JP7050382B2 - Polyimide film and its manufacturing method - Google Patents

Description

The present invention relates to a polyimide film and a method for producing the same.

In recent years, the use of a film made of polyimide has been studied as an alternative material to glass for use in a substrate of a liquid crystal display (LCD) or an organic EL (electroluminescence) display (OLED). As the polyimide film used for such LCDs and OLEDs, those having a low coefficient of thermal expansion (linear expansion coefficient: CTE) and retardation (Rth) in the thickness direction are desired, but these characteristics are trade-offs. Due to the relationship, polyimide films with various structures have been studied so far.

For example, Japanese Patent Application Laid-Open No. 2016-204568 (Patent Document 1) describes a polyimide film mainly composed of a polyimide obtained by polymerizing a tetracarboxylic acid component and a diamine component, wherein the tetracarboxylic acid component and the diamine component are described. It is composed of a compound selected from the group consisting of a compound having an aromatic ring and an alicyclic compound, and the proportion of the compound having an aromatic ring is 10 to 90 mol% in the total of 200 mol% of the tetracarboxylic acid component and the diamine component. There is disclosed a polyimide film in which the ratio of the alicyclic compound is 110 to 190 mol%, and either the tetracarboxylic acid component or the diamine component is composed of only the alicyclic compound. However, the conventional polyimide film as described in Patent Document 1 is not yet sufficient in that it has a sufficiently low Rth and a sufficiently low CTE in a well-balanced manner, and is sufficiently sufficient. The emergence of a polyimide film having a low Rth and a sufficiently low CTE in a well-balanced manner at a higher level is desired.

Japanese Unexamined Patent Publication No. 2016-204568

The present invention has been made in view of the problems of the prior art, and has a sufficiently low thickness direction polyimide (Rth) and a sufficiently low coefficient of thermal expansion (linear expansion coefficient: CTE) based on an absolute value. It is an object of the present invention to provide a polyimide film capable of having the above in a well-balanced manner at a higher level, and a method for producing a polyimide film capable of producing the polyimide film.

In order to use a film made of polyimide as a substrate for LCDs and OLEDs, the present inventors have performed the film when it is heated to a high temperature (for example, about 400 ° C. or higher) or when it is allowed to cool in the manufacturing process of those displays. Compared to the conventional polyimide film, it is more advanced in that it causes cracks and breaks, and that cracks and breaks occur in other layers laminated due to the expansion and contraction of the film. From the viewpoint of suppressing at a level and obtaining a higher display quality when used for LCD or OLED substrates, etc., the polyimide in the thickness direction is sufficiently low and the coefficient of thermal expansion is sufficiently low (linear expansion coefficient: CTE). As a result of diligent research on the subject of obtaining a polyimide having a more balanced balance with ()), a polyimide precursor containing a specific repeating unit (A') represented by the following general formula (7) and an organic solvent were obtained. After forming a coating film using the contained resin solution, the solvent is removed from the coating film, and the temperature is increased from (Tg-190) ° C. based on the glass transition temperature (Tg) of the polyimide to be finally formed. The polyimide obtained by firing (heating and curing) at a temperature within the range of (Tg-50) ° C. is brought into a specific temperature range in the TMA curve (graph showing the relationship between the temperature and the length of the film). It is possible to have an extreme value (the point at which the film changes from elongation to contraction in tensile TMA measurement) in which the ratio (inclination) of the amount of change in the length of the film to the amount of change changes from positive to negative. The present invention has been completed by finding that it is possible to make the CTE (absolute value) lower while making the Rth (absolute value) of the obtained polyimide film sufficiently low.
That is, the polyimide film of the present invention has the following general formula (1):

[In the formula (1), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming ^a cyclic structure, and Ra is the following general formulas (2) to (3). Indicates one of the divalent organic groups represented by. ]
A film made of polyimide containing a repeating unit (A) represented by.
The film contains a polyimide precursor containing a repeating unit (A') represented by the following general formula (7), an imidazole compound represented by the following general formula (X), and a polyimide precursor containing an organic solvent. It is a heat-cured product of the solvent-removed product of the coating film of the body resin solution, and
A thermal machine that measures the relationship between the temperature and the amount of change in the length of the film by pulling the film under the condition of a load of 20 mN while raising the temperature from 50 ° C to 450 ° C at a heating rate of 5 ° C / min under a nitrogen atmosphere. In the TMA curve obtained by analysis (TMA), the extreme value at which the ratio of the change in film length to the change in temperature changes from positive to negative exists in the temperature range of 200 to 430 ° C. It is a thing.

In the above formula (2), R ^a1 , R ^a2 , R ^a3 And R ^a4 Indicates one species independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group, respectively, and in the above formula (3), R ^a5 And R ^a6 Independently indicate one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group.
Further, in the above formula (7), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming a cyclic structure, and R ^a Indicates any of the divalent organic groups represented by the above general formulas (2) to (3), and Y ¹ And Y ² Indicates one species independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms and an alkylsilyl group having 3 to 9 carbon atoms, respectively.
Further, in the above formula (X), R ¹¹ Indicates one selected from the group consisting of a hydrogen atom and an alkyl group, and R ¹⁴ Is independently selected from the group consisting of a halogen atom, a hydroxyl group, a mercapto group, a sulfide group, a silyl group, a silanol group, a nitro group, a nitroso group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphonat group and an organic group. , M indicates an integer from 0 to 3, and R ³¹ , R ³² , R ³³ , R ³⁴ And R ³⁵ , Independently, hydrogen atom, hydroxyl group, mercapto group, sulfide group, silyl group, silanol group, nitro group, nitroso group, sulfino group, sulfo group, sulfonat group, phosphino group, phosphinyl group, phosphono group, phosphonat group, It is an amino group, an ammonio group, or an organic group, but R ³¹ , R ³² , R ³³ , R ³⁴ And R ³⁵ At least one of them is a group other than a hydrogen atom.

In the polyimide film of the present invention, A in the above formula (1) is the following general formula (4):

[In the formula (4), R ¹ , R ² , and R ³ each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, and a fluorine atom, and n is 0 to 0 to. Indicates an integer of 12. ]
It is preferably a tetravalent alicyclic hydrocarbon group represented by.

Further, as the polyimide film of the present invention, the polyimide is described in the following general formula (5).

[In the formula (5), A is synonymous with A in the above formula (1), and R ^b is the following general formula (6):

(In the formula (6), R ^b1 and R ^b2 each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group.)
Indicates a divalent organic group represented by. ]
It further contains the repeating unit (B) represented by, and the content of the repeating unit (A) in the polyimide is 50 to the total amount of the repeating unit (A) and the repeating unit (B). It is preferably 100 mol%.

In the method for producing a polyimide film of the present invention, a polyimide is formed by using a polyimide precursor resin solution containing a polyimide precursor and an organic solvent, and then the solvent is removed from the coating film and fired. Including the process of obtaining a film consisting of
The polyimide precursor has the following general formula (7):

[In the formula (7), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming ^a cyclic structure, and Ra is the above general formulas (2) to (3). It represents one of the represented divalent organic groups, and Y ¹ and Y ² are independently composed of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkylsilyl group having 3 to 9 carbon atoms, respectively. Indicates one type to be selected. ]
It contains a repeating unit (A') represented by.
The polyimide precursor resin solution further contains the imidazole compound represented by the general formula (X), and
At the time of firing, the film made of the polyimide is obtained by firing at a temperature in the range of (Tg-190) ° C. to (Tg-50) ° C. based on the glass transition temperature (Tg) of the obtained polyimide. Obtaining the polyimide film of the invention,
It is a method characterized by. In the method for producing a polyimide film of the present invention, the content of the imidazole compound in the polyimide precursor resin solution is 1 to 60 parts by mass with respect to 100 parts by mass of the solid content of the polyimide precursor in the solution. It is preferable to have.

According to the present invention, it is possible to have a sufficiently low polyimide (Rth) in the thickness direction and a sufficiently low coefficient of thermal expansion (linear expansion coefficient: CTE) at a higher level in a well-balanced manner based on an absolute value. It is possible to provide a polyimide film to be used and a method for producing a polyimide film capable of producing the polyimide film.

It is a graph which shows the TMA curve of the polyimide film obtained in Example 1 and the polyimide film obtained in Comparative Example 3.

Hereinafter, the present invention will be described in detail according to the preferred embodiment thereof.

[Polyimide film]
The polyimide film of the present invention is a film made of polyimide containing the repeating unit (A) represented by the above general formula (1), and is a film.
A thermal machine that measures the relationship between the temperature and the amount of change in the length of the film by pulling the film under the condition of a load of 20 mN while raising the temperature from 50 ° C to 450 ° C at a heating rate of 5 ° C / min under a nitrogen atmosphere. In the TMA curve obtained by analysis (TMA), it is found that the extreme value in which the ratio (inclination) of the change in film length to the change in temperature exists in the temperature range of 200 to 430 ° C. from positive to negative. It is a feature.

The polyimide contains a repeating unit (A) represented by the general formula (1). In such a repeating unit (A), A in the above general formula (1) has a number of carbon atoms forming a cyclic structure of 4 to 30 (more preferably 4 to 25, still more preferably 15 to 25, particularly 15 to 25). A tetravalent alicyclic hydrocarbon group, preferably 16 to 20), is shown. The "number of carbon atoms forming a cyclic structure" as used herein means the number of carbon atoms forming a cyclic structure portion of the main skeleton of an alicyclic hydrocarbon (cyclic aliphatic group), and the cyclic aliphatic group thereof. However, if it has a substituent containing carbon (such as a hydrocarbon group), the number of carbons in the substituent is not included. For example, 2-ethyl-cyclohexane is cyclic because the cyclic structure portion of the main skeleton is cyclohexane (carbon number: 6) and the substituent bonded to the cyclic structure is an ethyl group (carbon number: 2). The number of carbon atoms forming the structure is six. If the number of carbon atoms forming the cyclic structure of such a tetravalent alicyclic hydrocarbon group is less than the lower limit, the heat resistance tends to decrease and the coefficient of thermal expansion (linear expansion coefficient: CTE) tends to increase. On the other hand, if the upper limit is exceeded, synthesis and purification tend to be difficult. The alicyclic hydrocarbon may be derived from any of a monocyclic compound, a fused ring compound, a spiro ring compound, a polyspiro compound and the like.

Such a tetravalent alicyclic hydrocarbon group (A in the formula) may have a substituent bonded to a cyclic structure portion (alicyclic hydrocarbon) of the main skeleton. The alicyclic hydrocarbon (cyclic structure portion) of the main skeleton of such a tetravalent alicyclic hydrocarbon group is not particularly limited, and is, for example, cyclobutane, cyclopentane, cyclohexane, cycloheptane, and the like. Cyclic hydrocarbons such as cyclooctane, cyclodecane, bicyclo [2.1.1] hexane, bicyclo [2.2.1] heptane, bicyclo [3.2.1] octane, bicyclo [2.2.2] octane, etc. Condensed polycyclic hydrocarbons condensed from these cyclic hydrocarbons; Monospiro hydrocarbons having a spiro structure in which these cyclic hydrocarbons are linked by a single carbon atom (eg, Spiro [4.5] decane, etc.) and Polyspiro hydrocarbons (eg, dispiro [4.2.4.2] tetradecane, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane, etc.); etc. can be exemplified. .. The substituent that can be bonded to the cyclic structure portion (alicyclic hydrocarbon) of the main skeleton is not particularly limited, but from the viewpoint of heat resistance and transparency, an alkyl group and a halogen atom are preferable, and the number of carbon atoms is 1 to 1. More preferably, it is an alkyl group of 10 and a fluorine atom.

The tetravalent alicyclic hydrocarbon group includes a tetravalent alicyclic hydrocarbon group represented by the above general formula (4) and the following general formula (10) from the viewpoint of ease of film preparation. ~ (12):

[R ⁴ in equations (10) to (12) is synonymous with R ¹ in equation (4). ]
The tetravalent alicyclic hydrocarbon group represented by the above is preferable, and among them, the tetravalent alicyclic hydrocarbon group represented by the general formula (4) and the tetravalent represented by the general formula (10) are preferable. The alicyclic hydrocarbon group of is more preferable. Further, as such a tetravalent alicyclic hydrocarbon group, a tetravalent alicyclic hydrocarbon group represented by the above general formula (4) is used from the viewpoint of achieving a higher heat resistance. Especially preferable.

R ¹ , R ² , and R ³ in the above general formula (4) are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, and a fluorine atom, and n is 0. It is an integer of ~ 12. The alkyl group that can be selected as R ¹ , R ² , or R ³ in the formula (4) is an alkyl group having 1 to 10 carbon atoms. If the number of carbon atoms exceeds 10, the glass transition temperature drops and a sufficiently high degree of heat resistance cannot be achieved. Further, the carbon number of the alkyl group that can be selected as R ¹ , R ² and R ³ is preferably 1 to 6 and preferably 1 to 5 from the viewpoint of facilitating purification. Is more preferable, 1 to 4 is more preferable, and 1 to 3 is particularly preferable. Further, the alkyl group that can be selected as such R ¹ , R ² and R ³ may be linear or branched. Further, as such an alkyl group, a methyl group and an ethyl group are more preferable from the viewpoint of easiness of purification.

The R ¹ , R ² , and R ³ in the formula (4) are independently hydrogen atoms or 1 to 1 to carbon atoms from the viewpoint of obtaining higher heat resistance when the polyimide is manufactured. It is more preferably an alkyl group of 10, and above all, from the viewpoint of easy availability of raw materials and easier purification, each independently has a hydrogen atom, a methyl group, an ethyl group, an n-propyl group or It is more preferably an isopropyl group, and particularly preferably a hydrogen atom or a methyl group. Further, it is particularly preferable that a plurality of R ¹ , R ² , and R ³ in such a formula are the same from the viewpoint of ease of purification and the like.

