Poly(amic acid)-containing liquid and method for producing poly(amic acid)-containing liquid

Abstract

The present invention relates to a method for producing a poly(amic acid)-containing liquid, in which a prepolymer-containing liquid, which contains an amic acid prepolymer, a diamine, and a tetracarboxylic acid dianhydride are used to obtain the poly(amic acid)-containing liquid.

Description

Polyamic acid-containing liquid and method for producing polyamic acid-containing liquid

[0001] An embodiment of the present invention relates to a method for producing a polyamic acid-containing liquid, a polyamic acid-containing liquid, and methods for producing a polyimide, a molded article, and a printed circuit board.

[0002] Polyimides have high heat resistance, chemical resistance, excellent mechanical properties, and a low dielectric constant, and are therefore widely used in fields such as automobiles, electronic components, displays, etc. For example, semi-aromatic polyimides having a structure derived from an aliphatic or alicyclic diamine and a structure derived from an aromatic tetracarboxylic acid dianhydride, or a structure derived from an aromatic diamine and an aliphatic or alicyclic acid dianhydride, are expected to be used in high-frequency antennas, substrates such as FPCs (flexible printed circuit boards), and coil insulating coatings for inverter-driven motors, which are becoming increasingly high-frequency and high-voltage.

[0003] Patent Document 1 discloses a solvent-insoluble polyimide film using more than 15 mol % and less than 50 mol % of dimer diamine based on the total diamine components. Patent Document 1 also discloses that a polyamic acid solution can be obtained as an optically uniform solution by blending, for example, approximately equimolar amounts of tetracarboxylic acid dianhydride and diamine in a nitrogen-containing polar solvent, and polymerizing the resulting mixture at 10 to 70°C.

[0004] Japanese Patent Application Laid-Open No. 2020-76072

[0005] The present disclosure provides a method for easily producing a polyamic acid-containing liquid that can yield a polyimide exhibiting excellent dielectric properties. The present disclosure also provides a polyamic acid-containing liquid that can yield a polyimide exhibiting excellent dielectric properties and that exhibits excellent film-forming properties. Furthermore, the present disclosure provides methods for producing a polyimide, a molded product, and a printed circuit board exhibiting excellent dielectric properties.

[0006] Examples of embodiments are listed below. The present invention is not limited to the following embodiments. One embodiment relates to a method for producing a polyamic acid-containing liquid, which includes obtaining a polyamic acid-containing liquid using a prepolymer-containing liquid containing an amic acid prepolymer including a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride, an aliphatic or alicyclic diamine, and a tetracarboxylic dianhydride.

[0007] Another embodiment relates to a method for producing a polyamic acid-containing liquid, the method comprising obtaining a polyamic acid-containing liquid containing polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer including a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic acid dianhydride, a diamine, and a tetracarboxylic acid dianhydride.

[0008] Another embodiment relates to a polyamic acid-containing liquid containing a polyamic acid having a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, and a solvent, and satisfying one or both of the following conditions (1) and (2): (1) the content of components derived from amines and carboxylic anhydrides is 20.0% by mass or more, and the turbidity is 2.5 NTU or less, and (2) the content of the polyamic acid is 20.0% by mass or more, based on the total mass of the polyamic acid and the solvent.

[0009] Another embodiment relates to a polyamic acid-containing liquid containing a polyamic acid having a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, and a solvent, and satisfying one or both of the following conditions (3) and (4): (3) the turbidity is 2.5 NTU or less, and the ratio of the mass of components derived from amines and carboxylic anhydrides obtained by heating the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass% or more, and (4) the ratio of the mass of polyimide obtained by heating a filtrate of the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass% or more.

[0010] Some other embodiments relate to the polyamic acid-containing liquid for use in an insulating material, a heat-resistant insulating material, or a printed circuit board. Some other embodiments relate to methods for producing polyimides, molded articles, and printed circuit boards using the polyamic acid-containing liquid.

[0011] According to the present disclosure, there is provided a method for easily producing a polyamic acid-containing liquid from which a polyimide exhibiting excellent dielectric properties can be obtained. The present disclosure also provides a polyamic acid-containing liquid from which a polyimide exhibiting excellent dielectric properties can be obtained and which exhibits excellent film-forming properties. Furthermore, the present disclosure also provides methods for producing a polyimide, a molded product, and a printed circuit board exhibiting excellent dielectric properties.

[0012] The following describes embodiments of the present invention. The present invention is not limited to the following embodiments. The following embodiments can be implemented alone or in combination. Combinations of multiple embodiments are also included in the present invention.

[0013] In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range. Furthermore, the upper or lower limit value of a numerical range described in the present disclosure may be replaced with a value shown in the Examples. A numerical value may be selected from the upper and lower limit values ​​described in stages in the present disclosure to form a stepped numerical range. Furthermore, the upper and lower limit values ​​described in the present disclosure may be replaced with values ​​shown in the Examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, each structure in the polymer may contain multiple corresponding structures. When multiple structures corresponding to each structure are present in the polymer, the content or amount of each structure means the total content or amount of the multiple structures present in the polymer, unless otherwise specified. In this disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved. In this disclosure, the term "layer" includes not only a layer that is formed over the entire area when the area in which the layer exists is observed, but also a layer that is formed only in a part of the area.

[0014] <Method for Producing Polyamic Acid-Containing Liquid> A method for producing a polyamic acid-containing liquid includes obtaining a polyamic acid-containing liquid containing a polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer, a diamine, and a tetracarboxylic acid dianhydride.

[0015] In some embodiments, a method for producing a polyamic acid-containing liquid includes obtaining a polyamic acid-containing liquid using a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride, an aliphatic or alicyclic diamine, and a tetracarboxylic dianhydride. In the present disclosure, this production method may be referred to as "production method R."

[0016] In some other embodiments, a method for producing a polyamic acid-containing liquid includes obtaining a polyamic acid-containing liquid using a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, a diamine, and a tetracarboxylic dianhydride. In the present disclosure, this production method may be referred to as "production method L."

[0017] Polyamic acids are typically synthesized by addition condensation, i.e., polymerization of diamines and tetracarboxylic dianhydrides. In the polymerization of aromatic diamines and tetracarboxylic dianhydrides, the reaction generally proceeds easily at room temperature. However, in the polymerization of diamines, including aliphatic or alicyclic diamines, with tetracarboxylic dianhydrides, there is a problem of the formation of precipitates, which hinder the reaction from proceeding smoothly. Aliphatic or alicyclic diamines have significantly higher basicity than aromatic diamines. The precipitates are thought to include salts formed between unreacted aliphatic or alicyclic diamines, which exhibit high basicity, and carboxylic acids (i.e., ring-opened carboxylic dianhydrides) generated during the addition condensation process or polyamic acids having carboxyl groups obtained by addition condensation.

[0018] According to the present disclosure, even when the diamine contains an aliphatic or alicyclic diamine, the reaction can proceed by suppressing salt formation, dissolving the formed salt, or both, through a simple procedure of using an amic acid prepolymer, a diamine, and a tetracarboxylic dianhydride. This allows for easy production of a polyamic acid-containing liquid containing a polyamic acid containing a structure derived from an aliphatic or alicyclic diamine. Furthermore, according to some embodiments, a polyamic acid-containing liquid containing a high concentration of polyamic acid can be produced in a short period of time.

[0019] [Manufacturing Method R] Manufacturing Method R includes obtaining a polyamic acid-containing solution containing a polyamic acid using a prepolymer-containing solution containing an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride, an aliphatic or alicyclic diamine, and a tetracarboxylic dianhydride (sometimes referred to as "Step R2" in the present disclosure). Manufacturing Method R may further include preparing a prepolymer-containing solution containing an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride (sometimes referred to as "Step R1" in the present disclosure). In the present disclosure, tetracarboxylic dianhydride may be referred to as "acid dianhydride." In the present disclosure, an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride may be referred to as an "aromatic prepolymer," and a prepolymer-containing solution containing an aromatic prepolymer may be referred to as an "aromatic prepolymer-containing solution." Manufacturing Method R may include any step other than Step R1 and Step R2.

[0020] According to Production Method R, polymerization can proceed even when an aliphatic or alicyclic diamine is used. One reason for this is presumed to be as follows: In Production Method R, a polyamic acid is obtained by reacting an aromatic prepolymer with an aliphatic or alicyclic diamine and an acid dianhydride. The aliphatic or alicyclic diamine forms a salt with the aromatic prepolymer and the acid dianhydride, respectively. For a polyamic acid having the same composition, Production Method R forms a salt between the aliphatic or alicyclic diamine and the aromatic prepolymer, resulting in a smaller amount of salt between the aliphatic or alicyclic diamine and the acid dianhydride than when a polyamic acid is obtained using an aromatic diamine, an aliphatic or alicyclic diamine, and an acid dianhydride. Due to structural influences, salts of aromatic prepolymers are more soluble than salts of acid dianhydrides. In Production Method R, salts of the aromatic prepolymer, which are more soluble, are formed, while the formation of salts of the less soluble acid dianhydrides is suppressed. In other words, Production Method R is a method for promoting the dissolution of all salts by reducing the amount of sparingly soluble salts and incorporating easily soluble salts, thereby allowing the polymerization reaction to proceed. However, the present invention is not limited to this assumption.

[0021] In step R1, an aromatic prepolymer-containing liquid is prepared. In some embodiments, step R1 may be preparing an aromatic prepolymer-containing liquid using a prepolymer-containing liquid containing a prepolymer having a structure derived from an aromatic diamine and a structure derived from an acid dianhydride that has been previously prepared (step R1-s). Alternatively, in some embodiments, step R1 may be obtaining an aromatic prepolymer-containing liquid containing an aromatic prepolymer using an aromatic diamine, an acid dianhydride, and a solvent (step R1-i).

[0022] In step R2, a polyamic acid-containing liquid is obtained using an aromatic prepolymer-containing liquid, an aliphatic or alicyclic diamine, and an acid dianhydride. An aromatic diamine may also be used. For example, step R2 may be step R2-a), in which an aliphatic or alicyclic diamine and an acid dianhydride are added to the aromatic prepolymer-containing liquid to obtain a polyamic acid-containing liquid containing polyamic acid. An aliphatic or alicyclic diamine, an acid dianhydride, and further an aromatic diamine may be added to the aromatic prepolymer-containing liquid. In a method in which only an aliphatic or alicyclic diamine or an acid dianhydride is added to the aromatic prepolymer-containing liquid, the polymerization reaction is difficult to proceed because the reaction is easily affected by moisture present in the reaction system or a poorly soluble salt is easily generated.

[0023] Examples of embodiments of the production method R include a production method Rs including steps R1-s and R2-a, and a production method Ri including steps R1-i and R2-a. In the production method Ri, step R2-a is preferably carried out immediately after step R1-i.

[0024] In step R1-s, for example, a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from an acid dianhydride can be used as is to prepare an aromatic prepolymer-containing liquid for use in step R2. Alternatively, in step R1-s, for example, a prepolymer-containing liquid prepared in advance can be diluted or concentrated as necessary to adjust the concentration to prepare an aromatic prepolymer-containing liquid for use in step R2. The prepolymer-containing liquid used in step R1-s can be, for example, a prepolymer-containing liquid prepared separately or a commercially available prepolymer-containing liquid. The prepolymer-containing liquid can be prepared by a known method for producing a polyamic acid solution, a method for producing a polyamic acid-containing liquid according to the present disclosure, or the like.

