JP7803889B2 - Method for producing imide structure-containing acrylic resin - Google Patents

Description

The present invention relates to a method for producing an acrylic resin containing an imide structure.

Acrylic resins are excellent polymers used in large quantities in a variety of industrial fields due to their excellent transparency, color tone, appearance, weather resistance, gloss, and processability. They are used in a variety of applications, including polarizer protective films for liquid crystal display devices used in mobile phones, smartphones, TVs, and other displays; exterior materials for electrical appliances such as automobile interiors and exteriors; and interior and exterior building materials such as building flooring. Taking advantage of their excellent optical properties, acrylic resins have recently been expected to be used as insulating substrate materials for high-frequency printed circuits and antenna substrates. As their applications expand, there is a demand for them to be endowed with even greater heat resistance.

For example, Patent Document 1 proposes an imide structure-containing acrylic resin having an aromatic group on the nitrogen of the imide structure, and discloses that it has high heat resistance and low retardation properties.

JP 2016-65148 A

However, the inventors have found that when an aromatic amine compound is used as an imidizing agent, the manufacturing method described in Patent Document 1 may not be able to efficiently imidize the desired imide structure-containing acrylic resin. There is also room for improvement in yield.

The present invention aims to provide a method for efficiently producing an imide structure-containing acrylic resin by imidizing a (meth)acrylic polymer with an aromatic amine compound.

As a result of extensive research, the present inventors have discovered that when imidizing a (meth)acrylic polymer using an aromatic amine compound as an imidizing agent, the imidization reaction proceeds efficiently by including at least one imidization accelerator selected from the group consisting of ammonia, primary amines, and secondary amines, and by ensuring that the pKa of the imidization accelerator is 6 or higher. Specifically, one aspect of the present invention relates to the following:

(I) A method for producing an imide structure-containing acrylic resin having a structure represented by the following formula (1), comprising a step of heating a raw material composition containing a (meth)acrylic polymer, an imidizing agent, and an imidization accelerator, wherein the imidizing agent contains an aromatic amine compound, the imidization accelerator contains at least one selected from the group consisting of ammonia, primary amines, and secondary amines, and the pKa of the imidization accelerator is 6 or greater.

(In formula (1), ^R1 and ^R2 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and ^R3 represents an aromatic hydrocarbon group or a heteroaromatic group.)

(II) The method for producing an imide structure-containing acrylic resin according to (I), wherein the primary amine has a structure represented by the following formula (2):
R ⁴ NH ₂ (2)
(In formula (2), ^R4 is an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an arylalkyl group having 6 to 18 carbon atoms.)

(III) The method for producing an imide structure-containing acrylic resin according to (I), wherein the secondary amine has a structure represented by the following formula (3):
HN(R ⁵ )(R ⁶ ) (3)
(In formula (3), ^R5 and ^R6 each independently represent an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an arylalkyl group having 6 to 18 carbon atoms. ^R5 and ^R6 may also form a ring structure.)

(IV) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (III), wherein the pKa of the imidization accelerator is 8 or higher.

(V) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (IV), wherein the imidization accelerator comprises at least one selected from the group consisting of ammonia, methylamine, ethylamine, diethylamine, dimethylamine, N-methylethylamine, N-methylpropylamine, N-methylbutylamine, pyrrolidine, and piperidine.

(VI) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (V), wherein the imidizing agent includes at least one selected from the group consisting of aniline, toluidine, anisidine, aminopyridine, aminobiphenyl, and aminonaphthalene.

(VII) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (VI), wherein the raw material composition contains 1 to 80 parts by weight of the imidization accelerator per 100 parts by weight of the (meth)acrylic polymer.

(VIII) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (VII), wherein the raw material composition contains 0.1 mol to 10 mol of the imidization accelerator per 1 mol of the imidization agent.

(IX) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (VIII), wherein the raw material composition contains 1 to 100 parts by weight of the imidizing agent per 100 parts by weight of the (meth)acrylic polymer.

(X) A method for producing an imide structure-containing acrylic resin according to any one of claims (I) to (IX), wherein the (meth)acrylic polymer contains a methacrylic acid alkyl ester unit.

(XI) A method for producing an imide structure-containing acrylic resin described in (X), wherein the methacrylic acid alkyl ester unit has an alkyl group having 1 to 8 carbon atoms.

(XII) A method for producing an imide structure-containing acrylic resin described in (X) or (XI), wherein the (meth)acrylic polymer has a content of methacrylic acid alkyl ester units of 50% by weight or more relative to the total amount of the (meth)acrylic polymer.

(XIII) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (XII), comprising a step of mixing a mixture of the imidization accelerator and the imidization agent with the (meth)acrylic polymer.

(XIV) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (XIII), wherein the temperature in the step of heating the raw material composition containing the (meth)acrylic polymer, the imidizing agent, and the imidization accelerator is 180°C to 320°C.

(XV) A method for producing an imide structure-containing acrylic resin described in any one of (I) to (XIV), wherein the pressure in the step of heating the raw material composition containing the (meth)acrylic polymer, the imidizing agent, and the imidization accelerator is 0.1 MPa to 50 MPa.

The present invention provides a method for efficiently producing an imide structure-containing acrylic resin by imidizing a (meth)acrylic polymer with an aromatic amine compound.

The following describes an embodiment of the present invention.

The method for producing an imide structure-containing acrylic resin of this embodiment includes a step of heating a raw material composition containing a (meth)acrylic polymer, an imidizing agent, and an imidization accelerator.

(i) (Meth)acrylic polymer The (meth)acrylic polymer is a polymer obtained mainly by polymerizing acrylic acid, methacrylic acid, and derivatives thereof, and is not particularly limited as long as it does not impair the effects of the present invention, and any known (meth)acrylic polymer can be used. For example, the (meth)acrylic polymer can be produced by polymerizing a monomer composition containing a (meth)acrylic acid ester as a main component.

Examples of (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate, as well as aryl (meth)acrylates, alkyl aryl (meth)acrylates, and alicyclic alkyl (meth)acrylates having 6 to 12 carbon atoms such as phenyl (meth)acrylate, benzyl (meth)acrylate, and cyclohexyl (meth)acrylate. These may be used alone or in combination of two or more.

From the viewpoint of improving the heat resistance of the resulting imide structure-containing acrylic resin, it is preferable that the (meth)acrylic polymer contains methacrylic acid alkyl ester units.

Furthermore, since this allows for efficient production of an imide structure-containing acrylic polymer, it is preferable that the (meth)acrylic polymer contain (meth)acrylic acid alkyl ester units having an alkyl group having 1 to 8 carbon atoms. Among these, methyl (meth)acrylate units, ethyl (meth)acrylate units, n-propyl (meth)acrylate units, and n-butyl (meth)acrylate units are more preferred, with methyl (meth)acrylate units being particularly preferred.

There are no particular restrictions on the content of (meth)acrylic acid alkyl ester units in the (meth)acrylic polymer, but from the viewpoint of heat resistance, it is preferably 50% by weight or more, more preferably 75% by weight or more, and particularly preferably 90% by weight or more.

To further improve the heat resistance of the resulting imide structure-containing acrylic resin, a (meth)acrylic polymer having a ring structure in the main chain may be used. Examples of ring structures include a lactone ring structure, a maleic anhydride structure, a glutaric anhydride structure, a maleimide structure, and a glutarimide structure represented by the following formula (1):

(In the formula (1), ^R1 and ^R2 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and ^R3 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms.)

Methods for introducing a ring structure into the main chain of a (meth)acrylic polymer include known methods. Examples of (meth)acrylic polymers having a lactone ring structure include those described in JP 2004-168882 A and JP 2006-171464 A. Examples of (meth)acrylic polymers having a maleimide structure include (meth)acrylic polymers having N-substituted maleimide units, such as those described in JP 2007-31537 A. Examples of (meth)acrylic polymers containing glutaric anhydride structures include those described in JP 2004-70296 A, JP 2004-307834 A, JP 2008-74918 A, and WO 2007/26659 A.

The glass transition temperature (Tg) of a (meth)acrylic polymer having a ring structure in its main chain is not particularly limited, but is preferably 110°C or higher, more preferably 115°C or higher, and particularly preferably 120°C or higher. If the temperature is below this range, the heat resistance of the molded article will be poor, resulting in significant changes in physical properties at high temperatures and a narrower range of applications.

There are no particular restrictions on the content of ring structures in (meth)acrylic resins having ring structures in the main chain, but considering the balance between heat resistance and physical properties, there is no particular restriction as long as it is 2% by weight or more, with 2.5% by weight or more being more preferable. There is no particular upper limit as long as moldability is possible, and it can be selected appropriately based on the balance with physical properties, but 70% by weight or less is preferable, 50% by weight or less is more preferable, and 30% by weight or less is particularly preferable.

In addition to the monomers mentioned above, it is also possible to include aromatic monomers such as styrene and methylstyrene, nitrile monomers such as acrylonitrile and methacrylonitrile, and maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide.