Further, n in such an equation (4) represents an integer of 0 to 12. If such a value of n exceeds the upper limit, purification becomes difficult. Further, the upper limit of the numerical range of n in the general formula (4) is more preferably 5 and particularly preferably 3 from the viewpoint of facilitating purification. Further, the lower limit of the numerical range of n in the general formula (4) is more preferably 1 and particularly preferably 2 from the viewpoint of the stability of the raw material compound. As described above, it is particularly preferable that n in the general formula (4) is an integer of 2 to 3.

Further, R ⁴ in the above general formulas (10) to (12) has the same meaning as R ¹ in the formula (4), and suitable ones thereof also have the same meaning.

Further, in the repeating unit ( ^A ) according to the present invention, Ra in the general formula (1) is any one of the divalent organic groups represented by the general formulas (2) to (3) (the above). A divalent organic group represented by the general formula (2) and any of the divalent organic groups represented by the general formula (3)) are shown. The polyimide film obtained by the repeating unit containing any of the structures of the divalent organic groups represented by the general formulas (2) and (3) has a Tg of 350 ° C. or higher. It is possible to have heat resistance, to develop a point (extreme point) at which the film changes from elongation to shrinkage between 200 and 430 ° C. when the polyimide film is heated, and to obtain a lower Rth. Become.

Further, R ^a1 , R ^a2 , R ^a3 and R ^a4 in such a general formula (2) are independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group, respectively. R ^a5 and R ^a6 in the general formula (3) are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group. be.

Such an alkyl group having 1 to 10 carbon atoms which can be selected as R ^a1 to ^Ra6 in the formulas (2) to (3) has 1 to 10 carbon atoms which can be selected as ^R1 in the above formula (4). (Similar to the preferred ones). Further, the halogen atom that can be selected as ^{Ra1 to Ra6 in} the formulas (2) to (3) is not particularly limited, but a chlorine atom and a fluorine atom are preferable from the viewpoint of lowering Rth sufficiently. , Fluorine atom is particularly preferable.

Further, the groups that can be selected as ^{Ra1 to Ra6 in} such formulas (2) to (3) include hydrogen atoms and methyl groups from the viewpoints of heat resistance, transparency, low thermal expansion, and laser exfoliation. It is preferably an ethyl group, an n-propyl group, an isopropyl group, a fluoro group, a chloro group, a bromo group or a hydroxyl group, and more preferably a hydrogen atom, a methyl group, a fluoro group or a chloro group.

Further, as the divalent organic group represented by the general formulas (2) and (3), it is said that a sufficiently low Rth, a sufficiently low CTE, and sufficiently high heat resistance and laser peeling property are exhibited. From the viewpoint, the group represented by the general formula (2) is more preferable.

Further, such a repeating unit (A) is expressed by the following general formula (I):

[A in the formula (I) is synonymous with A in the above formula (1). ]
The tetracarboxylic dianhydride represented by the above formula: ^H2N -Ra _{-NH 2 [} ^Ra in the formula is synonymous with ^Ra in the above formula (1). ] Can be formed from the reaction with the diamine compound represented by. The tetracarboxylic dianhydride represented by the general formula (I) is not particularly limited, and known ones can be appropriately used. However, the following general formula (I-1):

[R ^{1, R 2, R 3, and n in the formula (I-1) are synonymous with R 1 , R 2 ,} R ³ , and n in the general formula (4). ]
The tetracarboxylic dianhydride represented by is preferable. Further, the method for producing such a tetracarboxylic dianhydride represented by the general formula (I) is not particularly limited, and a known method can be appropriately adopted. For example, the above general formula ( When the tetracarboxylic dianhydride represented by I-1) is produced and used, the method described in International Publication No. 2011/099518 can be appropriately adopted. Further, as these tetracarboxylic dianhydrides, commercially available products may be used. Further, these tetracarboxylic dianhydrides can be used alone or in combination of two or more.

Further, the diamine compound represented by the formula: H ₂ N-R ^a -NH ₂ may be any as long as ^Ra is the same as ^Ra in the above formula (1), and is not particularly limited, for example. 9,9-Bis (4-aminophenyl) fluorene (FDA), 9,9-bis (4-amino-3-fluorophenyl) fluorene (F-FDA), 9,9-bis (4-amino-3-3) Chlorophenyl) fluorene (Cl-FDA), 9,9-bis (4-amino-3-bromophenyl) fluorene, 9,9-bis (4-amino-3-methylphenyl) fluorene (Me-FDA), 9, 9-bis (4-amino-3-ethylphenyl) fluorene, 9,9-bis (4-amino-3-n-propylphenyl) fluorene, 9,9-bis (4-amino-3-isopropylphenyl) fluorene , 9,9-bis (4-amino-3-hydroxyphenyl) fluorene, 4,4'-diaminodiphenyl sulfone (4,4'-DDS), 3,3'-diaminodiphenyl sulfone (3,3'-DDS) ), 3,7-Diamino-2,8-dimethyldibenzothiophene sulfone, o-tridin sulfone, bis (3-amino-4-hydroxyphenyl) sulfone and the like. Commercially available products may be used as these diamine compounds. In addition, these diamine compounds can be used alone or in combination of two or more.

Further, the polyimide may contain one type of the repeating unit (A) alone, or two or more types having different types of ^A and Ra in the above formula (1). It may include a combination of repeating units (A). Further, the polyimide may contain other repeating units in addition to the repeating unit (A).

As such a polyimide, one containing the repeating unit (A) and the repeating unit (B) represented by the general formula (5) is preferable. That is, it is preferable that the polyimide further contains the repeating unit (B). Such A in the general formula (5) is synonymous with A in the above formula (1) (the preferred one is also synonymous). Further, R ^b in the general formula (5) is a divalent organic group represented by the general formula (6). Then, R ^b1 and R ^b2 in such formula (6) independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group, respectively. In addition, R ^b1 and R ^b2 in such a formula (6) are synonymous with R ^a1 in the above formula (2), respectively (the suitable ones are also synonymous).

Such a repeating unit (B) is a tetracarboxylic dianhydride represented by the above general formula (I) and a formula: H ₂ N R ^b -NH ₂ [ ^Ra in the formula is the above formula (5). ) Is synonymous with R ^b in. ] Can be formed from the reaction with the diamine compound represented by. For the tetracarboxylic acid dianhydride represented by the general formula (I), such a diamine compound represented by the formula: H2N _- ^Rb - _NH2 is, for example, 4,4'-diaminobenz. Anilides (4,4'-DABAN), 2,4'-diaminobenzanilide (2,4'-DABAN), 3,4'-diaminobenzanilide, 3,3'-diaminobenzanilide, 2-methylbenzanilide And so on. Commercially available products may be used as these diamine compounds. In addition, these diamine compounds can be used alone or in combination of two or more.

The polyimide may contain repeating units other than the repeating units (A) and (B) as long as the effects of the present invention are not impaired. Examples of the repeating unit other than the repeating units (A) and (B) are not particularly limited, and examples thereof include known repeating units that can be used as the repeating unit of polyimide. Examples of the repeating unit other than such repeating units (A) and (B) include tetracarboxylic acid dianhydrides other than the tetracarboxylic acid dianhydride represented by the general formula (I). For example, a repeating unit derived from the compound described in paragraph [0171] of International Publication No. 2014/0347060 or a diamine other than the diamine compound (for example, paragraph [0211] of International Publication No. 2017/030019]. The aromatic diamine described in the above, the repeating unit derived from the aromatic diamine described in paragraph [0157] of International Publication No. 2014/034760, etc.) may be used.

As the repeating unit other than the repeating units (A) and (B), the tetracarboxylic acid dianhydride represented by the above general formula (I) can be used from the viewpoint that the CTE can be made smaller. , P-phenylenediamine which may have a substituent, terphenyldiamine which may have a substituent, biphenyl-based diamine which may have a substituent (for example, m-trizine, o-tridin). , 3,3', 5,5'-tetramethylbenzidine, octafluorobenzidine, 2,2'-bis (trifluoromethyl) benzidine, etc.), ester group-containing diamines which may have substituents (eg 4). -At least one selected from the group consisting of a diamine having a hydroxyl group (for example, 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane) and a diamine having a hydroxyl group (for example, 4-aminophenyl aminobenzoate). A repeating unit formed by a reaction with an aromatic diamine (the R ^b portion of the group represented by the above general formula (5) is a residue obtained by removing two amino groups from the aromatic diamine). Unit) can be preferably used. The substituent of such an aromatic diamine is preferably one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group. The alkyl group having 1 to 10 carbon atoms, the halogen atom and the hydroxyl group as such a substituent are the same as those that can be selected as ^Ra1 in the above formula (2) (the same applies to suitable ones). be).

In such a polyimide, the content of the repeating unit (A) is preferably 50 to 100 mol%, more preferably 55 to 95 mol%, and 60 to 90 mol% with respect to all the repeating units. % Is particularly preferable, and 65 to 90 mol% is most preferable. When the content of the repeating unit (A) is less than the lower limit, it tends to be difficult to achieve a sufficiently low Rth, and when the content is within the range of the content, the Rth is sufficiently low. Higher performance tends to be obtained in that it has a sufficiently low CTE in a well-balanced manner.

When the polyimide contains the repeating unit (B) together with the repeating unit (A), the total amount of the repeating units (A) and (B) is 80 to 100 mol with respect to all the repeating units. %, More preferably 90 to 100 mol%, further preferably 95 to 100 mol%, and particularly preferably 98 to 100 mol%. If the ratio of the total amount (content) of the repeating units (A) and (B) is less than the lower limit, it becomes difficult to have a sufficiently low Rth and a sufficiently low CTE in a well-balanced manner. There is a tendency.

When the polyimide contains the repeating unit (B) together with the repeating unit (A), the repeating unit (A) with respect to the total amount of the repeating unit (A) and the repeating unit (B) in the polyimide. ) Is preferably 50 to 99 mol% (more preferably 55 to 95 mol%, still more preferably 60 to 90 mol%, particularly preferably 65 to 90 mol%). If the content of the repeating unit (A) is less than the lower limit, it tends to be difficult to achieve a sufficiently low Rth, while if the content exceeds the upper limit, it is difficult to achieve a sufficiently low CTE. It tends to be. Further, from the same viewpoint, when the polyimide contains the repeating unit (B) together with the repeating unit (A), the content ratio of the repeating unit (A) and the repeating unit (B) in the polyimide is determined. The molar ratio [(A): (B)] is preferably 50:50 to 99: 1 (more preferably 55:45 to 95: 5, still more preferably 60:40 to 90:10). As the polyimide, those consisting of only the repeating units (A) and (B) can be preferably used from the viewpoint of achieving low Rth and low CTE in a well-balanced manner at a higher level.

Further, in the polyimide film of the present invention, in the TMA curve (CTE curve), the extreme value at which the ratio (slope) of the amount of change in film length to the amount of change in temperature changes from positive to negative is 200 to 430 ° C. It exists within the range. As described above, in the TMA curve showing the relationship between the film length and the temperature, there is an extreme value in the above temperature range in which the ratio (inclination) of the change in the film length to the change in temperature changes from positive to negative. The polyimide film is expanded to such an extreme temperature by heat (the length of the film is extended), and in a temperature range higher than the temperature at the extreme position, the temperature is basically near Tg. Until then, the film shrinks due to heat (the length of the film shrinks) compared to the length of the film at such extreme temperatures. Then, when the position of the extreme value is within the above temperature range, the CTE of the polyimide film can be set to a lower value. In such a TMA curve, a polyimide having an extreme value in which the ratio (slope) of the amount of change in film length to the amount of change in temperature changes from positive to negative in the temperature range of 200 to 430 ° C. will be described later. By adopting the polyimide manufacturing method of the present invention, it can be efficiently manufactured. Here, a method for obtaining the "TMA curve" according to the present invention will be described below.

For such a TMA curve, a thermomechanical analyzer (for example, trade name "TMA8310" or "TMA8311" manufactured by Rigaku) is used as a measuring device in a tensile mode, and a film as a measurement sample is set in the measuring device. Then, in a nitrogen atmosphere, the film (measurement sample) is pulled in the vertical direction under the condition of a load of 20 mN while raising the temperature from 50 ° C. to 450 ° C. at a heating rate of 5 ° C./min to change the temperature and the length of the film. It can be obtained by a method of measuring the relationship with the quantity (so-called tensile TMA measurement). Further, in such a measurement, first, the polyimide film to be measured is vacuum-dried (pressure: 0.133 kPa, 120 ° C., 1 hour), and then under a nitrogen atmosphere and a temperature condition of 200 ° C. A step of drying for 1 hour is performed, and then a film having a length of 20 mm (grasping allowance total of 5 mm), a width of 5 mm, and a thickness of 10 μm is prepared (prepared by cutting out, etc.) from the obtained dried film, and a measurement sample is prepared. Use as. Here, when the measurement sample is set in the measuring device, the gripping tool (the gripping tool of the measuring device) is set so that the gripping allowance portion of the film is 5 mm in total in order to change the length in the vertical direction. The film is sandwiched between (jigs) and used (the length between the grips (jigs) of the measuring device at the start of measurement is 15 mm (the vertical length of the film at the start of measurement is 15 mm). Use by sandwiching). The "TMA curve" referred to here is a graph in which the vertical axis (Y) is the amount of change in the film length and the horizontal axis (X) is the measurement temperature in the above-mentioned tensile TMA measurement. Refers to the point where the ratio (slope: ΔY / ΔX) of the amount of change (ΔY) on the vertical axis to the amount of change (ΔX) on the horizontal axis changes from positive to negative, or the point where the ratio changes from negative to positive. In the tensile TMA measurement, a TMA curve having an extreme value at which the slope (ΔY / ΔX) changes from positive to negative is measured in a specific temperature region. In the tensile TMA measurement, the extreme value at which the ratio (inclination) of the change in film length to the change in temperature (increase) changes from positive to negative is due to the elongation of the film. It is measured as a point that changes to contraction. Therefore, the extreme value at which the ratio (ΔY / ΔX) of the change in film length (ΔY) to the change in temperature (ΔX) changes from positive to negative is that the length of the film changes from elongation to shrinkage. In other words.

