Method for producing resin, method for producing dope, and method for producing optical film

Abstract

To provide a method for producing a resin which improves drying efficiency of a solvent, and can enhance productivity of an optical film.SOLUTION: A method for producing a resin including a structural unit derived from α-methylene lactone, and a structural unit derived from alkyl (meth)acrylate includes a polymerization step of suspending and polymerizing a monomer containing the α-methylene lactone and the alkyl (meth)acrylate in a solvent, in the presence of a first polymerization initiator, a second polymerization initiator and an emulsifier, wherein a 10-hour half-life temperature T2 of the second polymerization initiator is higher than a 10-hour half-life temperature T1 of the first polymerization initiator by 10°C or higher, and the polymerization step includes a first temperature holding step of holding the temperature of a reaction liquid to be suspended and polymerized at T1±10°C, and starting the polymerization, and a second temperature holding step of raising the temperature of the reaction liquid by polymerization heat, then holding the temperature of the reaction liquid at a temperature higher than the temperature of the reaction liquid in the first temperature holding step by 10°C or higher, and further polymerizing the reaction liquid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for producing a resin, a method for producing a dope, and a method for producing an optical film.

Background Art

[0002] Optical films containing a copolymer containing a structural unit derived from α-methylene lactone are known. For example, Patent Document 1 discloses a method for producing a copolymer containing a structural unit derived from α-methylene lactone, and a copolymer produced by this production method. Further, an optical film produced by a solution casting method including a step of casting a dope containing this copolymer and a solvent onto a support, and a step of volatilizing the solvent from the cast dope is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When producing an optical film by volatilizing a solvent from a dope, if the drying efficiency of the solvent can be improved, the productivity of the optical film can be increased. Although the drying efficiency of the solvent can be improved by raising the drying temperature, if the drying temperature is raised, the solvent may boil over and foam marks may occur on the optical film. That is, there is a limit to improving the drying efficiency only by adjusting the drying temperature.

[0005] In order to solve such problems, the present disclosure provides a method for producing a resin that is a resin containing a structural unit derived from α-methylene lactone and can improve the drying efficiency of a solvent and increase the productivity of an optical film. Further, the present disclosure provides a method for producing a dope using such a resin and a method for producing an optical film.

Means for Solving the Problems

[0006] The present disclosure provides a method for producing a resin described in the following [1] to [7], a method for producing a dope described in [8], and a method for producing an optical film described in [9]. [1] A method for producing a resin containing a structural unit derived from α-methylene lactone and a structural unit derived from an alkyl (meth)acrylate, the method comprising a polymerization step of subjecting a monomer containing α-methylene lactone and an alkyl (meth)acrylate to suspension polymerization in a solvent in the presence of a first polymerization initiator, a second polymerization initiator, and an emulsifier, wherein the 10-hour half-life temperature T2 of the second polymerization initiator is 10°C or higher than the 10-hour half-life temperature T1 of the first polymerization initiator, and the polymerization step includes a first temperature holding step of holding the temperature of the reaction solution to be suspension polymerized at (T1 - 10) to (T1 + 10)°C to initiate polymerization, and a second temperature holding step of holding the temperature of the reaction solution at a temperature 10°C or higher than the temperature of the reaction solution in the first temperature holding step after the temperature of the reaction solution has risen due to the heat of polymerization to further polymerize. The method for producing a resin is characterized by having these steps. [2] The method for producing a resin according to [1], characterized in that the 10-hour half-life temperature T1 of the first polymerization initiator is 53 to 63°C. [3] The method for producing a resin according to [1] or [2], characterized in that in the first temperature holding step, the temperature of the reaction solution is held at 55 to 73°C. [4] The method for producing a resin according to [1], characterized in that the 10-hour half-life temperature T2 of the second polymerization initiator is 73 to 103°C. [5] The method for producing a resin according to [1] or [4], characterized in that in the second temperature holding step, the temperature of the reaction solution is held at 75 to 95°C. [6] The method for producing a resin according to any one of [1] to [5], characterized in that when the amount of the first polymerization initiator used is 100 parts by mass, the amount of the second polymerization initiator used is 5 to 300 parts by mass. [7] The method for producing a resin according to any one of [1] to [6], characterized in that the first polymerization initiator and the second polymerization initiator are organic peroxides. [8] A method for producing a dope, comprising a dope preparation step of mixing a resin obtained by the production method according to any one of [1] to [7] above with a solvent to obtain a dope. [9] A method for producing an optical film, comprising a casting step of casting the dope obtained by the production method according to [8] above onto a support to form a cast film, and a volatilization step of volatilizing the solvent from the cast film.

Advantages of the Invention

[0007] According to the present disclosure, a method for producing a resin containing a structural unit derived from α-methylene lactone, which can improve the drying efficiency of a solvent and enhance the productivity of an optical film, can be provided. Furthermore, according to the present disclosure, a method for producing a dope using such a resin and a method for producing an optical film can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described. However, the present disclosure is not limited by the following embodiments. The upper limit value and the lower limit value of the numerical range explicitly shown in the present disclosure may be replaced with any value shown in the examples. Further, the individually described upper limit value and lower limit value may be arbitrarily combined. In the present disclosure, the term “(meth)acrylic acid” means acrylic acid and methacrylic acid. The numerical range shown as X to Y means X or more and Y or less.

