, chloroform, 1,2-dichloroethane, and 1,1-dichloroethane; cyclic ketone solvents such as cyclohexanone (anone) and cyclopentanone; cyclic ester solvents such as γ-butyrolactone (GBL), γ-valerolactone, and δ-valerolactone; amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone (NMP), and N,N'-dimethylimidazolidinone (DMI); sulfoxide solvents such as dimethyl sulfoxide; aromatic solvents such as toluene, xylene, and benzene; and alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, 2-butanol, methyl cellosolve, ethyl cellosolve, and butyl cellosolve. These may be used alone or in combination of two or more. The dispersion medium is preferably a solvent containing a ketone solvent in a proportion of preferably 50% by mass or more, more preferably 70% by mass or more.

[0052] The content of the copolymer in the dope solution is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, based on the total amount of the dope solution, from the viewpoint of efficiently producing a film. The content of the copolymer in the dope solution is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, based on the total amount of the dope solution, from the viewpoint of ensuring fluidity for stable production in a production facility.

[0053] The dope may contain other polymers for the film described below. The content of the other polymers is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, even more preferably 0 to 30% by mass, particularly preferably 0 to 20% by mass, and most preferably 0 to 10% by mass, based on the total amount of the dope.

[0054] The dope may contain other additives for the film described below. The dope may contain one or more other additives. The content of the other additives is preferably 0 to 5 mass %, more preferably 0 to 2 mass %, and even more preferably 0 to 0.5 mass %, based on the total mass of the dope.

[0055] The yellowness index (YI) of the dope is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less, from the viewpoint of obtaining a film with little coloration.

[0056] From the viewpoint of obtaining a highly transparent film, the haze of the dope is preferably 40% or less, more preferably 30% or less, still more preferably 20% or less, and particularly preferably 10% or less.

[0057] [film] The film of one embodiment contains the above-described copolymer as a main component, and can be produced using a resin composition containing the above-described copolymer or a dope solution containing the above-described copolymer.

[0058] The content of the copolymer is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, even more preferably 70 to 100% by mass, particularly preferably 80 to 100% by mass, and most preferably 90 to 100% by mass, based on the total amount of the film. When the content of the copolymer is 50% by mass or more, a film with excellent transparency can be obtained.

[0059] The film may contain a polymer (other polymer) other than the above-mentioned copolymer. Examples of other polymers include olefin-based 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-based 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; polyethersulfone; polyoxybenzylene; polyamide imide; elastic organic particles such as polybutadiene rubber and acrylic rubber; and rubbery polymers such as ABS resin and ASA resin blended with polybutadiene rubber or acrylic rubber. The content of the other polymers is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, even more preferably 0 to 30% by mass, particularly preferably 0 to 20% by mass, and most preferably 0 to 10% by mass, based on the total amount of the film (resin composition).

[0060] The film may contain other additives. Examples of such additives include hindered phenol-based, phosphorus-based, and sulfur-based antioxidants; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; 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 or inorganic fillers; resin modifiers; organic or inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; fluidizing agents; and compatibilizers. The film may contain one or more other additives. The content of other additives is preferably 0 to 5 mass %, more preferably 0 to 2 mass %, and even more preferably 0 to 0.5 mass %, based on the total amount of the film.

[0061] One embodiment of the film manufacturing method includes a step of forming a resin composition containing the copolymer described above to obtain a film. The method for forming the resin composition is not particularly limited, but examples thereof include conventionally known methods such as melt extrusion, calendaring, and compression molding. Among these, the method for forming the resin composition is preferably melt extrusion.

[0062] The resin composition may contain, in addition to the copolymer described above, other polymers described above, other additives described above, etc., depending on the desired film. The contents of the copolymer, other polymers, other additives, etc. in the resin composition may be the same as the contents of each component exemplified for the film.

[0063] Specific examples of the melt extrusion method include a T-die method, an inflation method, etc. The molding temperature of the resin composition is preferably 150 to 350°C, more preferably 200 to 300°C.