As described above, in the polyimide film of the present invention, the TMA curve (CTE curve [the vertical axis (Y) obtained as an analysis result of the tensile TMA measurement is the amount of change in the length of the film, and the horizontal axis (X) is measured. Graph with temperature]), the ratio (inclination) of the amount of change in film length to the amount of change (increase) in temperature changes from positive to negative. The point of change to shrinkage) exists within the temperature range of 200 to 430 ° C. (more preferably 220 to 420 ° C., still more preferably 240 to 410 ° C.). If the extreme temperature at which such a slope changes from positive to negative is not within the above range, the absolute value of the CTE cannot be made sufficiently small, resulting in a sufficiently low CTE and a sufficiently low Rth. It will not be possible to have a good balance. The upper limit of the temperature range of the extreme value is more preferably 400 ° C, further preferably 375 ° C, particularly preferably 350 ° C, and most preferably 330 ° C.

Although it is not always clear why the present invention makes it possible to provide a polyimide film having a sufficiently low Rth and a sufficiently low CTE in a well-balanced manner at a higher level, the present inventors have described the following. In this way, the structure of the polyimide film of the present invention has been found. That is, first, the present inventors have found that the Rth can be made sufficiently low by the polyimide containing the repeating unit (A) according to the present invention, and further, the conditions at the time of manufacturing thereof are appropriately controlled. As a result, it has been found that it is possible to obtain a polyimide film having an extreme value in which the slope changes from positive to negative in the TMA curve (CTE curve). Then, as a result of further research by the present inventors based on such findings, in such a TMA curve (CTE curve), the ratio (inclination) of the amount of change in the length of the film to the amount of change in temperature. It was further found that there is a relationship between the position (temperature) of the extreme value and the value of CTE in the polyimide having an extreme value that changes from positive to negative. Then, they have found that it is possible to lower the CTE at a higher level when the position of the extreme value is controlled so as to be within the above-mentioned specific temperature range (200 to 430 ° C.). Normally, in a polyimide film, Rth and CTE have a trade-off relationship (a relationship in which one becomes larger when one is made smaller), so it is difficult to make both values well-balanced and sufficiently small. In the present invention, since it is possible to lower the CTE at a higher level as described above, for example, in a sufficiently small Rth numerical range such that Rth (absolute value) is 145 nm or less. Among them, the Rth (absolute value) is set to 145 nm to 50 nm, the CTE (absolute value) is set to 30 ppm / K or less, and the CTE (absolute value) is set to a sufficiently smaller value in relation to the Rth (absolute value) value. That; the CTE (absolute value) should be 45 ppm / K or less while the Rth (absolute value) should be a sufficiently small value such as less than 50 nm, and the CTE should be a sufficiently small value in relation to Rth; etc. Is also possible. In this way, the present inventors have made it possible to provide a polyimide film having a sufficiently low Rth and a sufficiently low CTE in a well-balanced manner at a higher level. In general polyimide, the length of general polyimide always increases as the temperature rises when the film is pulled, so an extreme value that causes the slope to change from positive to negative is not confirmed on the TMA curve. Become.

Further, in the polyimide film of the present invention, when the TMA curve is measured, the amount of increase in film length at the extreme value (for example, the amount of increase in length with respect to the film length of 15 mm before measurement: 30 to 400). The length extended by measurement at ° C.) is preferably 200 μm or less (more preferably 150 μm or less, still more preferably 0 to 100 μm). If the amount of increase in length exceeds the upper limit, the dimensional change during heating and cooling becomes large, which tends to cause curls and cracks.

Further, in the polyimide film of the present invention, the glass transition temperature (Tg) of the polyimide is preferably 300 ° C. or higher, more preferably 300 ° C. to 550 ° C., and further preferably 350 to 500 ° C. preferable. If the glass transition temperature (Tg) is less than the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if it exceeds the upper limit, it tends to be difficult to produce a polyimide having such characteristics. It is in. As such a method for measuring Tg, a film made of polyimide having a length of 5 mm, a width of 5 mm, and a thickness of 10 μm is prepared as a measurement sample, and a thermomechanical analyzer (trade name “TMA8310” manufactured by Rigaku) is prepared as a measurement device. Alternatively, using "TMA8311"), a transparent quartz pin (tip diameter: 0.5 mm) is needled at 500 mN pressure on the film in a temperature range of 30 ° C to 550 ° C at a temperature rise rate of 5 ° C / min under a nitrogen atmosphere. A method of measuring the point where the film is softened by heating and the quartz pin penetrates into the film as the glass transition temperature by adopting the so-called penetration (needle insertion) method (hereinafter, such a method is simply "500 mN" for convenience. It is called the "penetration (needle insertion) method" in which the needle is inserted by pressure).

In such a polyimide film, the absolute value of retardation (Rth) in the thickness direction measured at a wavelength of 589 nm is preferably 145 nm or less, more preferably 100 nm or less, and more preferably 85 nm in terms of a thickness of 10 μm. The following is more preferable. If the absolute value of the retardation (Rth) in the thickness direction exceeds the upper limit, a clear image cannot be obtained when used in a display device, and the display quality tends to deteriorate. When the absolute value of the retardation (Rth) is equal to or less than the upper limit, a clear image can be obtained and the display quality tends to be higher when used in a display device. As described above, it is preferable that the absolute value of the retardation (Rth) in the thickness direction is a lower value from the viewpoint of obtaining a clear image and improving the display quality when used in a display device.

For such "absolute value of retardation (Rth) in the thickness direction", the value of the refractive index (589 nm) of the polyimide film measured as described later using the trade name "AxoScan" manufactured by AXOMETRICS as a measuring device is used. After inputting to the measuring device, the retardation in the thickness direction of the polyimide film was measured using light having a wavelength of 589 nm under the conditions of temperature: 25 ° C. and humidity: 40%, and the obtained measured value of the retardation in the thickness direction was obtained. Based on (measured value by automatic measurement (automatic calculation) of the measuring device), a value (converted value) converted into a retardation value per 10 μm thickness of the film is obtained, and an absolute value is calculated from the converted value. As described above, the "absolute value of retardation (Rth) in the thickness direction" can be obtained by calculating the absolute value (| converted value |) of the converted value. The size of the polyimide film of the measurement sample is not particularly limited as long as it is larger than the photometric part (diameter: about 1 cm) of the stage of the measuring instrument. When a measurement sample having a thickness of 10 μm is used, the measured value by the automatic measurement (automatic calculation) of the measuring device is used as it is as the converted value to obtain the “absolute value of retardation (Rth) in the thickness direction”. Can be done.

Further, the value of "refractive index (589 nm) of the polyimide film" used for measuring the retardation (Rth) in the thickness direction is an unstretched film made of the same type of polyimide as the polyimide forming the film to be measured for retardation. After forming the above, the unstretched film is used as a measurement sample (when the film to be measured is an unstretched film, the film can be used as it is as a measurement sample) for measurement. Using a refractive index measuring device (trade name "NAR-1T SOLID" manufactured by Atago Co., Ltd.) as an apparatus, the average refractive index of the measured sample with respect to 589 nm light is measured under a temperature condition of 23 ° C. using a 589 nm light source. And ask. In this way, the value of the "refractive index of the polyimide film (589 nm)" is measured using the unstretched film, and the obtained measured value (the value of the average refractive index of the measured sample with respect to the light of 589 nm) is described above. It is used to measure the retardation (Rth) in the thickness direction. Here, the size of the polyimide film of the measurement sample may be any size as long as it can be used for the refractive index measuring device, and may be 1 cm square (1 cm in length and width) and 10 μm in thickness.

Further, as described above, the coefficient of thermal expansion (linear expansion coefficient: CTE) of polyimide is generally in a trade-off relationship with the value (absolute value) of Rth. From the viewpoint of use in a display, it is preferable that the Rth (absolute value) is 145 nm or less in terms of a thickness of 10 μm as described above. From this point of view, in the polyimide film of the present invention, when the Rth (absolute value) is in the region of 145 nm to 50 nm in terms of thickness of 10 μm, the absolute value of CTE is 30 ppm / K. The following (more preferably 0 to 25 ppm / K, still more preferably 0 to 20 ppm / K) is preferable, and Rth is very small so that the Rth (absolute value) is less than 50 nm in terms of the thickness of 10 μm. When it is in the region, the absolute value of CTE is preferably 45 ppm / K or less (more preferably 0 to 40 ppm / K, still more preferably 0 to 30 ppm / K). That is, in the polyimide film of the present invention, when Rth (absolute value: thickness 10 μm conversion) is in the range of 145 nm to 50 nm, the absolute value of CTE is 30 ppm / K or less, and Rth (absolute value: thickness 10 μm). The absolute value of CTE is preferably 45 ppm / K or less when the conversion) is less than 50 nm. It can be said that a polyimide film satisfying such a condition has a lower CTE at a higher level in relation to Rth, and has a sufficiently low thickness direction retardation (Rth) based on an absolute value. It can be said that it has a low coefficient of thermal expansion (CTE) at a very high level in a well-balanced manner. If the absolute value of such a coefficient of thermal expansion exceeds the upper limit, peeling or cracking tends to occur easily in the thermal history when the compound is combined with a metal or an inorganic substance. As a method for measuring the thermal expansion rate (CTE) of such a polyimide, the amount of change in the length of the sample (length in the vertical direction) is the same as the method adopted in the method for obtaining the “TMA curve” described above. After measuring the amount of change in the sample), a method is adopted in which the average value of the change in the length of the sample per 1 ° C. (1K) in the temperature range of 100 ° C. to 350 ° C. is calculated based on the data. .. From such a measuring method, it can be said that the coefficient of thermal expansion (linear expansion coefficient: CTE) of the polyimide is the value of the coefficient of thermal expansion of the polyimide film when the thickness is 10 μm.

Further, the coefficient of thermal expansion (linear expansion coefficient: CTE) of the polyimide film of the present invention preferably has an absolute value in the range of 0 to 30 ppm / K from the viewpoint of obtaining more advanced characteristics. It is more preferably in the range of 0 to 25 ppm / K, and even more preferably in the range of 0 to 20 ppm / K. As described above, the polyimide film of the present invention has a Rth (absolute value: 10 μm thickness conversion) in the range of 0 to 145 nm (more preferably 0 to 110 nm) from the viewpoint of obtaining more advanced characteristics (more preferably, 0 to 110 nm). The CTE (absolute value) is preferably 30 ppm / K or less, more preferably 0 to 25 ppm / K, and 0 to 20 ppm / K (regardless of the value within the above range). Is more preferable.

Further, as such a polyimide film, one having a yellowness (YI) of 20 to 0 (more preferably 10 to 0, particularly preferably 5 to 0) is more preferable from the viewpoint of obtaining a higher degree of transparency. preferable. Further, as such a polyimide, one having a total light transmittance of 80% or more (more preferably 85% or more, particularly preferably 87% or more) is more preferable from the viewpoint of obtaining a higher degree of transparency. Further, as such a polyimide, one having a haze (turbidity) of 5 to 0 (more preferably 4 to 0, particularly preferably 3 to 0) is more preferable from the viewpoint of obtaining a higher degree of transparency. .. For such measurement of yellowness (YI), the trade name "Spectrocolorimeter SD6000" manufactured by Nippon Denshoku Industries Co., Ltd. is used as a measuring device, and the total light transmittance and haze (turbidity) are measured. For the measurement, the trade name "Haze Meter NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd. is used as the measuring device. Further, as a sample for measuring yellowness, total light transmittance and haze, a film made of polyimide having a thickness of 10 μm ± 5 μm can be used (the vertical and horizontal sizes of the measurement sample are determined by the measuring device. Any size that can be placed at the measurement site). The turbidity (YI) is determined by measuring according to ASTM E313-05 (issued in 2005), and the total light transmittance is measured according to JIS K7631-1 (issued in 1997). Haze (turbidity) is determined by performing measurements in accordance with JIS K7136 (issued in 2000).