[0010] <Method for Producing Resin> A method for producing a resin according to an embodiment is a method for producing a resin containing a structural unit derived from α-methylene lactone and a structural unit derived from an alkyl (meth)acrylate, comprising a polymerization step of subjecting a monomer containing α-methylene lactone and an alkyl (meth)acrylate to suspension polymerization in a solvent in the presence of a first polymerization initiator, a second polymerization initiator, and an emulsifier, wherein the 10-hour half-life temperature T2 of the second polymerization initiator is 10°C or more higher than the 10-hour half-life temperature T1 of the first polymerization initiator, and the polymerization step includes a first temperature holding step of holding the temperature of the reaction solution to be suspension polymerized at (T1 - 10) to (T1 + 10)°C to initiate polymerization, and a second temperature holding step of holding the temperature of the reaction solution at a temperature 10°C or more higher than the temperature of the reaction solution in the first temperature holding step after the temperature of the reaction solution has risen due to the heat of polymerization to further polymerize.

[0011] The resin obtained by such a production method has sufficiently reduced monomers remaining in the resin by performing the first temperature holding step and the second temperature holding step using the first polymerization initiator and the second polymerization initiator. In the dope obtained by dissolving such a resin in a solvent, the drying efficiency of the solvent is improved. Therefore, the productivity of the optical film produced by such a dope can be enhanced.

[0012] [Resin] The resin contains a structural unit derived from α-methylene lactone and a structural unit derived from an alkyl (meth)acrylate.

[0013] [Structural unit derived from α-methylene lactone] α-Methylene lactone is a general term for compounds in which an exomethylene group is bonded to the carbon at the α-position of the lactone ring. The number of ring members of the lactone is not particularly limited, and may be a 4- to 8-membered ring, a 5- to 6-membered ring, or a 5-membered ring.

[0014] Examples of the α-methylene lactone having a 5-membered ring include the compounds represented by the following formula (1).

[0015] [Chemical formula]

[0016] R in formula (1) 1 ~R 4 are, independently of each other, a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. R 1 ~R 4 are, independently of each other, preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably all hydrogen atoms.

[0017] Examples of the compound represented by formula (1) include α-methylene-γ-butyrolactone, α-methylene-β-methyl-γ-butyrolactone, α-methylene-β-ethyl-γ-butyrolactone, α-methylene-γ-methyl-γ-butyrolactone, α-methylene-γ-ethyl-γ-butyrolactone, α-methylene-β,β-dimethyl-γ-butyrolactone, α-methylene-β-methyl-γ-methyl-γ-butyrolactone, α-methylene-γ,γ-dimethyl-γ-butyrolactone.

[0018] The structural unit derived from α-methylene lactone is formed by the polymerization of α-methylene lactone. The resin may contain only one kind of structural unit derived from α-methylene lactone, or may contain two or more kinds. The structural unit derived from α-methylene lactone preferably contains the structural unit represented by the following formula (2), more preferably contains the structural unit derived from α-methylene-γ-butyrolactone. The structural unit represented by the following formula (2) is formed, for example, by the polymerization of a monomer containing the compound represented by formula (1).

[0019] [Chemical formula]

[0020] R in formula (2) 1 ~R 4 is synonymous with R 1 ~R 4 in formula (1) and, independently of each other, is a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. R 1 ~R4 is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, independently of each other, and more preferably all hydrogen atoms. R 1 ~R 4 When all are hydrogen atoms, the structural unit represented by the formula (2) is a structural unit derived from α-methylene-γ-butyrolactone.

[0021] The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, and a cyclohexyl group. Examples of the aromatic hydrocarbon group include a phenyl group, a tolyl group, and a benzyl group.

[0022] The content of the structural unit derived from α-methylene lactone in the resin is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass. Thereby, the heat resistance, transparency, and strength of the optical film obtained from this resin can be further improved. Further, in the total amount of the structural units derived from α-methylene lactone, the content of the structural units derived from α-methylene-γ-butyrolactone is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, still more preferably 95 to 100% by mass, and particularly preferably 100% by mass.

[0023] ((Structural unit derived from alkyl (meth)acrylate)) (Alkyl (meth)acrylate) is a general term for esters of (meth)acrylic acid and monohydric alkyl alcohols. Examples of alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, and n-hexyl (meth)acrylate.

[0024] (Meta) The structural unit derived from an alkyl (meth)acrylate is formed by polymerization of an alkyl (meth)acrylate. The resin may contain only one type of structural unit derived from an alkyl (meth)acrylate, or may contain two or more types. The structural unit derived from an alkyl (meth)acrylate preferably contains a structural unit derived from an alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, more preferably contains a structural unit derived from an alkyl (meth)acrylate having an alkyl group with 1 to 3 carbon atoms, and still more preferably contains a structural unit derived from methyl methacrylate.

[0025] The content of the structural unit derived from an alkyl (meth)acrylate in the resin is preferably 50 to 95% by mass, and more preferably 60 to 90% by mass. Thereby, the heat resistance, transparency and strength of the optical film obtained from this resin can be further improved. Also, in the total amount of the structural unit derived from an alkyl (meth)acrylate, the content of the structural unit derived from methyl methacrylate is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, still more preferably 95 to 100% by mass, and particularly preferably 100% by mass.

[0026] (Other structural units) The resin may optionally contain a structural unit derived from α-methylene lactone and other structural units different from the structural unit derived from an alkyl (meth)acrylate. Examples of other structural units include structural units derived from monomers such as (meth)benzyl acrylate, (meth)chloromethyl acrylate, 2-chloroethyl (meth)acrylate, styrene, vinyltoluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, etc. The resin may contain only one type of other structural unit, or may contain two or more types. The content of other structural units in the resin may be 0 to 20% by mass, or may be 0 to 10% by mass.