[0025] Step R1-i can be carried out, for example, by the following method. First, an aromatic diamine is dissolved in a solvent to prepare an aromatic diamine solution. Next, an acid dianhydride is added to the aromatic diamine solution and stirred. The stirring time is, for example, 5 minutes to 5 hours, 10 minutes to 3 hours, or 30 minutes to 2 hours. The stirring temperature is, for example, 10 to 50°C, 15 to 40°C, or 20 to 35°C.

[0026] The acid dianhydride may be added to the aromatic diamine solution in one addition, or in two or more additions. The number of additions is, for example, 10 or less additions, 7 or less additions, or 4 or less additions. The interval between additions is, for example, 5 or more minutes, or 10 or more minutes. The interval between additions is, for example, 120 or less minutes, 60 or less minutes, 30 or less minutes, or 15 or less minutes.

[0027] Aromatic diamines are less likely to form salts with acid dianhydrides due to their low basicity, and therefore, in step R1-i, an aromatic prepolymer-containing liquid containing aromatic prepolymers at a high concentration can be easily prepared.

[0028] Step R2-a may be performed, for example, using the following method. First, an aliphatic or alicyclic diamine is dissolved in a solvent to prepare an aliphatic or alicyclic diamine solution. Next, the aliphatic or alicyclic diamine solution and an acid dianhydride are added to the aromatic prepolymer-containing liquid prepared in step R1, and the mixture is stirred. The stirring time is, for example, 10 minutes or more, 1 hour or more, or 3 hours or more. The stirring time is, for example, 72 hours or less, 48 ​​hours or less, 24 hours or less, 12 hours or less, or 5 hours or less. The stirring temperature is, for example, 10 to 50°C, 15 to 40°C, or 20 to 35°C. When a stirrer is used for stirring, the rotation speed is, for example, 50 to 2,000 min －１ , 200~1,000min －１ , or 300 to 800 min －１ is.

[0029] Although it depends on the amount of the aromatic prepolymer, the aliphatic or alicyclic diamine, and the acid dianhydride added, the addition method, etc., salt typically precipitates upon addition. The stirring time is preferably equal to or longer than the time required to dissolve the salt. On the other hand, from the viewpoint of production efficiency, a short stirring time is preferable. According to Production Method R, the salt can be dissolved in a short time, thereby enabling efficient production of a polyamic acid-containing liquid. The salt can be dissolved in a shorter time at a higher stirring temperature. Therefore, stirring may be performed while heating. On the other hand, from the viewpoint of ease of production, stirring without heating is preferable. According to Production Method R, the salt can be dissolved in a short time without heating, thereby enabling efficient production of polyamic acid. The salt can be dissolved in a short time by using an additive capable of dissolving salt, such as acetic acid. Therefore, stirring may be performed in the presence of an additive capable of dissolving salt. On the other hand, from the viewpoint of ease of production, stirring without using an additive is preferable. According to Production Method R, the salt can be dissolved in a short time without using an additive, thereby enabling efficient production of polyamic acid.

[0030] The aliphatic or alicyclic diamine solution and the acid dianhydride may be added simultaneously or separately to the aromatic prepolymer-containing liquid. The aliphatic or alicyclic diamine solution, the acid dianhydride, or both the aliphatic or alicyclic diamine solution and the acid dianhydride may be added to the aromatic prepolymer-containing liquid in one batch, or the entire amounts may be added in two or more batches. When adding two or more batches, the number of batches is, for example, 10 or less, 7 or less, or 4 or less. The interval between each batch is, for example, 5 minutes or more, or 10 minutes or more. The interval between each batch is, for example, 120 minutes or less, 60 minutes or less, 30 minutes or less, or 15 minutes or less. Alternatively, when adding two or more batches, there is no particular limitation. The solution may be added dropwise over a predetermined time, or the solid may be added in small amounts. The predetermined time is, for example, 10 to 60 minutes. When both the aliphatic or alicyclic diamine solution and the acid dianhydride are added to the aromatic prepolymer-containing liquid in two or more divided portions, the number of divided portions may be the same or different.

[0031] An aliphatic or alicyclic diamine and an aromatic diamine may be added to the aromatic prepolymer-containing liquid. In this case, the aliphatic or alicyclic diamine and the aromatic diamine may be added to the aromatic prepolymer-containing liquid simultaneously or separately. The aromatic diamine may be added in its entirety in one addition to the aromatic prepolymer-containing liquid, or in two or more additions.

[0032] When step R1-i and step R2-a are carried out consecutively, it is preferable to start adding at least one of the aliphatic or alicyclic diamine solution and the acid dianhydride while stirring in step R1-i is continuing or, for example, within 60 minutes after stirring is stopped. When step R1-i and step R2-a are carried out consecutively, the aliphatic or alicyclic diamine solution and the acid dianhydride can be added and stirred in the container in which the aromatic prepolymer-containing liquid was obtained in step R1-i.

[0033] The aromatic prepolymer may contain any structure other than the aromatic diamine-derived structure and the acid dianhydride-derived structure. For example, the aromatic prepolymer may contain any diamine-derived structure, such as an aliphatic or alicyclic diamine-derived structure. The content of the aromatic diamine-derived structure is, for example, more than 50 mass%, 70 mass% or more, 90 mass% or more, or 100 mass% based on the mass of all diamine-derived structures.

[0034] The weight average molecular weight of the aromatic prepolymer is preferably 500 to 80,000, more preferably 1,000 to 50,000, and even more preferably 5,000 to 30,000. The weight average molecular weight may be 20,000 or less, or 10,000 or less. When the weight average molecular weight is 500 or more, the salt formed between the aromatic prepolymer and the aliphatic or alicyclic diamine tends to have low crystallinity and be easily soluble. When the weight average molecular weight is 80,000 or less, excessive viscosity can be prevented, miscibility with the acid dianhydride and the aliphatic or alicyclic diamine is improved, and the dissolution rate of the salt tends to be increased. In the present disclosure, the weight average molecular weight can be measured by gel permeation chromatography (GPC) and calculated using a calibration curve of standard polystyrene. Specifically, the weight average molecular weight can be measured by the method described in the Examples.

[0035] The aromatic prepolymer content in the aromatic prepolymer-containing liquid is, for example, 30.0 mass% or less, 20.0 mass% or less, 12.0 mass% or less, or 8.0 mass% or less, based on the mass of the aromatic prepolymer-containing liquid, from the viewpoint of preventing the viscosity from becoming too high. The aromatic prepolymer content is, for example, 3.0 mass% or more, 5.0 mass% or more, or 10.0 mass% or more, based on the mass of the aromatic prepolymer-containing liquid, from the viewpoint of dissolving the salt in a short time.

[0036] The mass ratio of the aromatic prepolymer used in Production Method R is, for example, 10.0 mass% or more, 15.0 mass% or more, 20.0 mass% or more, 30.0 mass% or more, or 40.0 mass% or more relative to the mass of the resulting polyamic acid, from the viewpoint of dissolving the salt in a short time. The mass ratio of the aromatic prepolymer is, for example, 70.0 mass% or less, 60 mass% or less, 50 mass% or less, 40 mass% or less, or 30 mass% or less relative to the mass of the polyamic acid, taking into consideration the amounts of the aliphatic or alicyclic diamine and the acid dianhydride used.

[0037] In particular, when a polyamic acid-containing liquid having a high polyamic acid content is obtained, the aromatic prepolymer content in the aromatic prepolymer-containing liquid is, for example, 15.0 mass% or more, 18.0 mass% or more, or 20.0 mass% or more, based on the mass of the aromatic prepolymer-containing liquid. The aromatic prepolymer content is, for example, 30.0 mass% or less, or 25.0 mass% or less, based on the mass of the aromatic prepolymer-containing liquid.

[0038] In particular, when a polyamic acid-containing solution having a high content of polyamic acid is obtained, the mass ratio of the aromatic prepolymer used in Production Method R is, for example, 50.0 mass% or more, 65.0 mass% or more, or 65.0 mass% or more, relative to the mass of the resulting polyamic acid. The mass ratio of the aromatic prepolymer is, for example, 90.0 mass% or less, 80 mass% or less, or 75.0 mass% or less, relative to the mass of the polyamic acid, taking into account the amounts of aliphatic or alicyclic diamine and acid dianhydride used.

[0039] The polyamic acid-containing liquid obtained by production method R typically contains polyamic acid and a solvent. The polyamic acid content is not particularly limited and can be adjusted to an appropriate content depending on the application of the polyamic acid-containing liquid. Production method R allows for the production of a polyamic acid-containing liquid containing a high polyamic acid content. The polyamic acid content, based on the total mass of the polyamic acid and the solvent, may be, for example, 10.0 mass% or more, 15.0 mass% or more, 20.0 mass% or more, or 25.0 mass% or more. The polyamic acid content, based on the total mass of the polyamic acid and the solvent, may be, for example, 50.0 mass% or less, 40.0 mass% or less, or 30.0 mass% or less.

[0040] The polyamic acid obtained by Production Method R contains at least a structure derived from an aromatic diamine, a structure derived from an aliphatic or alicyclic diamine, and a structure derived from an acid dianhydride. The polyamic acid may further contain any structure. In Production Method R, a monomer such as a diamine or an acid dianhydride may be selected and used depending on the structure contained in the target polyamic acid. Preferred embodiments (e.g., type, content, etc.) of the polyamic acid-containing liquid and the polyamic acid contained therein, as well as amines such as diamines, acids such as acid dianhydrides, and solvents that can be used in Production Method R will be described below.

[0041] [Manufacturing Method L] Manufacturing Method L includes obtaining a polyamic acid-containing solution containing a polyamic acid using a prepolymer-containing solution containing an amic acid prepolymer having a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride, a diamine, and an acid dianhydride (sometimes referred to as "Step L2" in the present disclosure). Manufacturing Method L may further include preparing a prepolymer-containing solution containing an amic acid prepolymer having a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride (sometimes referred to as "Step L1" in the present disclosure). In the present disclosure, an amic acid prepolymer having a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride may be referred to as an "aliphatic or alicyclic prepolymer," and a prepolymer-containing solution containing an aliphatic or alicyclic prepolymer may be referred to as an "aliphatic or alicyclic prepolymer-containing solution." Manufacturing Method L may include any steps other than Steps L1 and L2.

[0042] According to Production Method L, when an aliphatic or alicyclic diamine is not used, polymerization can proceed because a salt of the aliphatic or alicyclic diamine is not formed. Alternatively, according to Production Method L, polymerization can proceed even when an aliphatic or alicyclic diamine is used. One reason for this is presumed to be as follows: In Production Method L, when the diamine contains an aliphatic or alicyclic diamine, an aliphatic or alicyclic prepolymer, an aliphatic or alicyclic diamine, and an acid dianhydride are reacted to obtain a polyamic acid. The aliphatic or alicyclic diamine forms a salt with the aliphatic or alicyclic prepolymer and the acid dianhydride, respectively. For polyamic acids with the same composition, Production Method L forms a salt of the aliphatic or alicyclic diamine and the aliphatic or alicyclic prepolymer, resulting in a smaller amount of salt of the aliphatic or alicyclic diamine and the acid dianhydride than when polyamic acids are obtained using an aliphatic or alicyclic diamine and an acid dianhydride. Salts of aliphatic or alicyclic prepolymers are more soluble than salts of acid dianhydrides due to structural influences. In Production Method L, salts of aliphatic or alicyclic prepolymers that are more soluble are formed, while the formation of salts of acid dianhydrides that are less soluble is suppressed. In other words, when the diamine contains an aliphatic or alicyclic diamine, Production Method L is a method that reduces the amount of sparingly soluble salts and adds more soluble salts to promote the dissolution of the entire salt, thereby allowing the polymerization reaction to proceed. However, the present invention is not limited by this assumption.