The structure of the (meth)acrylic polymer is not particularly limited and may be any of a linear polymer, block polymer, core-shell polymer, branched polymer, ladder polymer, crosslinked polymer, etc. In the case of a block polymer, it may be an A-B type, an A-B-C type, an A-B-A type, or any other type of block polymer. In the case of a core-shell polymer, it may consist of only one core layer and one shell layer, or each may consist of multiple layers.

(ii) Imidizing Agent The imidizing agent is not particularly limited as long as it is an aromatic amine compound capable of producing the glutarimide unit represented by the general formula (1) above. Here, the aromatic amine compound refers to an organic compound in which hydrogen atoms in an aromatic ring are replaced with amino groups, and the aromatic ring may be a heteroaromatic ring containing atoms other than carbon. Specific examples include aniline, toluidine, anisidine, xylidine, trimethylaniline, trichloroaniline, aminopyridine, aminobiphenyl, aminonaphthalene, aminoanthracene, and aminotetracene. These may be used alone or in combination of two or more.

The number of atoms constituting the aromatic ring of the aromatic amine compound is preferably 5 to 18, and more preferably 5 to 10, as this provides good reaction efficiency and good physical properties for the resulting imide structure-containing acrylic resin.

Of the imidizing agents exemplified above, one or more selected from aniline, toluidine, anisidine, xylidine, aminopyridine, aminobiphenyl, and aminonaphthalene are preferred due to their good reactivity with (meth)acrylic polymers and the heat resistance of the resulting imide structure-containing acrylic resin. One or more selected from aniline, toluidine, anisidine, and xylidine are more preferred, and aniline is particularly preferred due to its excellent balance of cost and physical properties.

In this imidization process, the proportion of glutarimide units in the resulting imide structure-containing acrylic resin can be adjusted by adjusting the addition ratio of the above-mentioned imidization agent.

In addition, by adjusting the degree of imidization, it is possible to adjust the physical properties of the resulting imide structure-containing acrylic resin and the optical properties of the optical film obtained by molding a resin composition containing the imide structure-containing acrylic resin.

The content of the imidizing agent in the raw material composition described above can be adjusted appropriately depending on the required properties. For example, it can be adjusted appropriately depending on the required properties as long as it is 1 part by weight or more per 100 parts by weight of the (meth)acrylic polymer, and 4 parts by weight or more is more preferable. If it is less than 1 part by weight, the heat resistance of the resulting resin composition containing the imide structure-containing acrylic resin may decrease. The upper limit can be selected appropriately in relation to moldability and physical properties, but from the perspective of ease of handling, 100 parts by weight or less is preferred, 80 parts by weight or less is more preferred, and 70 parts by weight or less is even more preferred.

(iii) Imidization Accelerator The imidization accelerator in this embodiment contains at least one selected from the group consisting of ammonia, primary amines, and secondary amines, and is not particularly limited as long as it has a pKa of 6 or more.

The primary amine preferably has a structure represented by the following formula (2):
R ⁴ NH ₂ (2)
(In formula (2), ^R4 is an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an arylalkyl group having 6 to 18 carbon atoms.)

Specific examples include linear or branched alkylamines such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, and n-hexylamine; cycloalkylamines such as cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine; and arylalkylamines such as benzylamine and phenethylamine.

The secondary amine preferably has a structure represented by the following formula (3):
HN(R ⁵ )(R ⁶ ) (3)
(In formula (3), ^R5 and ^R6 each independently represent an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an arylalkyl group having 6 to 18 carbon atoms. ^R5 and ^R6 may also form a ring structure.)

Specific examples include linear or branched dialkylamines such as dimethylamine, diethylamine, N-methylethylamine, N-methylpropylamine, N-methylbutylamine, and diisopropylamine; alicyclic amines such as pyrrolidine, piperidine, and morpholine, dicyclohexylamine, and dibenzylamine.

Preferred imidization accelerators include ammonia, methylamine, ethylamine, diethylamine, dimethylamine, N-methylethylamine, N-methylpropylamine, N-methylbutylamine, pyrrolidine, and piperidine.

In addition, although ammonia and primary amines are the aforementioned imidization accelerators, they may themselves react with the (meth)acrylic polymer to form an imide structure. Therefore, from the perspective of minimizing side reactions and obtaining the desired imide structure-containing acrylic resin, secondary amines such as diethylamine, dimethylamine, N-methylethylamine, N-methylpropylamine, N-methylbutylamine, pyrrolidine, and piperidine are more preferred, with N-methylpropylamine, diethylamine, and dimethylamine being particularly preferred.

The pKa of the imidization accelerator is not particularly limited as long as it is 6 or more, but is preferably 8 or more, more preferably 9 or more, and particularly preferably 10 or more, because it has a high effect of promoting imidization. The upper limit is not particularly limited, but is, for example, preferably 14 or less, more preferably 13 or less. Here, pKa is a value defined by the following formula.
pKa=-log ₁₀ Ka
The acid dissociation constant (Ka) in the reaction AH→A ⁻ +H ⁺ is a value calculated by Ka=[A ⁻ ][H ⁺ ]/[AH].

The content of the imidization accelerator in the raw material composition can be adjusted as needed depending on the desired properties. For example, it may be 1 part by weight or more, and 3 parts by weight or more is more preferable, per 100 parts by weight of the (meth)acrylic polymer. If it is less than 1 part by weight, the effect of promoting imidization is small, and it may not be possible to obtain an imide structure-containing acrylic resin with the desired imidization rate. The upper limit can be selected as appropriate in relation to moldability and physical properties. From the perspectives of ease of handling and preventing deterioration of the mechanical properties of molded products due to residual imidization accelerator, 80 parts by weight or less is preferable, 60 parts by weight or less is more preferable, and 40 parts by weight or less is particularly preferable.

The content of the imidization accelerator in the raw material composition is preferably 0.1 to 10 moles per mole of the imidizing agent. From the viewpoint of promoting efficient imidization and improving the yield of the imide structure-containing acrylic resin, the lower limit is preferably 0.5 moles or more, and 0.8 moles or more is particularly preferred. The upper limit is preferably 10 moles or less, more preferably 5 moles or less, and particularly preferably 3 moles or less.

(iv) Imide Structure-Containing Acrylic Resin The imide structure-containing acrylic resin of the present embodiment contains a structure represented by the following general formula (1).

(In formula (1), ^R1 and ^R2 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and ^R3 represents an aromatic hydrocarbon group or a heteroaromatic group.)

In the structure represented by formula (1), ^R1 and ^R2 are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. Examples of alkyl groups having 1 to 8 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, an n-octyl group, and a 2-ethylhexyl group. Among these, a hydrogen atom or an alkyl group having 1 to 4 carbon atoms is preferred because of their excellent heat resistance.

In the structure represented by formula (1), ^R3 is an aromatic hydrocarbon group or a heteroaromatic group. The number of atoms constituting the aromatic ring is preferably 5 to 18, and more preferably 5 to 10. Specific examples include a phenyl group, a tolyl group, anisyl group, a xylyl group, a trimethylphenyl group, a trichlorophenyl group, a pyridyl group, a biphenyl group, a naphthyl group, and an anthryl group. Among these, phenyl group, tolyl group, anisyl group, xylyl group, pyridyl group, biphenyl group, and naphthyl group are preferred because of their excellent heat resistance, and phenyl group, tolyl group, anisyl group, and xylyl group are more preferred.

In addition, the imide structure-containing acrylic resin may contain two or more types of structures represented by formula (1).

The weight average molecular weight of the imide structure-containing acrylic resin is not particularly limited, but is preferably 1 x 10 ⁴ to 5 x 10 ⁵ , and more preferably 5 x 10 ⁴ to 3 x 10 ^5. Within the above range, there is no decrease in moldability or insufficient mechanical strength during film processing.

The glass transition temperature of the imide structure-containing acrylic resin is not particularly limited, but is preferably 120°C or higher, more preferably 125°C or higher, even more preferably 130°C or higher, and particularly preferably 135°C or higher. If the temperature is below this range, the heat resistance of molded articles or films will be poor, resulting in significant changes in physical properties at high temperatures and a narrower range of applications. The glass transition temperature can be determined, for example, by using 10 mg of resin and measuring it using a differential scanning calorimeter (DSC, Shimadzu Corporation DSC-50 model) in a nitrogen atmosphere at a heating rate of 20°C/min, using the midpoint method.

The imidization rate of the imide structure-containing acrylic resin can be adjusted appropriately depending on the required properties and is not particularly limited. However, since this increases heat resistance, the lower limit of the imidization rate is preferably 10% or more, more preferably 15% or more, and particularly preferably 20% or more. Furthermore, from the perspective of preventing deterioration of handleability due to increased viscosity, the upper limit is preferably 80% or less, more preferably 75% or less, and particularly preferably 70% or less. Within the above range, a resin composition with an excellent balance of heat resistance and viscosity can be obtained. The imidization rate of the imide structure-containing acrylic resin can be determined using the method described below.