[0027] Note that the content of each structural unit in the resin is determined by dissolving the resin in a heavy solvent. 1Measure the 1H-NMR and calculate the area ratio of the peaks corresponding to each structural unit.

[0028] The weight average molecular weight (Mw) of the resin is preferably from 200,000 to 1,000,000, more preferably from 220,000 to 900,000, and still more preferably from 250,000 to 700,000. In particular, by setting the weight average molecular weight (Mw) of the copolymer to 200,000 or more, preferably 220,000 or more, the flex resistance of the optical film obtained from this resin can be further improved. The weight average molecular weight (Mw) of the resin is measured by gel permeation chromatography (GPC).

[0029] The number average molecular weight (Mn) of the resin is preferably from 80,000 to 400,000, more preferably from 90,000 to 300,000, and still more preferably from 100,000 to 250,000. In particular, by setting the number average molecular weight (Mn) of the copolymer to 80,000 or more, preferably 90,000 or more, the flex resistance of the optical film obtained from this resin can be further improved. The number average molecular weight (Mn) of the resin is measured by, for example, gel permeation chromatography (GPC).

[0030] The glass transition temperature (Tg) of the resin measured by the starting point method is preferably 115°C or higher, more preferably from 115 to 180°C, and still more preferably from 120 to 150°C. In particular, by setting the glass transition temperature (Tg) to 115°C or higher, preferably 120°C or higher, the heat resistance of the optical film obtained from this resin can be further improved. The glass transition temperature (Tg) of the resin is measured in accordance with the provisions of JIS K 7121.

[0031] [Polymerization step] In the polymerization step, a monomer containing the above-mentioned α-methylene lactone and alkyl (meth)acrylate is subjected to suspension polymerization in a solvent in the presence of a first polymerization initiator, a second polymerization initiator, and an emulsifier to obtain a resin.

[0032] The solvent in suspension polymerization is an aqueous solvent. The aqueous solvent is preferably water alone, but may contain a non-aqueous solvent (water-soluble organic solvent) within an acceptable range. Examples of the non-aqueous solvent (water-soluble organic solvent) include alcohol solvents such as methanol, ethanol, propanol, butanol, 2-methylpropyl alcohol, 2-methyl-2-propanol; ketone solvents such as acetone, methyl ethyl ketone; ester solvents such as ethyl acetate; and ether solvents such as dioxane, diethyl ether, tetrahydrofuran. The content of the non-aqueous solvent in the aqueous solvent may be 0 to 5% by mass, may be 0 to 2% by mass, or may be 0 to 1% by mass.

[0033] Examples of the first polymerization initiator and the second polymerization initiator include organic peroxides such as dilauroyl peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-amyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-amyl peroxy-2-ethylhexanoate, t-amyl peroxyisononanoate, t-butyl peroxy-2-ethylhexanoate; and azo compounds such as 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate). As the first polymerization initiator and the second polymerization initiator, those soluble in the monomer can be used. From the viewpoint of further promoting the reaction, it is preferable that both the first polymerization initiator and the second polymerization initiator are organic peroxides.

[0034] The 10-hour half-life temperature T2 of the second polymerization initiator is 10°C or higher than the 10-hour half-life temperature T1 of the first polymerization initiator. By using two types of polymerization initiators with a 10-hour half-life temperature difference of 10°C or more in this way, the reaction can be mainly promoted by the first polymerization initiator at the low-temperature stage in the initial stage of the polymerization reaction, and mainly by the second polymerization initiator at the high-temperature stage in the later stage of the polymerization reaction. By promoting the polymerization reaction in two stages in this way, the monomers remaining in the resin after the polymerization reaction can be reduced.

[0035] The 10-hour half-life temperature T1 of the first polymerization initiator is preferably 53 to 63°C, more preferably 57 to 62°C. When the 10-hour half-life temperature T1 of the first polymerization initiator is within this range, the reaction at low temperature can be further promoted.

[0036] The 10-hour half-life temperature T2 of the second polymerization initiator is preferably 73 to 103°C, more preferably 75 to 98°C. When the 10-hour half-life temperature T2 of the second polymerization initiator is within this range, the reaction at high temperature can be further promoted.

[0037] The half-life is the time until the concentration of the polymerization initiator is reduced to half of the initial concentration, and the 10-hour half-life temperature indicates the temperature at which the half-life is 10 hours. As the 10-hour half-life temperature, for example, the catalog value of the polymerization initiator supplier can be used.

[0038] Examples of the combination of the first polymerization initiator and the second polymerization initiator include, for example, dilauroyl peroxide (manufactured by NOF Corporation; Peroyl L, 10-hour half-life temperature: 62°C) or t-amyl peroxypivalate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) 554, 10-hour half-life temperature: 55°C), and t-amyl peroxyisooctanoate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) 570, 10-hour half-life temperature: 96°C), t-amyl peroxy 2-ethylhexanoate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) 575: 10-hour half-life temperature: 75°C) or t-butyl peroxyisopropyl carbonate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) TBIC, 10-hour half-life temperature: 99°C).

[0039] That is, the first polymerization initiator is preferably dilauroyl peroxide (manufactured by NOF Corporation; Peroyl L, 10-hour half-life temperature: 62°C) or t-amyl peroxypivalate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) 554, 10-hour half-life temperature: 55°C).

[0040] The second polymerization initiator is preferably t-amyl peroxyisooctanoate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) 570, 10-hour half-life temperature: 96°C), t-amyl peroxy 2-ethylhexanoate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) 575: 10-hour half-life temperature: 75°C) or t-butyl peroxyisopropyl carbonate (manufactured by Arkema Kishima Co., Ltd.; Lupersol (registered trademark) TBIC, 10-hour half-life temperature: 99°C).