[0043] In step L1, an aliphatic or alicyclic prepolymer-containing liquid is prepared. In some embodiments, step L1 may be preparing an aliphatic or alicyclic prepolymer-containing liquid using a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride that has been previously prepared (step L1-s). Alternatively, in some embodiments, step L1 may be obtaining an aliphatic or alicyclic prepolymer-containing liquid containing an aliphatic or alicyclic prepolymer using an aliphatic or alicyclic diamine, an acid dianhydride, and a solvent (step L1-i).

[0044] In step L2, a polyamic acid-containing liquid is obtained using an aliphatic or alicyclic prepolymer-containing liquid, a diamine, and an acid dianhydride. The diamine may include one or both of an aliphatic or alicyclic diamine and an aromatic diamine. For example, step L2 may be step L2-a, in which a diamine and an acid dianhydride are added to an aliphatic or alicyclic prepolymer-containing liquid to obtain a polyamic acid-containing liquid containing polyamic acid. In a method in which only a diamine or an acid dianhydride is added to an aliphatic or alicyclic prepolymer-containing liquid, the polymerization reaction is difficult to proceed because the reaction is easily affected by moisture present in the reaction system or a poorly soluble salt is easily formed.

[0045] Examples of embodiments of the production method L include a production method Ls including steps L1-s and L2-a, and a production method Li including steps L1-i and L2-a. In the production method Li, step L2-a is preferably carried out immediately after step L1-i.

[0046] The explanations regarding steps R1-s, R1-i, and R2-a in production method R can be applied, mutatis mutandis, to steps L1-s, L1-i, and L2-a in production method L. For example, the examples given for steps R1-s, R1-i, and R2-a can be used as the methods, times, temperatures, and the like in steps L1-s, L1-i, and L2-a.

[0047] However, in step L1-i, since the aliphatic or alicyclic diamine easily forms a salt with the acid dianhydride, the amounts of the aliphatic or alicyclic diamine, the acid dianhydride, and the solvent used may be adjusted to keep the concentration of the resulting aliphatic or alicyclic prepolymer-containing liquid low so as to prevent precipitation of the salt. The content of the aliphatic or alicyclic prepolymer is particularly preferably 15.0 mass% or less, based on the mass of the aliphatic or alicyclic prepolymer-containing liquid.

[0048] In step L2-a, when an alicyclic or aliphatic diamine and an aromatic diamine are added as diamines to the aliphatic or alicyclic prepolymer-containing liquid, it is preferable to add an alicyclic or aliphatic diamine solution and a solid aromatic diamine to the aliphatic or alicyclic prepolymer-containing liquid, or to add a solution containing an alicyclic or aliphatic diamine and an aromatic diamine to the aliphatic or alicyclic prepolymer-containing liquid.

[0049] The aliphatic or alicyclic prepolymer may contain any structure other than the structure derived from the aliphatic or alicyclic diamine and the structure derived from the acid dianhydride. For example, the aliphatic or alicyclic prepolymer may contain any diamine-derived structure, such as a structure derived from an aromatic diamine. The content of the aliphatic or alicyclic diamine-derived structure is, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass, based on the mass of all diamine-derived structures.

[0050] The weight average molecular weight of the aliphatic or alicyclic prepolymer is preferably 500 to 80,000, more preferably 1,000 to 50,000, and even more preferably 5,000 to 30,000. The weight average molecular weight may be 10,000 or more, 20,000 or more, or 30,000 or more. When the weight average molecular weight is 500 or more, the salt formed by the aliphatic or alicyclic prepolymer and the aliphatic or alicyclic diamine tends to have low crystallinity and be easily soluble. When the weight average molecular weight is 80,000 or less, excessive viscosity can be prevented, miscibility with the acid dianhydride and the diamine is improved, and the dissolution rate of the salt tends to be easily increased.

[0051] The content of the aliphatic or alicyclic prepolymer in the aliphatic or alicyclic prepolymer-containing liquid is, for example, 15.0 mass% or less, 13.0 mass% or less, 10.0 mass% or less, or 8.0 mass% or less, based on the mass of the aliphatic or alicyclic prepolymer-containing liquid, from the viewpoint of dissolving the salt in a short time. The content of the aliphatic or alicyclic prepolymer is, for example, 3.0 mass% or more, 5.0 mass% or more, or 10.0 mass% or more, based on the mass of the aliphatic or alicyclic prepolymer-containing liquid, from the viewpoint of dissolving the salt in a short time.

[0052] The mass ratio of the aliphatic or alicyclic prepolymer used in Production Method L is, for example, 10.0 mass% or more, 15.0 mass% or more, 20.0 mass% or more, 30.0 mass% or more, or 40.0 mass% or more relative to the mass of the resulting polyamic acid, from the viewpoint of dissolving the salt in a short time. The mass ratio of the aliphatic or alicyclic prepolymer is, for example, 70.0 mass% or less, 60 mass% or less, 50.0 mass% or less, 40.0 mass% or less, or 30.0 mass% or less relative to the mass of the polyamic acid, taking into account the amounts of diamine and acid dianhydride used.

[0053] The polyamic acid-containing liquid obtained by Production Method L typically contains polyamic acid and a solvent. The polyamic acid content is not particularly limited and can be adjusted to an appropriate content depending on the application of the polyamic acid-containing liquid. Production Method L allows for the production of a polyamic acid-containing liquid containing a high concentration of polyamic acid. The polyamic acid content, based on the mass of the polyamic acid-containing liquid, may be, for example, 10.0 mass% or more, 15.0 mass% or more, 20.0 mass% or more, or 25.0 mass% or more. The polyamic acid content, based on the mass of the polyamic acid-containing liquid, may be, for example, 50.0 mass% or less, 40.0 mass% or less, or 30.0 mass% or less.

[0054] The polyamic acid obtained by Production Method L contains at least a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride. The polyamic acid may further contain any structure. For example, the polyamic acid may contain any diamine-derived structure, such as a structure derived from an aromatic diamine. In Production Method L, monomers such as diamines and acid dianhydrides can be selected and used depending on the structure contained in the target polyamic acid. Preferred embodiments (e.g., type, content, etc.) of the polyamic acid-containing liquid and the polyamic acid contained therein, as well as amines such as diamines, acids such as acid dianhydrides, and solvents that can be used in Production Method L will be described below.

[0055] <Polyamic Acid-Containing Liquid> The polyamic acid-containing liquid contains a polyamic acid containing a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride, and a solvent. The polyamic acid may contain any structure, such as an amine-derived structure other than a structure derived from an aliphatic or alicyclic diamine, or a carboxylic acid anhydride-derived structure other than a structure derived from an acid dianhydride. The polyamic acid may further contain a diamine-derived structure, such as a structure derived from an aromatic diamine. The acid dianhydride-derived structure preferably contains a structure derived from pyromellitic dianhydride.

[0056] The polyamic acid content of the polyamic acid-containing liquid is preferably high. When the polyamic acid content is high, the amount of volatilized solvent is reduced when a molded body, such as a film, is produced using the polyamic acid-containing liquid, making it easier to obtain a film with a more uniform in-plane thickness. When the polyamic acid content is high, the viscosity of the polyamic acid-containing liquid can be increased, making it possible to produce a film with a large thickness depending on the application.

[0057] In some embodiments, the content of components derived from amines and carboxylic acid anhydrides in the polyamic acid-containing liquid is, for example, 20.0 mass% or more, based on the mass of the polyamic acid-containing liquid. In some embodiments, the ratio of the mass of components derived from amines and carboxylic acid anhydrides obtained by heating the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is, for example, 18.0 mass% or more. When either or both of this content and this ratio are high, a polyamic acid-containing liquid tends to have a high viscosity.

[0058] Examples of components derived from amines and carboxylic acid anhydrides (hereinafter sometimes referred to as "monomer-derived components") include polyamic acids, salts of aliphatic or alicyclic diamines and carboxylic acids, salts of aliphatic or alicyclic diamines and amide acid prepolymers, polyimides, etc. The monomer-derived component includes at least one selected from these.

[0059] In some embodiments, the polyamic acid content in the polyamic acid-containing liquid is, for example, 20.0 mass% or more, based on the total mass of the polyamic acid and the solvent. In some embodiments, the ratio of the mass of the polyimide obtained by heating the filtrate of the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is, for example, 18.0 mass% or more. When either or both of this content and this ratio are high, good film-forming properties tend to be obtained.

[0060] Depending on the method for producing the polyamic acid-containing liquid, precipitates such as salts derived from the monomers may occur during the production process. If the precipitates do not dissolve, they remain as solids in the polyamic acid-containing liquid. It is preferable that the polyamic acid-containing liquid does not contain any solids, or if it contains any solids, the content is low. If the polyamic acid-containing liquid does not contain any solids or has a low content, when a molded product such as a film is produced using the polyamic acid-containing liquid, a uniform film with excellent surface flatness is likely to be obtained.

[0061] In some embodiments, the turbidity of the polyamic acid-containing liquid is, for example, 2.5 NTU (Nephelometric Turbidity Unit) or less. When the turbidity is low, good film-forming properties tend to be obtained. When the solid content in the polyamic acid-containing liquid is high, the turbidity usually becomes high.

[0062] In a preferred embodiment, the polyamic acid-containing liquid contains a polyamic acid having a structure derived from an aliphatic or alicyclic diamine and a structure derived from an acid dianhydride, and a solvent, and satisfies at least one of the following (1) to (4). For example, the polyamic acid-containing liquid satisfies one or both of the following (1) and (2), or one or both of the following (3) and (4). (1) The content of components derived from amines and carboxylic acid anhydrides is 20.0% by mass or more, and the turbidity is 2.5 NTU or less. (2) The content of polyamic acid is 20.0% by mass or more, based on the total mass of the polyamic acid and the solvent. (3) The turbidity is 2.5 NTU or less, and the ratio of the mass of components derived from amines and carboxylic acid anhydrides obtained by heating the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0% by mass or more. (4) The ratio of the mass of polyimide obtained by heating the filtrate of the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass % or more.

[0063] The content of the monomer-derived component in the polyamic acid-containing liquid may be, based on the mass of the polyamic acid-containing liquid, preferably 20.0 mass% or more, 20.1 mass% or more, 20.2 mass% or more, 20.5 mass% or more, 21.0 mass% or more, 23.0 mass% or more, 25.0 mass% or more, or 25.1 mass% or more. The upper limit of the content of the monomer-derived component in the polyamic acid is not particularly limited. The content of the monomer-derived component is, based on the mass of the polyamic acid-containing liquid, for example, 50.0 mass% or less, 40.0 mass% or less, 30.0 mass% or less, 28.0 mass% or less, or 26.0 mass% or less.

[0064] The ratio of the monomer-derived component obtained by heating the polyamic acid-containing liquid may be, based on the mass of the polyamic acid-containing liquid, preferably 18.0 mass% or more, 18.3 mass% or more, 18.5 mass% or more, 19.0 mass% or more, 20.0 mass% or more, 22.0 mass% or more, 22.5 mass% or more, 23.0 mass% or more, or 23.5 mass% or more. The upper limit of the ratio of the monomer-derived component in the polyamic acid is not particularly limited. The ratio of the monomer-derived component is, for example, 48.0 mass% or less, 38.0 mass% or less, 28.0 mass% or less, 26.0 mass% or less, or 24.0 mass% or less, based on the mass of the polyamic acid-containing liquid.