The imidization ratio of the imide structure-containing acrylic resin can be determined by measuring the IR spectrum using a Fourier transform infrared spectrophotometer (FI/IR-4100 manufactured by JASCO Corporation). The imidization ratio is determined from the intensity ratio of the absorption attributable to the ester carbonyl group near 1720 cm ⁻¹ to the absorption attributable to the imide carbonyl group near 1680 cm ⁻¹ . Here, the imidization ratio is the proportion of the imide carbonyl group in the total of the ester carbonyl group and the imide carbonyl group.

The acid value of an imide structure-containing acrylic resin represents the content of carboxylic acid units and acid anhydride units in the imide structure-containing acrylic resin. The acid value can be calculated, for example, by the titration method described in WO 2005/054311. In this embodiment, the acid value of the imide structure-containing acrylic resin is preferably 0.10 to 1.00 mmol/g. If the acid value is within the above range, an imide structure-containing acrylic resin with an excellent balance of heat resistance, mechanical properties, and moldability can be obtained.

In particular, from the viewpoint of molding processability, the content of carboxylic acid among the acid components is preferably 0.25 mmol/g or less, and more preferably 0.20 mmol/g or less.

The amount of carboxylic acid can be measured by using the acid value (DMSO acid value) obtained by changing the solvent from methanol to dimethyl sulfoxide in the titration method described in WO 2005/054311. Specifically, the amount of carboxylic acid can be calculated using the formula: (amount of carboxylic acid) = 2 × (acid value) - (DMSO acid value).
The above formula can be applied because in titration with methanol, the acid anhydride is counted as one molecule, whereas in titration with dimethyl sulfoxide, the acid anhydride is counted as two molecules.

From the viewpoint of thermal stability, the acrylic acid ester units contained in the imide structure-containing acrylic resin in this embodiment are preferably less than 1% by weight, more preferably less than 0.5% by weight, and particularly preferably less than 0.3% by weight. There is no particular lower limit, and the lower the content, the better, and it is even more preferable that no acrylic acid ester units are contained.

Furthermore, the imide structure-containing acrylic resin in this embodiment preferably has an orientation birefringence value of −0.5×10 ⁻³ to 0.5×10 ⁻³ , and more preferably −0.25×10 ⁻³ to 0.25×10 ⁻³ .

If the orientation birefringence is within the above range, birefringence will not occur during molding processing even when the environment changes, and stable optical properties can be obtained.

In this specification, unless otherwise specified, the term "orientation birefringence" refers to the birefringence that appears when a thermoplastic resin is stretched 100% at a temperature 5°C higher than the glass transition temperature. Orientation birefringence (Δn) is calculated using the formula: Δn = nx - ny = Re/d
and can be measured using a retardation meter. In the above formula, nx and ny represent the refractive indexes in the X-axis and Y-axis directions, respectively, when the direction in which the in-plane refractive index is maximum is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the thickness direction of the film is the Z-axis. Furthermore, Re represents the in-plane retardation, and d represents the thickness of the film.

The photoelastic coefficient of the imide structure-containing acrylic resin is preferably 20×10 ⁻¹² m ² /N or less, more preferably 10×10 ⁻¹² m ² /N or less, and even more preferably 5×10 ⁻¹² m ² /N or less.

If the absolute value of the photoelastic coefficient is greater than 20×10 ⁻¹² m ² /N, light leakage is likely to occur, and this tendency becomes more pronounced in particular in high-temperature, high-humidity environments.

When an external force is applied to an isotropic solid to cause stress (ΔF), the solid temporarily exhibits optical anisotropy and birefringence (Δn). The ratio of stress to birefringence is called the photoelastic coefficient (c), and is expressed by the formula: c = Δn/ΔF
It is shown as follows.

In this embodiment, the photoelastic coefficient is a value measured using the Sénarmont method at a wavelength of 515 nm at 23°C and 50% RH.

(v) Method for Producing Imide Structure-Containing Acrylic Resin The method for producing an imide structure-containing acrylic resin of the present embodiment includes a step (imidization step) of heating a raw material composition containing a (meth)acrylic polymer, an imidizing agent, and an imidization accelerator, thereby producing an imide structure-containing acrylic resin.

The processing method for the imidization step is not particularly limited, and any conventionally known method can be used. For example, the (meth)acrylic polymer can be imidized to produce an imide structure-containing acrylic resin by reacting the polymer while heating and melting it using an extruder or a batch-type reaction tank (pressure vessel).

When using an extruder to heat and melt the raw material composition containing the (meth)acrylic polymer, imidization agent, and imidization accelerator, there are no particular restrictions on the extruder used, and various extruders can be used. Specifically, for example, a single-screw extruder, twin-screw extruder, or multi-screw extruder can be used.

Among these, it is preferable to use a twin-screw extruder. A twin-screw extruder can facilitate mixing of the imidization agent and imidization accelerator with the (meth)acrylic polymer.

Twin-screw extruders include non-intermeshing co-rotating, intermeshing co-rotating, non-intermeshing counter-rotating, and intermeshing counter-rotating types. Among these, intermeshing co-rotating types are preferred. Intermeshing co-rotating twin-screw extruders are capable of high-speed rotation, further facilitating the mixing of the imidizing agent and imidization accelerator with the (meth)acrylic polymer.

The method for mixing the (meth)acrylic polymer, imidizing agent, and imidization accelerator is not particularly limited, but the imidizing agent and imidization accelerator may be mixed together in advance and then mixed with the (meth)acrylic polymer, or the imidizing agent and imidization accelerator may be mixed separately. In this case, the imidizing agent may be mixed first, or the imidization accelerator may be mixed first.

The extruders exemplified above may be used alone or in combination with multiple extruders connected in series. For example, the tandem reactive extruder described in JP 2008-273140 A can be used.

When imidization is carried out in an extruder, for example, the raw resin (meth)acrylic polymer is fed into the raw material inlet of the extruder, the resin is melted, and the cylinder is filled with the melted resin. After that, a mixture of the imidization agent and the imidization accelerator is injected into the extruder using an additive pump, thereby allowing the imidization reaction to proceed in the extruder.

In this case, imidization is preferably carried out at a reaction zone temperature (resin temperature) in the extruder of 180°C to 320°C, and even more preferably at 220°C to 300°C. If the reaction zone temperature (resin temperature) is below 180°C, the imidization reaction hardly progresses, and heat resistance tends to decrease. If the reaction zone temperature exceeds 320°C, resin decomposition becomes significant, and the flex resistance of films that can be formed from the resulting imide structure-containing acrylic resin tends to decrease. Here, the reaction zone in the extruder refers to the region in the extruder cylinder between the injection position of the imidization agent and the resin discharge port (die section).

Imidization can be promoted by extending the reaction time in the reaction zone of the extruder. The reaction time in the reaction zone of the extruder is preferably longer than 10 seconds, and more preferably longer than 30 seconds. Reaction times of 10 seconds or less may result in little or no imidization.

The resin pressure in the extruder is preferably in the range of 0.1 MPa to 50 MPa, and more preferably in the range of 1 MPa to 30 MPa. If it is less than 0.1 MPa, the solubility of the imidizing agent is low, and the reaction tends to be inhibited. Furthermore, if it is 50 MPa or more, the mechanical pressure limit of a typical extruder will be exceeded, requiring special equipment, which is undesirable from a cost perspective.

When using an extruder, it is preferable to equip it with a vent hole that can reduce the pressure to below atmospheric pressure in order to remove unreacted imidizing agent, imidization accelerator, and by-products. This configuration makes it possible to remove unreacted imidizing agent and imidization accelerator, as well as by-products and monomers such as methanol and tertiary amines.

In addition, instead of an extruder, reaction equipment suitable for high viscosity, such as a horizontal twin-screw reaction apparatus like the Vivolac manufactured by Sumitomo Heavy Industries, Ltd., or a vertical twin-screw stirring tank like the Superblend, can also be suitably used to produce the above-mentioned imide structure-containing acrylic resin.

When the above-mentioned imide structure-containing acrylic resin is produced using a batch reaction tank (pressure vessel), the structure of the batch reaction tank (pressure vessel) is not particularly limited.

Specifically, the (meth)acrylic polymer may be melted by heating and stirred, and may have a structure that allows the imidization agent and imidization accelerator to be added, but it is preferable that the structure has good stirring efficiency.

This type of batch reactor (pressure vessel) can prevent the resin viscosity from increasing as the reaction progresses, resulting in insufficient mixing. An example of a batch reactor (pressure vessel) with this type of structure is the Max Blend mixing vessel manufactured by Sumitomo Heavy Industries, Ltd.

Specific examples of imidization methods include known methods such as those described in JP-A-2008-273140 and JP-A-2008-274187.

(Esterification step)
The method for producing an imide structure-containing acrylic resin according to the present embodiment can include a step of treating with an esterifying agent in addition to the imidization step, which allows the acid value of the imide structure-containing acrylic resin obtained in the imidization step to be adjusted within a desired range. Examples of the esterifying agent include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluene sulfonate, methyl trifluoromethyl sulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl-t-butylsilyl chloride, isopropenyl acetate, dimethyl urea, tetramethylammonium hydroxide, dimethyldiethoxysilane, tetra-n-butoxysilane, dimethyl(trimethylsilane) phosphite, trimethyl phosphite, trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether. Among these, dimethyl carbonate and trimethyl orthoacetate are preferred from the viewpoints of cost, reactivity, etc., and dimethyl carbonate is preferred from the viewpoint of cost.

