JP2019189872A - Polyimide, laminate, and electronic device containing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide exhibiting excellent C-V characteristics, particularly a polyimide in a film form, a laminated substrate using the polyimide, and an electronic device such as a flexible display including the same. SOLUTION: The maximum gradient of 0.005 / V or more is shown when the capacitance-voltage measurement of a laminated body in which a polyimide film having a thickness of 0.75 μm is formed on a silicon wafer having a resistance value of 4 Ωcm. (Wherein the maximum gradient is the capacitance of the DC voltage applied to the polyimide film with respect to the silicon wafer between the minimum voltage V1 and the maximum voltage V2 while performing positive scanning and negative scanning). Measurement is performed and means the maximum absolute value of the gradient in the standardized capacity-voltage curve at the time of the third forward scanning, and the standardized capacity-voltage curve is standardized with the capacity at the lowest voltage V1 as 1. Has been done.). [Selection diagram] Figure 2

Description

  The present invention relates to polyimide suitably used for electronic device applications such as a substrate of a flexible device, for example, and further relates to a polyimide film, a laminate including the polyimide film, and an electronic device including the polyimide or the laminate.

  Conventionally, glass has been used as a substrate for a display such as a liquid crystal display or an organic EL display. However, when glass is thinned for weight reduction, there is a problem that it is fragile due to insufficient strength. Therefore, a lightweight and flexible plastic substrate has been proposed as an alternative to a glass substrate. In a display such as a liquid crystal display or an organic EL display, a semiconductor element such as a TFT is formed on a substrate in order to drive each pixel. For this reason, the substrate is required to have heat resistance and dimensional stability. A polyimide film is expected as a substrate for a display because it is excellent in heat resistance, chemical resistance, mechanical strength, electrical characteristics, dimensional stability, and the like.

  Regarding TFT elements formed on a polyimide substrate, Non-Patent Documents 1 and 2 report that positive carriers are induced by negative charges existing at the polyimide substrate interface, and this affects TFT characteristics.

Junehwan Kim et al., “HighPerformance Reliebility LTPS Technology for Advanced Flexible Mobile Applications”, IDW / AD’16, pp.1356-1359 (2016) Yi-Da Ho et al., “Abnormal Vth Degradation Behavior of the Polycrystalline Silicon Thin-Film Transistors on the Polyimide Substrate”, IDW’17, pp. 1508-1511 (2017)

  As described above, Non-Patent Documents 1 and 2 report the influence of the polyimide interface on the TFT characteristics, but the evaluation of the interface state density at which a negative charge can specifically exist has not been performed. Moreover, there is no description about the detail of a polyimide, and since there is no data which changed the polyimide substrate and evaluated the TFT characteristic, the information of the polyimide suitable as a board | substrate is also unknown.

  As a method for evaluating the level density of the surface of an insulating film such as polyimide, there is a method of measuring capacitance-voltage characteristics (hereinafter referred to as CV characteristics). In general, the CV curve obtained by evaluating the voltage dependency of the capacitance of a semiconductor-insulating film-metal (electrode) capacitor may change in shape due to the presence of a level density existing at the semiconductor-insulating film interface. Are known. Therefore, to evaluate the CV characteristics that affect device characteristics such as TFT characteristics, to develop polyimide films that are optimal as substrates for semiconductor devices and electronic devices including displays, and to further expand the applications of polyimide. There is a need to provide polyimides having excellent CV characteristics.

  An object of this invention is to provide electronic devices, such as a polyimide which shows the outstanding CV characteristic, especially the polyimide of a film form, the laminated substrate using the polyimide, and a flexible display containing them.

The present invention relates to the following matters.
1. When a capacitance-voltage measurement is performed on a laminate in which a polyimide film is formed with a thick film of 0.75 μm on a silicon wafer having a resistance value of 4 Ωcm, the maximum gradient is 0.005 / V or more. Polyimide (however, the maximum gradient is the maximum DC voltage applied to the polyimide film with respect to the silicon wafer between the minimum voltage V1 and the maximum voltage V2, the forward scan from the minimum voltage V1 to the maximum voltage V2, and the maximum Capacitance measurement is performed at a measurement frequency of 2.5 kHz while negative direction scanning from voltage V2 to minimum voltage V1 is performed at a scanning speed of 0.25 V / sec. It means the maximum absolute value of the gradient in the voltage curve, where the minimum voltage V1 is a voltage at which the capacity of only the polyimide film is observed, and the normalized capacity The voltage curve is normalized with the capacity at the lowest voltage V1 being 1.)
2. Item 2. The polyimide according to Item 1, wherein the weight fraction of imide groups (—CONCO—) in the repeating unit of the polyimide is less than 38.3 wt%.
3. 3. The polyimide according to item 1 or 2, wherein the amine end group concentration in the whole polyimide calculated from the charging ratio is 29 μmol / g or less.
4). A tetracarboxylic acid component (A) containing at least 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride;
(B-1) 1,4-diaminobenzene, [1,1 ′: 4 ′, 1 ″ -terphenyl] -4,4 ″ -diamine, and 1,4-bis [2- (4-aminophenyl) -2-propyl] benzene, and (B-2) 9,9-bis (4-aminophenyl) fluorene, 4,4 ′-(((9H-fluorene-9,9-diyl ) Bis ([1,1′-biphenyl] -5,2-diyl)) bis (oxy)) diamine and 4,4 ′-([1,1′-binaphthalene] -2,2′-diylbis (oxy) )) A polyimide precursor comprising a repeating unit obtained by reacting with a diamine component (B) containing at least one diamine selected from diamines.
5. The polyimide precursor according to Item 4, wherein the diamine component (B) contains the diamine of (B-1) and the diamine of (B-2) in a proportion of 40 mol% or more.
6). 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and a repeating unit derived from the diamine (B-1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride The total of the ratio of the repeating unit derived from the diamine of said (B-2) is 40 mol% or more, The polyimide precursor of said claim | item 4 characterized by the above-mentioned.
7). A polyimide obtained by imidizing the polyimide precursor according to any one of Items 4 to 6.
8). The polyimide precursor solution which gives the polyimide of any one of said claim | item 1-3.
9. The polyimide solution which gives the polyimide of any one of said claim | item 1-3.
10. 9. A method for producing a polyimide solution, wherein the polyimide precursor solution according to item 8 is imidized.
11. 8. A polyimide film in the form of a polyimide film according to any one of items 1 to 3 and 7.
12 A laminate having a substrate and the polyimide film of Item 11.
13. The board | substrate containing the polyimide film of said claim | item 11 used for an electronic device use.
14 14. An electronic device comprising the polyimide film of item 11, the laminate of item 12, or the substrate of item 13.
15. Item 14. An electronic device comprising the polyimide film of Item 11, the laminate of Item 12, or a semiconductor layer formed on the substrate of Item 13.

ADVANTAGE OF THE INVENTION According to this invention, electronic devices, such as a polyimide which shows the outstanding CV characteristic, especially the polyimide of a film form, the laminated substrate using the polyimide, and a flexible display containing them, can be provided.
Since the polyimide film of the present invention has excellent CV characteristics, even if it is used as a substrate for a semiconductor element such as a TFT, for example, there is little fear of affecting the performance of the semiconductor element. There is little concern about changes or deterioration of device characteristics such as switching of switching characteristics due to.

It is a schematic diagram of the system for measuring the CV characteristic of a polyimide. It is a figure for demonstrating the method of calculating | requiring the maximum gradient from a CV characteristic.

<< CV characteristics >>
First, the measurement method and definition of the CV characteristic regarding a polyimide are demonstrated. FIG. 1 shows a schematic diagram of a CV measurement system. A polyimide film 2 is formed on the surface of the silicon wafer 1 to obtain a measurement sample. Mercury electrode 3 is formed by bringing mercury into contact with a predetermined area of the surface of polyimide film 2. A DC voltage is applied between the silicon wafer 1 (ground potential) and the mercury electrode 3 by a DC power supply 4, and a capacitance (capacitance) at the DC voltage is applied by an AC power supply 5 with an AC voltage having a predetermined frequency and amplitude. taking measurement. In the present application, the DC voltage is scanned between the minimum voltage V1 and the maximum voltage V2 in the positive direction scanning (increasing the DC voltage) and negative direction scanning (decreasing the DC voltage), and during that time, the capacitance is measured. A “maximum gradient” to be described later is obtained on the basis of the CV measurement data at the time of the first forward scanning.