Further, such a polyimide preferably has a 5% weight loss temperature of 400 ° C. or higher, and more preferably 450 to 550 ° C. If the 5% weight loss temperature is less than the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if it exceeds the upper limit, it tends to be difficult to produce a polyimide having such characteristics. It is in. Further, as such a polyimide, a polyimide having a softening temperature of 300 ° C. or higher is preferable, and a polyimide having a softening temperature of 350 to 550 ° C. is more preferable. If the softening temperature is less than the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if it exceeds the upper limit, it tends to be difficult to produce a polyimide having such characteristics. Further, as such a polyimide, a polyimide having a thermal decomposition temperature (Td) of 450 ° C. or higher is preferable, and a polyimide having a thermal decomposition temperature (Td) of 480 to 600 ° C. is more preferable. If the thermal decomposition temperature (Td) is less than the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if the thermal decomposition temperature (Td) exceeds the upper limit, a polyimide having such characteristics can be produced. It tends to be difficult. For such 5% weight loss temperature, softening temperature and pyrolysis temperature (Td), the methods described in paragraph [0178], paragraph [0180] and paragraph [0181] of International Publication No. 2015-163314 are adopted, respectively. Can be measured. Further, such a polyimide preferably has a pencil hardness of 6B to 6H (more preferably HB to 4H). If such hardness is less than the lower limit, it tends to be difficult to obtain a sufficiently high level of hardness, while if it exceeds the upper limit, a colorless and transparent polyimide having such characteristics can be produced. It tends to be difficult. It should be noted that such a pencil hardness value can be measured according to the method specified in JIS K5600-5-4 issued in 1999.

Further, the number average molecular weight (Mn) of such polyimide is preferably 1000 to 1000000 in terms of polystyrene, and more preferably 10,000 to 500,000. Further, the weight average molecular weight (Mw) of such a polyimide is preferably 1000 to 5000000 in terms of polystyrene, more preferably 5000 to 5000000, further preferably 10000 to 500000, and 20000 to 20000. It is particularly preferably 100,000. If Mn or Mw is less than the lower limit, the film tends to be brittle and the heat resistance of the polyimide tends to decrease. On the other hand, if it exceeds the upper limit, film forming becomes difficult and the film tends to be wrinkled. It is in. Further, the molecular weight distribution (Mw / Mn) of such a polyimide is preferably 1.1 to 5.0, more preferably 1.5 to 3.0. If the molecular weight distribution is less than the lower limit, it tends to be difficult to produce, while if it exceeds the upper limit, it tends to be difficult to obtain a uniform film. The molecular weight (Mw or Mn) and the distribution of the molecular weight (Mw / Mn) of such polyimide can be measured by a gel permeation chromatography (GPC) measuring device (HLC-8320GPC manufactured by Tosoh Corporation, column: manufactured by Tosoh Co., Ltd.) as a measuring device. Obtained by converting data measured by GPC column TSK-GEL SuperAW2500 (× 4), column temperature 40 ° C., DMAc solvent containing lithium bromide (10 mM-LiBr) (flow velocity 0.50 mL / min.) With polystyrene. be able to.

Further, the form of such a polyimide film may be a film shape, and is not particularly limited, and can be appropriately designed into various shapes (disk shape, cylindrical shape (film processed into a tubular shape), etc.). When manufactured using the polyimide precursor resin solution described later, the design can be changed more easily. Further, the thickness of the polyimide film of the present invention is not particularly limited, but is preferably 0.1 to 200 μm, more preferably 1 to 100 μm.

Such a polyimide film of the present invention is, for example, a film for a flexible wiring substrate (FPC substrate), an FCCL substrate, a heat-resistant insulating tape, an electric wire enamel, a protective coating agent for a semiconductor, a liquid crystal alignment film, a transparent conductive film for an organic EL, and the like. TFT substrate for organic EL, substrate for color filter, substrate for touch panel, cover glass substitute film, flexible substrate film, flexible transparent conductive film, transparent conductive film for organic thin film type solar cell, transparent conductive film for dye sensitized solar cell Sex film, flexible gas barrier film, touch panel film, seamless polyimide belt for copying machines (so-called transfer belt), transparent electrode substrate (transparent electrode substrate for organic EL, transparent electrode substrate for solar cells, transparent electrode substrate for electronic paper, etc.), Interlayer insulation film, sensor board, image sensor board, light emitting diode (LED) reflector (LED lighting reflector: LED reflector), LED lighting cover, LED reflector lighting cover, coverlay film, high Durable composite substrate, resist for semiconductors, lithium ion battery, substrate for organic memory, substrate for organic transistor, substrate for organic semiconductor, color filter base material, front film, TFT board for plastic LCD, color filter board for plastic LCD, plastic It can be appropriately and suitably used as a material used for applications such as a touch panel substrate for an LCD and a substrate for a transparent display.

[Method for manufacturing polyimide film of the present invention]
In the method for producing a polyimide film of the present invention, a polyimide is formed by using a polyimide precursor resin solution containing a polyimide precursor and an organic solvent, and then the solvent is removed from the coating film and fired. Including the process of obtaining a film consisting of
The polyimide precursor contains a repeating unit (A') represented by the general formula (7), and the polyimide precursor contains the repeating unit (A').
At the time of firing, the film made of the polyimide is obtained by firing at a temperature in the range of (Tg-190) ° C. to (Tg-50) ° C. based on the glass transition temperature (Tg) of the obtained polyimide. Obtaining the polyimide film of the invention,
It is a method characterized by.

First, the polyimide precursor, the organic solvent, and the polyimide precursor resin solution used in the method for producing the polyimide film of the present invention will be described.

Such a polyimide precursor contains a repeating unit (A') represented by the above general formula (7). In such a formula (7), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming ^a cyclic structure, and Ra represents the above general formulas (2) to (3). ) Indicates one of the divalent organic groups, and Y ¹ and Y ² are independently composed of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms and an alkylsilyl group having 3 to 9 carbon atoms, respectively. Shows one species selected from the group. In addition, A and Ra in the general formula (7) are synonymous with A and Ra in the general formula (1), respectively (the preferred ones are also synonymous).

When both Y ¹ and Y ² are hydrogen atoms (when they are repeating units of so-called polyamic acid), the production of polyimide tends to be easy.

Further, when Y ¹ and Y ² are alkyl groups having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms), the storage stability of the polyimide precursor resin tends to be more excellent. When Y ¹ and Y ² are alkyl groups having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms), it is more preferably a methyl group or an ethyl group.

Further, when Y ¹ and Y ² are alkylsilyl groups having 3 to 9 carbon atoms, the solubility of the polyimide precursor in an organic solvent tends to be more excellent. When Y ¹ and Y ² are alkylsilyl groups having 3 to 9 carbon atoms, it is more preferably a trimethylsilyl group or a t-butyldimethylsilyl group.

When Y ¹ and Y ² in such a formula are groups other than hydrogen atoms (alkyl groups and / or alkylsilyl groups), the introduction rate of the groups is not particularly limited, but among Y ¹ and Y ² . When at least a part is an alkyl group and / or an alkylsilyl group ⁽ at ^least a part of Y1 and Y2 in the repeating unit (A') contained in the polyimide precursor is an alkyl group and / or an alkylsilyl group. (When used as a group), 25% or more (more preferably 50% or more, further preferably 75% or more) of the total amount (total number) of Y ¹ and Y ² , respectively, shall be an alkyl group and / or an alkylsilyl group. (In this case, Y1 and Y2 ^{other than} the alkyl group and / or the alkylsilyl group are hydrogen atoms). By using an alkyl group and / or an alkylsilyl group for 25% or more of the total amount (total number) of the repeating units Y ¹ and Y ² contained in the polyimide precursor, the storage stability of the polyimide precursor resin is more excellent. It tends to be Regarding the substituents represented by Y ¹ and Y ² in the above general formula (7), the type of the substituent and the introduction rate of the substituent are appropriately changed under the production conditions of the polyimide precursor. It can be changed by.

As such a polyimide precursor, it is preferable that both Y ¹ and Y ² are hydrogen atoms, that is, polyamic acid, because the production of polyimide becomes easier.

Further, the polyimide precursor may be one containing one of the repeating units (A') alone, or may be ^A , Ra, Y ¹ and Y ² in the above formula (7). It may contain a combination of at least one of the two or more different types of repeating units (A'). Further, the polyimide precursor may contain other repeating units in addition to the repeating unit (A').

As such a polyimide precursor, together with the repeating unit (A'), the following general formula (8):

[In the formula (8), A is synonymous with A in the general formula (1) (the preferred one is also synonymous), and R ^b is synonymous with R ^b in the general formula (5). (The suitable ones are also synonymous), and Y ¹ and Y ² are synonymous with Y ¹ and Y ² in the above general formula (7), respectively (the preferred ones are also synonymous). ]
It is preferable to further contain the repeating unit (B') represented by.

Further, the polyimide precursor may contain repeating units other than the repeating units (A') and (B') as long as the effects of the present invention are not impaired. Examples of the repeating unit other than the repeating units (A') and (B') are not particularly limited, and examples thereof include known repeating units that can be used as the repeating unit of the polyimide precursor. ), A repeating unit derived from a tetracarboxylic acid dianhydride other than the tetracarboxylic acid dianhydride or the like may be appropriately used. As the repeating unit other than the repeating units (A') and (B'), the CTE of the finally formed polyimide can be made smaller, which is represented by the above general formula (I). The tetracarboxylic acid dianhydride to be used, p-phenylenediamine which may have a substituent, terphenyldiamine which may have a substituent, and biphenyl-based diamine which may have a substituent ( For example, m-trizine, o-tridine, 3,3', 5,5'-tetramethylbenzidine, octafluorobenzidine, 2,2'-bis (trifluoromethyl) benzidine, etc.), having a substituent. It consists of a good ester group-containing diamine (eg 4-aminophenyl 4-aminobenzoate) and a diamine having a hydroxyl group (eg 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane). A repeating unit formed by reaction with at least one aromatic diamine selected from the group (the ^Rb portion of the group represented by the above general formula (8) is two aminos from the aromatic diamine. A repeating unit that is a residue excluding the group (-NH ₂ )) can be preferably used. The substituent of such an aromatic diamine is preferably one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group. The alkyl group having 1 to 10 carbon atoms and the halogen atom as such a substituent can be selected as ^Ra1 in the above formula (2), and are similar to those (suitable ones are also the same). ).

In such a polyimide precursor, the content of the repeating unit (A') is preferably 50 to 100 mol%, more preferably 55 to 95 mol%, and 60 to 60 to all the repeating units. It is particularly preferably 90 mol%, most preferably 65-90 mol%. If the content of such a repeating unit (A') is less than the lower limit, it tends to be difficult to achieve a sufficiently low Rth, and if it is within the range of the content, it is sufficiently low. Higher performance tends to be obtained in that it has a sufficiently low CTE in a well-balanced manner while having Rth.

When the polyimide precursor contains a repeating unit (B') together with a repeating unit (A'), the total amount of the repeating units (A') and (B') is the total amount of the repeating units (B') with respect to all the repeating units. It is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, further preferably 95 to 100 mol%, and particularly preferably 98 to 100 mol%. If the ratio of the total amount (content) of such repeating units (A') and (B') is less than the lower limit, it is difficult to have a sufficiently low Rth and a sufficiently low CTE in a well-balanced manner. It tends to be.

When the polyimide contains a repeating unit (B') together with a repeating unit (A'), the repetition with respect to the total amount of the repeating unit (A') and the repeating unit (B') in the polyimide. The content of the unit (A') is preferably 50 to 99 mol% (more preferably 55 to 95 mol%, still more preferably 60 to 90 mol%, particularly preferably 65 to 90 mol%). If the content of the repeating unit (A) is less than the lower limit, it tends to be difficult to achieve a sufficiently low Rth, while if the content exceeds the upper limit, it is difficult to achieve a sufficiently low CTE. It tends to be. As the polyimide, those consisting only of repeating units (A') and (B') can be preferably used from the viewpoint of achieving low Rth and low CTE at a higher level in a well-balanced manner.

Further, when the polyimide precursor contains a repeating unit (B') together with a repeating unit (A'), groups other than hydrogen atoms are added to Y ¹ and Y ² in each formula of each repeating unit. When (alkyl group and / or alkylsilyl group) is contained, the introduction rate of the group is not particularly limited, but is 25% or more (more preferably 50% or more, more preferably 50% or more) of the total amount (total number) of Y ¹ and Y ² . It is preferable that 75% or more) is an alkyl group and / or an alkylsilyl group.

Further, when the polyimide precursor contains a repeating unit (B') together with the repeating unit (A'), the polyimide can be more easily prepared, and thus the repeating units (A') and (B'). ), It is more preferable that both Y ¹ and Y ² are hydrogen atoms. As described above, as the polyimide precursor, polyamic acid in which Y ¹ and Y ² in each formula are both hydrogen atoms is more preferable.

Further, as a polyamic acid suitable as such a polyimide precursor resin, the intrinsic viscosity [η] is preferably 0.05 to 3.0 dL / g, and 0.1 to 2.0 dL / g. Is more preferable. If the intrinsic viscosity [η] is smaller than 0.05 dL / g, the obtained film tends to be brittle when a film-shaped polyimide is produced using the intrinsic viscosity [η], while 3.0 dL / g is used. If it exceeds the viscosity, the viscosity is too high and the processability is lowered. For example, when a film is manufactured, wrinkles are formed and it becomes difficult to obtain a uniform film. Further, such intrinsic viscosity [η] can be measured as follows. That is, first, a measurement sample (solution) is obtained in which tetramethylurea (TMU) is used as a solvent and the polyamic acid is dissolved in TMU so as to have a concentration of 0.5 g / dL. Next, using the measurement sample, the viscosity of the measurement sample is measured using a kinematic viscosity meter under a temperature condition of 30 ° C., and the obtained value is adopted as the intrinsic viscosity [η]. As such a kinematic viscometer, an automatic viscosity measuring device (trade name "VMC-252") manufactured by Rigo Co., Ltd. is used.

The polyimide precursor according to the present invention is 1) polyamic acid (both Y ¹ and Y ² in the general formula of each repeating unit are hydrogen atoms); 2) polyamide, depending on the type of Y ¹ and Y ² . Since it can be classified into acid esters (at least a part of Y ¹ and Y ² are alkyl groups); 3) polyamic acid silyl esters (at least a part of Y ¹ and Y ² are alkyl silyl groups); The method for producing the above-mentioned classification will be described separately for each of the above categories. The method for producing such a polyimide precursor is not limited to the following production method.