In this esterification process, the amount of esterifying agent is preferably 0 to 12 parts by weight, and more preferably 0 to 8 parts by weight, per 100 parts by weight of the (meth)acrylic polymer.

If the esterification agent is within the above range, the acid value can be adjusted to an appropriate range. On the other hand, if it is outside the above range, unreacted esterification agent may remain in the resin, which may cause foaming or odor when the resin is molded.

In addition to the above esterifying agent, a catalyst can also be used. There are no particular limitations on the type of catalyst, but examples include aliphatic tertiary amines such as trimethylamine, triethylamine, and tributylamine. Among these, triethylamine is preferred from the standpoint of cost, reactivity, etc.

In this esterification step, it is also possible to perform only a heat treatment, etc., without treating with an esterifying agent. If only a heat treatment (kneading/dispersing the molten resin in the extruder) is performed, some or all of the carboxylic acids can be converted to acid anhydride groups through dehydration reactions between carboxylic acids in the imide structure-containing acrylic resin, which are by-produced in the imidization step, and/or dealcoholization reactions between carboxylic acids and alkyl ester groups. In this case, the aforementioned catalyst can also be used.

Even when treating with an esterifying agent, it is possible to promote the formation of acid anhydride groups by heat treatment.

(devolatilization process, filtration process)
The imide structure-containing acrylic resin that has undergone the imidization step and the esterification step contains unreacted imidization agent, imidization accelerator, esterification agent, volatile components by-produced by the reaction, resin decomposition products, etc., and therefore, it is possible to equip the resin with a vent hole that can reduce the pressure to below atmospheric pressure.

It is also possible to install a filter at the end of the extruder to reduce foreign matter in the imide structure-containing acrylic resin. It is preferable to install a gear pump before the filter to increase the pressure of the imide structure-containing acrylic resin. The preferred type of filter is a stainless steel leaf disc filter, which is capable of removing foreign matter from molten polymer, and the preferred filter element is a fiber type, powder type, or a combination of these.

(vi) Imide Structure-Containing Acrylic Resin Composition The imide structure-containing acrylic resin of this embodiment may be used to form an imide structure-containing acrylic resin composition by adding, as necessary, commonly used weather resistance stabilizers such as antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, and radical scavengers, as well as catalysts, plasticizers, lubricants, antistatic agents, colorants, shrinkage inhibitors, antibacterial and deodorizing agents, either singly or in combination, within a range that does not impair the object of the present invention. Furthermore, these additives can also be added when the imide structure-containing acrylic resin is molded and processed.

The imide structure-containing acrylic resin composition of this embodiment preferably contains an ultraviolet absorber. The imide structure-containing acrylic resin composition of this embodiment has good compatibility with ultraviolet absorbers, allowing for a wider range of applications. Examples of ultraviolet absorbers include triazine-based compounds, benzotriazole-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, benzoxazine-based compounds, and oxadiazole-based compounds. Among these, triazine-based compounds are preferred in terms of ultraviolet absorption performance relative to the amount added. Any commercially available triazine-based compound can be used.

The UV absorber has a maximum absorption wavelength of 300 nm or more and 370 nm or less. When exposed to UV light, an imide structure-containing acrylic resin composition containing such a UV absorber effectively suppresses degradation caused by UV-A rays (wavelengths of 320 nm or more and 400 nm or less). Therefore, a relatively small amount of UV absorber can be added, and bleed-out due to increased amounts of UV absorber is unlikely to occur.

The UV absorber must have a 1% weight loss temperature of 350°C or higher under a nitrogen atmosphere. Triazine-based compounds are preferred due to their high heat resistance and large molar absorption coefficient. The use of triazine-based compounds reduces the amount added and also reduces mold (roll, etc.) contamination during processing. Furthermore, UV absorbers using triazine-based compounds can enhance thermal stability without the addition of conventional heat stabilizers, as described in JP 2014-95926 A.

Examples of ultraviolet absorbers using such triazine-based compounds include Tinuvin 1577, Tinuvin 460, Tinuvin 477, Tinuvin 479 (all manufactured by BASF) and LA-F70 (manufactured by ADEKA).

When the imide structure-containing acrylic resin composition of this embodiment contains an ultraviolet absorber, the amount of ultraviolet absorber added is preferably 0.1 parts by weight or more and 5.0 parts by weight or less, and more preferably 0.4 parts by weight or more and 2.0 parts by weight or less, per 100 parts by weight of the imide structure-containing acrylic resin.

If the amount of UV absorber is less than 0.1 parts by weight, sufficient effect may not be obtained in applications requiring UV absorption, and if it is more than 2.0 parts by weight, bleeding may occur during film production.

(vii) Other Components Included in the Imide Structure-Containing Acrylic Resin Composition The imide structure-containing acrylic resin composition may contain a crosslinked elastomer to improve the mechanical strength of the imide structure-containing acrylic resin. The crosslinked elastomer can be produced by a known polymerization method such as suspension polymerization, dispersion polymerization, emulsion polymerization, solution polymerization, or bulk polymerization. In particular, to produce a crosslinked elastomer having a core-shell structure as described below, it is preferable to use a polymerization method such as suspension polymerization, dispersion polymerization, or emulsion polymerization.

Preferred crosslinked elastomers are core-shell elastomers having a core layer made of a rubbery polymer and a shell layer made of a glassy polymer (hard polymer). Furthermore, the core layer made of a rubbery polymer may have one or more layers made of a glassy polymer as the innermost or intermediate layer.

The glass transition temperature Tg of the rubbery polymer that makes up the core layer is preferably 20°C or lower, more preferably -60 to 20°C, and even more preferably -60 to 10°C. If the Tg of the rubbery polymer that makes up the core layer exceeds 20°C, the mechanical strength of the imide structure-containing acrylic resin may not be sufficiently improved. The Tg of the glassy polymer (hard polymer) that makes up the shell layer is preferably 50°C or higher, more preferably 50 to 140°C, and even more preferably 60 to 130°C. If the Tg of the glassy polymer that makes up the shell layer is lower than 50°C, the heat resistance of the imide structure-containing acrylic resin may be reduced.

In this specification, the glass transition temperatures of "rubbery polymers" and "glassy polymers" are calculated using the Fox formula using values listed in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, polymethyl methacrylate is 105°C, and polybutyl acrylate is -54°C).

The content of the core layer in the core-shell elastomer is preferably 30 to 95% by weight, more preferably 50 to 90% by weight. The content of the glassy polymer layer in the core layer is 0 to 60% by weight, preferably 0 to 45% by weight, more preferably 10 to 40% by weight, relative to the total amount of the core layer (100% by weight). The content of the shell layer in the core-shell elastomer is preferably 5 to 70% by weight, more preferably 10 to 50% by weight.

The above core-shell elastomer may contain any other appropriate components as long as they do not impair the effects of the present invention.

Any suitable polymerizable monomer may be used as the polymerizable monomer that forms the rubber-like polymer that constitutes the core layer.

The polymerizable monomer that forms the rubber-like polymer preferably contains alkyl(meth)acrylate. Of the polymerizable monomers (100% by weight) that form the rubber-like polymer, alkyl(meth)acrylate is preferably contained in an amount of 50% by weight or more, more preferably 50 to 99.9% by weight, and even more preferably 60 to 99.9% by weight.

Examples of the alkyl (meth)acrylate include alkyl (meth)acrylates having an alkyl group containing 2 to 20 carbon atoms, such as ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, lauroyl (meth)acrylate, and stearyl (meth)acrylate. These alkyl groups may have an alicyclic or aromatic cyclic substituent, a branched structure, or a functional group. Among these, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and cyclohexyl (meth)acrylate are preferred, with butyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate being more preferred. These may be used alone or in combination of two or more.

The polymerizable monomer that forms the rubber-like polymer preferably contains a polyfunctional monomer having two or more polymerizable functional groups in the molecule. The content of the polyfunctional monomer that forms the rubber-like polymer is preferably 0.01 to 20% by weight, more preferably 0.1 to 20% by weight, even more preferably 0.1 to 10% by weight, and particularly preferably 0.2 to 5% by weight.

Examples of polyfunctional monomers having two or more polymerizable functional groups within the molecule include aromatic divinyl monomers such as divinylbenzene, alkane polyol poly(meth)acrylates such as ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, oligoethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, and trimethylolpropane tri(meth)acrylate, as well as urethane di(meth)acrylate, epoxy di(meth)acrylate, and triallyl isocyanurate. Examples of polyfunctional monomers having polymerizable functional groups with different reactivities include allyl (meth)acrylate, diallyl maleate, diallyl fumarate, and diaryl itaconate. Among these, ethylene glycol dimethacrylate, butylene glycol diacrylate, and allyl methacrylate are preferred. These may be used alone or in combination.

The polymerizable monomers that form the rubbery polymer may include other polymerizable monomers that are copolymerizable with the alkyl (meth)acrylate and the polyfunctional monomer having two or more polymerizable functional groups in the molecule. The other polymerizable monomers are preferably contained in an amount of 0 to 49.9% by weight, more preferably 0 to 39.9% by weight, of the polymerizable monomers that form the rubbery polymer.