  When the silicon wafer is p-type as the minimum voltage V1 in the DC voltage range, a sufficient negative bias voltage is applied so that only the polyimide film has a capacity. In the examples of the present invention, the voltage is set to -40 V. However, depending on the properties of the polyimide film, a lower voltage (voltage having a large negative absolute value) may be required. The maximum voltage V2 in the DC voltage range is sufficiently higher than a voltage at which a maximum gradient, which will be described later, is observed, and is sufficiently high so that the maximum gradient is observed even in scanning in the negative direction. Moreover, both the absolute value of the minimum voltage V1 and the maximum voltage V2 are set broadly within the range that is equal to or lower than the dielectric breakdown voltage of the polyimide film and the capability of the apparatus. In the embodiment of the present invention, the scanning range is -40V to 40V.

  The scanning speed of the DC voltage is, for example, in the range of 10 mV / sec to 100 V / sec, and can be selected from this range in consideration of the purpose of measurement. In the embodiment of the present invention, 0.25 V / sec was adopted.

  The AC voltage (sinusoidal wave) for measuring the capacitance (capacitance) can be changed depending on the application of the polyimide film (that is, in accordance with the frequency range of interest), but for display applications, for example, 100 Hz to 1 MHz, particularly 500 Hz to 10 kHz Measurements can be made at a range of frequencies. In the embodiment of the present invention, 2.5 kHz was used. The amplitude may be any voltage as long as it is sufficiently smaller than the DC voltage, and can be selected as appropriate. In the embodiment of the present invention, the amplitude is set to 0.1V.

  In the present invention, when evaluating the CV measurement result, the capacitance value at the lowest voltage V1 is set to 1, and the standardized capacity-voltage curve (standardized CV curve) obtained by standardizing the measured CV curve is used to calculate polyimide. Evaluate the nature of This is to evaluate factors that affect the semiconductor, such as interface states, except for differences in capacitance values due to differences in film thickness errors and dielectric constants of polyimide films. Regarding the film thickness of the polyimide film to be measured, in order to minimize the evaluation error as much as possible, it is preferable to target a thickness of 0.65 μm to 0.85 μm, particularly 0.75 μm in the evaluation of the present application.

  In such a measurement system, when the DC voltage is scanned in the forward direction from the lowest voltage V1 to the highest voltage V2 (however, this is the third forward scan), typically, as shown in FIG. After the flat region, a first decrease region in which the capacity decreases relatively large appears, and then a relatively flat region is observed. Next, when the voltage is scanned in the negative direction from the highest voltage V2 to the lowest voltage V1, typically, the region is observed in the reverse order to the case of scanning in the positive direction. However, in many cases, hysteresis does not coincide with the curve of the forward scanning, and hysteresis is observed.

  The “first decreasing region” is understood as a process in which the vicinity of the interface in the silicon wafer is changed from the majority carrier accumulation layer to the depletion layer and the depletion layer expands. In the present invention, the maximum gradient (negative and maximum absolute value) in the first reduction region is defined as “maximum gradient”. Therefore, the “maximum slope” can be obtained as the absolute value of the apex of the negative peak appearing in the differential curve of the normalized CV curve.

  The polyimide of the present invention has a “maximum gradient” of 0.005 / V or more obtained by the above-mentioned CV measurement for a film having a film thickness of 0.75 μm formed on a silicon wafer having a resistivity of 4 Ωcm. Yes, preferably over 0.007 / V. The maximum gradient shows a larger value (absolute value is larger) as the interface state density is smaller. It is considered that the surface state density of the polyimide (for example, composition, functional groups (particularly surface functional groups), presence of impurities or additives, etc.) affects the interface state density. In the present invention, the polyimide surface at the interface with the semiconductor is considered. Since the state is in a very favorable state, it can be estimated that it has a large “maximum slope”. By having such a large “maximum gradient”, even if the polyimide of the present invention is used in an electronic device such as a display, the adverse effect on the operation and durability of the electronic device is small.

  There has been no report on the development of polyimide focusing on such CV characteristics, and no actual development has been carried out. Of course, existing polyimides do not satisfy the CV characteristics described above. Moreover, since it is thought that CV characteristic influences the surface state of a polyimide, if the CV characteristic is satisfied, the chemical structure of the polyimide may be anything.

<< Polyimide, polyimide precursor >>
The chemical structure of the polyimide of the present invention or its precursor (polyimide precursor) is not particularly limited as long as it satisfies the CV characteristics, and the chemical structure may be appropriately selected according to the function to be imparted. The polyimide precursor has the following general formula I:

(In the general formula I, X ₁ is a tetravalent aliphatic group or aromatic group, Y ₁ is a divalent aliphatic group or aromatic group, and R ₁ and R ₂ are each independently hydrogen. An atom, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms.)
It has the repeating unit represented by these. Particularly preferred is a polyamic acid in which R ₁ and R ₂ are hydrogen atoms. In addition, a polymer in which imidization has partially progressed, that is, a polymer containing a repeating unit in which at least one of the two amide structures in Formula I is imidized is also referred to as “polyimide precursor” and “polyamic acid” (residual R ₁ and R ₂ are hydrogen atoms).
Polyimide is represented by the following general formula II:

(Wherein, X ₁ is a tetravalent aliphatic group or an aromatic group, and Y ₁ is a divalent aliphatic group or an aromatic group.)
It has the repeating unit represented by these.

Below, the chemical structure of such a polyimide, the structure of X ₁ and Y _{2 in} the above repeating unit (general formula (II)) and the monomers used for production (tetracarboxylic acid component, diamine component, other components) The manufacturing method will be described subsequently.

In the present specification, the tetracarboxylic acid component is a tetracarboxylic acid, tetracarboxylic dianhydride, tetracarboxylic acid silyl ester, tetracarboxylic acid ester, tetracarboxylic acid chloride, or the like used as a raw material for producing polyimide. Contains carboxylic acid derivatives. Although not particularly limited, it is easy to use tetracarboxylic dianhydride in production, and in the following description, an example using tetracarboxylic dianhydride as a tetracarboxylic acid component will be described. Moreover, a diamine component is a diamine compound which has _two amino groups (-NH2) used as a raw material which manufactures a polyimide.

  Moreover, in this specification, a polyimide film means both what is formed on a board | substrate and exists in a lamination | stacking state, and what does not have the board | substrate which supports a film (a self-supporting film is included). The polyimide of the present invention is preferably in the form of a film when used as a substrate. The polyimide of the present invention may be in the form of a layer that exists discretely on a support substrate or a layer formed of a different material.

<< Structure and Monomer in Repeating Unit >>
_{<X 1} and tetracarboxylic acid component>

The tetravalent group having an aromatic ring of X ₁ is preferably a tetravalent group having an aromatic ring having 6 to 40 carbon atoms.

  Examples of the tetravalent group having an aromatic ring include the following.

(In the formula, Z ₁ is a direct bond or the following divalent group:

One of them. In the formula, Z2 is a divalent organic group, Z3 and Z4 are each independently an amide bond, an ester bond and a carbonyl bond, and Z5 is an organic group containing an aromatic ring. )

Specific examples of Z ₂ include an aliphatic hydrocarbon group having 2 to 24 carbon atoms and an aromatic hydrocarbon group having 6 to 24 carbon atoms.

The Z _5, specifically, an aromatic hydrocarbon group having 6 to 24 carbon atoms.

  As the tetravalent group having an aromatic ring, since the high heat resistance and high transparency of the obtained polyimide material can be compatible, the following are particularly preferable.

(In the formula, Z ₁ is a direct bond or a hexafluoroisopropylidene bond.)

Here, since the high heat resistance, high transparency, and low linear thermal expansion coefficient of the obtained polyimide material can be compatible, Z ₁ is more preferably a direct bond.

In addition, as a preferred group, in the above formula (9), Z ₁ is represented by the following formula (3A):

The compound which is a fluorenyl containing group represented by these is mentioned. Z ₁₁ and Z ₁₂ are each independently preferably the same, a single bond or a divalent organic group. As Z ₁₁ and Z ₁₂ , an organic group containing an aromatic ring is preferable. For example, Formula (3A1):

(Z ₁₃ and Z ₁₄ are each independently a single bond, —COO—, —OCO— or —O—, and when Z ₁₄ is bonded to a fluorenyl group, Z ₁₃ is —COO—, —OCO— Or —O— and Z ₁₄ is preferably a single bond structure; R ₉₁ is an alkyl group or phenyl group having 1 to 4 carbon atoms, preferably methyl, and n is an integer of 0 to 4, preferably 1)
And the structure is preferred.