[0064] Another embodiment of the film manufacturing method includes a step of applying the above-described dope solution to a support and a step of removing the dispersion medium from the applied dope solution to obtain a film. The support is not particularly limited, and any conventionally known support used in solution casting can be used. Examples of the support include a metal support such as a stainless steel endless belt or a rotating metal drum, and a film (e.g., a plastic film such as a polyimide film or a polyester film (biaxially oriented polyethylene terephthalate film)). The method for applying the dope solution is not particularly limited, and any conventionally known method can be used. Examples of methods for applying the dope solution include coating using a die coater, doctor blade coater, roll coater, comma coater, lip coater, etc.

[0065] The method for removing the dispersion medium from the dope liquid is not particularly limited, but may include, for example, a method in which the dope liquid is heated to volatilize the dispersion medium, etc. The heating temperature can be appropriately set depending on the dispersion medium used.

[0066] The film can be made into a stretched film by stretching, and is preferably a stretched film in that it has excellent flexibility and can be provided with a retardation in some cases.

[0067] As a method for stretching the film, a conventionally known stretching method can be applied, and examples thereof include uniaxial stretching such as free-width uniaxial stretching and fixed-width uniaxial stretching, and biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching. The method for stretching the film is preferably biaxial stretching, since it improves the bending resistance in any two orthogonal directions in the film plane.

[0068] The stretching temperature when stretching the film is preferably around the glass transition temperature of the copolymer, more specifically, preferably from (glass transition temperature - 30)°C to (glass transition temperature + 100)°C, more preferably from (glass transition temperature - 20)°C to (glass transition temperature + 50)°C, and even more preferably from (glass transition temperature - 10)°C to (glass transition temperature + 30)°C.

[0069] The stretching ratio when stretching the film may be, for example, in the range of 1.05 to 10 times in both the longitudinal and transverse directions.

[0070] The thickness of the film is preferably 1 μm or more and less than 350 μm, more preferably 10 μm or more and 300 μm or less.

[0071] The internal haze per 100 μm of film thickness may be 2.0% or less. The internal haze is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less. The internal haze per 100 μm of film thickness can be measured, for example, by the method described in the Examples.

[0072] The film of the present embodiment can be used in a variety of applications, including optical applications, such as light guide members, films, lenses (optical lenses, etc.), covers, and foam applications (such as cushioning materials, heat-insulating materials, vibration-damping materials, soundproofing materials, sealing materials, packing materials, etc.).

[0073] The film of this embodiment has excellent transparency, heat resistance, flexibility, and surface hardness, and therefore can be suitably used for flexible displays, and in particular, can be even more suitably used as a cover window on the outermost surface. Specific examples of flexible displays include thin, flexible organic electroluminescence (EL) displays, and smartphones that can be folded or rolled up. Furthermore, since the film of this embodiment has a low retardation, it can also be used as a protective film for each layer of a flexible display. Furthermore, the film of this embodiment can be suitably used for producing polarizing plates or touch panels.

[0074] When the film of the present embodiment is used as a cover window for a flexible display, it may be used as a laminate having other layers such as a hard coat layer, etc. Furthermore, 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 or the like. [Example]

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, "parts" means "parts by mass" unless otherwise specified. Various physical properties were measured and evaluated as follows.

[0076] [Monomer conversion rate and copolymer composition analysis at the end of polymerization] The monomer conversion rate at the completion of polymerization and the content of specific monomer units in the copolymer were determined by measuring the amount of unreacted monomer in the obtained polymerization reaction liquid using gas chromatography (Shimadzu Corporation, apparatus name: GC-2014).

[0077] [Weight average molecular weight and number average molecular weight of copolymer] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer were determined in terms of polystyrene using gel permeation chromatography (GPC) under the following conditions: System: Tosoh GPC system HLC-8220 Measurement column configuration: Guard column (Tosoh, TSKguardcolumn SuperHZ-L) Two separation columns (Tosoh TSKgel SuperHZM-M) connected in series Reference column configuration: Reference column (Tosoh, TSKgel SuperH-RC) Developing solvent: chloroform (Wako Pure Chemical Industries, special grade) Developing solvent flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (Tosoh, PS-oligomer kit) Column temperature: 40℃

[0078] [ML content in copolymer] The ML content in the copolymer (the content of structural units derived from α-methylene lactone) is 1 Specifically, deuterated DMSO or deuterated chloroform was used as the deuterated solvent, and a nuclear magnetic resonance spectrometer (BRUKER, AV300M) was used. 1 H-NMR measurement was performed and the obtained 1 It was calculated from the area ratio of the H-NMR profile.