Examples of the other polymerizable monomers include aromatic vinyls such as styrene, vinyl toluene, and α-methyl styrene; aromatic vinylidenes; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinylidene cyanide; methyl methacrylate; urethane acrylate; and urethane methacrylate. Other polymerizable monomers may also include monomers having functional groups such as epoxy groups, carboxyl groups, hydroxyl groups, and amino groups. Specifically, examples of monomers having epoxy groups include glycidyl methacrylate. Examples of monomers having carboxyl groups include methacrylic acid, acrylic acid, maleic acid, and itaconic acid. Examples of monomers having hydroxyl groups include 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate. Examples of monomers having amino groups include diethylaminoethyl methacrylate and diethylaminoethyl acrylate. These may be used alone or in combination.

The polymerizable monomers that form the rubbery polymer may also be used in combination with a small amount of a chain transfer agent. Widely known chain transfer agents can be used, including alkyl mercaptans such as octyl mercaptan, dodecyl mercaptan, and t-dodecyl mercaptan, and thioglycolic acid derivatives.

Any suitable polymerizable monomer may be used as the polymerizable monomer that forms the glassy polymer that constitutes the shell layer and the glassy polymer layer in the core layer.

The polymerizable monomer that forms the glassy polymer preferably contains at least one monomer selected from alkyl (meth)acrylates and aromatic vinyl monomers. Of the polymerizable monomers (100% by weight) that form the glassy polymer, the content of at least one monomer selected from alkyl (meth)acrylates and aromatic vinyl monomers is preferably 50 to 100% by weight, and more preferably 60 to 100% by weight.

The alkyl (meth)acrylate preferably has an alkyl group containing 1 to 8 carbon atoms. These alkyl groups may also have an alicyclic or aromatic cyclic substituent, a branched structure, or a functional group. Examples of such alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Of these, methyl methacrylate is particularly preferred. These may be used alone or in combination of two or more.

Examples of the aromatic vinyl monomer include styrene, vinyl toluene, and α-methyl styrene. Of these, styrene is preferred. These may be used alone or in combination of two or more.

The polymerizable monomers that form the glassy polymer may contain polyfunctional monomers having two or more polymerizable functional groups in the molecule. Of the polymerizable monomers (100% by weight) that form the glassy polymer, the polyfunctional monomers having two or more polymerizable functional groups in the molecule preferably account for 0 to 10% by weight, more preferably 0 to 8% by weight, and even more preferably 0 to 5% by weight.

Specific examples of the above-mentioned polyfunctional monomer having two or more polymerizable functional groups in the molecule include those similar to those described above.

The polymerizable monomers that form the glassy polymer may include other polymerizable monomers that are copolymerizable with the alkyl (meth)acrylate and the polyfunctional monomer having two or more polymerizable functional groups in the molecule. The other polymerizable monomers are preferably contained in an amount of 0 to 50% by weight, more preferably 0 to 40% by weight, of the polymerizable monomers (100% by weight) that form the glassy polymer.

Examples of the other polymerizable monomers mentioned above include vinyl cyanides such as acrylonitrile and methacrylonitrile, vinylidene cyanide, alkyl (meth)acrylates other than those mentioned above, urethane acrylate, and urethane methacrylate. They may also contain functional groups such as epoxy groups, carboxyl groups, hydroxyl groups, and amino groups. Examples of monomers containing epoxy groups include glycidyl methacrylate. Examples of monomers containing carboxyl groups include methacrylic acid, acrylic acid, maleic acid, and itaconic acid. Examples of monomers containing hydroxyl groups include 2-hydroxymethacrylate and 2-hydroxyacrylate. Examples of monomers containing amino groups include diethylaminoethyl methacrylate and diethylaminoethyl acrylate. These monomers may be used alone or in combination.

Furthermore, it is also preferable to use a small amount of a known chain transfer agent, similar to that used in the rubbery polymer layer, in combination with the polymerizable monomer that forms the glassy polymer.

In this embodiment, any suitable method capable of producing core-shell type particles can be used as the method for producing the core-shell type elastomer.

For example, one method involves suspending or emulsion-polymerizing a polymerizable monomer that forms the rubbery polymer that constitutes the core layer to produce a suspension or emulsion dispersion containing rubbery polymer particles, and then adding a polymerizable monomer that forms the glassy polymer that constitutes the shell layer to the suspension or emulsion dispersion and radically polymerizing it to obtain a core-shell elastomer having a multilayer structure in which the surfaces of the rubbery polymer particles are coated with glassy polymer. Here, the polymerizable monomer that forms the rubbery polymer and the polymerizable monomer that forms the glassy polymer may be polymerized in one stage, or in two or more stages with different composition ratios.

Preferred structures of the core-shell elastomer include, for example, (a) a structure having a soft, rubbery core layer and a hard, glassy shell layer, with the core layer having a (meth)acrylic crosslinked elastic polymer layer, and (b) a structure having a multilayer structure in which the rubbery core layer has one or more glassy layers therein, and further having a glassy shell layer on the outside of the core layer. By appropriately selecting the monomer species for each layer, the physical properties of the imide structure-containing acrylic resin can be controlled as desired.

Specific examples of more preferred structures of the core-shell type elastomer include, for example: (A) a core-shell type elastomer in which the shell layer is a non-crosslinked methacrylic resin containing 3% by weight or more, more preferably 10% by weight or more, and even more preferably 15% by weight or more of alkyl acrylate; (B) a core-shell type elastomer in which the shell layer is composed of two or more multi-layers with different alkyl acrylate contents and is a non-crosslinked methacrylic resin containing a total of 10% by weight or more, more preferably 15% by weight or more of alkyl acrylate; and (C) a core layer of the core-shell type elastomer in which the core layer is composed of two or more multi-layers with different alkyl acrylate contents and is a non-crosslinked methacrylic resin containing 10% by weight or more, more preferably 15% by weight or more of alkyl acrylate. Examples of suitable core-shell elastomers include (A) a multilayer structure in which a rubbery polymer layer is formed by polymerizing a mixture of alkyl acrylate, polyfunctional monomer, alkyl mercaptan, and other monomers in the presence of a glassy polymer layer obtained by polymerizing a mixture of alkyl acrylate, polyfunctional monomer, alkyl mercaptan, and other monomers as appropriate; and (D) a multilayer structure in which a core layer of the core-shell elastomer is formed by polymerizing a rubbery polymer layer using a peracid (persulfuric acid, perphosphate, etc.) as a thermal decomposition initiator in the presence of a glassy polymer layer obtained by polymerizing a mixture of alkyl acrylate, polyfunctional monomer, alkyl mercaptan, and other monomers as appropriate. The preferred core-shell elastomers may have only one structural design element, or two or more design elements may be used in combination. Having such a structure facilitates good dispersion of the core-shell elastomer in the imide structure-containing acrylic resin of this embodiment, resulting in fewer defects due to undispersion or aggregation when formed into a film. Furthermore, the film has excellent strength, toughness, heat resistance, transparency, and appearance, and is further inhibited from whitening due to temperature changes or stress, resulting in a high-quality film.

When the core-shell elastomer of this embodiment is produced by emulsion polymerization, suspension polymerization, or the like, known polymerization initiators can be used. Particularly preferred polymerization initiators include persulfates such as potassium persulfate, ammonium persulfate, and ammonium persulfate; perphosphates such as sodium perphosphate; organic azo compounds such as 2,2-azobisisobutyronitrile; hydroperoxide compounds such as cumene hydroperoxide, t-butyl hydroperoxide, and 1,1-dimethyl-2-hydroxyethyl hydroperoxide; peresters such as t-butyl isopropyloxycarbonate and t-butyl peroxybutyrate; and organic peroxide compounds such as benzoyl peroxide, dibutyl peroxide, and lauryl peroxide. These initiators may be used as thermal decomposition polymerization initiators, or as redox polymerization initiators in the presence of a catalyst such as ferrous sulfate and a water-soluble reducing agent such as ascorbic acid or sodium formaldehyde sulfoxylate. The initiator may be selected appropriately depending on the composition of the monomers to be polymerized, the layer structure, the polymerization temperature conditions, and the like.

When the core-shell elastomer of this embodiment is produced by emulsion polymerization, it can be produced by standard emulsion polymerization using a known emulsifier. Examples of known emulsifiers include anionic surfactants such as phosphate ester salts, such as sodium alkyl sulfonate, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sodium lauryl sulfate, sodium fatty acid, and sodium polyoxyethylene lauryl ether phosphate, as well as nonionic surfactants, such as reaction products of alkylphenols or aliphatic alcohols with propylene oxide or ethylene oxide. These surfactants may be used alone or in combination. If necessary, cationic surfactants, such as alkylamine salts, may also be used. Among these, from the viewpoint of improving the thermal stability of the resulting core-shell elastomer, polymerization using a phosphate ester salt (alkali metal or alkaline earth metal), such as sodium polyoxyethylene lauryl ether phosphate, is particularly preferred. The core-shell elastomer latex obtained by emulsion polymerization is spray-dried, or as is commonly known, by adding an electrolyte or organic solvent as a coagulant to the latex to coagulate the polymer component, and then drying the polymer component by appropriate procedures such as heating, washing, and separation of the aqueous phase, to obtain a core-shell elastomer in the form of a lump or powder. Known coagulants such as water-soluble electrolytes and organic solvents can be used as the coagulant, but from the viewpoint of improving the thermal stability of the obtained copolymer during molding and in terms of productivity, it is preferable to use magnesium salts such as magnesium chloride or magnesium sulfate, or calcium salts such as calcium acetate or calcium chloride.