Examples of the tetracarboxylic acid component that gives a repeating unit of the general formula (II) in which X ₁ is a tetravalent group having an aromatic ring include 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane. 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid, pyromellitic acid, 3,3 ′, 4,4′-benzophenone Tetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3,3 ′, 4′-biphenyltetracarboxylic acid, 4,4′-oxydiphthalic acid, bis (3,4-dicarboxyl) Phenyl) sulfone, m-terphenyl-3,4,3 ′, 4′-tetracarboxylic acid, p-terphenyl-3,4,3 ′, 4′-tetracarboxylic acid, biscarboxyphenyldimethylsilane Bis-dicarboxyphenoxy diphenyl sulfide, and include sulfonyl di phthalate, these dianhydrides as monomer is preferably used. Examples of the tetracarboxylic acid component that gives a repeating unit of the general formula (II) in which X ₁ is a tetravalent group having an aromatic ring containing a fluorine atom include 2,2-bis (3,4-dicarboxy). Phenyl) hexafluoropropane dianhydride. Further, as a preferred compound, (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis (1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) Is mentioned. A tetracarboxylic acid component may be used independently and can also be used in combination of multiple types.

The tetravalent group having an alicyclic structure of X ₁ is preferably a tetravalent group having an alicyclic structure having 4 to 40 carbon atoms, more preferably at least one aliphatic 4- to 12-membered ring, more preferably aliphatic. More preferably, it has a 4-membered ring or an aliphatic 6-membered ring. The following are mentioned as a tetravalent group which has a preferable aliphatic 4-membered ring or an aliphatic 6-membered ring.

(In the formula, R _{31 to} R ₃₈ are each independently a direct bond or a divalent organic group. R _{41 to} R ₄₇ are each independently a formula: —CH ₂ —, —CH═CH—, This is one selected from the group consisting of groups represented by —CH ₂ CH ₂ —, —O—, and —S—, and R ₄₈ is an organic group containing an aromatic ring or alicyclic structure.

As R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ , R ₃₆ , R ₃₇ , R ₃₈ , specifically, a direct bond, an aliphatic hydrocarbon group having 1 to 6 carbon atoms, or Examples include an oxygen atom (—O—), a sulfur atom (—S—), a carbonyl bond, an ester bond, and an amide bond.

Examples of the organic group containing an aromatic ring as R ₄₈ include the following.

(In the formula, W ₁ is a direct bond or a divalent organic group, n _{11 to} n ₁₃ each independently represents an integer of 0 to 4, and R ₅₁ , R ₅₂ , and R ₅₃ are each independent. And an alkyl group having 1 to 6 carbon atoms, a halogen group, a hydroxyl group, a carboxyl group, or a trifluoromethyl group.)

Specific examples of W ₁ include a direct bond, a divalent group represented by the following formula (5), and a divalent group represented by the following formula (6).

(R _{61 to} R ₆₈ in the formula (6) each independently represent a direct bond or a divalent group represented by the formula (5).)

  As the tetravalent group having an alicyclic structure, the following are particularly preferable because the polyimide obtained can have both high heat resistance, high transparency, and a low linear thermal expansion coefficient.

Examples of the tetracarboxylic acid component that gives a repeating unit of the formula (II) in which X ₁ is a tetravalent group having an alicyclic structure include 1,2,3,4-cyclobutanetetracarboxylic acid, isopropylidenediphenoxybis Phthalic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, [1,1′-bi (cyclohexane)]-3,3 ′, 4,4′-tetracarboxylic acid, [1,1′-bicarboxylic acid (Cyclohexane)]-2,3,3 ′, 4′-tetracarboxylic acid, [1,1′-bi (cyclohexane)]-2,2 ′, 3,3′-tetracarboxylic acid, 4,4′- Methylenebis (cyclohexane-1,2-dicarboxylic acid), 4,4 ′-(propane-2,2-diyl) bis (cyclohexane-1,2-dicarboxylic acid), 4,4′-oxybis (cyclohexane-1,2) -Dicarboxylic acid), 4,4 '-Thiobis (cyclohexane-1,2-dicarboxylic acid), 4,4'-sulfonylbis (cyclohexane-1,2-dicarboxylic acid), 4,4'-(dimethylsilanediyl) bis (cyclohexane-1,2- Dicarboxylic acid), 4,4 ′-(tetrafluoropropane-2,2-diyl) bis (cyclohexane-1,2-dicarboxylic acid), octahydropentalene-1,3,4,6-tetracarboxylic acid, bicyclo [2.2.1] Heptane-2,3,5,6-tetracarboxylic acid, 6- (carboxymethyl) bicyclo [2.2.1] heptane-2,3,5-tricarboxylic acid, bicyclo [2. 2.2] octane-2,3,5,6-tetracarboxylic acid, bicyclo [2.2.2] oct-5-ene-2,3,7,8-tetracarboxylic acid, tricyclo [4.2. 2.0 2,5] decane-3,4,7,8-tetracarboxylic acid, tricyclo [4.2.2.02,5] dec-7-ene-3,4,9,10-tetracarboxylic acid, 9- Oxatricyclo [4.2.1.02,5] nonane-3,4,7,8-tetracarboxylic acid, norbornane-2-spiro-α-cyclopentanone-α′-spiro-2 ″ -norbornane 5,5 ″, 6,6 ″ -tetracarboxylic acid, (4arH, 8acH) -decahydro-1t, 4t: 5c, 8c-dimethananaphthalene-2c, 3c, 6c, 7c-tetracarboxylic acid, (4arH , 8acH) -decahydro-1t, 4t: 5c, 8c-dimethanonaphthalene-2t, 3t, 6c, 7c-tetracarboxylic acid, these tetracarboxylic dianhydrides, tetracarboxylic silyl esters, tetracarboxylic acids Ether, and derivatives of such tetracarboxylic acid chloride. A tetracarboxylic acid component may be used independently and can also be used in combination of multiple types.

_{<Y 1} and a diamine component>
The divalent group having an aromatic ring of Y ₁ is preferably a divalent group having an aromatic ring having 6 to 40 carbon atoms, more preferably 6 to 20 carbon atoms.

  Examples of the divalent group having an aromatic ring include the following.

(In the formula, W ₁ is a direct bond or a divalent organic group, n _{11 to} n ₁₃ each independently represents an integer of 0 to 4, and R ₅₁ , R ₅₂ , and R ₅₃ are each independent. And an alkyl group having 1 to 6 carbon atoms, a halogen group, a hydroxyl group, a carboxyl group, or a trifluoromethyl group.)

Specific examples of W ₁ include a direct bond, a divalent group represented by the following formula (5), and a divalent group represented by the following formula (6).

(R _{61 to} R ₆₈ in the formula (6) each independently represent a direct bond or a divalent group represented by the formula (5).)

Here, since the polyimide obtained can have both high heat resistance, high transparency, and low linear thermal expansion coefficient, W ₁ is a direct bond, or a formula: —NHCO—, —CONH—, —COO—, —OCO—. It is especially preferable that it is 1 type selected from the group which consists of group represented by these. W ₁ is _one of R _{61 to} R ₆₈ directly selected from the group consisting of a direct bond or a group represented by the formula: —NHCO—, —CONH—, —COO—, —OCO—. It is also particularly preferable that it is any of the divalent groups represented by the formula (6).

In addition, as a preferred group, in the above formula (4), W ₁ represents the following formula (3B):

The compound which is a fluorenyl containing group represented by these is mentioned. Z ₁₁ and Z ₁₂ are each independently preferably the same, a single bond or a divalent organic group. As Z ₁₁ and Z ₁₂ , an organic group containing an aromatic ring is preferable. For example, Formula (3B1):

(Z ₁₃ and Z ₁₄ are each independently a single bond, —COO—, —OCO— or —O—, and when Z ₁₄ is bonded to a fluorenyl group, Z ₁₃ is —COO—, —OCO— or preferably _{Z 14} is a single bond structure _{-O-; R 91} is an alkyl group or a phenyl group having 1 to 4 carbon atoms, preferably phenyl, n is an integer of 0 to 4, preferably 1)
And the structure is preferred.

As another preferable group, a compound in which W ₁ is a phenylene group in the above formula (4), that is, a terphenyldiamine compound, is particularly preferable.

Another preferred group is a compound in which, in the above formula (4), W ₁ is the structure of one first phenyl ring in formula (6), and R ₆₁ and R ₆₂ are 2,2-propylidene groups.

As still another preferred group, in the above formula (4), W ₁ represents the following formula (3B2):

The compound represented by these is mentioned.

