KR20190053794A - Polyamic Acid Composition For Coating Conductor - Google Patents

Abstract

The present invention relates to a polyamic acid composition for coating a conductor, which comprises the polyamic acid and an organic solvent, wherein the polyamic acid is formed by reaction of a dianhydride monomer and a diamine monomer, and comprises less than 10 wt% of a polymer having low molecular weight which has 6,000 g/mole or less of the molecular weight with respect to the total polyamic acid. In addition, the equivalent ratio of the diamine monomer to the dianhydride monomer is 0.960 to 0.990 or 1.040 to 1.075.

Description

Technical Field [0001] The present invention relates to a polyamic acid composition coating composition,

The present invention relates to a polyamic acid composition for coating a conductor.

The insulating layer (insulating coating) covering the conductor is required to have excellent insulating property, adhesion to a conductor, heat resistance, mechanical strength, and the like.

Further, in an electric device having a high applied voltage, for example, a motor used at a high voltage, a high voltage is applied to an insulated electric wire constituting the electric device, and a partial discharge (corona discharge) is likely to occur on the insulated coated surface.

The occurrence of corona discharge may cause local temperature rise or ozone or ion generation, resulting in deterioration of the insulation coating of the insulated wire, leading to early breakdown of the insulation and shortening the service life of the electrical equipment .

It is known that the insulated wire used at a high voltage is required to have an improved corona discharge initiation voltage for the above reasons. For this purpose, it is known to lower the dielectric constant of the insulating layer.

Examples of the resin forming the insulating layer include polyimide resin, polyamideimide resin, and polyesterimide resin.

Generally, polyimide resin refers to a high heat-resistant resin prepared by preparing a polyamic acid derivative by combining an aromatic dianhydride with an aromatic diamine or an aromatic diisocyanate in solution, and then dehydrating and dehydrating the polymer at a high temperature.

The polyimide resin is superior in heat resistance and relatively low in dielectric constant, and is excellent in use as a material for coating a conductor.

On the other hand, however, since the polyimide resin has a rigid structure, it is also disadvantageous to be used as a conductor coating because of low elongation at break and flexibility.

For example, in a coil used for a motor, there is a case where the insulated electric wire is largely deformed by, for example, inserting a coil into the slot after winding the insulated electric wire to form a coil in order to increase the drop rate. At this time, if the flexibility of the insulating layer is low, the insulating coating tends to be damaged at the time of processing, resulting in poor electrical characteristics or cracking of the insulating coating.

On the other hand, when a polyimide resin is produced by reacting diamines and dianhydrides having a flexible structure in order to improve such flexibility, heat resistance is lowered compared with diamines having a flexible structure or polyimide resins containing no dianhydride there is a problem.

Therefore, there is a high need for a technique capable of fundamentally solving such problems.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The polyimic acid composition for coating a conductor according to the present invention contains less than 10% by weight of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less with respect to the entire polyamic acid, and an equivalent ratio of a diamine monomer to a dianhydride monomer contained in the polyamic acid To 0.960 to 0.990 or 1.040 to 1.075, the flexibility of the coating can be improved without lowering the heat resistance of the insulating coating prepared by imidizing the polyamic acid.

In order to accomplish the above object, the present invention provides a polyamic acid composition,

An insulating composition for covering a conductor comprising a polyamic acid and an organic solvent,

The polyamic acid is formed by the reaction of a dianhydride monomer with a dianhydride monomer,

And less than 10% by weight of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less based on the entire polyamic acid,

The equivalent ratio of the diamine monomer to the dianhydride monomer is 0.960 to 0.990 or 1.040 to 1.075.

At this time, the diamine monomer may include at least 80 mol% of a soft diamine monomer containing two or more benzene rings in the molecular structure with respect to the entire diamine monomer.

More specifically, the soft diamine monomer is selected from the group consisting of 4,4'-oxydianiline (ODA) and 4,4'-methylenedianiline (MDA) Or more.

The dianhydride monomer may be at least one selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride ), And oxydiphthalic anhydride (ODPA). [0033] The term " anionic surfactant "

On the other hand, the polyamic acid may have a polydispersity index of 1.57 to 1.82.

The viscosity of the polyamic acid composition may be between 30 and 150 poise.

The content of the polyamic acid may be 10 to 40% by weight.

The present invention also relates to a process for preparing said polyamic acid composition,

An organic solvent is added,

Adding at least one of a dianhydride monomer and a diamine monomer to the organic solvent to dissolve the organic solvent,

At least one of a dianhydride monomer and a diamine monomer is added to the organic solvent at least twice,

There is provided a method for producing a polyamic acid composition by stirring a composition comprising the organic solvent, a dianhydride monomer and a diamine monomer.