[0041] The total addition amount of the first polymerization initiator and the second polymerization initiator may be adjusted as appropriate, but is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the monomer.

[0042] When the amount of the first polymerization initiator used is 100 parts by mass, the amount of the second polymerization initiator used is preferably 5 to 300 parts by mass. From the viewpoint of further promoting the reaction, when the amount of the first polymerization initiator used is 100 parts by mass, the amount of the second polymerization initiator used is more preferably 30 to 200 parts by mass, still more preferably 50 to 150 parts by mass, and particularly preferably 75 to 125 parts by mass.

[0043] Examples of the emulsifier include water-soluble polymer-based dispersion stabilizers such as polyvinyl alcohol (PVA), polyvinyl pyrrolidone, cellulose, gelatin, sodium polyacrylate, and sodium polymethacrylate; anionic surfactants such as sodium lauryl sulfate and polyoxyethylene alkyl phenyl ether sulfate ester salts (for example, polyoxyethylene distyryl phenyl ether sulfate ester ammonium); cationic surfactants such as alkylamine salts and quaternary ammonium salts; zwitterionic surfactants such as lauryldimethylamine oxide; nonionic surfactants such as polyoxyethylene alkyl ether; and other alginates, zein, casein; and inorganic dispersants such as barium sulfate, calcium sulfate, barium carbonate, magnesium carbonate, calcium phosphate, talc, clay, diatomaceous earth, bentonite, titanium hydroxide, sodium hydroxide, and metal oxide powders. By adding the emulsifier, the stability of the polymerization reaction can be improved. The content of the emulsifier may be adjusted as appropriate, but is preferably 0.1 to 4 parts by mass, and more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the monomer.

[0044] The emulsifier is preferably an ammonium sulfate salt. Examples of the ammonium sulfate salt emulsifier include polyoxyethylene distyryl phenyl ether sulfate ester ammonium (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Hitenol (registered trademark) NF-08).

[0045] When performing suspension polymerization, when dispersing the monomer in an aqueous solvent, it may be dispersed by stirring with a paddle blade or the like, or may be dispersed using a device such as a high-speed shear turbine type disperser, a high-pressure jet homogenizer, an ultrasonic emulsifying disperser, a medium stirring disperser, or a forced gap passing type disperser.

[0046] When polymerizing the monomer, a chain transfer agent and an additive may be added as necessary.

[0047] Examples of the chain transfer agent include monofunctional thiol compounds such as n-dodecyl mercaptan and β-mercaptopropionic acid; bifunctional thiol compounds such as mercapto-modified polysiloxane with mercapto groups at both ends; and side-chain polyfunctional mercapto-modified polysiloxane with mercapto-modified side chains. The addition amount of the chain transfer agent may be adjusted as appropriate, but it is preferably 0.001 to 1 part by mass with respect to 100 parts by mass of the monomer.

[0048] Examples of the additive include water-insoluble organic solvents such as alkanes and radical scavengers. The addition amount of the additive may be adjusted as appropriate, but it is preferably 0.001 to 1 part by mass with respect to 100 parts by mass of the monomer.

[0049] The polymerization step includes a first temperature holding step of holding the temperature of the reaction solution to be suspension polymerized at (T1 - 10) to (T1 + 10) °C and starting the polymerization, and after the temperature of the reaction solution rises due to the heat of polymerization, holding the temperature of the reaction solution at a temperature 10 °C or higher than the temperature of the reaction solution in the first temperature holding step and further polymerizing, which is a second temperature holding step.

[0050] The first temperature holding step and the second temperature holding step in the polymerization process will be described below with reference to FIG. 1. FIG. 1 is a diagram schematically showing an example of the transition of the temperature of the reaction solution when the horizontal axis represents the reaction time and the vertical axis represents the temperature of the reaction solution in the polymerization process of the present disclosure. In FIG. 1, the first temperature holding step R1 is started at the first holding temperature T3. In the first temperature holding step, polymerization is mainly initiated by the first polymerization initiator, and when the polymerization proceeds to a certain extent, the temperature rises due to the heat of polymerization. This temperature rise is represented by the exothermic peak P shown in FIG. 1. After the exothermic peak P occurs, the temperature of the reaction solution is raised, and the second temperature holding step R2 is performed at the second holding temperature T4. At this time, in the second temperature holding step R2, the second polymerization initiator mainly promotes the polymerization reaction. By promoting the polymerization reaction in two steps in this way, the monomer remaining in the resin after the polymerization reaction can be reduced.

[0051] In the polymerization process, for example, by using a reactor generally used in the polymerization reaction, which is equipped with a temperature sensor for measuring the temperature of the reaction solution, the temperature can be controlled. That is, by setting the set temperature of the reactor, the temperature of the reaction solution can be maintained in the first temperature holding step and the second temperature holding step, and by raising the set temperature of the reactor, the temperature of the reaction solution can also be raised.

[0052] After the temperature rise of the reaction solution due to the heat of polymerization occurs, the timing of raising the set temperature of the reactor is not particularly limited. As shown in FIG. 1, after the exothermic peak P occurs, the set temperature may be raised after the temperature begins to drop, or the set temperature may be raised before the exothermic peak P occurs after the temperature rise due to the heat of polymerization occurs.

[0053] The first temperature holding step is a step of mainly activating the first polymerization initiator to initiate the polymerization reaction.