Examples of the diamine component that gives the repeating unit of the general formula (II) in which Y ₁ is a divalent group having an aromatic ring include p-phenylenediamine, m-phenylenediamine, benzidine, 3,3′-diamino- Biphenyl, 2,2′-bis (trifluoromethyl) benzidine, 3,3′-bis (trifluoromethyl) benzidine, m-tolidine, 4,4′-diaminobenzanilide, 3,4′-diaminobenzanilide, N, N′-bis (4-aminophenyl) terephthalamide, N, N′-p-phenylenebis (p-aminobenzamide), 4-aminophenoxy-4-diaminobenzoate, bis (4-aminophenyl) terephthalate, Biphenyl-4,4′-dicarboxylic acid bis (4-aminophenyl) ester, p-phenylenebis (p-aminoben) Ate), bis (4-aminophenyl)-[1,1′-biphenyl] -4,4′-dicarboxylate, [1,1′-biphenyl] -4,4′-diylbis (4-aminobenzoate) 4,4′-oxydianiline, 3,4′-oxydianiline, 3,3′-oxydianiline, p-methylenebis (phenylenediamine), 1,3-bis (4-aminophenoxy) benzene, 1 , 3-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) ) Biphenyl, 2,2-bis (4- (4-aminophenoxy) phenyl) hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, bis (4-a Nophenyl) sulfone, 3,3′-bis (trifluoromethyl) benzidine, 3,3′-bis ((aminophenoxy) phenyl) propane, 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoro Propane, bis (4- (4-aminophenoxy) diphenyl) sulfone, bis (4- (3-aminophenoxy) diphenyl) sulfone, octafluorobenzidine, 3,3′-dimethoxy-4,4′-diaminobiphenyl, 3 , 3′-dichloro-4,4′-diaminobiphenyl, 3,3′-difluoro-4,4′-diaminobiphenyl, 2,4-bis (4-aminoanilino) -6-amino-1,3,5- Triazine, 2,4-bis (4-aminoanilino) -6-methylamino-1,3,5-triazine, 2,4-bis (4-aminoanilino) Examples include -6-ethylamino-1,3,5-triazine and 2,4-bis (4-aminoanilino) -6-anilino-1,3,5-triazine. Examples of the diamine component that gives the repeating unit of the general formula (II) in which Y ₁ is a divalent group having an aromatic ring containing a fluorine atom include 2,2′-bis (trifluoromethyl) benzidine, 3 , 3′-bis (trifluoromethyl) benzidine, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, 2,2 And '-bis (3-amino-4-hydroxyphenyl) hexafluoropropane. In addition, as a preferable diamine compound, 4,4 ′-(((9H-fluorene-9,9-diyl) bis ([1,1′-biphenyl] -5,2-diyl)) bis (oxy)) diamine, [1,1 ′: 4 ′, 1 ″ -terphenyl] -4,4 ″ -diamine, 4,4 ′-([1,1′-binaphthalene] -2,2′-diylbis (oxy)) diamine Can be mentioned. A diamine component may be used independently and can also be used in combination of multiple types.

The divalent group having an alicyclic structure of Y ₁ is preferably a divalent group having an alicyclic structure having 4 to 40 carbon atoms, more preferably at least one aliphatic 4- to 12-membered ring, more preferably aliphatic. More preferably, it has a 6-membered ring.

  Examples of the divalent group having an alicyclic structure include the following.

(In the formula, V ₁ and V ₂ are each independently a direct bond or a divalent organic group, n _{21 to} n ₂₆ each independently represents an integer of 0 to 4, and R _{81 to} R _86. Are each independently an alkyl group having 1 to 6 carbon atoms, a halogen group, a hydroxyl group, a carboxyl group, or a trifluoromethyl group, and R ₉₁ , R ₉₂ , and R ₉₃ are each independently represented by the formula: —CH ₂ —, It is one selected from the group consisting of groups represented by —CH═CH—, —CH ₂ CH ₂ —, —O—, and —S—.

Specific examples of V ₁ and V ₂ include a direct bond and a divalent group represented by the above formula (5).

  As the divalent group having an alicyclic structure, the following can be particularly preferred since both the high heat resistance and low linear thermal expansion coefficient of the resulting polyimide can be achieved.

Among the divalent groups having an alicyclic structure, the following are preferable.

Examples of the diamine component that gives the repeating unit of the general formula (II) in which Y ₁ is a divalent group having an alicyclic structure include 1,4-diaminocyclohexane and 1,4-diamino-2-methylcyclohexane. 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1 , 4-Diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, 1,2-diaminocyclohexane, 1,3-diamino Cyclobutane, 1,4-bis (aminomethyl) cyclohexane, 1,3-bis (aminomethyl) cyclohexane Xanthone, diaminobicycloheptane, diaminomethylbicycloheptane, diaminooxybicycloheptane, diaminomethyloxybicycloheptane, isophoronediamine, diaminotricyclodecane, diaminomethyltricyclodecane, bis (aminocyclohexyl) methane, bis (aminocyclohexyl) Isopropylidene, 6,6′-bis (3-aminophenoxy) -3,3,3 ′, 3′-tetramethyl-1,1′-spirobiindane, 6,6′-bis (4-aminophenoxy) -3 3,3 ′, 3′-tetramethyl-1,1′-spirobiindane. A diamine component may be used independently and can also be used in combination of multiple types.

  In addition to the above tetracarboxylic acid component and diamine component, it is also preferable to add a carboxylic acid monoanhydride to cause the reaction. The carboxylic acid monoanhydride is particularly preferably a dicarboxylic acid monoanhydride, which may be an aromatic carboxylic acid monoanhydride or an aliphatic carboxylic acid monoanhydride. Aromatic carboxylic acid monoanhydrides are particularly preferred. The aromatic carboxylic acid monoanhydride preferably has an aromatic ring having 6 to 30 carbon atoms, more preferably has an aromatic ring having 6 to 15 carbon atoms, and has an aromatic ring having 6 to 10 carbon atoms. Further preferred.

  Examples of carboxylic acid monoanhydrides include phthalic anhydride, 2,3-benzophenone dicarboxylic acid anhydride, 3,4-benzophenone dicarboxylic acid anhydride, 1,2-naphthalenedicarboxylic acid anhydride, and 2,3-naphthalenedicarboxylic acid. Aromatic carboxylic acid monoesters such as acid anhydrides, 1,8-naphthalenedicarboxylic acid anhydrides, 1,2-anthracene dicarboxylic acid anhydrides, 2,3-anthracene dicarboxylic acid anhydrides, 1,9-anthracene dicarboxylic acid anhydrides Mention may be made of anhydrides and alicyclic carboxylic acid monoanhydrides such as maleic anhydride, succinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, itaconic anhydride, trimellitic anhydride. Of these, phthalic anhydride is preferred.

  When adding carboxylic acid monoanhydride, it is more preferable to satisfy | fill following Formula (1) and (2).

Formula (1) 0.97 <= X / Y <1.00
Formula (2) 0.5 ≦ (Z / 2) / (Y−X) ≦ 1.05
(Wherein X represents the number of moles of the tetracarboxylic acid component, Y represents the number of moles of the diamine component, and Z represents the number of moles of the carboxylic acid monoanhydride.)

  When X / Y is 0.97 or more, the molecular weight of the polyimide precursor (especially polyamic acid) is increased, and the strength and heat resistance of the resulting polyimide film are improved. X / Y is preferably 0.98 or more. When X / Y is less than 1.00, the diamine component is excessive with respect to the tetracarboxylic acid component. By carrying out like this, the amino group which can be end-capped with carboxylic acid monoanhydride can be formed. X / Y is preferably 0.99 or less.

  Moreover, (Z / 2) / (Y-X) represents the molar ratio between the carboxylic acid monoanhydride and the end-capping amino group. When X / Y is less than 1.00 and (Z / 2) / (Y-X) is 0.5 or more, the terminal blocking rate of the polyimide precursor can be increased, and the CV characteristics Can be improved. (Z / 2) / (YX) is preferably closer to 1. (Z / 2) / (Y-X) is preferably 0.6 or more, more preferably 0.7 or more. When (Z / 2) / (YX) is 1.05 or less, the amount of free carboxylic acid monoanhydride can be reduced, and the strength and CV characteristics of the resulting polyimide film can be improved. (Z / 2) / (Y-X) is preferably 1.03 or less, more preferably 1.01 or less.

  In one embodiment of the present invention, the weight fraction of the imide group (—C (O) NC (O) —) in the polyimide repeating unit (that is, the general formula II) is preferably less than 38.3 wt%. . In a specific embodiment, it is more preferably 30% by weight or less.

  Here, the polyimide may be a copolymer, that is, at least one of the tetracarboxylic acid component and the diamine component that give the polyimide may contain two or more kinds of compounds. In this case, the weight fraction of imide groups is calculated by a weighted average based on the monomer charge ratio. It calculates similarly about the weight fraction of groups other than an imide group. In the following description, when referring to the weight fraction of a specific group, the polyimide includes both the case of being a homopolymer and the case of being a copolymer.

In one embodiment of the present invention, it is preferable that the functional group weight fraction in the polyimide repeating unit is small. The “functional group in the repeating unit” defined herein is a moiety other than the aromatic ring and the saturated alkyl chain in the polyimide repeating unit, and includes —O— (ether bond), —CO— (carbonyl group), —COO. - (ester), - SO ₂ - and the like. F and Cl replacing hydrogen in the aromatic ring and saturated alkyl chain are not included in the “functional group in the repeating unit”.