Specifically, at least one of the dianhydride monomer and the diamine monomer may be added at least twice or more and 10 times or less.

The present invention also provides a polyimide coating formed by applying and imidizing the polyamic acid composition onto a conductor surface.

Also, the thermal expansion coefficient (CTE) of the coating may be 20 to 40 ppm / 캜.

Also, the tan 隆 of the coating may be 280 to 420 캜.

The present invention also provides a wire comprising a polyimide coating prepared by applying and imidizing the polyamic acid composition onto a wire surface.

Further, there is provided an electronic device including the electric wire.

As described above, the polyamic acid composition according to the present invention contains less than 10% by weight of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less based on the total amount of the polyamic acid, and the amount of the diamine monomer relative to the dianhydride monomer contained in the polyamic acid By adjusting the equivalence ratio to be 0.960 to 0.990 or 1.040 to 1.075, the flexibility of the coating can be improved without lowering the heat resistance of the insulating coating prepared by imidizing the polyamic acid.

Further, the present invention can provide a highly reliable insulated electric wire which has excellent heat resistance and has no defect in an insulating coating.

Hereinafter, the present invention will be described in more detail.

The polyamic acid composition according to the present invention is an insulating composition for covering a conductor comprising a polyamic acid and an organic solvent, wherein the polyamic acid is formed by reaction of a dianhydride monomer and a diamine monomer, and has a molecular weight of 6,000 g / mole of the low molecular weight polymer, and the equivalent ratio of the diamine monomer to the dianhydride monomer is 0.960 to 0.990 or 1.040 to 1.075.

The polyamic acid composition can be prepared by polymerizing a dianhydride monomer and a diamine monomer in an organic solvent.

The organic solvent may be an amide-based solvent, and in particular, it may be an aprotic polar solvent. The organic solvent may be selected from the group consisting of N, N'-dimethylformamide (DMF), N, N'-dimethylacetamide, N-methylpyrrolidone (NMP), gammabutyrolactone (Diglyme), and the like. However, it is not limited thereto, and they may be used singly or in combination of two or more as necessary.

The dianhydride monomer and the diamine monomer may be added in the form of powder, lump and solution. In the initial stage of the reaction, the dianhydride monomer and the diamine monomer are added in powder form to proceed the reaction. .

For example, the dianhydride monomer and the diamine monomer may be added in powder form to conduct the reaction, and dianhydride may be added in the form of a solution to allow the reaction until the viscosity of the polyarylate composition reaches a certain range.

In the present invention, in order to contain less than 10% by weight of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less with respect to the entire polyamic acid, at least one of the dianhydride monomer and the diamine monomer may be dividedly introduced two or more times .

Specifically, when the polyamic acid composition contains 10% by weight or more of a low molecular weight polymer having a weight-average molecular weight of 6,000 g / mole or less, the polyimide coating formed by applying and imidizing the polyamic acid composition on the surface of the conductor may have protrusions or pin holes It is undesirable because appearance defects may occur.

More specifically, the polyamic acid composition may include not more than 8.1% by weight, particularly not more than 7.5% by weight, of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less based on the entire polyamic acid.

Meanwhile, in order to control the content of the low molecular weight polymer having a molecular weight of 6,000 g / mole or less with respect to the entire polyamic acid, the equivalent ratio of the diamine monomer to the dianhydride monomer may be controlled to be 0.960 to 0.990 or 1.040 to 1.075.

At this time, if the equivalent ratio of the polyamic acid is out of the above range, the content of the low molecular weight polymer may increase or the molecular weight distribution of the polyamic acid may increase, which is not preferable.

In one specific example, the molecular weight of the polyamic acid may range from 10,000 to 40,000 g / mole.

In addition, the polyamic acid may have a polydispersity index of 1.57 to 1.82, and more specifically 1.65 to 1.75.

When the molecular weight distribution diagram satisfies this range, there is an advantage that the physical property variation of the coating is reduced and the coating process for the conductor stably proceeds. On the other hand, when the molecular weight distribution of the polyamic acid exceeds or falls below the above range, And the variation of the physical properties of the coating increases, so that the reliability may be lowered.

The diamine monomers according to the present invention are, for example, 4,4-oxydianiline, 3,4-oxydianiline, 4,4-methylenedianiline, paraphenylenediamine, 1,3- At least one member selected from the group consisting of benzene (TPE-R), 1,3-bis (3-aminophenoxy) benzene, 4,4'-diaminophenylsulfide and 3,4- . ≪ / RTI >

At this time, the polyamic acid composition may contain at least 80 mol% of a soft diamine monomer containing two or more benzene rings in the molecular structure with respect to the entire diamine monomer.