1) Polyamic acid As a method that can be suitably used for producing such a polyamic acid, for example, a tetracarboxylic acid dianhydride represented by the above general formula (I) and a formula: H ₂ are used. N-R ^a -NH ₂ [ ^Ra in the formula is synonymous with ^Ra in the above formula (1). ], A method for obtaining a polyamic acid by reacting with a diamine compound represented by] can be preferably adopted.

In this way, when the tetracarboxylic dianhydride and the diamine compound are reacted, it is preferable to react them in the presence of a polymerization solvent. As such a polymerization solvent, an organic solvent capable of dissolving both the tetracarboxylic dianhydride and the diamine compound is preferable. Examples of such an organic solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone. Aprotonic polar solvents such as (GBL), propylene carbonate, tetramethylurea (tetramethylurea: TMU), 1,3-dimethyl-2-imidazolidinone (DMI), hexamethylphosphoric triamide, pyridine; m -Pharmonal solvents such as cresol, xylenol, phenol, halogenated phenol; ethereal solvents such as tetrahydrofuran, dioxane, cellosolve, glyme; aromatic solvents such as benzene, toluene, xylene; cyclopentanone, cyclohexanone, etc. Ketone-based solvent; Examples thereof include nitrile-based solvents such as acetonitrile and benzonitrile. Such an organic solvent may be used alone or in combination of two or more.

Further, as such a polymerization solvent, it is more preferable to use an aprotic polar solvent from the viewpoint of solubility in the tetracarboxylic acid dianhydride and the diamine compound, among which DMAc, DMI or TMU is used. Especially preferable. As described above, when DMAc, DMI, or TMU is used as the polymerization solvent, these are excellent in solubility in the tetracarboxylic acid dianhydride and the diamine compound, so that the polymerization reaction can be further promoted. It becomes possible to proceed efficiently (the reaction becomes easier to proceed), and thereby it becomes possible to obtain a polyamic acid varnish having a high degree of polymerization in a shorter time.

Here, when the obtained polyamic acid contains the repeating unit (A') and the repeating unit (B') in which both Y ¹ and Y ² in the formula are hydrogen atoms, the formula: H ₂ N-R ^b -NH ₂ [R ^{b in the formula is synonymous with R b in} the above formula (5). ] Is further used, and the diamine compound represented by the above formula: H2N _- R ^a -NH ₂ is compared with the tetracarboxylic dianhydride represented by the above general formula (I). And the above formula: a mixture with a diamine compound represented by H ₂ N-R ^b -NH ₂ may be reacted. It should be noted that such an equation: H ₂ N-R ^b -NH ₂ [R ^{b in the equation is synonymous with R b in} the above equation (5). ], And the reaction between the diamine compound represented by the above general formula (I) and the tetracarboxylic dianhydride represented by the above general formula (I) makes it possible to contain the repeating unit (B').

Further, the tetracarboxylic acid dianhydride and the diamine compound (the diamine compound represented by the formula: H2N-R ^a -NH ₂ and the diamine compound represented by the formula: H ₂ N R ^b _{-NH 2 )} are present. When the above is used, the ratio of the mixture) to 1 equivalent of the amino group in the diamine compound is the amount of all the acid anhydride groups in the tetracarboxylic acid dianhydride used in the reaction. The amount is preferably 0.2 to 2 equivalents, and more preferably 0.3 to 1.2 equivalents. If the suitable ratio of the tetracarboxylic acid dianhydride and the diamine compound is less than the lower limit, the polymerization reaction does not proceed efficiently and a high molecular weight polyamic acid (reaction intermediate) tends not to be obtained. On the other hand, if the upper limit is exceeded, a high molecular weight polyamic acid (reaction intermediate) tends not to be obtained as in the above.

Further, as for the amount of the polymerization solvent (organic solvent) used, the total amount of the tetracarboxylic acid dianhydride and the diamine compound is 0.1 to 50% by mass (more preferably 10 to 10 to the total amount of the reaction solution). The amount is preferably 30% by mass). If the amount of such an organic solvent used is less than the lower limit, it tends to be impossible to efficiently obtain polyamic acid, while if it exceeds the upper limit, stirring tends to be difficult due to high viscosity.

Further, from the viewpoint of improving the reaction rate and obtaining a polyamic acid having a high degree of polymerization when the tetracarboxylic acid dianhydride is reacted with the diamine compound, a basic compound is further added to the organic solvent. May be good. Such basic compounds are not particularly limited, but for example, triethylamine, tetrabutylamine, tetrahexylamine, 1,8-diazabicyclo [5.4.0] -undecene-7, pyridine, isoquinoline, α-picoline, imidazole. And so on. The amount of such a basic compound used is preferably 0.001 to 10 equivalents, preferably 0.01 to 10 equivalents, relative to 1 equivalent of the tetracarboxylic dianhydride represented by the above general formula (I). It is more preferable to set it to 0.1 equivalent. If the amount of such a basic compound used is less than the lower limit, the addition effect tends not to be seen, while if it exceeds the upper limit, it tends to cause coloring or the like.

Further, the reaction temperature at the time of reacting the tetracarboxylic dianhydride with the diamine compound may be appropriately adjusted to a temperature at which these compounds can be reacted, and is not particularly limited, depending on the case. The temperature is preferably −40 to 450 ° C., more preferably −20 to 400 ° C., further preferably −20 to 200 ° C., and particularly preferably 0 to 100 ° C. Further, the tetracarboxylic acid dianhydride, the diamine compound (diamine compound represented by the formula: H2N-R ^a -NH ₂ ), and the diamine represented by the formula: H ₂ N R ^b _- NH ₂ When a compound is used, as a method for reacting with the mixture thereof), a known method (conditions, etc.) capable of carrying out a polymerization reaction between the tetracarboxylic acid dianhydride and the aromatic diamine is appropriately used. It can be, but is not particularly limited, for example, after the diamine compound is dissolved in the polymerization solvent in an inert atmosphere such as nitrogen, helium, argon, etc., at the reaction temperature, the tetra. A method in which the carboxylic acid dianhydride is added and then reacted for 10 to 48 hours. The diamine compound and the tetracarboxylic acid dianhydride are placed in a reaction vessel under an inert atmosphere such as atmospheric pressure, nitrogen, helium and argon. A method of adding the compound, adding the polymerization solvent, dissolving each component in the solvent, and then reacting at the reaction temperature for 10 to 48 hours may be appropriately adopted. If the reaction temperature or reaction time is less than the lower limit, it tends to be difficult to sufficiently react, while if the reaction temperature or reaction time exceeds the upper limit, the probability of mixing a substance (oxygen or the like) that deteriorates the polymer increases and the molecular weight increases. It tends to decrease.

In this way, the polyamic acid containing the repeating unit (A') in which Y ¹ and Y ² in the general formula are both hydrogen atoms (in some cases, both Y ¹ and Y ² in the general formula are hydrogen atoms). Including the repeating unit (B') which is

2) Polyamic acid ester Next, a method that can be suitably used for producing the polyamic acid ester will be described. That is, first, the tetracarboxylic acid dianhydride represented by the above general formula (I) is reacted with an arbitrary alcohol to obtain a diesterdicarboxylic acid, and then a chlorination reagent (for example, thionyl chloride, oxalyl chloride, etc.) is used. The reaction is carried out to obtain a diester dicarboxylic acid chloride (a derivative of tetracarboxylic acid). Next, as the monomer component, a compound containing at least the diester dicarboxylic acid chloride is used (note that the monomer component includes the diester dicarboxylic acid chloride and the tetra represented by the general formula (I). A mixture with a carboxylic acid dianhydride may be used), the monomer component and the diamine compound are mixed in the range of −20 to 120 ° C. (more preferably −5 to 80 ° C.) for 1 to 72 hours. By stirring and reacting, a polyamic acid ester containing a repeating unit (A') in which at least a part of Y ¹ and Y ² in the formula is an alkyl group can be obtained. When the reaction is carried out at a temperature of 80 ° C. or higher during stirring, the molecular weight tends to fluctuate depending on the temperature history during polymerization, and imidization may proceed due to heat. Therefore, the polyimide precursor It tends to be difficult to stably produce. Further, by dehydrating and condensing the diester dicarboxylic acid and the diamine compound using a phosphorus-based condensing agent, a carbodiimide condensing agent, or the like, a polyimide precursor composed of the polyamic acid ester can be easily obtained. Since the polyimide precursor made of a polyamic acid ester obtained by such a method is stable, purification such as reprecipitation can be performed by adding a solvent such as water or alcohol.

3) Polyamic Acid Cyril Ester Hereinafter, methods that can be suitably used for producing the polyamic acid silyl ester will be briefly described separately by the so-called indirect method and the direct method.

<Indirect method>
As a method that can be suitably used for producing the polyamic acid silyl ester, the following method (indirect method) can be adopted. That is, first, the diamine compound is reacted with a silylating agent to obtain a silylated diamine compound. If necessary, the diamine compound silylated by distillation or the like may be purified. Next, a silylated diamine compound or a mixture of the silylated diamine compound and the diamine compound (not silylated) is dissolved in the dehydrated solvent to obtain a solution. Then, while stirring the solution, the tetracarboxylic acid dianhydride represented by the general formula (I) is gradually added to the solution in the range of 0 to 120 ° C (preferably 5 to 80 ° C). By stirring for 1 to 72 hours, a polyimide precursor composed of a polyamic acid silyl ester containing a repeating unit (A') in which at least a part of Y ¹ and Y ² is an alkylsilyl group can be obtained. When the reaction is carried out at such a stirring temperature of 80 ° C. or higher, the molecular weight tends to fluctuate depending on the temperature history at the time of polymerization, and imidization may proceed due to heat. It tends to be difficult to stably produce a polyimide precursor.

As the silylating agent, it is preferable to use a silylating agent that does not contain a chlorine atom. By using the silylating agent containing no chlorine atom as described above, it is not necessary to purify the silylated aromatic diamine, so that the process can be further simplified. Examples of such a chlorine atom-free silylating agent include N, O-bis (trimethylsilyl) trifluoroacetamide, N, O-bis (trimethylsilyl) acetamide, and hexamethyldisilazane. Further, as the silylating agent, N, O-bis (trimethylsilyl) acetamide and hexamethyldisilazane are particularly preferable because they do not contain a fluorine atom and are low in cost.

Further, in the silylation reaction of the diamine compound, an amine-based catalyst such as pyridine, piperidine, or triethylamine can be used to accelerate the reaction. Such an amine-based catalyst can be used as it is as a polymerization catalyst for a polyimide precursor.

<Direct method>
First, a method that can be suitably used for producing the polyamic acid described in the above-mentioned "1) Polyamic acid" column is carried out, and the reaction solution obtained after the reaction is prepared as it is as a polyamic acid solution. .. Then, the silylating agent is mixed with the obtained polyamic acid solution, and the mixture is stirred in the range of 0 to 120 ° C. (preferably 5 to 80 ° C.) for 1 to 72 hours to obtain the polyimide composed of the polyamic acid silyl ester. A precursor resin can be obtained (direct method). When the reaction is carried out at a temperature of 80 ° C. or higher during stirring, the molecular weight tends to fluctuate depending on the temperature history during polymerization, and imidization may proceed due to heat. Therefore, the polyimide precursor It tends to be difficult to stably produce. As the silylating agent that can be used in such a direct method, it is not necessary to purify the silylated polyamic acid or the obtained polyimide, so that a silylating agent that does not contain a chlorine atom can be used. preferable. Examples of such a chlorine atom-free silylating agent include N, O-bis (trimethylsilyl) trifluoroacetamide, N, O-bis (trimethylsilyl) acetamide, and hexamethyldisilazane. Further, as such a silylating agent, N, O-bis (trimethylsilyl) acetamide and hexamethyldisilazane are particularly preferable because they do not contain a fluorine atom and are low in cost.

Any of the methods for producing the polyimide precursor described above can be carried out in an organic solvent (the polymerization solvent). In this way, when the polyimide precursor is produced in an organic solvent, a resin solution of the polyimide precursor (varnish: polyimide precursor resin solution) can be easily obtained.

The polyimide precursor resin solution according to the present invention contains the polyimide precursor and an organic solvent. As such an organic solvent, the polymerization solvent described in the method for producing the polyimide precursor can be preferably used. Therefore, as a method for producing the polyimide precursor resin solution according to the present invention, from the viewpoint of ease of production, after producing the polyimide precursor in an organic solvent (the polymerization solvent), polyimide is prepared from the reaction solution. It is preferable to adopt a method of producing the reaction solution by using the reaction solution as it is as a varnish (polyimide precursor resin solution) of the polyimide precursor without isolating the precursor.

The content of the polyimide precursor resin (preferably polyamic acid) in such a polyimide precursor resin solution (preferably a resin solution of polyamic acid) is not particularly limited, but is preferably 1 to 80% by mass. More preferably, it is ~ 50% by mass. If the content is less than the lower limit, it tends to be difficult to produce a polyimide film, while if it exceeds the upper limit, stirring and film formation become difficult, and it tends to be difficult to produce a uniform polyimide film. In addition, such a polyimide precursor resin solution (preferably a polyamic acid solution) can be suitably used for producing the above-mentioned polyimide of the present invention, and can be suitably used for producing polyimides having various shapes.