[0065] The content and ratio of monomer-derived components can be adjusted by changing the amounts of diamine, acid dianhydride, solvent, etc. used to prepare the polyamic acid-containing solution. The content and ratio of components derived from amine and carboxylic acid anhydride can be measured by the method described in the Examples. The calculation formula for correcting the water content can be used by appropriately changing the type and average molecular weight of the monomer.

[0066] The polyamic acid content, based on the mass of the polyamic acid-containing liquid, may be preferably 20.0 mass% or more, 20.1 mass% or more, 20.2 mass% or more, 20.5 mass% or more, 21.0 mass% or more, 23.0 mass% or more, 25.0 mass% or more, or 25.1 mass% or more. The upper limit of the polyamic acid content is not particularly limited. The polyamic acid content, based on the mass of the polyamic acid-containing liquid, may be, for example, 50.0 mass% or less, 40.0 mass% or less, 30.0 mass% or less, 28.0 mass% or less, or 26.0 mass% or less.

[0067] The proportion of polyimide obtained by heating the filtrate of the polyamic acid-containing liquid may be, based on the mass of the polyamic acid-containing liquid, preferably 18.0 mass% or more, 18.3 mass% or more, 18.5 mass% or more, 19.0 mass% or more, 20.0 mass% or more, 22.0 mass% or more, 22.5 mass% or more, 23.0 mass% or more, or 23.5 mass% or more. The upper limit of the polyimide proportion is not particularly limited. The polyimide proportion, based on the mass of the polyamic acid-containing liquid, is, for example, 48.0 mass% or less, 38.0 mass% or less, 28.0 mass% or less, 26.0 mass% or less, or 24.0 mass% or less.

[0068] A polyamic acid-containing solution having a high polyamic acid content or a high polyimide ratio can be easily produced, for example, by the manufacturing method of the above-described embodiment. The polyamic acid content and polyimide ratio can be measured using the filtrate obtained by filtering the polyamic acid-containing solution to remove solids such as salts derived from the monomers. A 150-mesh stainless steel filter can be used for filtration. The polyamic acid content and polyimide ratio can be measured specifically by the method described in the Examples. The calculation formula for correcting the water content can be used by appropriately changing the type of monomer and the average molecular weight.

[0069] The polyamic acid content and polyimide ratio may each be the content or ratio at the temperature at which the polyamic acid-containing liquid is actually used. Alternatively, the temperature of the polyamic acid-containing liquid when these contents and ratios are determined may differ from the temperature at which the polyamic acid-containing liquid is actually used. These contents and ratios may be, for example, the content or ratio when the temperature of the polyamic acid-containing liquid is anywhere from 20 to 35°C, and preferably the content or ratio when the temperature of the polyamic acid-containing liquid is 25°C. In this case, the polyamic acid-containing liquid is filtered at a temperature of anywhere from 20 to 35°C (preferably 25°C), and the content or ratio can be measured using the obtained filtrate.

[0070] The turbidity of the polyamic acid-containing liquid is preferably 2.5 NTU or less, 2.0 NTU or less, 1.5 NTU or less, 1.0 NTU or less, or 0.5 NTU or less, or 0 NTU. In the present disclosure, turbidity is the turbidity based on a formazin standard solution measured by a transmitted scattered light method. Specifically, turbidity can be measured by the method described in the Examples. Typically, the lower the turbidity, the lower the content of solids such as salts. The turbidity may be the turbidity at the temperature at which the polyamic acid-containing liquid is actually used. Alternatively, the temperature of the polyamic acid-containing liquid when determining the turbidity may be different from the temperature at which the polyamic acid-containing liquid is actually used. The turbidity may be, for example, the turbidity when the temperature of the polyamic acid-containing liquid is between 20 and 35°C, and is preferably the turbidity when the temperature of the polyamic acid-containing liquid is 25°C.

[0071] The viscosity (ηinh) of the polyamic acid-containing liquid is preferably 0.3 dL / g or more, more preferably 0.5 dL / g or more, and even more preferably 0.6 dL / g or more. The viscosity of the polyamic acid-containing liquid is, for example, 1.5 dL / g or less, 1.3 dL / g or less, or 1.0 dL / g or less. The viscosity of the polyamic acid-containing liquid is measured at 30°C using an Ostwald viscometer. Specifically, the viscosity can be measured by the method described in the Examples.

[0072] The weight average molecular weight of the polyamic acid is preferably 5,000 to 130,000, more preferably 10,000 to 120,000, still more preferably 15,000 to 110,000, and particularly preferably more than 15,000 but not more than 100,000. When the weight average molecular weight is within this range, good film-forming properties tend to be obtained.

[0073] In the polyamic acid, the content of the structure derived from an aliphatic or alicyclic diamine, based on the mass of all diamine-derived structures contained in the polyamic acid, is preferably 20% by mass or more, for example, 30% by mass or more, 50% by mass or more, 70% by mass or more, or 80% by mass or more, or 100% by mass. When it is 20% by mass or more, excellent dielectric properties tend to be obtained. The content of the structure derived from an aliphatic or alicyclic diamine, based on the mass of all diamine-derived structures contained in the polyamic acid, may be, for example, 80% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less.

[0074] In the polyamic acid, the content of the aromatic diamine-derived structure is preferably 80% by mass or less, for example, 70% by mass or less, 50% by mass or less, 30% by mass or less, or 20% by mass or less, or 0% by mass, based on the mass of all diamine-derived structures contained in the polyamic acid. When the polyamic acid contains an aromatic diamine-derived structure, the content of the aromatic diamine-derived structure may be 20% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, based on the mass of all diamine-derived structures contained in the polyamic acid, from the viewpoint of mechanical strength.

[0075] In the polyamic acid, the content of the structure derived from pyromellitic dianhydride is preferably 50% by mass or more, for example, 70% by mass or more, or 85% by mass or more, or 100% by mass, based on the mass of all structures derived from acid dianhydrides contained in the polyamic acid.

[0076] In the polyamic acid, the content of structures derived from aliphatic or alicyclic diamines is preferably 20% by mass or more, based on the mass of all diamine-derived structures contained in the polyamic acid, and the content of structures derived from acid dianhydrides is preferably 50% by mass or more, based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid. The molar ratio of the diamine-derived structures to the acid dianhydride-derived structures is, for example, 1.00:0.90 to 1.00:1.10, and preferably 1.00:0.95 to 1.00:1.05.

[0077] Examples of diamine-derived structures and acid dianhydride-derived structures that can be contained in polyamic acid will be described later. The aliphatic or alicyclic diamine-derived structure preferably contains an alicyclic diamine-derived structure, and more preferably contains a dimer diamine-derived structure. When polyamic acid contains a dimer diamine-derived structure, the dielectric constant and dielectric loss tangent of the polyimide can be reduced. Polyimides with low dielectric constants and dielectric loss tangents can suppress transmission loss, and are therefore suitable for applications such as substrates for FPCs and high-frequency antennas.

[0078] The polyamic acid-containing liquid contains a solvent. The polyamic acid-containing liquid may contain any component other than polyamic acid and the solvent. Examples of solvents that the polyamic acid-containing liquid may contain will be described later. The solvent may be a polar organic solvent, and preferably contains an amide-based solvent containing an amide bond.

[0079] The method for producing the polyamic acid-containing liquid is not particularly limited, but the production method of the above-described embodiment can be preferably used.

[0080] <Diamine> The diamine that can be used in the method for producing a polyamic acid-containing liquid of the above-described embodiment, and the diamine in the "structural unit derived from diamine" contained in the polyamic acid contained in the polyamic acid-containing liquid of the above-described embodiment, may include an aromatic diamine, an aliphatic or alicyclic diamine, or both of these.

[0081] In the present disclosure, the aromatic diamine may be a diamine having at least one aromatic ring and two amino groups bonded to at least one aromatic ring. When the aromatic diamine has two or more aromatic rings, the two or more aromatic rings may be the same or different from each other. When the aromatic diamine has two or more aromatic rings, the two amino groups may be bonded to one aromatic ring, or the two amino groups may be bonded to different aromatic rings. The aromatic diamine may further have at least one group selected from an aliphatic hydrocarbon group and an alicyclic hydrocarbon group.

[0082] In the present disclosure, an aliphatic or alicyclic diamine may be a diamine that has at least one group selected from an aliphatic hydrocarbon group and an alicyclic hydrocarbon group and two amino groups, and does not fall under the category of an aromatic diamine. An aliphatic or alicyclic diamine may further have at least one aromatic ring. At least one of the two amino groups is bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group. Both of the two amino groups may be bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, or only one of the two amino groups may be bonded to an aliphatic or alicyclic diamine. When an aliphatic or alicyclic diamine has two or more groups selected from an aliphatic hydrocarbon group and an alicyclic hydrocarbon group, the two or more groups may be the same or different from each other. When an aliphatic or alicyclic diamine has two or more groups selected from aliphatic hydrocarbon groups and alicyclic hydrocarbon groups, the two amino groups may be bonded to one group selected from aliphatic hydrocarbon groups and alicyclic hydrocarbon groups, or the two amino groups may be bonded to different groups selected from aliphatic hydrocarbon groups and alicyclic hydrocarbon groups. Amino groups bonded to aliphatic hydrocarbon groups or alicyclic hydrocarbon groups are more basic than amino groups bonded to aromatic rings and therefore more likely to form salts with carboxylic acids.

[0083] Examples of aromatic diamines include 1,4-phenylenediamine, 1,2-phenylenediamine, 1,3-phenylenediamine, 4,4'-(biphenyl-2,5-diylbisoxy)bisaniline, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, and bis(4-(4-aminophenoxy)phenyl)sulfonate. bis(4-(3-aminophenoxy)phenyl)sulfone, 1,3-bis(4-aminophenoxy)neopentane, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diamino-3,3'-dihydroxybiphenyl, bis(4-amino-3-carboxyphenyl)methane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diamino 4,4'-diamino-2-(trifluoromethyl)diphenyl ether, 5-trifluoromethyl-1,3-benzenediamine, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl ... Examples of such diamines include diamines having an aromatic hydrocarbon group or an aromatic heterocyclic group, such as [4-{4-amino-2-(trifluoromethyl)phenoxy}phenyl]hexafluoropropane, 2-trifluoromethyl-p-phenylenediamine, 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane, 4,4'-(9-fluorenylidene)dianiline, 2,7-diaminofluorene, 1,5-diaminonaphthalene, and 3,7-diamino-2,8-dimethyldibenzothiophene 5,5-dioxide.