In detail, the polyamic acid composition may contain at least 85 mol% of a soft diamine monomer containing two or more benzene rings in the molecular structure with respect to the entire diamine monomer.

More specifically, the polyamic acid composition may contain at least 90 mol% of a soft diamine monomer containing two or more benzene rings in the molecular structure with respect to the entire diamine monomer.

That is, in the present invention, by including the soft diamine monomer having a flexible structure in the molecular structure, it is possible to improve the flexibility of the polyimide insulation coating fabricated using the polyamic acid composition, It is possible to solve the problem that cracking of the insulation coating occurs.

In one specific example, the soft diamine monomer may have a structure containing two or more benzene rings in the molecular structure, for example, the soft diamine monomer may be 4,4'-oxydianiline (4,4'- oxydianiline (ODA), and 4,4'-methylenedianiline (MDA). However, the present invention is not limited thereto.

On the other hand, the dianhydride monomer may be selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride (BTDA) And at least one monomer selected from the group consisting of oxydiphthalic anhydride (ODPA).

In addition, the viscosity of the polyamic acid composition may be 30 to 150 poise, and the content of polyamic acid may be 10 to 40 wt% based on the entire polyamic acid composition.

According to another aspect of the present invention, there is provided a method for producing the polyamic acid composition, which comprises: introducing an organic solvent, adding at least one of a dianhydride monomer and a diamine monomer to the organic solvent to dissolve the dianhydride monomer, Wherein at least one of the organic monomers, the dianhydride monomers and the diamine monomers is added to the polyamic acid composition in an amount of at least two times, and the polymerization is stirred to polymerize the composition.

As described above, the molecular weight distribution of the polyamic acid can be kept low through the step of separately feeding dianhydride monomer and diamine monomer.

Specifically, at least one of the dianhydride monomer and the diamine monomer may be added at least twice or more and 10 times or less.

The present invention also provides a polyimide coating formed by applying and imidizing the polyamic acid composition onto a conductor surface.

The coating may have a thermal expansion coefficient (CTE) of 20 to 40 ppm / [deg.] C, and the coating of the composition may have a tan? Of 280 [deg.] C or more as measured using a DS9 TD9000 Tangent Delta Tester, To 420 < 0 > C.

On the other hand, in order to indirectly measure the elongation and the glass transition temperature of the coating, the elongation of the film may be 20 to 100% when a 25 탆 thick polyimide film having the same composition as the coating is prepared, The film may have a glass transition temperature of 300 ° C or higher, and such mechanical properties and heat resistance can be similarly exhibited in coatings coated on such wires.

Hereinafter, the present invention will be further described with reference to Examples of the present invention, but the scope of the present invention is not limited thereto.

Preparation of polyamic acid composition

≪ Example 1 >

A 1 L reactor was charged with 850 g of dimethylformamide as a solvent in a nitrogen atmosphere.

After the temperature was set to 25 占 폚, 72.82 g (0.36 mol) of 4,4'-ODA as a diamine monomer was added to dissolve and 77.18 g (0.35 mol) of PMDA as dianhydride monomer was added thereto at the intervals of 30 minutes And then the polyamic acid was polymerized. At this time, the equivalent ratio of the diamine monomer to the dianhydride monomer was 0.973.

A polyamic acid solution containing 6.7 wt% of a low molecular weight polymer having a weight average molecular weight of 16,000 g / mole, a molecular weight distribution (Mw / Mn) of 1.73 and a molecular weight of 6,000 g / mole or less, as measured by GPC (Agilent Technology 1260 infinity 2) A composition was prepared.

≪ Example 2 >

52.56 g (0.26 mol) of 4,4'-ODA and 17.35 g (0.09 mol) of 4,4'-MDA were added as diamine monomers and 4,4'-ODA was added to the entire diamine monomer (Mw / Mn) of 1.69, a molecular weight of 6,000 g / mole or less as measured by GPC and having a weight average molecular weight of 16,500 g / mole, a molecular weight distribution The same polyamic acid composition as in Example 1 was prepared, except that 7.1 wt% of the polymer was included.

≪ Example 3 >

35.04 g (0.175 mol) of 4,4'-ODA and 34.7 g (0.175 mol) of 4,4'-MDA were added as diamine monomers and 4,4'-ODA was added to the entire diamine monomer (Mw / Mn) of 1.71, a molecular weight of 6,000 g / mole or less as measured by GPC and having a weight average molecular weight of 17,000 g / mole, a molecular weight distribution The same polyamic acid composition as in Example 1 was prepared, except that 6.3 wt% of the polymer was included.