  The total of the imide group and the “functional group in the repeating unit” is preferably less than 38.3 wt% in the polyimide repeating unit, more preferably 30 wt% or less, and even more preferably 25 wt% or less.

  In a preferred embodiment of the present invention, the tetracarboxylic acid component forming the repeating unit contains a tetracarboxylic dianhydride having a fluorene structure in the molecule and a functional group other than the two acid anhydride groups (the above “in the repeating unit”). It is preferable to include a compound selected from tetracarboxylic dianhydrides having three or more benzene rings per group) corresponding to “functional group of”. In addition to the two acid anhydride groups, a compound having no functional group corresponding to “functional group in repeating unit” is also included in the preferable compound. In this case, the number of benzene rings is preferably 2 or more. Yes, more preferably 3 or more.

  In a preferred embodiment of the present invention, the diamine component forming the repeating unit includes a diamine having a fluorene structure in the molecule, and a functional group other than two amine groups (a group corresponding to the above “functional group in the repeating unit”). It is preferable to include a compound selected from diamines having three or more benzene rings per one. In addition to the two amine groups, a compound having no functional group corresponding to the “functional group in the repeating unit” is also included in the preferred compound. In this case, the number of benzene rings is preferably 2 or more, More preferably, it is 3 or more.

  In a preferred embodiment of the present invention, each of the tetracarboxylic acid component and the diamine component forming the repeating unit is a compound having the above-described conditions, that is, a compound having a fluorene structure in the molecule, and one “functional group in the repeating unit”. On the other hand, it is preferable to include a compound selected from compounds having 3 or more benzene rings (including the case of 0 functional group).

In one embodiment of the present invention, it is also preferable that the “terminal functional group amount” is small. "Terminal functional group amount" refers to the ratio of the tetracarboxylic acid component and the diamine component used in the production of polyimide (when producing polyamic acid), the purity of each component, the added amount of the end-capping agent, and the reactive additive It is calculated based on the amount of addition. The terminal functional group amount is calculated from the charged ratio of the tetracarboxylic acid component and the diamine component as follows.
Since the degree of polymerization of a polyimide obtained with a tetracarboxylic dianhydride / diamine ratio = 1 is theoretically ∞, the end group is 1 / ∞ = 0. When the charge of tetracarboxylic dianhydride and diamine is not equimolar, taking the case of excess diamine as an example, theoretically, a polyimide having a degree of polymerization n of the structure of formula (II-B) can be formed. To do. n is
(Formula) Tetracarboxylic dianhydride / diamine ratio = n / (n + 1)
It is obtained by calculating n satisfying. Assuming that the formula weight of the repeating unit is a and the molecular weight of one terminal diamine is a _b , the formula weight of the polyimide having a polymerization degree n is (a * n + a _b ).
2 / (a * n + a _b ) [unit: mol / g]
Is required. In the examples of the present application, it is expressed in μmol / g.

  In one embodiment of the present invention, the amount of terminal amine groups is preferably 30 μmol / g or less, more preferably 20 μmol / g or less, and even more preferably 10.5 μmol / g or less. In another embodiment of the present invention, the total amount of terminal functional groups is preferably 30 μmol / g or less, more preferably 20 μmol / g or less, and further preferably 10.5 μmol / g or less.

  In a preferred embodiment of the present invention, the combined weight fraction of the imide group and the “functional group in the repeating unit” is preferably 30% by weight or less and the “terminal functional group amount” is preferably 20 μmol / g or less. In the embodiment, the combined weight fraction of the imide group and the “functional group in the repeating unit” is preferably 40% by weight or less and the “terminal functional group amount” is preferably 10.5 μmol / g or less. Further, it is very preferable that the weight fraction of the imide group and the “functional group in the repeating unit” is 30% by weight or less and the “terminal functional group amount” is 10.5 μmol / g or less.

  Control of the functional groups (imide group, functional group in the repeating unit, terminal functional group) in the polyimide as described above is an element to be considered in order to obtain the polyimide having the CV characteristics of the present invention.

<< New polyimide precursor and polyimide >>
The present application also discloses polyimide precursors and polyimides containing novel structures. New polyimide precursor and polyimide
A tetracarboxylic acid component (A) containing at least 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA);
(B-1) 1,4-diaminobenzene, [1,1 ′: 4 ′, 1 ″ -terphenyl] -4,4 ″ -diamine, and 1,4-bis [2- (4-aminophenyl) -2-propyl] benzene, and (B-2) 9,9-bis (4-aminophenyl) fluorene, 4,4 ′-(((9H-fluorene-9,9-diyl ) Bis ([1,1′-biphenyl] -5,2-diyl)) bis (oxy)) diamine and 4,4 ′-([1,1′-binaphthalene] -2,2′-diylbis (oxy) )) A repeating unit obtained by reacting a diamine component (B) containing at least one diamine selected from diamines. That is, in General Formula I and General Formula II, X ₁ includes a repeating unit derived from the tetracarboxylic acid component (A) and Y ₁ derived from the diamine component (B).

  The tetracarboxylic acid component (A) preferably contains 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) in a proportion of 40 mol% or more. Further, as tetracarboxylic acid component (A), in addition to s-BPDA, (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis (1,3-dioxo-1, 3-dihydroisobenzofuran-5-carboxylate) is also preferred. In addition to these, the tetracarboxylic dianhydrides listed above can be contained. For example, a tetracarboxylic dianhydride having a fluorene structure in the molecule and three functional groups other than two acid anhydride groups (a group corresponding to “functional group in repeating unit”) have three benzene rings. The compound chosen from the tetracarboxylic dianhydride which has one or more can be included. Other than s-BPDA and (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis (1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) The amount of tetracarboxylic dianhydride is preferably 30 mol% or less, more preferably 20 mol% or less, and may be 0 mol%.

  The diamine component (B) preferably contains the diamine of (B-1) and the diamine of (B-2) in a proportion of 40 mol% or more. In addition to the diamine of (B-1) and the diamine of (B-2), the diamine compounds listed above can be contained as the diamine component (B). For example, it is selected from a diamine having a fluorene structure in the molecule and a diamine having three or more benzene rings for one functional group other than two amine groups (a group corresponding to the “functional group in the repeating unit”). Compounds can be included, and preferred compounds include 1,1 ′: 4 ′, 1 ″: 4 ″, 1 ″ ′-quarterphenyl-4,4 ″ ′-diamine and the like. The amount of the diamine compound other than the diamine (B-1) and the diamine (B-2) is preferably 30 mol% or less, more preferably 20 mol% or less, and may be 0 mol%.

  Moreover, the total of the ratio of the repeating unit derived from the diamine of s-BPDA and (B-1) and the repeating unit derived from the diamine of s-BPDA and (B-2) in the repeating unit of a polyimide precursor or a polyimide is the sum. 40 mol% or more is preferable.

  This new polyimide has excellent CV characteristics, and the weight fraction of the imide group in the polyimide repeating unit, the weight fraction of the imide group combined with the “functional group in the repeating unit”, and the “terminal functional group amount”. It is preferable to select the combination compound, the charged tetracarboxylic dianhydride / diamine ratio, and the like so that at least one, preferably two, and more preferably three are in the above-described range (particularly, a preferable range).

<< Method for producing polyimide film >>
A method for producing polyimide, particularly a method for producing a polyimide film via a laminate in which a polyimide film is formed on a carrier substrate, will be described below.

When schematically showing an example of a method for producing a polyimide film,
(1) A polyimide precursor (especially polyamic acid) solution, or a polyimide precursor solution composition in which an imidization catalyst, a dehydrating agent, inorganic fine particles, and the like are selected and added to a polyimide precursor solution as necessary is provided on a carrier substrate. A method of forming a polyimide film by casting, dehydrating cyclization and desolvation by heating (thermal imidization);
(2) Add a cyclization catalyst and a dehydrating agent to a polyimide precursor (especially polyamic acid) solution, and further cast a polyimide precursor solution composition added by selecting inorganic fine particles as necessary on a carrier substrate. A method of chemically dehydrating and cyclizing and removing the solvent by heating to form a polyimide film by imidization (chemical imidization);
(3) When the polyimide is soluble in an organic solvent, the polyimide solution composition added by selecting additives such as inorganic fine particles as necessary is cast on a carrier substrate, and the solvent is removed by heating to a predetermined temperature. The method of forming a polyimide film by heating, etc. are mentioned.

<Polyimide precursor solution, polyimide solution>
First, the production of a polyimide precursor solution and a polyimide solution will be described. A polyimide precursor solution or a polyimide solution is obtained by polymerizing approximately equimolar tetracarboxylic acid components and diamine components in an organic solvent. Alternatively, it combines the two or more polyimide precursors in which either component is excessive, after combining each polyimide precursor solution may be mixed under reaction conditions.