Further, such a polyimide precursor resin solution (preferably a resin solution of polyamic acid) may use a so-called accelerator in the firing step described later from the viewpoint of promoting high molecular weight and imidization. As such an accelerator, a known reaction accelerator (for example, an imidazole compound, a pyridine compound, a tertiary amine compound such as triethylamine, an amino acid compound, etc.) may be appropriately used. The amount of such an accelerator used is not particularly limited, but is 1 to 60 parts by mass (more preferably 5 to 50 parts by mass) with respect to 100 parts by mass of the solid content (polyamic acid) in the polyamic acid solution. Is preferable. As such an accelerator, an imidazole-based compound is preferable from the viewpoint of various physical properties such as optical properties, thermal properties, and mechanical properties of the film. Examples of such an imidazole-based compound include the imidazole-based compound described in International Publication No. 2017/026448. Further, as such an imidazole compound, the following general formula (X):

[In the formula (X), R ¹¹ represents one selected from the group consisting of a hydrogen atom and an alkyl group, and R ¹⁴ is independently a halogen atom, a hydroxyl group, a mercapto group, a sulfide group, a silyl group, a silanol group, respectively. Indicates one selected from the group consisting of a nitro group, a nitroso group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphonat group and an organic group, where m indicates an integer of 0 to 3 and R ³¹ , R ³² , R ³³ . , R ³⁴ and R ³⁵ are independently hydrogen atom, hydroxyl group, mercapto group, sulfide group, silyl group, silanol group, nitro group, nitroso group, sulfino group, sulfo group, sulfonato group, phosphino group, phosphinyl group, respectively. It is a phosphono group, a phosphonat group, an amino group, an ammonio group, or an organic group, but at least one of R ³¹ , R ³² , R ³³ , R ³⁴ and R ³⁵ is a group other than a hydrogen atom. ]
The compound represented by is more preferable.

As R ¹¹ in the above general formula (X), a hydrogen atom, a methyl group and an ethyl group are preferable, a hydrogen atom and a methyl group are more preferable, and a hydrogen atom is particularly preferable from the viewpoint of the effect as an accelerator. preferable. When R ¹⁴ in the general formula (X) is an organic group, the organic group is preferably an alkyl group, an aromatic hydrocarbon group, and an aromatic heterocyclic group. When such R ¹⁴ is an alkyl group, a linear or branched alkyl group having 1 to 8 carbon atoms is preferable, and a methyl group, an ethyl group, an n-propyl group, and an isopropyl group are more preferable. When R ¹⁴ is an aromatic hydrocarbon group, a phenyl group is particularly preferable as the aromatic hydrocarbon group. Further, when R ¹⁴ is an aromatic heterocyclic group, a frill group and a thienyl group are more preferable. Further, the value of m in the general formula (X) is more preferably an integer of 0 to 2 from the viewpoint of the effect as an accelerator for increasing the molecular weight and the effect as an accelerator for imidization. .. Further, the value of m in the general formula (X) is more preferably 0 from the viewpoint of the effect as an accelerator. Further, in the compound represented by the above general formula (X), at least one of R ³¹ , R ³² , R ³³ , R ³⁴ and R ³⁵ has the formula: —OR ³⁰ (R ³⁰ is a hydrogen atom or an organic substance. It is preferably a group represented by (), and it is particularly preferable that R ³⁵ is a group represented by the formula: —OR ³⁰ . Further, when R ³⁵ is a group represented by the above formula: —OR ³⁰ , it is preferable that R ³¹ , R ³² , R ³³ and R ³⁴ are hydrogen atoms. As such R ³⁰ , an alkyl group is preferable, an alkyl group having 1 to 8 carbon atoms is more preferable, an alkyl group having 1 to 3 carbon atoms is particularly preferable, and a methyl group is most preferable.

Further, such a polyimide precursor resin solution (preferably a resin solution of polyamic acid) can be used with various additives (deterioration inhibitor, antioxidant, etc.) that can be used for the preparation of polyimide in addition to the accelerator. Light stabilizer, UV absorber, modifier, antistatic agent, flame retardant, plasticizer, nucleating agent, stabilizer, adhesion improver, lubricant, mold release agent, dye, foaming agent, defoaming agent, surface modification A pledge agent, a hard coat agent, a leveling agent, a surfactant, a filler (glass fiber, filler, talc, mica, silica, etc.) may be appropriately added and used. Further, when such an additive is used, the content of the additive in the polyamic acid solution is not particularly limited, but is about 0.0001 to 80% by mass (more preferably 0.1 to 50% by mass). Is preferable.

Next, a step of obtaining a film made of polyimide adopted in the method for producing a polyimide film of the present invention will be described. Such a step is a step of forming a coating film using the polyimide precursor resin solution, removing the solvent from the coating film, and firing to obtain a film made of polyimide.

In such a step, the method for forming the coating film made of the polyimide precursor resin solution is not particularly limited, and a known method can be appropriately used. For example, the polyimide precursor resin solution can be used on a substrate. Can be mentioned as a method of forming a coating film by applying the above. Such a base material is not particularly limited, and a base material made of a known material (for example, glass) that can be used for forming a film made of a polymer depending on the shape of a film made of a target polyimide or the like. (Plate or metal plate) can be used as appropriate.

Further, the method of applying the polyimide precursor resin solution on the substrate is not particularly limited, and for example, a spin coating method, a spray coating method, a dip coating method, a dropping method, a gravure printing method, a screen printing method, and a letterpress. Known methods such as a printing method, a die coating method, a slit coating method, a curtain coating method, and an inkjet method can be appropriately adopted.

The thickness of the coating film of the polyimide precursor resin solution formed on the substrate is not particularly limited, but the thickness of the film after curing is 0.1 to 200 μm from the viewpoint of processability and handleability. It is preferable that the thickness is 1 to 100 μm, and it is more preferable that the thickness is 1 to 100 μm.

Further, in the step, after forming the coating film of the polyimide precursor resin solution, the solvent is removed from the coating film (solvent removal treatment). The method of such a solvent removing treatment is not particularly limited, but it is preferable to heat the coating film to 0 to 150 ° C. (more preferably 20 to 80 ° C.) to remove the solvent from the coating film. Further, in such a solvent removing treatment method, the atmosphere at the time of heating is not particularly limited, and air can be used, but from the viewpoint of suppressing coloring and preventing deterioration, an inert gas atmosphere (inert gas atmosphere). For example, a nitrogen atmosphere) is more preferable. Further, from the viewpoint of more efficient drying, the pressure condition in such a solvent removing treatment is preferably 0.133 to 101.3 kPa (1 to 760 mmHg). By such a solvent removal treatment, the polyimide precursor (preferably polyamic acid) can be isolated in the form of a film or the like, and then a firing treatment can be performed.

Further, in the step, the coating film after the solvent removal treatment is cured by firing to obtain the polyimide film of the present invention. As described above, in the present invention, "firing" refers to a heating step (heat curing step) for curing the coating film after the solvent removal treatment. In such firing, it is necessary to fire at a temperature within the range of (Tg-190) ° C. to (Tg-50) ° C. based on the glass transition temperature (Tg) of the obtained polyimide. When such a firing (heating) temperature is not within the above temperature range, even if the TMA curve of the obtained polyimide is measured, the ratio of the change in film length to the change in temperature in the TMA curve. The extreme value at which (inclination) changes from positive to negative cannot be confirmed within the temperature range of 200 to 430 ° C., and the polyimide of the present invention cannot be obtained. In the conventional method for producing polyimide as described in Patent Document 1 (Japanese Unexamined Patent Publication No. 2016-204568), the glass transition temperature (Tg) of the polyimide finally forming the polyamic acid is used as a reference. A polyimide film is formed by firing at a temperature near Tg (Tg ± 15 to 20 ° C. in the examples of JP-A-2016-204568). When such conventional general polyimide firing conditions (Tg ± 15 to 20 ° C. firing conditions) are simply adopted, the ratio of the amount of change in film length to the amount of temperature change is positive. The position (temperature) of the extreme value that turns negative cannot be controlled to 200 to 430 ° C. On the other hand, in the present invention, after removing the solvent from the coating film of the polyimide precursor (preferably polyamic acid), it is fired at a temperature in the range of (Tg-190) ° C. to (Tg-50) ° C. By doing so, it is necessary to prepare a polyimide in which the position (temperature) of the extreme value at which the ratio (inclination) of the amount of change in film length to the amount of change in temperature changes from positive to negative is within the temperature range of 200 to 430 ° C. It is possible to make the CTE of the polyimide obtained thereby a lower value. If the firing (heating) temperature is not within the temperature range, the absolute value of CTE cannot be set to a desired level (preferably 50 ppm / ° C. or lower).

Further, such a firing temperature is preferably set to (Tg-180) ° C. to (Tg-50) ° C. from the viewpoint of expressing a sufficiently low Rth and expressing a sufficiently low CTE in a well-balanced manner. , (Tg-170) ° C to (Tg-60) ° C, more preferably (Tg-160) ° C to (Tg-70) ° C. Further, in such firing, the firing time is preferably 0.5 to 10 hours, preferably 0.8 to 5 in order to sufficiently imidize and cure the polyimide precursor (preferably polyamic acid). In the present invention, when the coating film after the solvent removal treatment is fired, the temperature conditions are changed in multiple steps in order to heat-cure the coating film after the solvent removal treatment. You may heat it while letting it. In such a heating step, at any stage (for example, the temperature at which the final heating is performed), the heating temperature may be set to a temperature within the range of the firing temperature, and the firing treatment may be performed at any stage. .. For example, the coating film after the solvent removal treatment is heated in advance to a temperature at which imidization of the polyimide precursor proceeds (the imidization itself varies depending on the type of the polyimide precursor, but is advanced to about 80 ° C. or higher. It is also possible), and after heating at a temperature lower than the firing temperature (preferably 100 to 250 ° C.) for 0.5 to 10 hours to promote imidization of the polyimide precursor to some extent, at the firing temperature. It may be heated for 0.5 to 10 hours to further promote imidization and then fired (heat-cured). Further, the firing may be carried out by changing the temperature step by step within the range of the firing temperature. As described above, in the firing step, the heating temperature to be adopted may be applied as the firing temperature at any stage of heating and curing the coating film (when imidizing and curing).

Further, as the atmospheric conditions during such a firing treatment, from the viewpoint of suppressing coloring and deterioration of physical properties due to oxygen, an inert gas atmosphere (for example, a nitrogen atmosphere, an atmosphere having a low oxygen concentration (an atmosphere having an oxygen concentration of 1 to 300 ppm)). )). If it is possible to suppress coloration due to oxygen when the calcination treatment is performed to imidize, the heat treatment may be performed in a high oxygen concentration atmosphere (oxygen concentration: atmosphere of more than 300 ppm and 10,000 ppm or less).

By removing the solvent from the coating film and firing in this way, the polyimide precursor (preferably polyamic acid) in the film can be efficiently ring-closed and heat-cured, whereby the polyimide precursor can be heated and cured. It is possible to imidize a body (preferably a polyamic acid) to efficiently form a polyimide. Then, by performing the firing treatment under specific temperature conditions in this way, the polyimide film of the present invention can be obtained.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. First, a method for evaluating the characteristics of the polyimide film or the like obtained in each Example and each Comparative Example will be described.

<Identification of molecular structure>
IR measurements were performed on the films obtained in each example and each comparative example using an IR measuring machine (manufactured by Nippon Spectroscopy Co., Ltd., trade name: FT / IR-4100), and the obtained IR spectrum was imidecarbonyl. By confirming the peak based on the C = O expansion and contraction vibration, it was confirmed whether or not the material was made of polyimide.

<Measurement of intrinsic viscosity [η]>
The polyamic acid obtained as an intermediate in each Example and each Comparative Example was prepared in the same manner, and the value of intrinsic viscosity [η] (unit: dL / g) was measured. In the measurement, a solution having a concentration of 0.5 g / dL using tetramethylurea (TMU) as a solvent was prepared and used as a measurement sample, and an automatic viscosity measuring device manufactured by Rigosha (trade name "VMC-252") was used. Was measured under a temperature condition of 30 ° C.

<Measurement of TMA curve and CTE>
The TMA curves and CTEs of the polyimide films obtained in each Example and each Comparative Example were determined as follows. That is, first, each polyimide film is vacuum-dried by heating at 0.133 kPa and 120 ° C. for 1 hour, and then heat-treated under a nitrogen atmosphere at 200 ° C. for 1 hour. Obtained a dry film. Next, using the obtained dried film, a measurement sample (a film having a length of 20 mm (grasping allowance total of 5 mm), a width of 5 mm, and a thickness of 10 μm) was prepared. After that, the measurement sample (film) was set in a thermomechanical analyzer (trade name "TMA8310" manufactured by Rigaku) as a measuring device, and a tension mode (20 mN) was adopted, under a nitrogen atmosphere. The measurement sample was pulled in the vertical direction while raising the temperature to 50 ° C. to 450 ° C. at a heating rate of 5 ° C./min, and the change in the vertical length of the sample at 50 ° C. to 450 ° C. was measured (tensile TMA). measurement). Then, as a result of such tensile TMA measurement, a TMA curve which is a graph showing the relationship between the temperature and the amount of change in the length in the vertical direction is obtained, and 1 ° C. (1K) in the temperature range of 100 ° C. to 350 ° C. The average value of the change in the per-length was calculated to obtain the coefficient of thermal expansion (CTE: the value of the coefficient of thermal expansion of a polyimide film having a thickness of 10 μm). In the graph of the TMA curve, the extreme value (hereinafter, for convenience, simply referred to as "extreme value A") in which the ratio (slope) of the amount of change in length to the amount of change (increase) in temperature changes from positive to negative. ) Was observed, the temperature of the extreme value A was obtained. The temperature of such an extreme value A is the temperature at which the change in the length of the measurement sample (film) changes from elongation to contraction in the tensile TMA measurement.