[0079] [Glass transition temperature (Tg) of copolymer] The glass transition temperature of the copolymer was determined in accordance with the provisions of JIS K 7121. Specifically, using a differential scanning calorimeter (Rigaku Thermo plus EVO DSC-8230), approximately 10 mg of a sample was heated from room temperature to 200°C (heating rate 20°C / min) under a nitrogen gas atmosphere, and the DSC curve was obtained and evaluated by the starting point method. α-Alumina was used as a reference.

[0080] [Internal haze of copolymer] The haze was determined in accordance with the provisions of JIS K 7136. Specifically, an unstretched film was prepared by heat-pressing the copolymer at 240°C and 40 MPa for 10 minutes, and the film was immersed in a quartz cell with an optical path length of 10 mm filled with 1,2,3,4-tetrahydronaphthalene (tetralin) using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-1001DP) to measure the haze, which was calculated as the internal haze value per 100 μm.

[0081] [Haze of copolymer in solvent containing MEK] A dope solution was prepared by dissolving the copolymer in a solvent containing methyl ethyl ketone (MEK) at 25% by mass, and the haze of the prepared dope solution was measured. The haze was measured using a haze meter (Nippon Denshoku Industries, NDH-1001DP) with a quartz cell with an optical path length of 10 mm. Specifically, the haze of the dope solution was measured after standard calibration using an empty quartz cell.

[0082] [Dope Yellowness Index (YI)] The yellowness index (YI) of the dope solution was measured in transmission mode using a spectrophotometer (Nippon Denshoku Industries: Colormeter ZE6000) with a quartz cell with an optical path length of 10 mm. Specifically, the YI of the dope solution was measured after standard calibration using an empty quartz cell.

[0083] [Dope haze] The haze of the dope solution was measured using a haze meter (NDH-1001DP, manufactured by Nippon Denshoku Industries Co., Ltd.) with a quartz cell having an optical path length of 10 mm. Specifically, the haze of the dope solution was measured after standard calibration with an empty quartz cell.

[0084] [Internal haze of film] The haze was determined in accordance with the provisions of JIS K 7136. Specifically, a stretched film was prepared, and a haze meter (NDH-1001DP, manufactured by Nippon Denshoku Industries Co., Ltd.) was used to measure the haze by immersing the film in a quartz cell with an optical path length of 10 mm filled with 1,2,3,4-tetrahydronaphthalene (tetralin), and calculating the internal haze value per 100 μm.

[0085] [Film Thickness] The film thickness was measured using a Digimatic Micrometer (Mitutoyo).

[0086] Methyl methacrylate (MMA), α-methylene-γ-butyrolactone (ML), methyl ethyl ketone (MEK), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc) were obtained from Tokyo Chemical Industry Co., Ltd. Peroyl L (dilauroyl peroxide, LPO) was obtained from NOF Corporation. t-Amylperoxy 2-ethylhexanoate (Luperox® 575) was obtained from Arkema Yoshitomi. Polyoxyethylene distyrylphenyl ether sulfate ester ammonium (Hitenol® NF-08) was obtained from Daiichi Kogyo Seiyaku Co., Ltd. nDM stands for n-dodecyl mercaptan.

[0087] <Synthesis of copolymer, preparation of dope solution, and fabrication of film> Example 1 A reactor equipped with a stirrer, temperature sensor, cooling tube, and nitrogen inlet tube was prepared. 75 parts of deionized water containing 0.25 parts of Hitenol (registered trademark) NF-08 was charged into the vessel. Next, a mixture of 13 parts of ML as a monomer, 37 parts of MMA, and 0.25 parts of LPO as a polymerization initiator was charged into the vessel, and the mixture was stirred at 3,000 rpm for 15 minutes using a TK homomixer MARK II model 2.5 (manufactured by Primix) to form a uniform suspension.