  The organic solvent is not particularly limited. For example, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N Amide solvents such as vinyl-2-pyrrolidone, cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ-butyrolactone, ethylene carbonate, propylene Carbonate solvents such as carbonate, glycol solvents such as triethylene glycol, phenol solvents such as m-cresol, p-cresol, 3-chlorophenol, 4-chlorophenol, acetophenone, 1,3-dimethyl-2-imidazolide Non, sulfolane, dimethyls Sulfoxide and the like. Furthermore, other common organic solvents such as alcohol solvents such as methanol and ethanol, phenol, o-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl Cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, Toluene, chlorobenzene, N-methylcaprolactam, hexamethylphosphorotriamide, bis ( -Methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, bis [2- (2-methoxyethoxy) ethyl] ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, diphenyl sulfone, Tetramethylurea, anisole, terpenes, mineral spirits, petroleum naphtha solvents, biodegradable methyl lactate, ethyl lactate, butyl lactate and the like can also be used. The organic solvent to be used may be one type or two or more types.

  When carrying out the polymerization reaction to obtain the polyimide precursor solution and the polyimide solution respectively, the concentration of all monomers (substantially equal to the solid content concentration of the polyimide precursor solution or the polyimide solution) in the organic solvent depends on the purpose of use and production What is necessary is just to select suitably according to the objective to do. The solid content concentration of the obtained polyimide precursor solution or polyimide solution is not particularly limited, but is preferably 5% by mass to 45% by mass with respect to the total amount of the polyimide precursor or polyimide and the solvent. Preferably they are 7 mass%-40 mass%, More preferably, they are 9 mass%-30 mass%. When the solid content concentration is lower than 5% by mass, productivity and handling during use may be deteriorated, and when it is higher than 45% by mass, the fluidity of the solution may be lost.

  The solution viscosity at 30 ° C. of the polyimide precursor solution or polyimide solution is not particularly limited, but is preferably 1000 Pa · s or less, more preferably 0.1 to 500 Pa · s, and still more preferably 0.1 to 300 Pa · s. Particularly preferably, the pressure is 0.1 to 200 Pa · s in view of handling. When the solution viscosity exceeds 1000 Pa · s, fluidity is lost, and uniform application to a carrier substrate such as metal or glass may be difficult, and when it is lower than 0.1 Pa · s, metal or glass Such as dripping or repelling may occur during application to a carrier substrate, and it may be difficult to obtain a polyimide film having high characteristics.

  As an example of the production of the polyimide precursor solution, the polymerization reaction of the tetracarboxylic acid component and the diamine component is carried out by, for example, substantially equimolar or a little of either component (acid component or diamine component). The polyimide precursor solution can be obtained by mixing in excess and carrying out the reaction at a reaction temperature of 100 ° C. or lower, preferably 80 ° C. or lower for about 0.2 to 60 hours.

  As an example of a polyimide solution production example, the polymerization reaction of the tetracarboxylic acid component and the diamine component described above is carried out by, for example, substantially equimolar or each component (acid component or diamine component) being slightly excessive. The polyimide solution can be obtained by a known method, for example, by reacting at a reaction temperature of 140 ° C. or higher, preferably 160 ° C. or higher (preferably 250 ° C. or lower, further 230 ° C. or lower) for about 1 to 60 hours. It can implement by and can obtain a polyimide solution.

  In addition, when adding a carboxylic acid monoanhydride (particularly a dicarboxylic acid monoanhydride) as described above, generally a tetracarboxylic acid component and a diamine component are preferably used in a molar ratio that satisfies the above-described formula (1). The first step of reacting in a solvent to obtain a polyimide precursor having an amino group at the terminal (particularly polyamic acid), and then the carboxylic acid monoanhydride, preferably a molar ratio satisfying the above-mentioned formula (2) The method including the second step of sealing the terminal of the polyimide precursor (especially polyamic acid) by adding and reacting with is preferable.

  In the first step, in order to suppress the imidization reaction, for example, it is performed at a relatively low temperature of 100 ° C. or less, preferably 80 ° C. or less. Although not limited, the reaction temperature is usually 25 ° C to 100 ° C, preferably 40 ° C to 80 ° C, more preferably 50 ° C to 80 ° C, and the reaction time is usually about 0.1 to 24 hours. It is preferably about 2 to 12 hours. By setting the reaction temperature and the reaction time within the above ranges, a solution composition of a high molecular weight polyimide precursor can be obtained efficiently. The reaction can be performed in an air atmosphere, but is usually performed in an inert gas atmosphere, preferably in a nitrogen gas atmosphere.

  In the second step, the reaction temperature may be appropriately set, but from the viewpoint of reliably sealing the end of the polyimide precursor, it is preferably 25 ° C to 70 ° C, more preferably 25 ° C to 60 ° C, and even more preferably. 25 ° C to 50 ° C. The reaction time is usually about 0.1 to 24 hours.

  The polyimide precursor solution or polyimide solution thus obtained can be used for the production of a polyimide film as it is, or if necessary, by removing the organic solvent or newly adding an organic solvent.

  If necessary, an imidization catalyst, an organic phosphorus-containing compound, inorganic fine particles, and the like may be added to the polyimide precursor solution as long as it is thermal imidization. A cyclization catalyst, a dehydrating agent, inorganic fine particles, and the like may be added to the polyimide precursor solution as necessary if chemical imidization. If necessary, inorganic fine particles and the like may be added to the polyimide solution.

  Examples of the imidization catalyst include a substituted or unsubstituted nitrogen-containing heterocyclic compound, an N-oxide compound of the nitrogen-containing heterocyclic compound, a substituted or unsubstituted amino acid compound, an aromatic hydrocarbon compound having a hydroxyl group, or an aromatic heterocyclic compound. Cyclic compounds such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 5-methylbenzimidazole and the like. Benzimidazoles such as alkylimidazole and N-benzyl-2-methylimidazole, isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 4-n- Preferred are substituted pyridines such as propylpyridine It can be used for. The amount of the imidization catalyst used is preferably about 0.01 to 2 times equivalent, particularly about 0.02 to 1 times equivalent to the amic acid unit of the polyamic acid. By using an imidization catalyst, properties of the resulting polyimide film, particularly elongation and end resistance, may be improved.

  Examples of the organic phosphorus-containing compounds include monocaproyl phosphate, monooctyl phosphate, monolauryl phosphate, monomyristyl phosphate, monocetyl phosphate, monostearyl phosphate, triethylene glycol monotridecyl Monophosphate of ether, monophosphate of tetraethylene glycol monolauryl ether, monophosphate of diethylene glycol monostearyl ether, dicaproyl phosphate, dioctyl phosphate, dicapryl phosphate, dilauryl phosphate, dimyristyl phosphate, Dicetyl phosphate, distearyl phosphate, diethylene phosphate of tetraethylene glycol mononeopentyl ether, triethyl Diphosphate of glycol mono tridecyl ether, diphosphate of tetraethyleneglycol monolauryl ether, and phosphoric acid esters such as diphosphate esters of diethylene glycol monostearyl ether, amine salts of these phosphates. As amine, ammonia, monomethylamine, monoethylamine, monopropylamine, monobutylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, monoethanolamine, diethanolamine, triethanolamine Etc.

  Cyclization catalysts include aliphatic tertiary amines such as trimethylamine and triethylenediamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic tertiary amines such as isoquinoline, pyridine, α-picoline and β-picoline. Etc.

  Examples of the dehydrating agent include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride.

  Inorganic fine particles include fine particle titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, inorganic oxide powder such as zinc oxide powder, fine particle silicon nitride powder, and titanium nitride powder. Inorganic nitride powder such as silicon carbide powder, inorganic carbide powder such as silicon carbide powder, and inorganic salt powder such as particulate calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. These inorganic fine particles may be used in combination of two or more. In order to uniformly disperse these inorganic fine particles, a means known per se can be applied.

  In one embodiment, the polyimide precursor solution or the polyimide solution preferably does not contain a silane coupling agent such as alkoxysilane. In a polyimide film using a silane coupling agent, the silane coupling agent may bleed out. Thereby, problems, such as a fall of the CV characteristic of a polyimide film, a further adhesive force fall, and a swelling of a laminated body, arise. Furthermore, when a silane coupling agent is added to or reacted with the polyimide precursor solution, there is a problem that the viscosity stability of the polyimide precursor solution is lowered. In order to avoid such a problem, it is preferable not to use a silane coupling agent.