[0084] Examples of aliphatic or alicyclic diamines include diamines having a saturated aliphatic hydrocarbon group such as 1,2-ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,14-diaminotetradecane, and 1,16-diaminohexadecane; diamines having an unsaturated aliphatic hydrocarbon group such as 1,9-diaminononene, 1,10-diaminodecene, 1,11-diaminoundecene, 1,12-diaminododecene, 1,14-diaminotetradecene, and 1,16-diaminohexadecane;1,4-diaminocyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, isophoronediamine, bis(aminomethyl)norbornane, 1,3-diaminoadamantane, 4,4'-diaminodicyclohexylmethane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 3,3'-diethyl-4,4'-diaminodi Cyclohexylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodicyclohexylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodicyclohexylmethane, 3,5-diethyl-3',5'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexyl ether, 3,3'-dimethyl-4,4'-diaminodicyclohexyl ether, 3,3' -diethyl-4,4'-diaminodicyclohexyl ether, 3,3',5,5'-tetramethyl-4,4'-diaminodicyclohexyl ether, 3,3',5,5'-tetraethyl-4,4'-diaminodicyclohexyl ether, 3,5-diethyl-3',5'-dimethyl-4,4'-diaminodicyclohexyl ether, 2,2-bis(4-aminocyclohexyl)propane, 2,2-bis(3-methyl diamines having a saturated aliphatic hydrocarbon group such as 2,2-bis(3-ethyl-4-aminocyclohexyl)propane, 2,2-bis(3,5-dimethyl-4-aminocyclohexyl)propane, 2,2-bis(3,5-diethyl-4-aminocyclohexyl)propane, 2,2-bis(3,5-diethyl-3',5'-dimethyl-4,4'-diaminodicyclohexyl)propane; diamines having an unsaturated alicyclic hydrocarbon group such as bis(aminomethyl)norbornene and 4,4'-diaminodicyclohexenylmethane; monounsaturated fatty acids such as crotonic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, and nervonic acid; diunsaturated fatty acids such as linoleic acid, eicosadienoic acid, and docosadienoic acid;Examples include diamines derived from dimers (also called dimer acids) of unsaturated fatty acids such as triunsaturated fatty acids such as linolenic acid, pinolenic acid, eleostearic acid, mead acid, dihomo-γ-linolenic acid, and eicosatrienoic acid; and dimer diamines such as hydrogenated diamines in which the carbon-carbon double bonds contained in the molecule of these diamines are hydrogenated.

[0085] The diamine preferably contains an alicyclic diamine from the viewpoint of reducing the dielectric constant. In particular, the diamine more preferably contains at least one selected from dimer diamine (non-hydrogenated dimer diamine and hydrogenated dimer diamine). When the polyamic acid contains a structure derived from dimer diamine, the dielectric constant and dielectric loss tangent of the polyimide can be reduced. The diamine preferably contains an aromatic diamine from the viewpoint of maintaining mechanical strength.

[0086] In the polyamic acid, the content of the structure derived from an aliphatic or alicyclic diamine is preferably 20% by mass or more, more preferably 30% by mass or more, 50% by mass or more, 70% by mass or more, or 90% by mass or more, or 100% by mass, based on the mass of all diamine-derived structures contained in the polyamic acid. The content of the structure derived from an aliphatic or alicyclic diamine is 100% by mass or less, for example, 90% by mass or less, or 70% by mass or less, based on the mass of all diamine-derived structures contained in the polyamic acid.

[0087] <Tetracarboxylic acid dianhydride> The tetracarboxylic acid dianhydride that can be used in the method for producing a polyamic acid-containing liquid of the above-described embodiment, and the tetracarboxylic acid dianhydride in the "structural unit derived from a tetracarboxylic acid dianhydride" contained in the polyamic acid contained in the polyamic acid-containing liquid of the above-described embodiment, may include an aromatic tetracarboxylic acid dianhydride, an aliphatic or alicyclic tetracarboxylic acid dianhydride, or both of them.

[0088] In the present disclosure, the aromatic tetracarboxylic dianhydride may be a compound having at least one aromatic ring and two acid anhydride groups bonded to at least one aromatic ring. When the aromatic tetracarboxylic dianhydride has two or more aromatic rings, the two or more aromatic rings may be the same or different from each other. When the aromatic tetracarboxylic dianhydride has two or more aromatic rings, the two acid anhydride groups may be bonded to one aromatic ring, or the two acid anhydride groups may be bonded to different aromatic rings. The aromatic tetracarboxylic dianhydride may further have at least one group selected from an aliphatic hydrocarbon group and an alicyclic hydrocarbon group.

[0089] In the present disclosure, the aliphatic or alicyclic tetracarboxylic acid dianhydride may be a diamine having at least one group selected from an aliphatic hydrocarbon group and an alicyclic hydrocarbon group and two acid anhydride groups, and not corresponding to an aromatic tetracarboxylic acid dianhydride. The aliphatic or alicyclic tetracarboxylic acid dianhydride may further have at least one aromatic ring.

[0090] Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3 ... bis(3,4-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,2',3,3'-benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, 4,4-(p-phenylenedioxy)diphthalic dianhydride, 4,4-(m-phenylenedioxy)di Phthalic dianhydride, 2,2',6,6'-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2'-bis(trifluoromethyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluorotrimethylene)-diphthalic dianhydride, Examples of the tetracarboxylic acid dianhydride include tetracarboxylic acid dianhydrides having an aromatic hydrocarbon group, such as 4,4'-(octafluorotetramethylene)-diphthalic dianhydride, 1,2,5,6-naphthalenedicarboxylic acid dianhydride, 1,4,5,8-naphthalenedicarboxylic acid dianhydride, 2,3,6,7-naphthalenedicarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, and 1,2,7,8-phenanthrenetetracarboxylic acid dianhydride.

[0091] Examples of the aliphatic or alicyclic tetracarboxylic dianhydride include tetracarboxylic dianhydrides having a saturated aliphatic hydrocarbon group such as ethylene tetracarboxylic dianhydride and butane tetracarboxylic dianhydride; tetracarboxylic dianhydrides having a saturated alicyclic hydrocarbon group such as 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride and 1,2,3,4-tetramethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride; 1,1-bis(2,3-dicarboxycyclohexyl)ethane dianhydride, bis(2,3-dicarboxycyclohexyl)methane dianhydride, bis(3,4-dicarboxycyclohexyl)methane dianhydride, 3,3',4,4'-bicyclohexyltetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxycyclohexyl)propane dianhydride, 2,2-bis(2,3-dicarboxycyclohexyl)propane dianhydride, bis(3,4-dicarboxycyclohexyl)sulfone dianhydride, bis(3,4-dicarboxycyclohexyl)ether dianhydride, bis(2,3-dicarboxycyclohexyl)ether dianhydride, 2,2',6,6'-bicyclohexyl tetracarboxylic acid dianhydrides having an alicyclic hydrocarbon group, such as 1,2,5,6-decahydronaphthalenedicarboxylic acid dianhydride, 1,4,5,8-decahydronaphthalenedicarboxylic acid dianhydride, 2,3,6,7-decahydronaphthalenedicarboxylic acid dianhydride, octahydrobiphenylene-4a,8b:4b,8a-tetracarboxylic acid dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic acid dianhydride, and 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride.

[0092] In the polyamic acid, the tetracarboxylic dianhydride preferably includes an aromatic tetracarboxylic dianhydride, and particularly preferably includes at least one selected from pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0093] The content of the pyromellitic dianhydride-derived structure is preferably 50% by mass or more, more preferably 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, or 100% by mass, based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid. The content of the pyromellitic dianhydride-derived structure is 100% by mass or less, for example, 90% by mass or less, or 70% by mass or less, based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid.

[0094] <Other Monomers> In the method for producing a polyamic acid-containing liquid of the above-described embodiment, any monomer, such as an amine other than a diamine or an acid anhydride other than a tetracarboxylic dianhydride, can be used. The polyamic acid contained in the polyamic acid-containing liquid of the above-described embodiment can include any structure, such as a structure derived from an amine other than a diamine or a structure derived from an acid anhydride other than a tetracarboxylic dianhydride. Examples of amines include diamines, monoamines, and trifunctional or higher amines. Examples of acid anhydrides include tetracarboxylic dianhydrides, dicarboxylic anhydrides, and tricarboxylic anhydrides.

[0095] In the polyamic acid, the content of the diamine-derived structure is, for example, 90% by mass or more, 95% by mass or more, or 100% by mass based on the mass of all amine-derived structures contained in the polyamic acid. In the polyamic acid, the content of the tetracarboxylic dianhydride structure is, for example, 90% by mass or more, 95% by mass or more, or 100% by mass based on the mass of all acid anhydride-derived structures contained in the polyamic acid.

[0096] <Solvent> Examples of solvents that can be used in the method for producing a polyamic acid-containing liquid of the above-described embodiment and that can be contained in the polyamic acid-containing liquid of the above-described embodiment include polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), γ-butyrolactone (GBL), 3-methoxy-N,N-dimethylpropanamide (MPA), N,N′-dimethylformamide, N,N′-dimethylpropyleneurea [1,3-dimethyl-3,4,5,6-tetrahydropyridimine-2(1H)-one], dimethyl sulfoxide, dimethylacetamide (DMAc), diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether. The solvent preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), γ-butyrolactone (GBL), 3-methoxy-N,N-dimethylpropanamide (MPA), and dimethylacetamide (DMAc), and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), γ-butyrolactone (GBL), 3-methoxy-N,N-dimethylpropanamide (MPA), and dimethylacetamide (DMAc).

[0097] <Polyamic Acid-Containing Liquid for Insulating Materials, Heat-Resistant Insulating Materials, or Printed Circuit Boards> The polyamic acid-containing liquid can be preferably used as a composition for an insulator, a composition for a heat-resistant insulator, or a composition for a printed circuit board. Depending on the application, these compositions may further contain optional components such as polyamide, polyethersulfone, acrylic polymer, epoxy compound, isocyanate compound, melamine compound, filler, defoamer, preservative, surfactant, etc. The composition can be produced, for example, by mixing and stirring the polyamic acid-containing liquid with optional components to be used as needed. The polyamic acid content can be within a range appropriate for the application of the composition. The polyamic acid content is, for example, 5 to 30 mass%, 8 to 25 mass%, or 10 to 23 mass%, based on the mass of the composition.

[0098] <Polyimide> Polyimide is obtained by dehydrating and cyclizing polyamic acid (sometimes referred to as "imidization"). The method for producing polyimide includes obtaining polyimide using a polyamic acid-containing liquid. The method for imidization is not particularly limited. A method of heating the polyamic acid-containing liquid is preferably used because it is simple. The heating temperature is, for example, 250 to 400°C.

[0099] <Molded body, insulator, or heat-resistant insulator> Polyamic acid can be used to produce a molded body, insulator, or heat-resistant insulator. The methods for producing a molded body, insulator, or heat-resistant insulator include obtaining them using a polyamic acid-containing liquid. The shape of the molded body, insulator, or heat-resistant insulator is not particularly limited and may be any shape suitable for the application. For example, it may be in the shape of a film, plate, membrane, layer, or the like. The molded body, insulator, and heat-resistant insulator can be used in various electronic and mechanical components.

[0100] <Printed Circuit Board> Polyamic acid can be used to manufacture a printed circuit board. The method for manufacturing a printed circuit board includes obtaining a printed circuit board using a polyamic acid-containing solution. Examples of printed circuit boards include printed wiring boards and printed circuit boards. Examples of printed circuit boards include flexible boards and rigid boards. Examples of printed circuit boards include single-sided boards, double-sided boards, and multilayer boards. For example, materials, protective films, insulating layers, etc. for these boards can be obtained using a polyamic acid-containing solution.

[0101] An example of a flexible substrate is a substrate having a base film, the base film being obtained using a polyamic acid-containing liquid. Another example of a flexible substrate is a substrate having a base film and a heat-resistant insulating layer formed on the base film, at least the heat-resistant insulating layer being obtained using a polyamic acid-containing liquid.

[0102] <Examples of Embodiments> Preferred examples of embodiments of the present invention are listed below: The embodiments of the present invention are not limited to the following examples.