[0054] In the first temperature holding step, the temperature of the reaction solution is maintained at (T1 - 10) to (T1 + 10) °C. Preferably, the temperature of the reaction solution is maintained at (T1 - 8) to (T1 + 8) °C, and more preferably at (T1 - 6) to (T1 + 6) °C. In the first temperature holding step, for example, the temperature of the reaction solution may be maintained at 55 to 73 °C, may be maintained at 58 to 70 °C, or may be maintained at 60 to 68 °C.

[0055] The holding time in the first temperature holding step is the time from when the temperature of the reaction solution reaches the first holding temperature T3 until the temperature of the reaction solution rises due to the heat of polymerization. For example, it may be 0.5 to 5 hours, may be 0.75 to 4 hours, or may be 1 to 3 hours.

[0056] The second temperature holding step is a step of raising the temperature of the reaction solution after the temperature of the reaction solution has risen due to the heat of polymerization, mainly activating the second polymerization initiator, and further advancing the polymerization reaction.

[0057] In the second temperature holding step, the temperature of the reaction solution is maintained at a temperature 10 °C or higher than the temperature of the reaction solution in the first temperature holding step. In the second temperature holding step, for example, the temperature of the reaction solution may be maintained at 75 to 95 °C, may be maintained at 80 to 93 °C, or may be maintained at 83 to 90 °C.

[0058] The holding time in the second temperature holding step may be a time sufficient to react the unreacted monomers that have not reacted before the second temperature holding step. For example, it may be 1 to 10 hours, may be 2 to 8 hours, or may be 3 to 6 hours.

[0059] [Drying Step] After the polymerization step, a drying step of drying the resin obtained in the polymerization step may be performed. By the drying step, the solvent (aqueous solvent) used in the suspension polymerization can be removed, and the resin obtained in the polymerization step can be obtained as a powder. Before the drying step, the resin obtained in the polymerization step may be subjected to solid-liquid separation. Examples of the method of solid-liquid separation include filtration, centrifugation, and combinations thereof. By performing solid-liquid separation, the aqueous solvent can be removed more efficiently in the drying step.

[0060] The drying temperature in the drying process is preferably 80 to 105°C, more preferably 85 to 100°C. Thereby, the aqueous solvent can be removed more efficiently.

[0061] The drying time in the drying process is preferably 1 to 24 hours, more preferably 3 to 15 hours, and even more preferably 5 to 12 hours. Thereby, the aqueous solvent can be removed more efficiently.

[0062] According to the resin of this embodiment, when manufacturing an optical film, the drying efficiency of the solvent in the dope can be improved, and the productivity of the optical film can be enhanced.

[0063] <Method for manufacturing dope> The method for manufacturing a dope according to one embodiment includes a dope preparation step of mixing the resin obtained by the above-described method for manufacturing a resin and a solvent to obtain a dope. The dope can be suitably used for manufacturing an optical film.

[0064] The content of the resin in the dope is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 15 to 40% by mass. Thereby, the productivity of the optical film can be further enhanced.

[0065] Examples of the solvent include chain ketone solvents such as acetone and methyl ethyl ketone; cyclic ketone solvents such as cyclohexanone (anone) and cyclopentanone; alkyl chloride solvents such as methylene chloride, chloroform, 1,2-dichloroethane, and 1,1-dichloroethane; 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. The solvent is preferably a solvent obtained by mixing methylene chloride and ethanol at a volume ratio of 9:1 to 7:3, methyl ethyl ketone, or N,N-dimethylacetamide.

[0066] (Other polymers) The dope may contain other polymers different from the above-mentioned resin, if necessary. Examples of other polymers include olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly(4-methyl-1-pentene), etc.; halogen-containing polymers such as vinyl chloride, chlorinated vinyl resin, etc.; acrylic polymers such as polymethyl methacrylate, etc.; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer, etc.; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.; polyamides such as nylon 6, nylon 66, nylon 610, etc.; polyacetal; polycarbonate; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polysulfone; polyether sulfone; polyoxybenzylene; polyamideimide; elastic organic fine particles such as polybutadiene-based rubber, acrylic rubber, etc.; rubbery polymers such as ABS resin and ASA resin blended with polybutadiene-based rubber and acrylic rubber. The dope may contain only one kind of other polymer or two or more kinds. The content of other polymers in the dope may be appropriately adjusted according to the composition of the optical film to be obtained.

[0067] (Additive) The dope may contain additives, if necessary. Examples of additives include antioxidants; stabilizers such as light stabilizers, weather stabilizers, heat stabilizers, etc.; reinforcing materials such as glass fibers, carbon fibers, etc.; ultraviolet absorbers; near-infrared absorbers; flame retardants; antistatic agents; colorants such as inorganic pigments, organic pigments, dyes, etc.; organic or inorganic antiblocking agents; resin modifiers; plasticizers; lubricants; fluidizing agents; compatibilizers. The dope may contain only one kind of additive or two or more kinds. The content of additives in the dope may be appropriately adjusted according to the composition of the optical film to be obtained.

[0068] (Method for manufacturing optical film) The manufacturing method of the optical film according to one embodiment is the so-called solution casting method, and includes a casting step of casting the above-described dope onto a support to form a cast film, and a volatilization step of volatilizing the solvent from the cast film. The optical film of the present embodiment can be manufactured using the dope prepared by mixing the above-described resin and solvent.

[0069] Examples of the support include an endless belt of stainless steel; a rotating metal drum; a metal sheet such as an aluminum or copper foil; and a plastic film such as a polyimide film or a polyester film (polyethylene terephthalate film).

[0070] When casting the dope, for example, an applicator such as a die coater, a doctor blade coater, a roll coater, a comma coater, or a lip coater may be used.