<Manufacture of laminates and electronic devices>
In the production of an electronic device, first, a polyimide precursor solution or a polyimide solution (including a composition solution containing an additive if necessary) is cast on a carrier substrate, and imidization and desolvation by heat treatment ( In the case of a polyimide solution, a polyimide film is formed by mainly removing the solvent, and a laminate of the carrier substrate and the polyimide film is obtained. Although there is no restriction | limiting in a carrier substrate, Generally, glass substrates, such as soda-lime glass, borosilicate glass, an alkali free glass, and metal substrates, such as iron and stainless steel, are used. The method for casting the polyimide precursor solution and the polyimide solution onto the carrier substrate is not particularly limited, and examples thereof include conventionally known methods such as a spin coating method, a screen printing method, a bar coater method, and an electrodeposition method. The heat treatment conditions when the polyimide precursor solution is used are not particularly limited. For example, after drying in a temperature range of 50 ° C. to 150 ° C., the maximum heating temperature is, for example, 150 ° C. to 600 ° C., preferably 200 ° C. It is preferable to perform the treatment at ˜550 ° C., more preferably at 250 ° C. to 500 ° C. The heat treatment conditions when the polyimide solution is used are not particularly limited, but the maximum heating temperature is, for example, 100 ° C. to 600 ° C., preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and preferably 500 ° C. Below, it is 450 degrees C or less more preferably.

  The thickness of the polyimide film is preferably 1 μm or more. When the thickness is less than 1 μm, the polyimide film cannot maintain sufficient mechanical strength. For example, when used as a flexible device substrate, the polyimide film cannot withstand stress and may be destroyed. Moreover, it is preferable that the thickness of a polyimide film is 20 micrometers or less. If the thickness of the polyimide film exceeds 20 μm, it may be difficult to reduce the thickness of the flexible device. In order to make the film thinner while maintaining sufficient resistance as a flexible device, the thickness of the polyimide film is more preferably 2 to 10 μm.

  The obtained polyimide film is firmly laminated on a carrier substrate such as a glass substrate. When measured according to JIS K6854-1, the peel strength between a carrier substrate such as a glass substrate and a polyimide film is generally 50 mN / mm or more, preferably 100 mN / mm or more, more preferably 200 mN / mm or more. More preferably, it is 300 mN / mm or more.

Further, a flexible device substrate may be formed by laminating a second layer such as a resin film or an inorganic film on the obtained polyimide film. In particular, the inorganic film can be used as a water vapor barrier layer and is suitable. Examples of the water vapor barrier layer include silicon nitride (SiN _x ), silicon oxide (SiO _x ), silicon oxynitride (SiO _x N _y ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), and zirconium oxide. Examples thereof include an inorganic film containing an inorganic material selected from the group consisting of metal oxides such as (ZrO ₂ ), metal nitrides, and metal oxynitrides. In general, these thin film formation methods include physical vapor deposition such as vacuum vapor deposition, sputtering, and ion plating, and chemical vapor deposition such as plasma CVD and catalytic chemical vapor deposition (Cat-CVD). The method (chemical vapor deposition method) is known. The second layer may be a plurality of layers. Even in the case of a device having a second layer on a polyimide film, the influence of the polyimide film may reach the semiconductor layer via the second layer, so that device characteristics and durability are improved. In addition, the polyimide having good CV characteristics of the present invention is preferably used.

  A flexible device substrate may be formed by laminating a polyimide film on a resin film or an inorganic film. A polyimide film can be laminated on a resin film or an inorganic film using a polyimide precursor solution or a polyimide solution in the same manner as in the case of a carrier substrate.

  The polyimide film obtained in the present invention is firmly laminated even when the inorganic film is a substrate. The peel strength between the polyimide film and the inorganic film (for example, silicon oxide film) is generally 20 mN / mm or more, preferably 30 mN / mm or more, more preferably 40 mN, when measured according to JIS K6854-1. / Mm or more, more preferably 50 mN / mm or more.

  In the manufacture of electronic devices, elements and circuits necessary for the device are formed on the formed laminate (particularly polyimide film). The elements and circuits to be formed and the manufacturing process thereof vary depending on the type of device. In the case of manufacturing a TFT liquid crystal display device, for example, an amorphous silicon TFT is formed on a polyimide film. The TFT includes, for example, a gate metal layer, a semiconductor layer such as an amorphous silicon film, a silicon nitride gate dielectric layer, and an ITO pixel electrode. Further, a structure necessary for a liquid crystal display can be formed by a known method. Since the polyimide film obtained in the present invention is excellent in various properties such as heat resistance and toughness, the method for forming a circuit or the like is not particularly limited.

  When a flexible device is intended as an electronic device, a device substrate (particularly a polyimide film) on which a circuit or the like is formed is peeled from the carrier substrate. There is no restriction | limiting in particular in the peeling method, For example, it can peel by irradiating a laser etc. from the carrier substrate side.

  Examples of the flexible device in which the polyimide of the present invention is suitably used include display devices such as liquid crystal displays, organic EL displays and electronic paper, and light receiving devices such as solar cells and CMOS. The present invention is particularly suitable for application to a device that is desired to be thin and flexible.

  The polyimide of the present invention can be used for various applications. However, in order to achieve the effect of excellent CV characteristics, the polyimide and the semiconductor are in direct contact with each other, or a thin film (for example, 200 nm or less, preferably 100 nm). It is preferably used in a device laminated via the following thin film, such as the second layer described above.

  In the above description, the method of forming an element or circuit on the polyimide film-carrier substrate laminate has been described. If there is no problem in forming the element or circuit, a single film polyimide film is formed. An element or a circuit may be formed.

  Examples of the semiconductor include silicon such as single crystal silicon, amorphous silicon, and polysilicon (these may be p-type or n-type impurity-doped), and gallium nitride and other compound semiconductors.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

  A method for measuring the characteristics used in the following examples is shown below.

<Measurement method of CV characteristics>
The CV characteristics were implemented under the following conditions by the system shown in the schematic diagram of FIG.
Measuring device: Mercury probe type CV measuring device manufactured by Horiba Joban Yvon (Mercury probe Model 802-150 (Materials Development Corporation)
Mercury electrode area: 0.00475 cm ²
DC voltage scanning condition: After holding at +40 V for 30 s, scan in the negative direction from +40 V to −40 V, hold at −40 V for 30 s, and then scan in the positive direction to +40 V. This was repeated for 3 cycles.
AC voltage condition: AC sine wave with frequency of about 2.5 kHz and amplitude of 0.1 V Measurement temperature: Room temperature

<How to find the gradient>
As an approximation of the derivative function of the normalized C-V curves, and the normalized capacity _{C n1} when the certain voltage _{V n1,} the normalized capacitance _{C n2} when the V n1 +1.5 _{V n2} is [V], The absolute value “| (C _n2 −C _n1 ) / (V _n2 −V _n1 ) |” is calculated for the entire normalized CV curve, and | (C _n2 −C _n1 ) / (V _n2 − The maximum value of V _n1 ) | was adopted as the gradient of the composition.

Monomers and additives used in Examples and Comparative Examples are shown.
Monomer A: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (formula weight 294.22), purity (%) 99.9
Monomer A2: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (formula weight 294.22), purity (%) 99.0 (low purity)
Monomer B: (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis (1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) (formula weight) 726.66), purity (%) 98.2
Monomer C: 1,4-diaminobenzene (formula weight 108.14), purity (%) 100.0
Monomer D: 4,4 ′-(((9H-fluorene-9,9-diyl) bis ([1,1′-biphenyl] -5,2-diyl)) bis (oxy)) diamine (formula 684. 78), purity (%) 99.0
Monomer E: [1,1 ′: 4 ′, 1 ″ -terphenyl] -4,4 ″ -diamine (formula weight 260.31), purity (%) 99.1
Monomer F: 4,4 ′-([1,1′-binaphthalene] -2,2′-diylbis (oxy)) diamine (formula 468.51), purity (%) 99.1
Monomer G: 1,4-bis [2- (4-aminophenyl) -2-propyl] benzene (formula 344.48), purity (%) 99.7
Monomer H: 9,9-bis (4-aminophenyl) fluorene (formula weight 348.43), purity (%) 99.2
Monomer I: phthalic anhydride (formula weight 148.11), purity (%) 100.0
Additive: 3-aminopropyltriethoxysilane (formula weight 218.32), purity (%) 99.7

  The chemical structure of the monomer is shown below.

[Reference Example 1] (Composition of Example 1)
(Monomer A 50 / Monomer B 50 // Monomer C 50 / Monomer D 50)
In a reaction vessel substituted with nitrogen gas, 1,4-diaminobenzene (50 mol%) and 4,4 ′-(((9H-fluorene-9,9-diyl) bis ([1,1′-biphenyl] -5,2-diyl)) bis (oxy)) diamine (50 mol%) and NMP were charged and heated and stirred at 40 ° C for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (50 mol%) and (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis ( 1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) (50 mol%), stirred for another 30 minutes, and a liquid polyimide precursor resin composition having a viscosity of 1.82 Pa · s (25 ° C.) A product (polyamic acid solution) was obtained.