When the imide structure-containing acrylic resin composition of this embodiment contains a core-shell type elastomer, it preferably contains 1 to 40 parts by weight of the core-shell type elastomer relative to 100 parts by weight of the imide structure-containing acrylic resin, more preferably 2 to 35 parts by weight, and even more preferably 3 to 25 parts by weight. If the content of the core-shell type elastomer is less than 1 part by weight, the mechanical strength of the imide structure-containing acrylic resin will not be sufficiently improved, and if it exceeds 40 parts by weight, the heat resistance of the imide structure-containing acrylic resin may be reduced.

The preferred particle size of the soft core layer of the core-shell elastomer is preferably 1 to 500 nm, more preferably 10 to 400 nm, even more preferably 50 to 300 nm, and particularly preferably 70 to 300 nm. If the particle size of the core layer of the core-shell elastomer is less than 1 nm, the mechanical strength of the imide structure-containing acrylic resin will not be sufficiently improved, and if it is greater than 500 nm, the heat resistance and transparency of the imide structure-containing acrylic resin may be impaired.

The particle diameter of the core layer of the core-shell type elastomer can be determined by molding a compound in which the core-shell crosslinked elastomer and Sumipex EX are blended in a weight ratio of 50:50, photographing the resulting film with a transmission electron microscope (JEM-1200EX manufactured by JEOL Ltd.) at an acceleration voltage of 80 kV using _RuO4 staining ultrathin sectioning, randomly selecting 100 rubber particle images from the resulting photograph, and determining the average particle diameter of those images.

(viii) Film Containing Imide Structure-Containing Acrylic Resin Composition The imide structure-containing acrylic resin composition can be formed into a film containing the imide structure-containing acrylic resin composition by, for example, a known molding method.

The haze value of a film containing an imide structure-containing acrylic resin composition is preferably 2.0% or less, and more preferably 1.0% or less. The transmittance is preferably 85% or more, and more preferably 90% or more. Having both the haze value and transmittance within the above ranges is preferable, as it broadens the range of applications in which the film can be used.

While there are no particular restrictions on optical anisotropy, it may be preferable that not only the optical anisotropy in the in-plane directions (length direction and width direction) but also the optical anisotropy in the thickness direction be small. In other words, it may be preferable that both the in-plane retardation and the thickness direction retardation be small. More specifically, the in-plane retardation at a wavelength of 590 nm is preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 1 nm or less. Furthermore, the thickness direction retardation is preferably 40 nm or less, more preferably 15 nm or less, and even more preferably 3 nm or less.

The in-plane retardation (Re) and the thickness direction retardation (Rth) can be calculated by the following formulas.
Re=(nx-ny)×d Rth=|(nx+ny)/2-nz|×d
In the above formula, nx, ny, and nz respectively represent the refractive index in the direction in which the in-plane refractive index is maximum as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the film as the Z axis. d represents the thickness of the film, and ∥ represents the absolute value.

The film obtained from the imide structure-containing acrylic resin composition of this embodiment has a low amount of foreign matter. The number of foreign matters is preferably 50 or less per square ^meter , more preferably 40 or less per square ^meter , and particularly preferably 30 or less per ^square meter. The number of foreign matters is determined by cutting out a 1 ^m2 piece of the obtained stretched film, counting the number of foreign matters of 20 μm or more using a microscope, and adding them together.

Films containing the imide structure-containing acrylic resin composition of this embodiment can be used as substrates for electronic materials. They can be used in a variety of applications, including antenna substrates, flexible display substrates, foldable display substrates, rollable display substrates, touch panel substrates, transparent display substrates, spatial display substrates, hologram substrates, signage substrates, head-up display peripheral components (viewpoint adjustment film, image adjustment film, image projection screen, retroreflective film, lens sheet, dust cover), brightness enhancement film, cover glass replacement film, glass substrate replacement film, reflective film, anti-reflective film, anti-glare film, substrates for double-sided and single-sided tapes and adhesive films for electronic devices, AR glass optical waveguides, light-adjusting device substrates, light-shielding device substrates, high-frequency circuit board film, transparent flexible printed circuit boards, battery separator film, smartphone back covers, release films, and X-ray inspection equipment detector substrates.

It can also be used in the imaging field, such as taking lenses and viewfinders for cameras, VTRs, and projectors, filters, prisms, and Fresnel lenses; the lens field, such as pickup lenses for optical discs such as CD players, DVD players, and MD players; the optical recording field for optical discs such as CD players, DVD players, and MD players; the information equipment field, such as light guide plates for liquid crystal displays, polarizer protective films, and retardation films, and surface protection films; the optical communications field, such as optical fibers, optical switches, and optical connectors; the vehicle field, such as automobile headlight and taillight lenses, inner lenses, instrument covers, and sunroofs; the medical equipment field, such as glasses, contact lenses, endoscopic lenses, and medical supplies that require sterilization; the construction and building materials field, such as road translucent panels, double-glazed lenses, skylights and carports, lighting lenses and covers, and sizing for building materials; and microwave cooking containers (tableware).

As mentioned above, the film in this embodiment has excellent optical properties such as optical homogeneity and transparency. Therefore, by utilizing these optical properties, it can be particularly well-suited for use in well-known optical applications such as optically isotropic films, polarizer protective films, transparent conductive films, and the like in the periphery of liquid crystal display devices.

The film of this embodiment can be attached to a polarizer and used as a polarizing plate. That is, the film of this embodiment can be used as a polarizer protective film for a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. Specific examples include polarizers obtained by incorporating iodine into stretched polyvinyl alcohol.

(Film manufacturing method)
An example of a method for producing a film containing the imide structure-containing acrylic resin composition of the present embodiment will be described below, but the method for producing the film of the present embodiment is not limited to this. In other words, the method for producing the film of the present embodiment can be any conventionally known method as long as it is a method that can produce a film by molding the imide structure-containing acrylic resin of the present embodiment.

Specific examples include injection molding, melt extrusion molding, inflation molding, blow molding, and compression molding. Furthermore, the film of this embodiment can be produced by a solution casting method or spin coating method, in which the imide structure-containing acrylic resin of this embodiment is dissolved in a solvent and then molded. Among these, the melt extrusion method, which does not use a solvent, is preferred. The melt extrusion method can reduce production costs and the burden on the global environment and working environment caused by solvents.

As an example of a method for producing a film in this embodiment, a method for producing a film by melt extrusion of the imide structure-containing acrylic resin in this embodiment will be described in detail below. In the following description, films obtained by melt extrusion will be referred to as "melt-extruded films" to distinguish them from films obtained by other methods such as solution casting.

When the imide structure-containing acrylic resin of this embodiment is formed into a film by melt extrusion, the imide structure-containing acrylic resin of this embodiment is first supplied to an extruder, and the imide structure-containing acrylic resin is heated and melted.

It is preferable to pre-dry the imide structure-containing acrylic resin before feeding it to the extruder. Such pre-drying can prevent foaming of the resin extruded from the extruder. The pre-drying method is not particularly limited, but for example, the raw material (i.e., the imide structure-containing acrylic resin in this embodiment) can be formed into pellets or the like and pre-dried using a hot air dryer, vacuum dryer, or the like.

Next, the imide structure-containing acrylic resin that has been heated and melted in the extruder is fed to a T-die via a gear pump and filter. Using a gear pump improves the uniformity of the resin extrusion rate and reduces thickness variations in the longitudinal direction of the film. On the other hand, using a filter removes foreign matter from the imide structure-containing acrylic resin, resulting in a film with a defect-free, excellent appearance.

Next, the imide structure-containing acrylic resin supplied to the T-die is extruded from the T-die as a sheet-like molten resin. The sheet-like molten resin is then sandwiched between two cooling rolls and cooled to form a film. Of the two cooling rolls sandwiching the sheet-like molten resin, one is preferably a rigid metal roll with a smooth surface, and the other is preferably a flexible roll equipped with a smooth, elastically deformable metallic outer sleeve.

By sandwiching the sheet-like molten resin between such a rigid metal roll and a flexible roll equipped with an elastic metal outer cylinder, cooling it, and forming it into a film, minute surface irregularities and die lines can be corrected, resulting in a film with a smooth surface and thickness variations of 5 μm or less.

In this specification, the term "cooling roll" is used to encompass "touch roll" and "cooling roll."

Even when using the above-mentioned rigid metal roll and flexible roll, the surfaces of both chill rolls are metal, so if the film being produced is thin, the surfaces of the chill rolls may come into contact with each other, scratching the outer surface of the chill roll or damaging the chill roll itself.