[0071] Examples of the method for volatilizing the solvent from the cast film include a method of heating the cast film within a temperature range in which no foaming marks occur on the optical film.

[0072] The heating temperature when volatilizing the solvent from the cast film is preferably 20 to 200°C, more preferably 20 to 150°C, and even more preferably 20 to 100°C. Thereby, while suppressing the generation of foaming marks, the drying efficiency of the solvent can be further improved, and the productivity of the optical film can be further enhanced.

[0073] The heating time when volatilizing the solvent from the cast film is preferably 5 to 120 minutes, and more preferably 10 to 80 minutes. Thereby, while suppressing the generation of foaming marks, the drying efficiency of the solvent can be further improved, and the productivity of the optical film can be further enhanced.

[0074] The residual solvent amount in the optical film after volatilizing the solvent from the cast film is preferably 0.1 to 60% by mass, more preferably 0.1 to 50% by mass, and even more preferably 0.1 to 45% by mass.

[0075] The residual solvent amount is calculated as follows. First, an optical film whose mass has been measured in advance is dried in an oven at 200°C for 1 hour, the mass of the dried optical film is measured, and the difference in the mass of the optical film before and after drying is calculated as the absolute content of the residual solvent (unit: g). Then, the calculated absolute content of the residual solvent (unit: g) is divided by the mass of the optical film before drying (unit: g) to obtain the residual solvent amount (mass%).

[0076] After the solvent is volatilized from the cast film, the optical film can be peeled off from the support. The optical film peeled off from the support is made into a film roll by a winder.

[0077] The optical film peeled off from the support is preferably dried again before being made into a film roll.

[0078] The drying temperature of the optical film is preferably 100 to 250°C, more preferably 120 to 230°C.

[0079] The drying time of the optical film is preferably 5 to 120 minutes, more preferably 10 to 80 minutes.

[0080] The residual solvent amount in the dried optical film is preferably 0.1 to 2.5 mass%, more preferably 0.1 to 1.5 mass%, still more preferably 0.1 to 1.3 mass%, particularly preferably 0.1 to 1.0 mass%, and particularly preferably 0.1 to 0.8 mass%. The residual solvent amount in the dried optical film can be calculated by the same method as the residual solvent amount in the above-described optical film.

[0081] The optical film is preferably stretched. Thereby, an optical film having sufficient strength can be obtained. The stretching of the optical film may be performed at any time after the optical film is peeled off from the support. For example, it may be stretched after being dried again and before being formed into a film roll. Also, after being formed into a film roll once, the film may be drawn out from the film roll and stretched.

[0082] Examples of the stretching method of the optical film include uniaxial stretching such as free-width uniaxial stretching and constant-width uniaxial stretching; and biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching.

[0083] The heating temperature in the stretching of the optical film is near the glass transition temperature (Tg) of the above-described resin. More specifically, it is preferably (Tg - 30) to (Tg + 100)°C, more preferably (Tg - 20) to (Tg + 50)°C, and still more preferably (Tg - 10) to (Tg + 30)°C.

[0084] The stretching speed in the stretching of the optical film is preferably 5 to 500% / min.

[0085] The stretching ratio in the stretching of the optical film is preferably in the range of 1.05 to 10 times in both the longitudinal and transverse directions.

[0086] The thickness of the optical film before stretching is preferably 40 to 200 μm, more preferably 50 to 150 μm, and still more preferably 60 to 120 μm.

[0087] The thickness of the optical film after stretching is preferably 15 to 50 μm, more preferably 20 to 45 μm, and still more preferably 25 to 40 μm.

[0088] The content of the resin in the optical film is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, and even more preferably 90 to 100% by mass. Thereby, an optical film having sufficient heat resistance, transparency, and strength can be obtained.

[0089] The optical film may contain the above-mentioned other polymers as needed. The optical film may contain only one kind of other polymer, or may contain two or more kinds of other polymers. The content of the other polymer in the optical film may be 0 to 50% by mass, may be 0 to 30% by mass, or may be 0 to 10% by mass.

[0090] The optical film may contain the above-mentioned additives as needed. The optical film may contain only one kind of additive, or may contain two or more kinds of additives. The content of the additive in the optical film may be 0 to 5% by mass, may be 0 to 2% by mass, or may be 0 to 0.5% by mass.

[0091] The optical film of the present embodiment can be suitably used for, for example, both flat panel displays and foldable displays. In particular, it can be suitably used as a film for a foldable display (for example, a cover window) that requires foldability.

Examples

[0092] Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples. However, the present disclosure is not limited by the examples. Also, various physical properties were measured and evaluated as follows.

[0093] [Weight average molecular weight (Mw) and number average molecular weight (Mn) of the resin] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the resin were measured in terms of polystyrene using gel permeation chromatography (GPC). The measuring apparatus and measuring conditions are as follows. Device Name: HLC-8220 GPC System manufactured by Tosoh Corporation Column Configuration on the Measurement Side: · Guard Column: TSKgel guardcolumn SuperHZ-L manufactured by Tosoh Corporation · Separation Column: Two TSKgel SuperHZM-M columns manufactured by Tosoh Corporation connected in series Column Configuration on the Reference Side: · Reference Column: TSKgel SuperH-RC manufactured by Tosoh Corporation Developing Solvent: Chloroform (manufactured by Wako Pure Chemical Industries, Ltd.; special grade) Flow Rate of Developing Solvent: 0.6 mL / min Standard Sample: TSK Standard Polystyrene (manufactured by Tosoh Corporation; PS-Oligomer Kit) Column Temperature: 40°C

[0094] [Glass Transition Temperature (Tg) of Resin] The glass transition temperature of the resin was measured in accordance with the provisions of JIS K 7121. Specifically, using a differential scanning calorimeter (manufactured by Rigaku Corporation; Thermo plus EVO DSC-8230), in a nitrogen gas atmosphere, a sample of approximately 10 mg was heated from room temperature to 200°C (heating rate: 20°C / min), and the measurement was performed by the starting point method from the DSC curve obtained. α-Alumina was used as the reference.