[Reference Example 2] (Composition of Example 2)
(Monomer A 50 / Monomer B 50 // Monomer D 50 / Monomer E 50)
In a reaction vessel purged with nitrogen gas, [1,1 ′: 4 ′, 1 ″ -terphenyl] -4,4 ″ -diamine (50 mol%) (50 mol%) and 4,4 ′-(( (9H-fluorene-9,9-diyl) bis ([1,1′-biphenyl] -5,2-diyl)) bis (oxy)) diamine (50 mol%) and NMP were charged, and 15 minutes at 40 ° C. The mixture was heated and stirred to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (50 mol%) and (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis ( 1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) (50 mol%), stirred for another 30 minutes, and a liquid polyimide precursor resin composition having a viscosity of 0.742 Pa · s (25 ° C.) A product (polyamic acid solution) was obtained.

[Reference Example 3] (Composition of Example 3)
(Monomer A 50 / Monomer B 50 // Monomer E 50 / Monomer F 50)
In a reaction vessel purged with nitrogen gas, [1,1 ′: 4 ′, 1 ″ -terphenyl] -4,4 ″ -diamine (50 mol%) and 4,4 ′-([1,1′- Binaphthalene] -2,2′-diylbis (oxy)) diamine (50 mol%) and NMP were charged, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (50 mol%) and (9H-fluorene-9,9-diyl) bis (2-methyl-4,1-phenylene) bis ( 1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) (50 mol%), stirred for another 30 minutes, and a liquid polyimide precursor resin composition having a viscosity of 0.886 Pa · s (25 ° C.) A product (polyamic acid solution) was obtained.

[Reference Example 4] (Composition of Example 4)
(Monomer A 100 // Monomer G 50 / Monomer H 50)
In a reaction vessel substituted with nitrogen gas, 1,4-bis [2- (4-aminophenyl) -2-propyl] benzene (50 mol%) and 9,9-bis (4-aminophenyl) fluorene (50 Mol%) and NMP were charged, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (100 mol%) was added, and the mixture was further stirred for 30 minutes, and a liquid polyimide precursor resin composition having a viscosity of 3.249 Pa · s (25 ° C.). A product (polyamic acid solution) was obtained.

[Reference Example 5] (Composition of Example 5)
(Monomer A 100 // Monomer G 50 / Monomer H 50)
In a reaction vessel substituted with nitrogen gas, 1,4-bis [2- (4-aminophenyl) -2-propyl] benzene (50 mol%) and 9,9-bis (4-aminophenyl) fluorene (50 Mol%) and NMP were charged, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (100 mol%) was added, and the mixture was further stirred for 30 minutes to obtain a polyamic acid solution. Thereafter, the temperature was raised to 190 ° C., and then imidization was carried out for 3 hours to obtain a liquid polyimide resin composition (polyimide solution) having a viscosity of 4.03 Pa · s (25 ° C.).

[Reference Example 6] (Composition of Example 6)
(Monomer A 100 // Monomer C 100)
1,4-diaminobenzene (100 mol%) and NMP were charged into a reaction vessel substituted with nitrogen gas, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (100 mol%) was added, and the mixture was further stirred for 30 minutes, and a liquid polyimide precursor resin composition having a viscosity of 6.6 Pa · s (25 ° C.). A product (polyamic acid solution) was obtained.

[Reference Example 7] (Composition of Example 7)
(Monomer A 98 // Monomer C 100 // Monomer I 4)
1,4-diaminobenzene (100 mol%) and NMP were charged into a reaction vessel substituted with nitrogen gas, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (98 mol%) and were added, and the mixture was further stirred for 30 minutes. Thereafter, phthalic anhydride (4 mol%) was added, and the mixture was further stirred for 30 minutes to obtain a liquid polyimide precursor resin composition (polyamic acid solution) having a viscosity of 3.11 Pa · s (25 ° C.).

[Reference Example 8] (Composition of Comparative Example 1)
(Monomer A 100 // Monomer C 100 // Additive)
1,4-diaminobenzene (100 mol%) and NMP were charged into a reaction vessel substituted with nitrogen gas, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (99.5 mol%) and 3-aminopropyltriethoxysilane (0.05 parts based on the total amount of monomers) were added, and an additional 30 The mixture was stirred for a minute to obtain a liquid polyimide precursor resin composition (polyamic acid solution) having a viscosity of 28.75 Pa · s (25 ° C.).

[Reference Example 9] (Composition of Comparative Example 2)
(Monomer A 98 // Monomer C 100)
1,4-diaminobenzene (100 mol%) and NMP were charged into a reaction vessel substituted with nitrogen gas, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (98 mol%) was added, and the mixture was further stirred for 30 minutes to give a liquid polyimide precursor resin composition having a viscosity of 3.11 Pa · s (25 ° C.). A product (polyamic acid solution) was obtained.

[Reference Example 10] (Composition of Comparative Example 3)
(Monomer A2 100 // Monomer C 100)
1,4-diaminobenzene (100 mol%) and NMP were charged into a reaction vessel substituted with nitrogen gas, and the mixture was heated and stirred at 40 ° C. for 15 minutes to dissolve the monomer. Thereafter, 3,3 ′, 4,4′-tetracarboxylic acid biphenyl dianhydride (monomer A2; low purity) (100 mol%) was added, and the mixture was further stirred for 30 minutes to give a liquid having a viscosity of 480 Pa · s (25 ° C.). A polyimide precursor resin composition (polyamic acid solution) was obtained.

<Examples 1-3>
A 6-inch silicon wafer (625 μm thick, resistivity 4 Ωcm, p-type (impurity boron)) is spin-coated with a solution obtained by further diluting the polyamic acid solution produced in Reference Examples 1 to 3, and is subjected to 120 ° C., 150 ° C., 200 ° C. A polyimide film having a thickness of 0.75 μm was formed by heat treatment at 10 ° C. and 250 ° C. for 10 minutes each and 330 ° C. for 5 minutes. Table 1 shows the results of CV measurement using the obtained polyimide film and the composition of the reference example used.

<Example 4>
In the same manner as in Example 1, a solution obtained by further diluting the polyamic acid solution prepared in Reference Example 4 was spin-coated on a 6-inch silicon wafer, and each of them was subjected to 360 minutes at 120 ° C., 150 ° C., 200 ° C., and 250 ° C. for 360 minutes. A heat treatment was performed at 5 ° C. for 5 minutes to form a polyimide film having a thickness of 0.75 μm. The results are shown in Table 1.

<Example 5>
In the same manner as in Example 1, a solution obtained by further diluting the polyimide solution produced in Reference Example 5 was spin-coated on a 6-inch silicon wafer, and each of these was 300 minutes at 120 ° C., 150 ° C., 200 ° C. and 250 ° C. A heat treatment was performed at 5 ° C. for 5 minutes to form a polyimide film having a thickness of 0.75 μm. The results are shown in Table 1.

<Examples 6 and 7, Comparative Examples 1, 2, and 3>
Similarly to Example 1, a solution obtained by further diluting the polyamic acid solution produced in Reference Examples 6, 7, 8, 9, and 10 was spin-coated on a 6-inch silicon wafer, and 120 ° C., 150 ° C., 200 ° C., Heat treatment was performed at 250 ° C. for 10 minutes each and at 450 ° C. for 5 minutes to form a polyimide film having a thickness of 0.75 μm. The results are shown in Table 1.

  The polyimide of this invention is used suitably for electronic device uses, such as a board | substrate of a flexible device, for example.

1 Silicon wafer 2 Polyimide film 3 Mercury electrode 4 DC power supply 5 AC power supply

Claims (1)

  When a capacitance-voltage measurement is performed on a laminate in which a polyimide film is formed with a thick film of 0.75 μm on a silicon wafer having a resistance value of 4 Ωcm, the maximum gradient is 0.005 / V or more. Polyimide (however, the maximum gradient is the maximum DC voltage applied to the polyimide film with respect to the silicon wafer between the minimum voltage V1 and the maximum voltage V2, the forward scan from the minimum voltage V1 to the maximum voltage V2, and the maximum Capacitance measurement is performed at a measurement frequency of 2.5 kHz while negative direction scanning from voltage V2 to minimum voltage V1 is performed at a scanning speed of 0.25 V / sec. It means the maximum absolute value of the gradient in the voltage curve, where the minimum voltage V1 is a voltage at which the capacity of only the polyimide film is observed, and the normalized capacity The voltage curve is normalized with the capacity at the lowest voltage V1 being 1.)