Therefore, when forming a film by sandwiching a sheet of molten resin between two chilled rolls as described above, the sheet of molten resin is first sandwiched between the two chilled rolls and cooled to obtain a relatively thick raw film. It is then preferable to uniaxially or biaxially stretch this raw film to produce a film of the desired thickness.

More specifically, to produce a 40 μm thick film, the sheet-shaped molten resin is sandwiched between the two cooling rolls and cooled to obtain a 150 μm thick raw film. This raw film is then stretched biaxially in both the longitudinal and transverse directions to produce a 40 μm thick film.

In this way, when the film in this embodiment is a stretched film, the imide structure-containing acrylic resin in this embodiment is first formed into an unstretched raw film, and then uniaxially or biaxially stretched to produce a stretched film.

In order to improve the bending resistance of the optical film in this embodiment in both the longitudinal direction (MD direction) and the width direction (TD direction), it is preferable to perform biaxial stretching.

For ease of explanation, in this specification, the film obtained by molding the imide structure-containing acrylic resin of this embodiment into a film and before stretching it, i.e., the unstretched film, will be referred to as the "raw film."

When stretching raw film, the raw film may be stretched continuously immediately after being formed, or the raw film may be stored or moved after being formed and then stretched.

When stretching raw film immediately after forming it into a roll of film, if the raw film remains in this state for a very short time (sometimes even instantaneously) during the film manufacturing process, it does not need to be in a perfect film state as long as it maintains a film shape sufficient for stretching. Furthermore, the raw film does not need to have the properties of a finished film.

(Film stretching method)
The method for stretching the raw film is not particularly limited, and any conventionally known stretching method may be used. Specifically, for example, transverse stretching using a tenter, longitudinal stretching using rolls, and sequential biaxial stretching, which is a sequential combination of these, may be used.

It is also possible to use a simultaneous biaxial stretching method in which the film is stretched lengthwise and widthwise at the same time, or a method in which vertical stretching is performed with a roll and then horizontal stretching is performed with a tenter. When stretching raw film, it is preferable to first preheat the raw film to a temperature 0.5°C to 5°C higher, preferably 1°C to 3°C higher than the stretching temperature, and then cool it to the stretching temperature before stretching.

By preheating within the above range, the thickness of the raw film in the width direction can be maintained with precision, and the thickness precision of the stretched film will not decrease or thickness unevenness will not occur. Furthermore, the raw film will not stick to the roll or sag under its own weight.

On the other hand, if the preheating temperature of the raw film is too high, problems such as the raw film sticking to the roll or sagging under its own weight tend to occur. Furthermore, if the difference between the preheating temperature of the raw film and the stretching temperature is small, it becomes difficult to maintain the thickness precision of the raw film before stretching, thickness unevenness tends to increase, and thickness precision tends to decrease.

In this embodiment, it is difficult to improve the thickness accuracy of the imide structure-containing acrylic resin by utilizing the necking phenomenon when stretching it after molding it into a raw film. Therefore, in this embodiment, managing the preheating temperature is important for maintaining or improving the thickness accuracy of the resulting film.

The stretching temperature when stretching the raw film is not particularly limited and can be changed depending on the mechanical strength, surface properties, thickness accuracy, etc. required for the stretched film to be produced. Generally, when the glass transition temperature of the raw film (imide structure-containing acrylic resin composition) determined by DSC is Tg, the temperature range is preferably (Tg - 30°C) to (Tg + 30°C), more preferably (Tg - 20°C) to (Tg + 30°C), even more preferably (Tg) to (Tg + 30°C), and even more preferably (Tg + 10°C) to (Tg + 30°C). In other words, when the glass transition temperature of the imide structure-containing acrylic resin composition is Tg, the stretching temperature for biaxial stretching of the optical film is preferably in the range of Tg - 30°C to Tg + 30°C.

When the stretching temperature is within the above temperature range, thickness unevenness of the resulting stretched film can be reduced, and the mechanical properties of elongation, tear propagation strength, and MIT flex resistance can be improved. Furthermore, problems such as the film sticking to the roll can be prevented.

On the other hand, if the stretching temperature is higher than the above temperature range, the thickness of the resulting stretched film tends to be uneven, and mechanical properties such as elongation, tear propagation strength, and fatigue resistance tend not to be sufficiently improved. Furthermore, problems such as the film sticking to the rolls tend to occur more easily.

Furthermore, if the stretching temperature is lower than the above temperature range, the internal haze of the resulting stretched film will tend to increase, and in extreme cases, processing problems such as tearing or cracking of the film will occur.

When stretching the raw film, the stretching ratio is also not particularly limited and can be determined depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film to be produced. Although it also depends on the stretching temperature, it is generally preferable to select the stretching ratio in the range of 1.1 to 3 times, more preferably in the range of 1.3 to 2.5 times, and even more preferably in the range of 1.5 to 2.3 times.

When the stretching ratio is within the above range, the film's mechanical properties, such as elongation, tear propagation strength, and flexural fatigue resistance, can be significantly improved. Therefore, it is possible to produce a stretched film with a thickness variation of 5 μm or less and an internal haze of 1.0% or less.

When the imide structure-containing acrylic resin in this embodiment contains a crosslinked elastomer, the resulting film has excellent mechanical strength and can be suitably used as an unstretched film, a uniaxially stretched film, or a biaxially stretched film.

(ix) Antenna Substrate Containing Imide Structure-Containing Acrylic Resin Composition In the present embodiment, the antenna substrate containing the imide structure-containing acrylic resin composition can be a film formed from the imide structure-containing acrylic resin composition.

Due to its excellent dielectric properties, heat resistance, weather resistance, and transparency, the antenna substrate of this embodiment can be used for vehicle window glass, building window glass, industrial machinery display units, and displays for electronic devices and display devices in homes.

As for dielectric properties, when measured at a frequency of 3 GHz, the dielectric loss tangent Df value is preferably 0.010 or less, and more preferably 0.007 or less. A Df value in this range results in low loss. The relative dielectric constant Dk value is preferably 3.2 or less, and more preferably 3.0 or less.

When the substrate expands and contracts due to a rise in temperature, the antenna portion formed from the conductor is also pulled by the expansion and contraction of the substrate, causing the antenna dimensions to change. Because antenna dimensions are uniquely determined by the wavelength of the resonating frequency, it is undesirable for antenna dimensions to change due to a rise in temperature, etc., so the linear expansion coefficient is preferably 100 ppm or less, and particularly preferably 80 ppm or less.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. The evaluation methods for imide-structure acrylic resins are as follows. Below, "parts" and "%" mean "parts by weight" and "% by weight" unless otherwise specified.

(glass transition temperature)
Using 10 mg of the imide structure-containing acrylic resin, a differential scanning calorimeter (DSC, manufactured by SII Corporation, DSC7020) was used to measure in a nitrogen atmosphere at a temperature increase rate of 20° C./min, and the calorific value was determined by the midpoint method.

(average refractive index)
Measurement was carried out using an Abbe refractometer 3T manufactured by Atago Co., Ltd.

(Calculation of ring structure content)
The obtained imide structure-containing acrylic resin was measured using ^1H -NMR BRUKER Avance III (400 MHz). The molar ratio of the target ring structure portion to the other portions was converted into weight and calculated. Specifically, in the case of N-phenylglutarimide in which ^R3 in the above general formula (1) is phenyl, the ring structure content (mol) was calculated using the following formula from the peak area A near 0.5 to 2.5 ppm derived from the methylene group _CH2 and methyl group _CH3 of the main chain, the peak area B near 6.8 to 7.2 ppm derived from the protons of the aromatic ring of N-phenylglutarimide, and the peak area C near 7.3 ppm to 7.6 ppm. The calculated molar ratio can be used to convert into weight and calculate.
Ring structure content (mol) = (B + C) / A

(yield)
The yield was calculated from the molar ratio of the imidizing agent added to the content of the imide ring structure in the imide structure-containing acrylic resin having the structure represented by formula (1) using the following formula.
Yield (mol %)=content of ring structure (mol)/added imidizing agent (mol)×100

(Imidization rate)
The imidization ratio of the imide structure-containing acrylic resin was determined by measuring the IR spectrum using a Fourier transform infrared spectrophotometer (FI/IR-4100 manufactured by JASCO Corporation). The imidization ratio was determined using the following formula from the intensity ratio of the absorption attributable to the ester carbonyl group near 1720 cm ⁻¹ to the absorption attributable to the imide carbonyl group near 1680 cm ⁻¹ . Here, the imidization ratio is the proportion of the imide carbonyl group in the total of the ester carbonyl group and the imide carbonyl group.
Imidization rate (%) = absorption intensity of imide carbonyl group / (absorption intensity of ester carbonyl group + absorption intensity of imide carbonyl group)

(Thickness measurement)
The thickness of the optical film was measured using a Digimatic Indicator (manufactured by Mitutoyo Corporation).

(Optical properties)
The in-plane retardation Δnd and the thickness direction retardation Rth were measured using a retardation measuring device KOBRA-WR manufactured by Oji Scientific Instruments Co., Ltd. The measurement was carried out at a wavelength of 590 nm.