[0095] [Contents of Methyl Methacrylate and α-Methylene-γ-Butyrolactone in Resin] The contents of methyl methacrylate and α-methylene-γ-butyrolactone in the resin were measured using gas chromatography (GC). The measuring device and measuring conditions are as follows.

[0096] Device Name: GC-2014 manufactured by Shimadzu Corporation Column: DB-1 manufactured by Shimadzu Corporation

[0097] [Thickness of Optical Film] The thickness of the optical film was measured using a digital micrometer (manufactured by Mitutoyo Corporation; ID-C112).

[0098] [Residual Solvent Amount in the Optical Film] After measuring the mass of the prepared optical film, it was dried in an oven at 200 °C for 1 hour. The residual solvent amount (g) in the film was calculated from the difference between the film mass after drying and the film mass before drying. The calculated residual solvent amount was divided by the mass of the prepared optical film to obtain the residual solvent amount (% by mass) based on the total amount of the optical film.

[0099] Methyl methacrylate was obtained from Sumitomo Chemical Co., Ltd. α-Methylene-γ-butyrolactone was obtained from Fujifilm Wako Pure Chemical Corporation. Dilauroyl peroxide (Peroyl L) was obtained from NOF Corporation. t-Amyl peroxyisooctanoate (Luperox® 570) and t-Amyl peroxy-2-ethylhexanoate (Luperox® 575) were obtained from Arkema Kishida Co., Ltd. Ammonium polyoxyethylene distyrylphenyl ether sulfate (Hytenol® NF-08) was obtained from Daiichi Kogyo Seiyaku Co., Ltd.

[0100] In the following description, compound names are abbreviated and represented as follows. MMA: Methyl methacrylate MBL: α-Methylene-γ-butyrolactone LPO: Dilauroyl peroxide (Peroyl L) NF-08: Ammonium polyoxyethylene distyrylphenyl ether sulfate (Hytenol® NF-08) n-DM: n-Dodecyl mercaptan

[0101] The 10-hour half-life temperature of LPO is 62 °C, the 10-hour half-life temperature of Luperox® 570 is 96 °C, and the 10-hour half-life temperature of Luperox® 575 is 75 °C.

[0102] (Example 1) [Preparation of Resin 1] A reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe was prepared. 75 parts by mass of deionized water containing 0.25 part by mass of NF-08 was charged into a separate container. Then, a solution prepared in advance by mixing 37.5 parts by mass of MMA, 12.5 parts by mass of MBL, 0.25 part by mass of LPO (the first polymerization initiator), 0.25 part by mass of Luperox (registered trademark) 570 (the second polymerization initiator), and 0.05 part by mass of n-DM was added thereto. And the mixture in the container was stirred at 3000 rpm using a disperser (manufactured by Primix Corporation; Homomixer MARK II model 2.5). After adding 125 parts by mass of deionized water thereto, it was transferred to the reactor.

[0103] In the reactor, while continuing stirring and supplying nitrogen gas, the reaction solution was heated until it reached 65°C. The point when the internal temperature reached 65°C was regarded as the start of polymerization. After the liquid temperature reached the peak temperature due to self-heating, 2 hours after the start of polymerization, the reaction solution was heated to 90°C and stirred for 4 hours. Thus, the polymerization reaction was completed. At this time, the reaction rates of MMA and MBL were 99.6% and 99.8% respectively.

[0104] Thereafter, the reaction solution was cooled, the resin was collected by filtration, and further subjected to a drying process at 100°C for 10 hours using a hot air dryer to obtain Resin 1 (powder). The weight average molecular weight (Mw) of Resin 1 was 270,000, the number average molecular weight (Mn) was 125,000, and the glass transition temperature Tg was 127°C.

[0105] The contents of MMA and MBL contained in Resin 1 were measured. As a result, the content of MMA in Resin 1 was 0.20% by mass, and the content of MBL was 0.06% by mass.

[0106] <Preparation of Dope> The obtained Resin 1 was dissolved in a mixed solvent of methylene chloride and ethanol with a volume ratio of 9:1 so that the solid content became 28% by mass, and then filtered through a 10-μm filter to prepare a dope.

[0107] <Production of Optical Film A-1> Using a Baker applicator, the dope was cast onto a stainless steel plate to form a cast film. The gap of the Baker applicator was set to 380 μm. Using a hot plate, the cast film was heated at 25 °C for 10 minutes to obtain an optical film A-1. After peeling the optical film A-1 from the stainless steel plate, the residual solvent amount of the optical film A-1 was determined. The residual solvent amount of the optical film A-1 was 40% by mass.

[0108] <Production of Optical Film B-1> An optical film was produced in the same manner as the production of optical film A. The top, bottom, left, and right of the obtained optical film were fixed respectively, and heated in an oven at 120 °C for 60 minutes to obtain an optical film B-1 with a thickness of 100 μm. The residual solvent amount of the optical film B-1 was determined. The residual solvent amount of the optical film B was 1.0% by mass.