[0088] 125 parts of deionized water was added to the suspension, which was then transferred to a reactor. While stirring and blowing in nitrogen gas, the reaction solution (suspension) was heated to 70°C. The reaction started when the internal temperature reached 70°C. The reactor was maintained at 70°C until the liquid temperature reached a peak due to self-heating, after which it was maintained at 75°C. Two hours after the start of the reaction, the reaction solution (suspension) was heated to 90°C and stirred for 4 hours to complete the polymerization reaction. The reaction solution was then cooled, filtered, and the copolymer was collected. It was then dried in a hot air dryer to obtain a copolymer (powder). The monomer conversion at the end of polymerization was 98.2% for ML and 99.1% for MMA. The resulting copolymer had an Mw of 252,000, an Mn of 119,000, a Tg of 127°C, a haze in MEK of 7.8%, and an internal haze of 0.2%.

[0089] The resulting copolymer was dissolved in MEK to prepare a dope solution containing 25% copolymer by mass, which was then pressure-filtered through a 5 μm filter. Visual inspection of the prepared dope revealed uniform dispersion, and no precipitation occurred even after leaving it overnight, nor was any change in the appearance of the dope observed. The haze of the dope was 7.8%, and the YI was 2.4.

[0090] The prepared dope solution was then dropped onto a polyimide (PI) film and spread to a thickness of 1 mm using an applicator. The film was then dried in a dryer, heating from 40°C to 180°C, to obtain a 160 μm-thick unstretched cast film. The resulting unstretched cast film was cut into 96 mm x 96 mm pieces and sequentially biaxially stretched in the machine direction (MD) and transverse direction (TD) at a stretching temperature of Tg + 20°C at a stretching rate of 300% / min, respectively, using a sequential biaxial stretching machine (Toyo Seiki Seisakusho, X6-S), to a stretching ratio of 2.0x. The film was then cooled to produce a 40 μm-thick stretched film. The internal haze of the stretched film was 0.1%.

[0091] Example 2 A copolymer (powder) was obtained in the same manner as in Example 1, except that a mixture of 7.5 parts of ML as the monomer, 42.5 parts of MMA, and 0.25 parts of LPO as the polymerization initiator was used. The monomer conversion upon completion of polymerization was 98.3% for ML and 99.2% for MMA. The resulting copolymer had an Mw of 299,000, an Mn of 142,000, a Tg of 121°C, a haze in MEK of 8.1%, and an internal haze of 0.2%.

[0092] The resulting copolymer was dissolved in a 7:3 (mass ratio) mixed solvent of MEK and DMF to prepare a dope solution containing 25% copolymer by mass, which was then pressure-filtered through a 5 μm filter. Visual inspection of the prepared dope revealed uniform dispersion, and no precipitation occurred even after leaving it overnight, nor was any change in the appearance of the dope observed. The haze of the dope was 7.7%, and the YI was 2.8.

[0093] Using the prepared dope solution, a stretched film having a thickness of 40 μm was produced in the same manner as in Example 1. The internal haze of the stretched film was 0.2%.

[0094] (Comparative Example 1) A reactor equipped with a stirrer, temperature sensor, cooling tube, and nitrogen inlet tube was charged with 13 parts of ML as a monomer, 37 parts of MMA, and 60 parts of dimethyl sulfoxide (DMSO) as a solvent, and the mixture was heated to 83°C while nitrogen was passed through. Then, 0.15 parts of Luperox (registered trademark) 575 was added as a polymerization initiator, and the solution was stirred and polymerized at 83-90°C for 6 hours. The resulting polymerization solution was vacuum dried (133 Pa (1 mmHg)) at 240°C for 1 hour to obtain a copolymer. The monomer conversion rates at the completion of polymerization were 94.1% for MMA and 95.5% for ML. The resulting copolymer had an Mw of 252,000, an Mn of 119,000, a Tg of 127°C, a haze in MEK of 78.1%, and an internal haze of 2.6%.