[0103] [1] A method for producing a polyamic acid-containing liquid, comprising obtaining a polyamic acid-containing liquid containing polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer, a diamine, and a tetracarboxylic acid. In the present disclosure, the amic acid prepolymer is a polyamic acid containing a structure derived from a diamine and a structure derived from a tetracarboxylic acid. [2] A method for producing a polyamic acid-containing liquid according to [1] above, comprising either step (1) or step (2) below: (1) Obtaining a polyamic acid-containing liquid containing polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer containing a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic acid dianhydride, an aliphatic or alicyclic diamine, and a tetracarboxylic acid dianhydride. (2) Obtaining a polyamic acid-containing liquid containing polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer containing a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic acid dianhydride, a diamine, and a tetracarboxylic acid dianhydride. Preferred embodiments of step (1) above include the following steps [3] to

[10] . Preferred embodiments of the above step (2) include the following

[11] to

[17] . The obtained polyamic acid is preferably any one of the following

[18] to

[31] .

[0104] [3] A method for producing a polyamic acid-containing liquid, comprising obtaining a polyamic acid-containing liquid using a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride, an aliphatic or alicyclic diamine, and a tetracarboxylic dianhydride. [4] A method for producing a polyamic acid-containing liquid according to [3] above, comprising obtaining the prepolymer-containing liquid using an aromatic diamine, a tetracarboxylic dianhydride, and a solvent, and adding the aliphatic or alicyclic diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid to obtain the polyamic acid-containing liquid. [5] A method for producing a polyamic acid-containing liquid according to [3] or [4] above, comprising adding one or both of the aliphatic or alicyclic diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid in two or more portions. [6] A method for producing a polyamic acid-containing liquid according to any one of [3] to [5] above, wherein the content of the amic acid prepolymer in the prepolymer-containing liquid is 30.0% by mass or less. [7] The method for producing a polyamic acid-containing liquid according to any one of [3] to [6] above, wherein the mass of the amic acid prepolymer relative to the mass of the polyamic acid is 10.0 mass% or more. [8] The method for producing a polyamic acid-containing liquid according to any one of [3] to [7] above, wherein the content of the amic acid prepolymer in the prepolymer-containing liquid is 15.0 mass% or more and the mass of the amic acid prepolymer relative to the mass of the polyamic acid is 50.0 mass% or more. [9] The method for producing a polyamic acid-containing liquid according to any one of [3] to [8] above, wherein the amic acid prepolymer further contains a structure derived from an aliphatic or alicyclic diamine.

[10] The method for producing a polyamic acid-containing liquid that satisfies any one of the embodiments [3] to [9] above and any one of the embodiments

[18] to

[31] below.

[0105]

[11] A method for producing a polyamic acid-containing liquid, comprising obtaining a polyamic acid-containing liquid using a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, a diamine, and a tetracarboxylic dianhydride.

[12] A method for producing a polyamic acid-containing liquid according to

[11] above, comprising obtaining the prepolymer-containing liquid using an aliphatic or alicyclic diamine, a tetracarboxylic dianhydride, and a solvent, and adding the diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid to obtain the polyamic acid-containing liquid.

[13] A method for producing a polyamic acid-containing liquid according to

[11] or

[12] above, comprising adding one or both of the diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid in two or more portions.

[14] A method for producing a polyamic acid-containing liquid according to any one of

[11] to

[13] above, wherein the content of the amic acid prepolymer in the prepolymer-containing liquid is 15.0 mass% or less.

[15] A method for producing a polyamic acid-containing liquid according to any one of

[11] to

[14] above, wherein the mass of the amic acid prepolymer relative to the mass of the polyamic acid is 10.0 mass% or more.

[16] A method for producing a polyamic acid-containing liquid according to any one of

[11] to

[15] above, wherein the amic acid prepolymer further contains a structure derived from an aromatic diamine.

[17] A method for producing a polyamic acid-containing liquid that satisfies any one of the embodiments

[11] to

[16] above and any one of the embodiments

[18] to

[31] below.

[0106]

[18] A polyamic acid-containing liquid containing a polyamic acid having a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, and a solvent, and satisfying one or both of the following (1) and (2): (1) The content of components derived from amines and carboxylic anhydrides is 20.0 mass% or more, and the turbidity is 2.5 NTU or less. (2) The content of the polyamic acid is 20.0 mass% or more, based on the total mass of the polyamic acid and the solvent.

[19] The polyamic acid-containing liquid according to

[18] above, satisfying (1).

[20] The polyamic acid-containing liquid according to

[18] or

[19] above, satisfying (2).

[21] A polyamic acid-containing liquid containing a polyamic acid having a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, and a solvent, and satisfying one or both of the following (3) and (4). (3) The turbidity is 2.5 NTU or less, and the ratio of the mass of components derived from amines and carboxylic acid anhydrides obtained by heating the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass% or more. (4) The ratio of the mass of polyimide obtained by heating a filtrate of the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass% or more.

[22] The polyamic acid-containing liquid according to

[21] above, which satisfies (3). The polyamic acid-containing liquid may further satisfy any one of (18) to (20).

[23] The polyamic acid-containing liquid according to

[21] or (22) above, which satisfies (4). The polyamic acid-containing liquid may further satisfy any one of (18) to (20).

[24] The polyamic acid-containing liquid according to any one of (18) to (23) above, wherein the tetracarboxylic acid dianhydride-derived structure includes a pyromellitic dianhydride-derived structure.

[25] The polyamic acid-containing liquid according to any one of

[18] to

[24] above, wherein the polyamic acid further contains a structure derived from an aromatic diamine.

[26] The polyamic acid-containing liquid according to any one of

[18] to

[25] above, wherein the content of the structure derived from an aliphatic or alicyclic diamine is 20 mass % or more based on the mass of all diamine-derived structures contained in the polyamic acid.

[27] The polyamic acid-containing liquid according to

[24] above, wherein the content of the pyromellitic dianhydride-derived structure is 50% by mass or more, based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid.

[28] The polyamic acid-containing liquid according to any one of

[24] to

[27] above, wherein the content of the aliphatic or alicyclic diamine-derived structure is 20% by mass or more, based on the mass of all diamine-derived structures contained in the polyamic acid, and the content of the pyromellitic dianhydride-derived structure is 50% by mass or more, based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid.

[29] The polyamic acid-containing liquid according to any one of

[18] to

[28] above, wherein the aliphatic or alicyclic diamine-derived structure includes an alicyclic diamine-derived structure.

[30] The polyamic acid-containing liquid according to any one of

[18] to

[29] above, wherein the aliphatic or alicyclic diamine-derived structure includes a dimer diamine-derived structure.

[31] The polyamic acid-containing liquid according to any one of

[18] to

[30] above, which is for use in an insulating material, a heat-resistant insulating material, or a printed circuit board.

[0107]

[32] A method for producing a polyimide, comprising obtaining a polyimide using the polyamic acid-containing liquid according to any one of the above items

[18] to

[31] .

[33] A method for producing a molded body, comprising obtaining a molded body using the polyamic acid-containing liquid according to any one of the above items

[18] to

[31] .

[34] A method for producing a printed circuit board, comprising obtaining a printed circuit board using the polyamic acid-containing liquid according to any one of the above items

[18] to

[31] .

[0108] The embodiments of the present invention will be described in more detail with reference to examples, but the embodiments of the present invention are not limited to the following examples.

[0109] The abbreviations used in the examples represent the following: PMDA: pyromellitic dianhydride ODA: oxydianiline PACM: paradiaminodicyclohexylmethane NBDA: norbornanediamine DDA: dimer diamine (molecular weight 534.99, "PRIAMINE 1075", Croda Japan Co., Ltd.) DMAc: dimethylacetamide

[0110] <Preparation and Evaluation of Polyamic Acid-Containing Liquid (1)> Polyamic acid-containing liquids were prepared using production method Rs or production method Ls and evaluated.

[0111] Example 1: In a draft chamber, a 50 mL screw tube was prepared with an amic acid prepolymer-containing solution containing the amic acid prepolymer (0.586 g) shown in Table 1 and dehydrated DMAc (4.696 g). Next, ODA (0.295 g, 1.47 mmol), PACM (0.575 g, 2.73 mmol), and dehydrated DMAc (4.683 g) were placed in a sample bottle and stirred to prepare a diamine solution. The entire diamine solution and PMDA (0.910 g, 0.417 mmol) were added to the amic acid prepolymer-containing solution, and the mixture was stirred at room temperature for a total of 24 hours to obtain polyamic acid-containing solution 1.

[0112] Example 2 In a draft chamber, a 50 mL screw tube was prepared with an amic acid prepolymer-containing solution containing the amic acid prepolymer (0.588 g) shown in Table 1 and dehydrated DMAc (4.694 g). Next, PACM (0.863 g, 4.10 mmol) and dehydrated DMAc (4.683 g) were placed in a sample bottle and stirred to prepare a diamine solution. The entire diamine solution and PMDA (0.900 g, 0.410 mmol) were added to the amic acid prepolymer-containing solution, and the mixture was stirred at room temperature for 8 hours to obtain polyamic acid-containing solution 2.

[0113] Example 3 In a draft chamber, a 50 mL screw tube containing an amic acid prepolymer solution containing the amic acid prepolymer (0.588 g) shown in Table 1 and dehydrated DMAc (4.694 g) was prepared. Next, PACM (0.863 g, 4.10 mmol) and dehydrated DMAc (4.683 g) were charged into a sample bottle and stirred to prepare a diamine solution. Subsequently, the diamine solution and PMDA (0.900 g, 4.10 mmol) were each divided into four equal portions, and the amic acid prepolymer was added in four portions every 10 minutes while stirring. The mixture was stirred at room temperature for a total of 8 hours to obtain polyamic acid-containing solution 3. The stirring time was measured from the first addition to the end of stirring.

[0114] Example 4 In a draft chamber, a 50 mL screw tube was prepared with an amic acid prepolymer-containing solution containing the amic acid prepolymer (0.586 g) shown in Table 1 and dehydrated DMAc (7.027 g). Next, ODA (0.575 g, 2.87 mmol), PACM (0.288 g, 1.37 mmol), and dehydrated DMAc (2.342 g) were placed in a sample bottle and stirred to prepare a diamine solution. The entire diamine solution and PMDA (0.923 g, 4.23 mmol) were then added to the amic acid prepolymer-containing solution, followed by stirring at room temperature for 3 hours, yielding polyamic acid-containing solution 4.

[0115] Example 5: In a draft chamber, a 50 mL screw tube was prepared with an amic acid prepolymer-containing solution containing the amic acid prepolymer (0.360 g) shown in Table 1 and dehydrated DMAc (6.123 g). Next, ODA (0.575 g, 2.87 mmol), PACM (0.400 g, 1.90 mmol), and dehydrated DMAc (3.278 g) were placed in a sample bottle and stirred to prepare a diamine solution. The entire diamine solution and PMDA (1.04 g, 4.77 mmol) were added to the amic acid prepolymer-containing solution, and the mixture was stirred at room temperature for 24 hours to obtain polyamic acid-containing solution 5.

[0116] [Method for measuring polyamic acid content, turbidity, etc.] The polyamic acid content, turbidity, etc. of the polyamic acid-containing liquid were measured by the following method. The measurement results are shown in Table 1. In the polyamic acid-containing liquids of Examples 1 to 5, precipitates formed during the polymerization reaction were dissolved, so that solid residues could not be recovered by filtration.