<Measurement of Rth>
For the polyimide films obtained in each Example and each Comparative Example, Rth was measured as follows. That is, using each polyimide film, a film having a length of 20 mm, a width of 20 mm, and a thickness of 10 μm is prepared as a measurement sample, and a trade name “AxoScan” manufactured by AXOMETRICS is used as a measuring device, and the polyimide film measured in advance on the device is used. The value of the refractive index (589 nm) was input, and Rth was obtained as the measured value obtained by automatically measuring using light having a wavelength of 589 nm under the conditions of temperature: 25 ° C. and humidity: 40%. Since the thickness is 10 μm, the obtained Rth is the polyimide value per 10 μm as it is). Here, the value of the refractive index (589 nm) of the polyimide film is 1 cm square (thickness 10 μm) from each of these polyimide films because the polyimide films obtained in each Example and each comparative example are unstretched films. The film was cut out as a measurement sample, and a refraction index measuring device (trade name "NAR-1T SOLID" manufactured by Atago Co., Ltd.) was used as a measuring device, and a measuring sample was used at a temperature condition of 23 ° C. using a 589 nm light source. The value obtained in advance by measuring the average refractive index with respect to the light of 589 nm was adopted.

<Measurement of glass transition temperature (Tg)>
With respect to the polyimide films obtained in each Example and each Comparative Example, the glass transition temperature (Tg) was measured by using a thermomechanical analyzer (trade name "TMA8311" manufactured by Rigaku) as a measuring device, and the above-mentioned "500 mN". The measurement was performed by adopting the "penetration (needle insertion) method" in which the needle is inserted by pressure.

<Measurement of yellowness (YI)>
With respect to the polyimide films obtained in each Example and each Comparative Example, the yellowness (YI) was measured by ASTM E313-05 (2005) using the trade name "Spectrocolorimeter SD6000" manufactured by Nippon Denshoku Industries Co., Ltd. Obtained by performing measurements in accordance with (issued in the year).

(Synthesis Example 1: Adjustment of CpODA)
According to the methods described in Synthesis Example 1, Example 1 and Example 2 of International Publication No. 2011/099518, the following formula (21):

Compounds represented by (norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'', 6,6''-tetracarboxylic dianhydride: hereinafter, Simply referred to as "CpODA") was prepared.

(Synthesis Example 2: Preparation of imidazole compound (reaction accelerator))
Based on the method described in Synthesis Example 1 of International Publication No. 2017/026448, the following formula (22):

The imidazole compound represented was prepared.

(Example 1)
<Preparation process of resin solution of polyamic acid>
First, a 100 ml three-necked flask was heated with a heat gun and sufficiently dried. Next, the atmosphere gas in the three-necked flask was replaced with nitrogen to create a nitrogen atmosphere in the three-necked flask. In a three-necked flask, 2.7875 g (8.00 mmol) of 9,9-bis (4-aminophenyl) fluorene (manufactured by Seika Sangyo: FDA) and 4,4'-diaminobenzanilide (manufactured by Nippon Pure Chemical Industries, Ltd .: DABAN) ) 0.4545 g (2.00 mmol) was added, followed by 28.34 g of N, N, N', N'-tetramethylurea (TMU). The contents of the three-necked flask were stirred to obtain a slurry liquid in which diamine compounds (FDA and DABAN: aromatic diamine) were dispersed in TMU.

Next, 3.8438 g (10.00 mmol) of CpODA prepared in Synthesis Example 1 was added to the three-necked flask, and then the contents of the flask were stirred at room temperature (25 ° C.) for 12 hours under a nitrogen atmosphere to prepare a reaction solution. Obtained. In this way, a reaction solution (resin solution of polyamic acid) having 20% by mass (TMU solvent: 80% by mass) of polyamic acid in the reaction solution was obtained.

Next, 2.1258 g of the imidazole compound prepared in Synthesis Example 2 (amount of 30 parts by mass with respect to 100 parts by mass of the solid content of polyamic acid) was added to the reaction solution thus obtained under a nitrogen atmosphere. rice field. Then, the reaction solution was stirred at 25 ° C. for 12 hours to obtain a polyimide precursor resin solution (resin solution of polyamic acid) containing an imidazole compound.

<Preparation process of polyimide film>
A polyimide precursor resin solution containing the imidazole compound obtained as described above is placed on a glass substrate (non-alkali glass, trade name "Eagle XG" manufactured by Corning, length: 100 mm, width 100 mm, thickness 0.7 mm). The coating film was spin-coated so that the thickness of the coating film after firing (heat curing) was 10 μm to form a coating film. Next, the glass substrate on which the coating film was formed was placed on a hot plate at 70 ° C. and allowed to stand for 2 hours, and the solvent was removed from the coating film by evaporation. Next, the glass substrate on which the coating film was formed after removing the solvent was put into an inert oven in which nitrogen was flowing at a flow rate of 3 L / min. After that, it is allowed to stand in an inert oven under a nitrogen atmosphere under a temperature condition of 25 ° C. for 0.5 hours, heated under a temperature condition of 135 ° C. for 0.5 hours, and then heated at a firing temperature of 300 ° C. for 1 hour. By firing the coating film after removing the solvent and curing the coating film, a polyimide-coated glass in which a thin film (polyimide film) made of polyimide was coated on the glass substrate was obtained. The polyimide-coated glass thus obtained is immersed in hot water at 90 ° C. to peel off the polyimide film from the glass substrate to form a polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm). Got

(Examples 2 to 6)
The firing temperature in the polyimide film preparation step was changed from 300 ° C to 320 ° C (Example 2), 340 ° C (Example 3), 360 ° C (Example 4), 380 ° C (Example 5), and 400 ° C (Example 5), respectively. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 1 except that the film was changed to Example 6).

(Comparative Examples 1 and 2)
The polyimide film (length 100 mm, width 100 mm) was the same as in Example 1 except that the firing temperature in the polyimide film preparation step was changed from 300 ° C. to 260 ° C. (Comparative Example 1) and 280 ° C. (Comparative Example 2), respectively. , A film having a thickness of 10 μm) was obtained.

(Comparative Example 3)
In the step of preparing the resin solution of polyamic acid, the amount of DABAN used was changed to 2.2726 g (10 mmol) without using FDA, and the amount of TMU used was changed to 24.47 g. Similarly, a polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained.

Table 1 shows the results of measuring the characteristics of the films obtained in Examples 1 to 6 and Comparative Examples 1 to 3 based on the above-mentioned evaluation method. As a result of IR measurement, it was confirmed that the films obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were all made of polyimide. Table 1 shows the positions where the peak based on the C = O expansion and contraction vibration of imidecarbonyl was confirmed in the IR spectrum. Further, the TMA curves of the polyimide film obtained in Example 1 and the polyimide film obtained in Comparative Example 3 are shown in FIG.

As is clear from the results shown in Table 1, all the polyimide films obtained in Examples 1 to 6 are polyimides containing the repeating unit (A) represented by the general formula (1) depending on the type of the monomer used. It was found that the film was made of, and the extreme value A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve. On the other hand, the polyimide films obtained in Comparative Examples 1 and 2 are films made of polyimide containing a repeating unit represented by the general formula (1) depending on the type of the monomer used, but the extreme value A is set in the TMA curve. It was confirmed at 176 ° C. (Comparative Example 1) and 188 ° C. (Comparative Example 2), and it was confirmed that the extremum A was not within the temperature range of 200 to 430 ° C.

Here, as is clear from the description in Table 1, the films obtained in Examples 1 to 6 and the films obtained in Comparative Examples 1 and 2 having the same type and amount (molar ratio) of the monomers used were obtained. When compared with the film, when the extremum A is in the temperature range of 200 to 430 ° C. (Examples 1 to 6), the absolute value of Rth is 85 nm or less and the absolute value of CTE is 30 ppm / It turned out to be K or less. On the other hand, when the extreme value A is confirmed at 176 ° C. (Comparative Example 1) and 188 ° C. (Comparative Example 2) and the extreme value A is not within the temperature range of 200 to 430 ° C. (in the case of Comparative Examples 1 and 2). In each case, it was confirmed that the absolute value of CTE was 61.2 ppm / K or more.

From these results, first, the films obtained in Examples 1 to 6 and the films obtained in Comparative Examples 1 and 2 were obtained by using the same amount of the same monomer, and these films were obtained. Since Rth is sufficiently low in each case (because Rth is 145 nm or less), a sufficiently low Rth can be obtained due to the structure of the repeating unit of the polyimide constituting the film. It became clear that there was. Further, from the results shown in Table 1, even if the types and amounts (molar ratios) of the monomers used are the same between polyimides (Examples 1 to 6 and Comparative Examples 1 to 2), there is a difference in firing temperature during production. As a result, the position of the extremum A is different in the TMA curve, and the polyamic acid obtained based on the monomer shown in Table 1 so that the position of the extremum A is within a specific temperature range (the above general formula (7)). The polyamic acid containing the repeating unit (A') represented by (A') is fired under temperature conditions of Tg-190 ° C. to Tg-50 ° C. to reduce the Rth (absolute value) to a sufficiently low value of 145 nm or less. , It has been found that it is possible to set the CTE (absolute value) to a higher value such as 30 ppm / K or less.

As is clear from the results shown in FIG. 1, in the polyimide film obtained in Example 1, the extremum A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve, whereas it was confirmed in the temperature range of 200 to 430 ° C. In the polyimide film obtained in Comparative Example 3 in which the type of monomer is different from that of Example 1, even if the polyimide film is fired under temperature conditions of Tg-190 ° C. to Tg-50 ° C. at the time of production, the extreme value A in the TMA curve. Was not confirmed. From these results, when the polyimide film is obtained by firing under the above-mentioned specific temperature conditions and contains the above-mentioned repeating unit (A) (in the case of Examples 1 to 6), the obtained film It was found that the extremum A can be present in the temperature range of 200 to 430 ° C. in the TMA curve.

As described above, from the results shown in Table 1, according to the polyimide film of the present invention (Examples 1 to 6), the retardation (Rth) in the thickness direction which is sufficiently low and the thermal expansion which is sufficiently low are sufficiently low based on the absolute value. It was confirmed that it is possible to have a well-balanced rate (CTE) at a higher level.

(Example 7)
In the process of preparing the resin solution of polyamic acid, the amount of FDA used was changed to 2.0906 g (6 mmol), the amount of DABAN used was changed to 0.9090 g (4 mmol), and the amount of TMU used was 27.37 g. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 1 except that the film was changed to.

(Example 8)
In the process of preparing the resin solution of polyamic acid, the amount of FDA used was changed to 3.1360 g (9 mmol), the amount of DABAN used was changed to 0.2273 g (1 mmol), and the amount of TMU used was changed to 28.83 g. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 1 except that the film was changed to.

(Example 9)
In the step of preparing the resin solution of the polyamic acid, DABAN was not used, the amount of FDA used was changed to 3.4844 g (10 mmol), and the amount of TMU used was changed to 29.31 g. Similarly, a polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained.

(Example 10)
In the process of preparing the resin solution of polyamic acid, the amount of FDA used was changed to 2.4391 g (7 mmol), the amount of DABAN used was changed to 0.6818 g (3 mmol), and the amount of TMU used was changed to 27.86 g. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 1 except that the film was changed to. For the polyimide film obtained in this example, the glass transition temperature (Tg: DMA) was also measured by so-called DMA measurement for reference. In such measurement, a dynamic viscoelasticity measuring device (trade name "DMS6100" manufactured by Seiko SII) is used as a measuring device, and a tension (tension) is adopted under a nitrogen atmosphere and a heating rate of 3 ° C./min. DMA measurements were performed with a temperature program of 100 mN), frequency (1 Hz, 10 Hz), and 30 ° C to 550 ° C. The glass transition temperature (Tg: DMA) measured by such a DMA measurement was 470 ° C. The Tg value (measured value by the penetration (needle insertion) method) shown in Table 2 described later and the Tg measured value by the DMA method were almost the same values.

(Examples 11 to 15)
The firing temperature in the polyimide film preparation step was changed from 300 ° C to 320 ° C (Example 11), 340 ° C (Example 12), 360 ° C (Example 13), 380 ° C (Example 14), and 400 ° C (Example), respectively. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 10 except that the film was changed to Example 15).

Table 2 shows the results of measuring the characteristics of the films obtained in Examples 7 to 15 based on the above-mentioned evaluation method. As a result of IR measurement, it was confirmed that all the films obtained in Examples 7 to 15 were made of polyimide. Table 2 shows the positions where the peak based on the C = O expansion and contraction vibration of imidecarbonyl was confirmed in the IR spectrum. For reference, the characteristics of the film obtained in Example 1 are also shown in Table 2.

As shown in Table 2, all of the polyimide films obtained in Examples 7 to 15 are films made of polyimide containing the repeating unit (A) represented by the general formula (1) depending on the type of the monomer used. Moreover, it was found that the extremum A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve. From the production conditions, the polyamic acid obtained based on the monomers shown in Table 2 is fired under the temperature conditions of Tg-190 ° C. to Tg-50 ° C., and the extreme value A in the TMA curve of the polyimide film obtained is obtained. Was found to be found in the temperature range of 200-430 ° C. Further, from the results shown in Table 2, the polyimide film of the present invention (Examples 1 and 7 to 15) has an absolute value of Rth of 145 nm or less and an absolute value of CTE of 30 ppm / K or less. It was confirmed that it would be. As described above, according to the polyimide film of the present invention, it is possible to set the Rth (absolute value) to a sufficiently low value of 145 nm or less and the CTE (absolute value) to a much lower value such as 30 ppm / K or less. It was confirmed that it is possible to have a sufficiently low thickness direction polyimide (Rth) and a sufficiently low coefficient of thermal expansion (CTE) at a higher level in a well-balanced manner based on the absolute value.