[0095] A dope solution was prepared using the obtained copolymer in the same manner as in Example 1. Visual inspection of the prepared dope solution revealed that it was turbid overall, and after leaving it to stand overnight, precipitation occurred. Note that adding Hitenol (registered trademark) NF-08 to the prepared dope solution did not improve the turbidity of the dope solution.

[0096] Using the prepared dope solution, a stretched film having a thickness of 40 μm was produced in the same manner as in Example 1. The internal haze of the stretched film was 2.6%.

[0097] (Comparative Example 2) A copolymer (powder) was obtained in the same manner as in Example 1, except that a mixture of 27.5 parts of ML as monomers, 22.5 parts of MMA, and 0.25 parts of LPO as a polymerization initiator was used. The monomer conversion upon completion of polymerization was 98.2% for ML and 99.5% for MMA. The Mw of the obtained copolymer was 227,000, Mn was 95,000, and Tg was 144°C.

[0098] A dope solution was prepared using the obtained copolymer in the same manner as in Example 1. Visual inspection of the prepared dope solution revealed that it was cloudy overall and that MEK-insoluble matter had precipitated, making it impossible to measure the physical properties of the dope solution. Furthermore, since a stretched film could not be formed from the dope solution, the physical properties of the stretched film could not be measured either.

[0099] (Comparative Example 3) A copolymer (powder) was obtained in the same manner as in Example 1, except that a mixture of 2.5 parts of ML as the monomer, 47.5 parts of MMA, and 0.25 parts of LPO as the polymerization initiator was used. The monomer conversion upon completion of polymerization was 99.0% for ML and 99.0% for MMA. The resulting copolymer had an Mw of 290,000, an Mn of 136,000, a Tg of 112°C, a haze in MEK of 8.1%, and an internal haze of 0.2%.

[0100] A dope solution was prepared using the obtained copolymer in the same manner as in Example 1. Visual inspection of the prepared dope solution revealed uniform dispersion, and no precipitation occurred even after leaving it to stand overnight, and no change in the appearance of the dope solution was observed. The haze of the dope solution was 7.8%, and the YI was 3.2.

[0101] Using the prepared dope solution, a stretched film having a thickness of 40 μm was produced in the same manner as in Example 1. The internal haze of the stretched film was 0.2%.

Claims

1. A method for producing a copolymer containing a structural unit derived from α-methylene lactone and a structural unit derived from alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, comprising: a polymerization step of polymerizing the α-methylene lactone and the alkyl (meth)acrylate monomer in an aqueous solvent, the α-methylene lactone is α-methylene-γ-butyrolactone, the content of the α-methylene lactone-derived structural unit in the copolymer is 10 to 40% by mass, The weight average molecular weight of the copolymer is 220,000 or more and 1,000,000 or less, A method for producing a copolymer, wherein the entire amount of the monomer is present in the system from the early stage of the polymerization step.

2. The method for producing a copolymer according to claim 1, wherein the content of the structural units derived from alkyl (meth)acrylate in the copolymer is 90 to 50% by mass.

3. The method for producing a copolymer according to claim 1 or 2, wherein the polymerization is carried out in the presence of a chain transfer agent.

4. The method for producing a copolymer according to any one of claims 1 to 3, wherein the polymerization is suspension polymerization.

5. A copolymer comprising 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 structural unit derived from α-methylene lactone is a structural unit derived from α-methylene-γ-butyrolactone, the haze of a solution obtained by dissolving the copolymer in a solvent containing a ketone solvent at 25% by mass is 40% or less; 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 115°C or higher.

6. The copolymer according to claim 5, wherein the content of the structural unit derived from α-methylene lactone in the copolymer is 10 to 40% by mass.

7. The copolymer according to claim 5 or 6, wherein the content of the structural units derived from alkyl (meth)acrylate in the copolymer is 90 to 50% by mass.

8. A dope solution comprising the copolymer according to any one of claims 5 to 7 and a dispersion medium.

9. 9. The dope according to claim 8, wherein the haze is 40% or less.

10. A film comprising the copolymer according to any one of claims 5 to 7.

11. 11. The film according to claim 10, having an internal haze of 2.0% or less per 100 μm thickness.

12. A method for using the copolymer according to any one of claims 5 to 7 as a film for forming a flexible display.

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