[0117] (Polyamic Acid Content ((2) in the Table)) The polyamic acid content was measured by the following procedure. The polyamic acid-containing solution (25°C) was pressure-filtered using a stainless steel mesh (150 mesh, "Stainless Steel Mesh #150" (material: SUS316, mesh count: 150, wire diameter: 0.06 mm, mesh size: 0.109 mm, aperture ratio: 41.6%, weave: plain weave), Tantore Co., Ltd.), to remove solid residue and obtain a polyamic acid solution as a filtrate. 1.5 g (initial mass) of the polyamic acid solution was weighed out using a high-precision electronic balance and added to an aluminum dish. The polyamic acid solution added to the aluminum dish was heated at 200°C for 2 hours to volatilize the solvent and to dehydrate and ring-close the polyamic acid to obtain a polyimide. The polyimide was weighed using a high-precision electronic balance, and the value obtained was used as the mass after heating. The NV2 value (mass %) (nonvolatile content) was obtained by dividing the mass after heating by 1.5 g (initial mass) and multiplying the result by 100. The polyamic acid content was determined by correcting for the amount of water lost by the cyclodehydration reaction of the polyamic acid using the following formula. The average molecular weight of the diamine was calculated using the molecular weight and molar fraction of each diamine in the structure derived from the "diamine" contained in the polyamic acid. The average molecular weight of the tetracarboxylic dianhydride was calculated using the molecular weight and molar fraction of each tetracarboxylic dianhydride in the structure derived from the "tetracarboxylic dianhydride" contained in the polyamic acid. Polyamic acid content (mass %) = NV2 value × {(average molecular weight of diamine) + (average molecular weight of tetracarboxylic dianhydride)} / {(average molecular weight of diamine) + (average molecular weight of tetracarboxylic dianhydride) - molecular weight of water 18.01 × 2}

[0118] (Content of Components Derived from Amine and Carboxylic Acid Anhydride ((1) in the Table)) The NV1 value (mass %) was determined using the same procedure as above (Content of Polyamic Acid) except that the unfiltered polyamic acid-containing liquid was heated. The NV1 value (mass %) was used in place of the NV2 value (mass %) in the above calculation formula, and the content of the components derived from amine and carboxylic acid anhydride relative to the mass of the polyamic acid-containing liquid was determined using the average molecular weight of the diamine and the average molecular weight of the tetracarboxylic acid dianhydride in the components derived from amine and carboxylic acid anhydride contained in the polyamic acid-containing liquid.

[0119] (Mass ratio of polyimide ((4) in the table)) The NV2 value (mass %) obtained above was taken as the ratio of the mass of polyimide obtained by heating the filtrate of the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid.

[0120] (Content of components derived from amines and carboxylic acid anhydrides after heating ((3) in the table)) The NV1 value (mass %) obtained above was defined as the ratio of the mass of components derived from amines and carboxylic acid anhydrides obtained by heating the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid.

[0121] (Turbidity) Turbidity was measured by the transmitted scattered light method and determined based on a calibration curve using a formazin standard solution. The measurement conditions are as follows: Measurement device: Spectrocolorimeter "COH400" (Nippon Denshoku Industries Co., Ltd.) Light source: Tungsten lamp, color temperature 2500 degrees (absolute temperature) Cell size (optical path length): 10 mm Acceptance angle to incident light: 90±30° Peak sensitivity characteristic: 500 nm Sample temperature: 25°C

[0122] (Viscosity) Viscosity (ηinh) was measured using an Ostwald viscometer in a thermostatic bath KINEMATIC VISCOSITY BATH TV-5S (THOMAS KAGAKU CO., LTD.) A sample was prepared by dissolving polyamic acid in DMAc to a concentration of 0.5 g / dL, and the flow time was measured at 30°C.

[0123] (Weight-average molecular weight) The weight-average molecular weight was measured by gel permeation chromatography (GPC) and converted using a calibration curve of standard polystyrene. The calibration curve was approximated by a cubic equation using a set of five standard polystyrene samples ("TSK standard POLYSTYRENE", Tosoh Corporation). The GPC conditions are as follows: GPC apparatus: High-speed GPC apparatus "HLC-8320GPC" (Tosoh Corporation) Detector: Ultraviolet absorption detector "UV-8320" (Tosoh Corporation) Column: "Gelpack GL-S300MDT-5" (total of 2 columns) (Showa Denko Materials Co., Ltd.) Eluent: THF / DMF = 1 / 1 (volume ratio) + LiBr (0.06 mol / L) + H ３ P.O. ４ (0.06 mol / L) Flow rate: 1 mL / min Column size: 8 mm ID x 300 mm Sample concentration: 5 mg / 1 mL Injection volume: 5 μL Measurement temperature: 40°C

[0124] <Evaluation of Polyamic Acid-Containing Liquid> (Film Preparation) A film was prepared using a polyamic acid-containing liquid (varnish) according to the following procedure. The surface of a commercially available glass substrate was degreased with acetone, and a polyamic acid varnish was applied using a film applicator with a film thickness adjustment function so that the film thickness after imidization would be 25 μm. The applied varnish was pre-dried using a hot plate at 80°C for 60 minutes to form a polyamic acid layer. Next, the polyamic acid layer was heated in an inert gas oven in a nitrogen atmosphere at 350°C for 1 hour to obtain polyimide film 1. The glass substrate on which the film was formed was immersed in warm water for approximately 15 minutes, and then film 1 was peeled off from the glass substrate. Furthermore, polyimide film 2 was obtained using the same procedure as above, except that the polyamic acid-containing liquid (varnish) was applied so that the film thickness after imidization would be 50 μm, and film 2 was peeled off from the glass substrate.

[0125] (Dielectric Constant and Dielectric Loss Tangent) Film 1 was cut into a size of 60 mm x 60 mm, dried at 125°C for 1 hour, and then quickly measured. The dielectric properties (dielectric constant Dk and dielectric loss tangent Df) of the film were measured using a cavity resonator method (TE mode). A compact USB vector network analyzer ("MS46122B", Anritsu Corporation) was used for the measurement. The measurement conditions were a frequency of 10 GHz and a measurement temperature of 25°C.

[0126] (Film Formability) Film 1 and Film 2 were cut into a size of 140 mm length × 70 mm width, and then the film thickness was measured at 15 points (5 points lengthwise and 3 points widthwise at intervals of 20 to 30 mm) using a high-precision Digimatic Micrometer ("MDH-25MB", Mitutoyo Corporation), and evaluated according to the following criteria. ◎: When coated so that the film thickness after imidization would be 50 μm, the variation in the film thickness distribution within the plane was within 50 μm ± 3 μm (i.e., the film thickness at all 15 points was 47 to 53 μm). ○: When coated so that the film thickness after imidization would be 25 μm, the variation in the film thickness distribution within the plane was within 25 μm ± 3 μm (i.e., the film thickness at all 15 points was 22 to 28 μm). ×: When coated so that the film thickness after imidization would be 25 μm, the variation in the film thickness distribution within the plane was greater than 25 μm ± 3 μm (i.e., the film thickness at one or more points was less than 22 μm or greater than 28 μm).

[0127]

[0128] <Preparation and Evaluation of Polyamic Acid-Containing Liquid (2)> A polyamic acid-containing liquid was prepared using Production Method Ri or Production Method Li and evaluated.

[0129] [Example 6] ODA (0.575 g, 2.87 mmol), PMDA (0.586 g, 2.67 mmol), and dehydrated DMAc (7.025 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Separately, PACM (0.575 g, 2.73 mmol) and dehydrated DMAc (2.342 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution and PMDA (0.637 g, 2.92 mmol) were placed in the screw tube and stirred at room temperature for a total of 24 hours to obtain polyamic acid-containing solution 6.

[0130] [Example 7] In a draft, ODA (0.626 g, 3.13 mmol), PMDA (0.634 g, 2.91 mmol), and dehydrated DMAc (9.366 g) were placed in a 50 mL screw tube and stirred for 1 hour. Separately, NBDA (0.626 g, 4.06 mmol) and dehydrated DMAc (1.873 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution and PMDA (0.933 g, 4.28 mmol) were placed in the screw tube and stirred at room temperature for a total of 8 hours to obtain polyamic acid-containing solution 7.

[0131] [Example 8] ODA (0.870 g, 4.34 mmol), PMDA (0.220 g, 1.01 mmol), and dehydrated DMAc (7.025 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Separately, DDA (0.378 g, 0.71 mmol) and dehydrated DMAc (2.342 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution and PMDA (0.881 g, 4.04 mmol) were placed in the screw tube and stirred at room temperature for a total of 8 hours, yielding polyamic acid-containing solution 8.

[0132] [Example 9] ODA (0.703 g, 3.51 mmol), PMDA (0.204 g, 0.94 mmol), and dehydrated DMAc (7.025 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Separately, DDA (0.626 g, 1.17 mmol) and dehydrated DMAc (2.342 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution and PMDA (0.817 g, 3.74 mmol) were placed in the screw tube and stirred at room temperature for a total of 3 hours to obtain polyamic acid-containing solution 9.

[0133] [Example 10] ODA (0.402 g, 2.01 mmol), PMDA (0.175 g, 0.80 mmol), and dehydrated DMAc (7.025 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Separately, DDA (1.073 g, 2.01 mmol) and dehydrated DMAc (2.342 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution and PMDA (0.700 g, 3.21 mmol) were placed in the screw tube and stirred at room temperature for a total of 3 hours, yielding polyamic acid-containing solution 10.

[0134] [Example 11] In a draft, ODA (0.288 g, 1.44 mmol), PACM (0.288 g, 1.37 mmol), PMDA (0.613 g, 2.81 mmol), and dehydrated DMAc (8.429 g) were placed in a 50 mL screw tube and stirred for 1 hour. Separately, PACM (0.288 g, 1.37 mmol) and dehydrated DMAc (0.937 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire amount of the diamine solution, ODA (0.288 g, 1.44 mmol), and PMDA (0.610 g, 2.80 mmol) was placed in the screw tube and stirred at room temperature for a total of 8 hours, thereby obtaining polyamic acid-containing liquid 11.

[0135] [Example 12] PACM (0.575 g, 2.73 mmol), PMDA (0.596 g, 2.73 mmol), and dehydrated DMAc (9.366 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Next, ODA (0.575 g, 2.87 mmol) and PMDA (0.627 g, 2.87 mmol) were added to the screw tube, and the entire amount was stirred at room temperature for a total of 3 hours to obtain polyamic acid-containing liquid 12.

[0136] [Example 13] PACM (0.575 g, 2.73 mmol), PMDA (0.596 g, 2.73 mmol), and dehydrated DMAc (8.429 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Separately, PACM (0.288 g, 1.37 mmol) and dehydrated DMAc (0.937 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution, ODA (0.288 g, 1.44 mmol), and PMDA (0.627 g, 2.87 mmol) were placed in the screw tube and stirred at room temperature for a total of 8 hours to obtain polyamic acid-containing solution 13.

[0137] [Example 14] PACM (0.577 g, 2.74 mmol), PMDA (0.598 g, 2.74 mmol), and dehydrated DMAc (8.429 g) were placed in a 50 mL screw tube in a draft and stirred for 1 hour. Separately, PACM (0.577 g, 2.74 mmol) and DMAc (0.937 g) were placed in a sample bottle and stirred to prepare a diamine solution. Then, the entire diamine solution and PMDA (0.637 g, 2.92 mmol) were placed in the screw tube and stirred at room temperature for a total of 8 hours, yielding polyamic acid-containing solution 14.