(Total light transmittance and haze value)
The total light transmittance and haze value of the resin composition (molded article) or film were measured using an NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. according to the method described in JIS K7105.

(Light transmittance at 380 nm)
The light transmittance of the optical film at a wavelength of 380 nm was measured using an ultraviolet-visible spectrophotometer (JASCO: V-560).

(relative permittivity Dk, dielectric loss tangent Df)
The dielectric constant Dk and the dielectric loss tangent Df were measured using a network analyzer N5224B (manufactured by Keysight Technologies), a cavity resonator, and cavity resonator perturbation analysis software CP-MA (manufactured by Kanto Electronics Application Development Co., Ltd.). The film to be measured was cut into a piece of 2 mm x 100 mm, and after 24 hours of humidity conditioning in a 23°C/50% RH environment, measurements were performed at 3 GHz.

Coefficient of Linear Expansion (CTE)
The linear expansion coefficient was estimated using a thermomechanical analyzer manufactured by SII Nano Technology Corporation, product name: TMA/SS6100, by heating from 10°C to 100°C at 10°C/min, then cooling to 10°C at 40°C/min, and further heating at 10°C/min, at the second heating time from 50 to 100°C. The measurement conditions are shown below.
Sample shape: width 3 mm, length 10 mm
Load: 1g
Atmosphere: Air atmosphere

(weather resistance)
Weather resistance was evaluated using a xenon weatherometer, measuring the changes in YI and total light transmittance after 300 hours under conditions of irradiation energy of 63 W/ ^m2 , temperature of 40°C (black panel temperature: 63°C), and rainfall. A change in YI of 1 or more or a change in total light transmittance of 1% or more was marked as x.

(Measurement of Yellowness Index YI)
The tristimulus values X, Y, and Z were measured using a handy color difference meter NR-11B manufactured by Nippon Denshoku Industries Co., Ltd., and the yellowness index YI was calculated from the tristimulus values in accordance with JIS-K7103.

(Flexibility (MIT flex test))
The film was cut into 15 mm wide strips to serve as test specimens. These test specimens were subjected to measurement using a MIT flexible fatigue tester, Model D, manufactured by Toyo Seiki Co., Ltd., under conditions of a test load of 1.96 N, a speed of 175 times/min, a bending clamp curvature radius R of 0.38 mm, and a bending angle of 135° to the left and right. Measurements were performed in both the MD and TD directions, and the arithmetic average value was used as the MIT round-trip bending count.

Example 1
The resin was produced using a 40 mm diameter fully intermeshing co-rotating twin-screw extruder reactor. The extruder used was a 40 mm diameter co-intermeshing twin-screw extruder with an L/D (ratio of the extruder length L to diameter D) of 90. The raw resin was fed into the extruder's raw material supply port using a constant weight feeder (KUBOTA CE-T-2E). The pressure reduction in the extruder's vent was set to -0.10 MPa. The resin (strand) discharged from the extruder was cooled in a cooling water tank and then cut into pellets using a pelletizer. A resin pressure gauge was installed at the extruder outlet to check the internal pressure of the extruder or to assess extrusion fluctuations.

An imide structure-containing acrylic resin was produced using polymethyl methacrylate resin (Mw: 100,000) as the raw (meth)acrylic polymer, aniline (Fujifilm Wako Pure Chemical Industries, Ltd.) as the imidization agent, and diethylamine (Fujifilm Wako Pure Chemical Industries, Ltd.) as the imidization accelerator. The extruder maximum temperature was 280°C, the screw speed was 100 rpm, the polymethyl methacrylate resin was 10 kg/h, the aniline was added at 8.0 parts per 100 parts of polymethyl methacrylate resin, and the diethylamine was added at 6.3 parts per 100 parts of polymethyl methacrylate resin. The imidization agent and imidization accelerator were mixed in advance, and the aniline and diethylamine mixture was added to the extruder using a liquid addition pump. The resulting imide structure-containing acrylic resin had an imidization rate of 27.2%, an acid value of 0.77 mmol/g, a Tg of 134°C, and a yield of 81%.

This pellet-shaped imide structure-containing acrylic resin was dried at 100°C for 8 hours, and then extruded at 240°C using a 40mmφ single-screw extruder and a 400mm wide T-die. The resulting sheet-shaped molten resin was cooled on a cooling roll to produce a film 300mm wide and 150μm thick. This film was then uniaxially stretched at a stretch ratio of 2x and a temperature 5°C higher than the Tg to produce a uniaxially stretched film.

(Examples 2 , 4 to 9 , Reference Example 3 , Comparative Examples 1 to 6)
Examples 2 , 4 to 9 , Reference Example 3 , and Comparative Examples 1 to 6 were carried out in the same manner as Example 1, except that the type and the number of parts added of the imidizing agent and the type and the number of parts added of the imidization accelerator were changed according to Table 1. The results are shown in Table 1.

As shown in Table 1, when imidization is performed using an aromatic amine compound, the addition of an imidization accelerator with a pKa of 6 or higher can efficiently proceed imidization, enabling the production of an imide structure-containing acrylic resin in good yield. In Comparative Examples 2 and 3, the imidization accelerator added was a tertiary amine, which resulted in an inefficient imidization reaction and a low glass transition temperature for the resulting resin. The glass transition temperatures of the imide structure acrylic resins obtained in Examples 1 , 2, 4 to 9 , and Reference Example 3 were higher than those of Comparative Examples 1 to 5, demonstrating their suitability for applications requiring heat resistance. In Comparative Example 6, the imidization agent added was monomethylamine, resulting in large thickness direction retardation and in-plane retardation.

Claims (13)

A method for producing an imide structure-containing acrylic resin having a structure represented by the following formula (1):
The method includes a step of heating a raw material composition containing a (meth)acrylic polymer, an imidizing agent, and an imidization accelerator,
the imidizing agent contains an aromatic amine compound,
the imidization accelerator is a secondary amine,
The secondary amine has a structure represented by the following formula (3):
the imidization accelerator has a pKa of 6 or more;
the raw material composition has an imidizing agent content of 1 to 61.6 parts by weight relative to 100 parts by weight of the (meth)acrylic polymer, and an imidization accelerator content of 6.3 to 80 parts by weight relative to 100 parts by weight of the (meth)acrylic polymer.
(In formula (1), ^R1 and ^R2 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and ^R3 represents an aromatic hydrocarbon group or a heteroaromatic group.)
HN(R ⁵ )(R ⁶ ) (3)
(In formula (3), R5 ^and R6 ^each independently represent an alkyl group having 1 to 8 carbon atoms.) The method for producing an imide structure-containing acrylic resin according to claim 1, wherein the raw material composition contains 1 to 46.6 parts by weight of the imidizing agent per 100 parts by weight of the (meth)acrylic polymer. The method for producing an imide structure-containing acrylic resin according to claim 1 or 2, wherein the imidization rate of the imide structure-containing acrylic resin is 10 to 75%. The method for producing an imide structure-containing acrylic resin according to any one of claims 1 to 3 , wherein the imidization accelerator has a pKa of 8 or more. The method for producing an imide structure-containing acrylic resin according to any one of claims 1 to 4 , wherein the secondary amine comprises at least one selected from the group consisting of diethylamine, dimethylamine, N-methylethylamine, N-methylpropylamine, and N-methylbutylamine. The method for producing an imide structure-containing acrylic resin according to any one of claims 1 to 5 , wherein the imidizing agent comprises at least one selected from the group consisting of aniline, toluidine, anisidine, xylidine, aminopyridine, aminobiphenyl, and aminonaphthalene. 7. The method for producing an imide structure-containing acrylic resin according to claim 1, wherein the raw material composition contains 0.1 mol to 10 mol of the imidization accelerator per 1 mol of the imidizing agent. The method for producing an imide structure-containing acrylic resin according to any one of claims 1 to 7 , wherein the (meth)acrylic polymer contains a methacrylic acid alkyl ester unit. The method for producing an imide structure-containing acrylic resin according to claim 8 , wherein the methacrylic acid alkyl ester unit has an alkyl group having 1 to 8 carbon atoms. 10. The method for producing an imide structure-containing acrylic resin according to claim 8 , wherein the (meth)acrylic polymer has a content of the methacrylic acid alkyl ester unit of 50% by weight or more based on the total amount of the (meth ) acrylic polymer. The method for producing the imide structure-containing acrylic resin according to any one of claims 1 to 10 , comprising a step of mixing a mixture of the imidization accelerator and the imidizing agent with the (meth)acrylic polymer. The method for producing an imide structure-containing acrylic resin according to any one of claims 1 to 11 , wherein a temperature in the step of heating a raw material composition containing the (meth)acrylic polymer, the imidizing agent, and the imidization accelerator is 180°C to 320°C. The method for producing an imide structure-containing acrylic resin according to any one of claims 1 to 12 , wherein a pressure in the step of heating a raw material composition containing the (meth)acrylic polymer, the imidizing agent, and the imidization accelerator is 0.1 MPa to 50 MPa.