[0109] (Example 2) Resin 2 (powder) was prepared in the same manner as in Example 1, except that the second polymerization initiator was Luperox (registered trademark) 575. The reaction rates of MMA and MBL when the polymerization reaction was completed were 99.3% and 99.7% respectively. The weight average molecular weight (Mw) of resin 2 was 267000, the number average molecular weight (Mn) was 124000, and the glass transition temperature Tg was 126 °C.

[0110] The contents of MMA and MBL contained in resin 2 were measured. As a result, the content of MMA in resin 2 was 0.32% by mass, and the content of MBL was 0.08% by mass.

[0111] A dope and an optical film A-2 were prepared in the same procedure as in Example 1, and the residual solvent amount of the optical film A-2 was determined. Also, an optical film B-2 was prepared in the same procedure as in Example 1, and the residual solvent amount was determined. The residual solvent amount of the optical film A-2 was 45% by mass. The residual solvent amount of the optical film B-2 was 1.1% by mass.

[0112] (Comparative Example) <Production of Resin 3> A reactor equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe was prepared. 75 parts by mass of deionized water containing 0.25 part by mass of NF-08 was charged into a separate container. Then, a liquid mixture prepared in advance by mixing 37.5 parts by mass of MMA, 12.5 parts by mass of MBL, and 0.50 part by mass of LPO (the first polymerization initiator) was added thereto. And the mixture in the container was stirred at 3000 rpm using a disperser (manufactured by Primix Corporation; Homomixer MARK II model 2.5). After adding 125 parts by mass of deionized water thereto, it was transferred to the reactor.

[0113] In the reactor, while continuing stirring and supplying nitrogen gas, the reaction solution was heated until it reached 65°C. The time when the internal temperature reached 65°C was regarded as the start of polymerization. After the liquid temperature reached the peak temperature due to self-heating, 2 hours after the start of polymerization, the reaction solution was heated to 90°C and stirred for 4 hours. In this way, the polymerization reaction was completed. The reaction rates of MMA and MBL at this time were 98.1% and 98.0% respectively.

[0114] Thereafter, the reaction solution was cooled, the resin was collected by filtration, and further subjected to a drying process at 100°C for 10 hours using a hot air dryer to obtain Resin 3 (powder). The weight average molecular weight (Mw) of the resin was 270,000, the number average molecular weight (Mn) was 125,000, and the glass transition temperature Tg was 126°C.

[0115] The contents of MMA and MBL contained in Resin 3 were measured. As a result, the content of MMA in Resin 3 was 0.68% by mass, and the content of MBL was 0.35% by mass.

[0116] A dope and an optical film A-3 were prepared in the same procedure as in Example 1, and the residual solvent amount of the optical film A-3 was determined. Also, an optical film B-3 was prepared in the same procedure as in Example 1, and the residual solvent amount of the optical film B-3 was determined. The residual solvent amount of the optical film A-3 was 70% by mass. The residual solvent amount of the optical film B-3 was 2.9% by mass.

[0117] When comparing the residual solvent amounts of the optical films A and B produced in each of the examples and the comparative examples, it can be seen that when the optical films were produced under the same conditions, the residual solvent amount was less when the resin of the examples was used. As a result, the drying efficiency of the dope was higher and the productivity of the optical film was excellent when the resins of the examples obtained using the first polymerization initiator and the second polymerization initiator were used, compared to the case of the resin obtained using only the first polymerization initiator.

Claims

1. A method for producing a resin containing a structural unit derived from an α-methylene lactone and a structural unit derived from an alkyl (meth)acrylate, comprising the steps of: The method includes a polymerization step of suspension-polymerizing a monomer including α-methylene lactone and an alkyl (meth)acrylate in a solvent in the presence of a first polymerization initiator, a second polymerization initiator, and an emulsifier; The 10-hour half-life temperature T of the second polymerization initiator ２ is the 10-hour half-life temperature T of the first polymerization initiator １ More than 10 degrees higher than The polymerization step is performed by adjusting the temperature of the reaction solution to be subjected to suspension polymerization (T １ -10) ~ (T １ a first temperature holding step of holding the mixture at a temperature of +10) ° C. and initiating polymerization; and a second temperature holding step in which, after a temperature rise in the reaction liquid occurs due to heat of polymerization, the temperature of the reaction liquid is held at a temperature that is 10°C or more higher than the temperature of the reaction liquid in the first temperature holding step, and further polymerization is performed.

2. The 10-hour half-life temperature T of the first polymerization initiator １ The method for producing a resin according to claim 1, wherein the temperature is 53 to 63°C.

3. 3. The method for producing a resin according to claim 1, wherein in the first temperature holding step, the temperature of the reaction liquid is held at 55 to 73°C.

4. The 10-hour half-life temperature T of the second polymerization initiator ２ The method for producing a resin according to claim 1, characterized in that the temperature is 73 to 103°C.

5. The method for producing a resin according to claim 1 or 4, wherein in the second temperature holding step, the temperature of the reaction liquid is held at 75 to 95°C.

6. The method for producing a resin according to claim 1 or 2, characterized in that the amount of the second polymerization initiator used is 5 to 300 parts by mass when the amount of the first polymerization initiator used is 100 parts by mass.

7. 3. The method for producing a resin according to claim 1, wherein the first polymerization initiator and the second polymerization initiator are organic peroxides.

8. 3. A method for producing a dope, comprising: a step of mixing the resin obtained by the method according to claim 1 or 2 with a solvent to obtain a dope.

9. A casting step of casting the dope obtained by the method according to claim 8 onto a support to form a casting film; a volatilization step of volatilizing the solvent from the casting membrane; A method for producing an optical film, comprising:

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