[0138] Example 15: PACM (0.288 g, 1.37 mmol) and dehydrated DMAc (4.683 g) were placed in a 50 mL screw tube and stirred in a draft to prepare diamine solution 1. Next, PMDA (0.300 g, 1.37 mmol) was added to diamine solution 1 and stirred for 10 minutes. Separately, PACM (0.863 g, 4.10 mmol) and dehydrated DMAc (4.683 g) were placed in a sample bottle and stirred to prepare diamine solution 2. Then, PMDA (0.900 g, 4.10 mmol) and diamine solution 2 were each divided into three equal portions and added to a screw tube in three portions every 10 minutes while stirring the screw tube. The mixture was stirred at room temperature for a total of 8 hours to obtain polyamic acid-containing solution 15. The stirring time was measured from the first addition to the end of stirring.

[0139] Example 16: In a draft chamber, NBDA (0.575 g, 3.73 mmol), PMDA (0.586 g, 2.69 mmol), and dehydrated DMAc (8.429 g) were placed in a 50 mL screw tube and stirred for 1 hour. Separately, PACM (0.575 g, 2.73 mmol) and dehydrated DMAc (0.937 g) were placed in a sample bottle to prepare a diamine solution. The diamine solution and PMDA (0.637 g, 2.92 mmol) were then added to the screw tube in two and three portions, respectively, every 10 minutes, and stirred at room temperature for a total of 8 hours to obtain polyamic acid solution 16. The diamine solution was divided into two equal portions, and PMDA was divided into three portions at a ratio of 5:4:1.

[0140] Comparative Example 1: PACM (1.151 g, 5.47 mmol) and dehydrated DMAc (9.366 g) were placed in a 50 mL screw tube in a draft chamber to prepare a diamine solution. PMDA (1.195 g, 5.48 mmol) was then added in four portions every 10 minutes. After the addition, the mixture was stirred at room temperature for a total of 24 hours to obtain a polyamic acid-containing solution.

[0141] [Comparative Example 2] PACM (0.342 g, 1.62 mmol) and dehydrated DMAc (9.366 g) were placed in a 50 mL screw tube in a draft to prepare a diamine solution. Then, ODA (0.797 g, 3.98 mmol) and PMDA (1.221 g, 5.60 mmol) were added in their entirety. After the addition, the mixture was stirred at room temperature for a total of 24 hours to obtain a polyamic acid-containing solution.

[0142] [Method for measuring polyamic acid content, turbidity, etc.] Measurements were performed in the same manner as in Preparation and evaluation of polyamic acid-containing liquid (1). The measurement results are shown in Tables 2-1 to 2-3. In the polyamic acid-containing liquids of Examples 6 to 16, precipitates formed during the polymerization reaction were dissolved, so that solid residues could not be recovered by filtration.

[0143] <Evaluation of Polyamic Acid-Containing Liquid> Evaluation was carried out in the same manner as in Preparation and Evaluation of Polyamic Acid-Containing Liquid (1). The evaluation results are shown in Table 2. Note that in Comparative Examples 1 and 2, it was not possible to produce a film using the polyamic acid-containing liquid.

[0144]

[0145]

[0146]

[0147] <Preparation and Evaluation of Polyamic Acid-Containing Solution (3)> [Example 17] (Preparation of Polyamic Acid-Containing Solution 17a) Polyamic acid-containing solution 17a was prepared using production method Ri. In a draft, ODA (24.5 g, 0.122 mol), PMDA (7.11 g, 0.033 mol), and dehydrated DMAc (300.0 g) were charged into a 500 mL three-neck flask and stirred for 1 hour. Separately, DDA (21.8 g, 0.041 mol) and dehydrated DMAc (20.0 g) were charged into a sample bottle and stirred to prepare diamine solution a. Then, the entire amount of diamine solution a and PMDA (26.6 g, 0.122 mol) was charged into a screw tube and stirred at room temperature for a total of 8 hours, thereby obtaining polyamic acid-containing solution 17a.

[0148] (Preparation of polyamic acid-containing solution 17b) Using polyamic acid-containing solution 17a as an aromatic prepolymer-containing solution, polyamic acid-containing solution 17b was prepared by production method Rs. ODA (10.2 g, 0.051 mol) and PMDA (2.97 g, 0.014 mol) were charged into a 500 mL three-neck flask containing polyamic acid-containing solution 17a and stirred for 1 hour. Separately, DDA (9.10 g, 0.017 mol) and dehydrated DMAc (18.2 g) were charged into a sample bottle and stirred to prepare diamine solution b. Then, the entire amount of diamine solution b and PMDA (11.1 g, 0.051 mol) was charged into a screw tube and stirred at room temperature for a total of 8 hours to obtain polyamic acid-containing solution 17b.

[0149] [Method for measuring polyamic acid content, turbidity, etc.] Measurements were performed in the same manner as in Preparation and Evaluation of Polyamic Acid-Containing Liquid (1), except that the viscosity was measured by the following method. The measurement results are shown in Table 3. In the polyamic acid-containing liquid of Example 17, precipitates formed during the polymerization reaction were dissolved, so that no solid residue could be recovered by filtration.

[0150] (Viscosity) The viscosity was measured using a rotary B-type viscometer (TVB-10M, Toki Sangyo Co., Ltd.) with the temperature of the polyamic acid-containing liquid set at 30° C. and a No. 3 rotor.

[0151] <Evaluation of Polyamic Acid-Containing Liquid> The polyamic acid-containing liquid was evaluated in the same manner as in Preparation and Evaluation of Polyamic Acid-Containing Liquid (1). The evaluation results are shown in Table 3.

[0152]

Claims

1. A method for producing a polyamic acid-containing liquid includes obtaining a polyamic acid-containing liquid containing a polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer having a structure derived from an aromatic diamine and a structure derived from a tetracarboxylic dianhydride, an aliphatic or alicyclic diamine, and a tetracarboxylic dianhydride.

2. Obtaining the prepolymer-containing liquid using an aromatic diamine, a tetracarboxylic dianhydride, and a solvent; and 2. The method for producing a polyamic acid-containing liquid according to claim 1, comprising the step of adding the aliphatic or alicyclic diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid to obtain the polyamic acid-containing liquid.

3. 2. The method for producing a polyamic acid-containing liquid according to claim 1, comprising adding one or both of the aliphatic or alicyclic diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid in two or more portions.

4. 2. The method for producing a polyamic acid-containing liquid according to claim 1, wherein a content of the amic acid prepolymer in the prepolymer-containing liquid is 30.0 mass % or less.

5. 2. The method for producing a polyamic acid-containing liquid according to claim 1, wherein a ratio of a mass of the amic acid prepolymer to a mass of the polyamic acid is 10.0 mass% or more.

6. 2. The method for producing a polyamic acid-containing liquid according to claim 1, wherein a content of the amic acid prepolymer in the prepolymer-containing liquid is 15.0% by mass or more, and a mass of the amic acid prepolymer relative to a mass of the polyamic acid is 50.0% by mass or more.

7. The method for producing a polyamic acid-containing liquid according to claim 1 , wherein the amic acid prepolymer further contains a structure derived from an aliphatic or alicyclic diamine.

8. A method for producing a polyamic acid-containing liquid includes obtaining a polyamic acid-containing liquid containing a polyamic acid using a prepolymer-containing liquid containing an amic acid prepolymer including a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic acid dianhydride, a diamine, and a tetracarboxylic acid dianhydride.

9. Obtaining the prepolymer-containing liquid using an aliphatic or alicyclic diamine, a tetracarboxylic dianhydride, and a solvent; and 9. The method for producing a polyamic acid-containing liquid according to claim 8, comprising the step of adding the diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid to obtain the polyamic acid-containing liquid.

10. 9. The method for producing a polyamic acid-containing liquid according to claim 8, further comprising adding one or both of the diamine and the tetracarboxylic dianhydride to the prepolymer-containing liquid in two or more portions.

11. 9. The method for producing a polyamic acid-containing liquid according to claim 8, wherein a content of the amic acid prepolymer in the prepolymer-containing liquid is 15.0 mass % or less.

12. 9. The method for producing a polyamic acid-containing liquid according to claim 8, wherein a ratio of a mass of the amic acid prepolymer to a mass of the polyamic acid is 10.0 mass% or more.

13. The method for producing a polyamic acid-containing liquid according to claim 8 , wherein the amic acid prepolymer further contains a structure derived from an aromatic diamine.

14. The composition comprises a polyamic acid including a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, and a solvent; A polyamic acid-containing liquid that satisfies one or both of the following (1) and (2): (1) The content of components derived from amines and carboxylic acid anhydrides is 20.0 mass% or more, and the turbidity is 2.5 NTU or less. (2) The content of the polyamic acid is 20.0 mass % or more based on the total mass of the polyamic acid and the solvent.

15. The polyamic acid-containing liquid according to claim 14 , which satisfies the above (1).

16. The polyamic acid-containing liquid according to claim 14 , which satisfies the above (2).

17. The composition comprises a polyamic acid including a structure derived from an aliphatic or alicyclic diamine and a structure derived from a tetracarboxylic dianhydride, and a solvent; A polyamic acid-containing liquid that satisfies one or both of the following (3) and (4): (3) The turbidity is 2.5 NTU or less, and the ratio of the mass of components derived from amines and carboxylic acid anhydrides obtained by heating the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass% or more. (4) The ratio of the mass of the polyimide obtained by heating the filtrate of the polyamic acid-containing liquid to the mass of the polyamic acid-containing liquid is 18.0 mass % or more.

18. The polyamic acid-containing liquid according to claim 17 , which satisfies the above (3).

19. The polyamic acid-containing liquid according to claim 17 , which satisfies the above (4).

20. The polyamic acid-containing liquid according to claim 14 , wherein the structure derived from the tetracarboxylic dianhydride includes a structure derived from pyromellitic dianhydride.

21. The polyamic acid-containing liquid according to claim 14 , wherein the polyamic acid further comprises a structure derived from an aromatic diamine.

22. 15. The polyamic acid-containing liquid according to claim 14, wherein the content of the structure derived from the aliphatic or alicyclic diamine is 20 mass% or more based on the mass of all diamine-derived structures contained in the polyamic acid.

23. The polyamic acid-containing liquid according to claim 20, wherein the content of the pyromellitic dianhydride-derived structure is 50 mass% or more based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid.

24. the content of the structure derived from the aliphatic or alicyclic diamine is 20 mass% or more based on the mass of all diamine-derived structures contained in the polyamic acid, The polyamic acid-containing liquid according to claim 20, wherein the content of the pyromellitic dianhydride-derived structure is 50 mass% or more based on the mass of all tetracarboxylic dianhydride-derived structures contained in the polyamic acid.

25. The polyamic acid-containing liquid according to claim 14 , wherein the structure derived from an aliphatic or alicyclic diamine includes a structure derived from an alicyclic diamine.

26. The polyamic acid-containing liquid according to claim 14 , wherein the structure derived from an aliphatic or alicyclic diamine includes a structure derived from a dimer diamine.

27. The polyamic acid-containing liquid according to any one of claims 14 to 26, which is for use in a printed circuit board.

28. A method for producing a polyimide, comprising obtaining a polyimide by using the polyamic acid-containing liquid according to any one of claims 14 to 26.

29. A method for producing a molded article, comprising obtaining a molded article using the polyamic acid-containing liquid according to any one of claims 14 to 26.

30. A method for producing a printed circuit board, comprising obtaining a printed circuit board by using the polyamic acid-containing liquid according to any one of claims 14 to 26.