(Example 16)
Instead of changing the type of diamine compound used in the process of preparing the resin solution of polyamic acid and adding FDA and DABAN in the three-necked flask, 4,4'-diaminodiphenyl sulfone (4,4') in the three-necked flask. -DDS) 2.4830 g (10 mmol) was added, and the size of the polyimide film (length 100 mm, width 100 mm, thickness 10 μm) was the same as in Example 1 except that the amount of TMU used was changed to 25.31 g. Film) was obtained.

(Example 17)
Instead of changing the type of diamine compound used in the process of preparing the resin solution of polyamic acid and adding FDA and DABAN in the three-necked flask, 9,9-bis (4-amino-3-fluoro) in the three-necked flask. Polyimide film (length 100 mm, width 100 mm, 100 mm in length, 100 mm in width, in the same manner as in Example 1 except that 3.8443 g (10 mmol) of phenyl) fluorene (F-FDA) was added and the amount of TMU used was changed to 30.75 g. A film having a thickness of 10 μm) was obtained.

(Example 18)
Instead of changing the type of diamine compound used in the process of preparing the resin solution of polyamic acid and adding FDA and DABAN in the three-necked flask, 9,9-bis (4-amino-3-methyl) in the three-necked flask. Polyimide film (length 100 mm, width 100 mm, the same as in Example 1 except that 3.7650 g (10 mmol) of phenyl) fluorene (Me-FDA) was added and the amount of TMU used was changed to 30.44 g. A film having a thickness of 10 μm) was obtained.

Table 3 shows the results of measuring the characteristics of the films obtained in Examples 16 to 18 based on the above-mentioned evaluation method. As a result of IR measurement, it was confirmed that all the films obtained in Examples 16 to 18 were made of polyimide. Table 3 shows the positions where the peak based on the C = O expansion and contraction vibration of imidecarbonyl was confirmed in the IR spectrum.

As shown in Table 3, all of the polyimide films obtained in Examples 16 to 18 are films made of polyimide containing the repeating unit (A) represented by the general formula (1) depending on the type of the monomer used. Moreover, it was found that the extremum A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve. From the production conditions, the polyamic acid obtained based on the monomer shown in Table 3 (polyamic acid containing the repeating unit (A') represented by the above general formula (7)) can be finally obtained from the polyimide. It was found that the extreme value A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve of the obtained polyimide film by firing under the temperature condition of Tg-190 ° C. to Tg-50 ° C. with Tg as a reference. .. Further, from the results shown in Table 3, it was confirmed that in each of the polyimide films of the present invention (Examples 16 to 18), the absolute value of Rth was 145 nm or less and the absolute value of CTE was 30 ppm / K or less. According to the polyimide film of the present invention, it is possible to have a sufficiently low thickness direction retardation (Rth) and a sufficiently low coefficient of thermal expansion (CTE) at a higher level in a well-balanced manner based on the absolute value. It was confirmed that In particular, in Examples 17 to 18, it is possible to set the CTE to 30 ppm / K or less while setting the absolute value of Rth to a value of less than 50 nm, and the polyimide film obtained in these examples is sufficient. It was also found that it has a low thickness direction polyimide (Rth) and a sufficiently low coefficient of thermal expansion (CTE) at a higher level in a well-balanced manner.

(Example 19)
Instead of using CpODA in the step of preparing the resin solution of polyamic acid, 1.9611 g (10.00 mmol) of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) is used, and the amount of TMU used. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 1 except that the amount was changed to 20.81 g.

(Comparative Example 4)
A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 19 except that the firing temperature in the step of preparing the polyimide film was changed from 300 ° C. to 380 ° C.

Table 4 shows the results of measuring the characteristics of the films obtained in Example 19 and Comparative Example 4 based on the above-mentioned evaluation method. As a result of IR measurement, it was confirmed that all of these films were made of polyimide. Table 4 shows the positions where the peak based on the C = O expansion and contraction vibration of imidecarbonyl was confirmed in the IR spectrum.

As shown in Table 4, the polyimide film obtained in Example 19 is a film made of polyimide containing the repeating unit (A) represented by the general formula (1) according to the type of the monomer used, and the film thereof. It was found that the extremum A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve. On the other hand, although the polyimide film obtained in Comparative Example 4 is a film made of polyimide containing the repeating unit (A) represented by the general formula (1) depending on the type of the monomer used, the extreme value A in the TMA curve thereof. Could not be confirmed. From the production conditions, the polyamic acid obtained based on the monomer shown in Table 4 (polyamic acid containing the repeating unit (A') represented by the above general formula (7)) can be finally obtained from the polyimide. By firing under the temperature condition of Tg-190 ° C. to Tg-50 ° C. with Tg as a reference, the extreme value A is confirmed in the temperature range of 200 to 430 ° C. in the TMA curve of the obtained polyimide film. It turned out.

Further, from the results shown in Table 4, it was confirmed that the polyimide film of the present invention (Example 19) had an absolute value of Rth of less than 50 nm and an absolute value of CTE of 45 ppm / K or less. On the other hand, in the polyimide film (Comparative Example 4) in which the extreme value A is not within the temperature range of 200 to 430 ° C. on the TMA curve, the absolute value of Rth is less than 50 nm, but the absolute value of CTE is 60 ppm /. It is K, and the CTE cannot be set to a sufficiently low value in relation to the value of Rth, and has a sufficiently low polyimide (Rth) and a sufficiently low coefficient of thermal expansion (CTE) in a well-balanced manner. Couldn't.

From these results, according to the polyimide film of the present invention (Example 19), the retardation (Rth) in the thickness direction which is sufficiently low and the coefficient of thermal expansion (CTE) which is sufficiently low are higher based on the absolute value. It was confirmed that it is possible to have a well-balanced level.

(Example 20)
In the process of preparing the resin solution of polyamic acid, 1.9864 g (8 mmol) of 4,4'-diaminodiphenyl sulfone (4,4'-DDS) was used instead of FDA, and the amount of TMU used was 25.14 g. A polyimide film (a film having a length of 100 mm, a width of 100 mm, and a thickness of 10 μm) was obtained in the same manner as in Example 1 except for the modification.

Table 5 shows the results of measuring the characteristics of the film obtained in Example 20 based on the above-mentioned evaluation method. As a result of IR measurement, it was confirmed that all of these films were made of polyimide. Table 5 shows the positions where the peak based on the C = O expansion and contraction vibration of imidecarbonyl was confirmed in the IR spectrum.

As shown in Table 5, the polyimide film obtained in Example 20 is a film made of polyimide containing the repeating unit (A) represented by the general formula (1) depending on the type of the monomer used, and the film thereof. It was found that the extremum A was confirmed in the temperature range of 200 to 430 ° C. in the TMA curve. Further, from the results shown in Table 5, it was confirmed that the polyimide film of the present invention (Example 20) had an absolute value of Rth of 145 nm or less and an absolute value of CTE of 30 ppm / K or less. Based on these results, according to the polyimide film of the present invention (Example 20), the retardation (Rth) in the thickness direction, which is sufficiently low, and the coefficient of thermal expansion (CTE), which is sufficiently low, are higher based on the absolute value. It was confirmed that it is possible to have a well-balanced level.

As described above, according to the present invention, a sufficiently low thickness direction polyimide (Rth) and a sufficiently low coefficient of thermal expansion (linear expansion coefficient: CTE) are balanced at a higher level based on the absolute value. It is possible to provide a polyimide film that can be held well and a method for producing a polyimide film that can produce the polyimide film. Such a polyimide film of the present invention is particularly useful as a substrate for LCDs and OLEDs because of its characteristics.

Claims (5)

The following general formula (1):

[In the formula (1), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming ^a cyclic structure, and Ra is the following general formulas (2) to (3). :

(In the formula (2), Ra ¹ , Ra ² , Ra ³ and Ra ⁴ each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group.
In the formula (3), ^Ra 5 and Ra ⁶ each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group. )
Indicates any of the divalent organic groups represented by. ]
A film made of polyimide containing a repeating unit (A) represented by.
The film has the following general formula (7):

[In the formula (7), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming a cyclic structure, and ^Ra is the above general formulas (2) to (3). Indicates one of the divalent organic groups represented by, and Y ¹ and Y ² are independently composed of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkylsilyl group having 3 to 9 carbon atoms, respectively. Shows one selected from. ]
A polyimide precursor containing a repeating unit (A') represented by the following, and the following general formula (X):

[In the formula (X), R ¹¹ represents one selected from the group consisting of a hydrogen atom and an alkyl group, and R ¹⁴ is independently a halogen atom, a hydroxyl group, a mercapto group, a sulfide group, a silyl group, a silanol group, respectively. Indicates one selected from the group consisting of a nitro group, a nitroso group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphonat group and an organic group, where m represents an integer of 0 to 3 and R ³¹ , R ³² , R ³³ . , R ³⁴ and R ³⁵ are independently hydrogen atom, hydroxyl group, mercapto group, sulfide group, silyl group, silanol group, nitro group, nitroso group, sulfino group, sulfo group, sulfonato group, phosphino group, phosphinyl group, respectively. It is a phosphono group, a phosphonat group, an amino group, an ammonio group, or an organic group, but at least one of R ³¹ , R ³² , R ³³ , R ³⁴ and R ³⁵ is a group other than a hydrogen atom. ]
It is a heat-cured product of the solvent-removed product of the coating film of the polyimide precursor resin solution containing the imidazole compound represented by
A thermal machine that measures the relationship between the temperature and the amount of change in the length of the film by pulling the film under the condition of a load of 20 mN while raising the temperature from 50 ° C to 450 ° C at a heating rate of 5 ° C / min under a nitrogen atmosphere. In the TMA curve obtained by analysis (TMA), the extreme value at which the ratio of the change in film length to the change in temperature changes from positive to negative exists in the temperature range of 200 to 430 ° C. Polyimide film. A in the above formula (1) is the following general formula (4):

[In the formula (4), R ¹ , R ² , and R ³ each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, and a fluorine atom, and n is 0 to 0 to. Indicates an integer of 12. ]
The polyimide film according to claim 1, wherein the polyimide film is a tetravalent alicyclic hydrocarbon group represented by. The polyimide has the following general formula (5).

[In the formula (5), A is synonymous with A in the above formula (1), and R ^b is the following general formula (6):

(In the formula (6), R ^b1 and R ^b2 each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group.)
Indicates a divalent organic group represented by. ]
It further contains the repeating unit (B) represented by, and the content of the repeating unit (A) in the polyimide is 50 to the total amount of the repeating unit (A) and the repeating unit (B). The polyimide film according to claim 1 or 2, wherein the polyimide film is 100 mol%. A step of forming a coating film using a polyimide precursor resin solution containing a polyimide precursor and an organic solvent, removing the solvent from the coating film, and firing to obtain a film made of polyimide is included.
The polyimide precursor has the following general formula (7):

[In the formula (7), A represents a tetravalent alicyclic hydrocarbon group having 4 to 30 carbon atoms forming ^a cyclic structure, and Ra is the following general formulas (2) to (3). :

(In the formula (2), Ra ¹ , Ra ² , Ra ³ and Ra ⁴ each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group.
In the formula (3), ^Ra 5 and Ra ⁶ each independently represent one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogen atom and a hydroxyl group. )
Indicates one of the divalent organic groups represented by, and Y ¹ and Y ² are independently composed of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms and an alkylsilyl group having 3 to 9 carbon atoms, respectively. Shows one selected from. ]
It contains a repeating unit (A') represented by.
The polyimide precursor resin solution has the following general formula (X):

[In the formula (X), R ¹¹ represents one selected from the group consisting of a hydrogen atom and an alkyl group, and R ¹⁴ is independently a halogen atom, a hydroxyl group, a mercapto group, a sulfide group, a silyl group, a silanol group, respectively. Indicates one selected from the group consisting of a nitro group, a nitroso group, a sulfonato group, a phosphino group, a phosphinyl group, a phosphonat group and an organic group, where m indicates an integer of 0 to 3 and R ³¹ , R ³² , R ³³ . , R ³⁴ and R ³⁵ are independently hydrogen atom, hydroxyl group, mercapto group, sulfide group, silyl group, silanol group, nitro group, nitroso group, sulfino group, sulfo group, sulfonato group, phosphino group, phosphinyl group, respectively. It is a phosphono group, a phosphonat group, an amino group, an ammonio group, or an organic group, but at least one of R ³¹ , R ³² , R ³³ , R ³⁴ and R ³⁵ is a group other than a hydrogen atom. ]
It further contains the imidazole compound represented by, and
Claimed as a film made of the polyimide by firing at a temperature in the range of (Tg-190) ° C. to (Tg-50) ° C. with reference to the glass transition temperature (Tg) of the obtained polyimide at the time of firing. Obtaining the polyimide film according to any one of 1 to 3,
A method for manufacturing a polyimide film. The fourth aspect of claim 4, wherein the content of the imidazole compound in the polyimide precursor resin solution is 1 to 60 parts by mass with respect to 100 parts by mass of the solid content of the polyimide precursor in the solution. Method for manufacturing polyimide film.

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