<Example 4>

69.4 g (0.35 mol) of 4,4'-MDA as a diamine monomer was charged and, as shown in the following Table 1, 100 mol% of 4,4'-MDA was contained and the weight average molecular weight measured by GPC was 17,300 g / mole, a molecular weight distribution (Mw / Mn) of 1.62, and 6.2 wt% of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less.

&Lt; Example 5 >

The molecular weight distribution (Mw / Mn) was 1.61, the molecular weight was 6,000 g / mole, and the molecular weight distribution (Mw / Mn) The polyamic acid composition of Example 1 was prepared in the same manner as in Example 1, except that the low molecular weight polymer was contained in an amount of 7.8% by weight.

&Lt; Example 6 >

The molecular weight distribution (Mw / Mn) was 1.82, the molecular weight was 6,000 g / mole, the weight average molecular weight (Mw / Mn) The polyamic acid composition of Example 1 was prepared in the same manner as in Example 1, except that the low molecular weight polymer was contained in an amount of 7.9% by weight.

&Lt; Example 7 >

54.56 g (0.27 mol) of 4,4'-ODA and 18.01 g (0.09 mol) of 4,4'-MDA were charged as diamine monomers and the equivalent ratio of the diamine monomer to the dianhydride monomer was 0.977 as shown in Table 1 below. , 75% by mole of 4,4'-ODA and 25% by mole of 4,4'-MDA relative to the entire diamine monomer, a weight average molecular weight of 27,000 g / mole as measured by GPC, a molecular weight distribution (Mw / Mn) of 1.63 and 8.1 wt% of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less was prepared.

&Lt; Comparative Example 1 &

73.56 g (0.37 mol) of 4,4'-ODA as a diamine monomer was charged and 100.4 mol% of 4,4'-ODA was contained and 76.83 g (0.35 mol) of PMDA was added as dianhydride monomer as shown in Table 1 (Mw / Mn) of 1.56 and a molecular weight of 6,000 g / mole or less as measured by GPC and having a weight average molecular weight of 9,600 g / mole, a molecular weight distribution The same polyamic acid composition as in Example 1 was prepared, except that the polymer was included in an amount of 5.6 wt%.

&Lt; Comparative Example 2 &

72.06 g (0.36 mol) of 4,4'-ODA as a diamine monomer was charged and 100% by mole of 4,4'-ODA was contained and 77.94 g (0.355 mol) of PMDA was added as dianhydride monomer as shown in Table 1 , The equivalent ratio of the diamine monomer to the dianhydride monomer was adjusted to be 0.993, and the molecular weight distribution (Mw / Mn) of 1.83 and the molecular weight of 6,000 g / mole or less The same polyamic acid composition as in Example 1 was prepared, except that 8.2 wt% of the polymer was included.

&Lt; Comparative Example 3 &

The dianhydride monomer was added once without being added in portions, and the resultant mixture was added once, and the weight average molecular weight measured by GPC was 18,000 g / mole, the molecular weight distribution (Mw / Mn) was 2.54 and the molecular weight was 6,000 g / mole or less The same polyamic acid composition as in Example 1 was prepared, except that the low molecular weight polymer was contained in an amount of 12.7 wt%.

Diamine monomer (mol%) Equivalence ratio Molecular Weight
Distribution chart Low molecular weight
Polymer
content
(weight%) 4,4'-ODA 4,4`-MDA Example 1 100 0 0.973 1.73 6.7 Example 2 75 25 0.973 1.69 7.1 Example 3 50 50 0.973 1.71 6.3 Example 4 0 100 0.973 1.62 6.2 Example 5 100 0 0.964 1.61 7.8 Example 6 100 0 0.989 1.82 7.9 Example 7 25 75 0.977 1.63 8.1 Comparative Example 1 100 0 0.954 1.56 5.6 Comparative Example 2 100 0 0.993 1.83 8.2 Comparative Example 3 100 0 0.973 2.54 12.7

Experimental Example 1: Evaluation of viscosity

The polyamic acid composition prepared in Example 1 to Example 7 and the polyamic acid composition prepared in Comparative Example 1 to Comparative Example 3 were each mixed so that the solid content was 15% The viscosity was measured using a field viscometer. The viscosity retention was measured after storage at room temperature for 30 days. The results are shown in Table 2 below.

Viscosity (poise) Storage stability
(%) Example 1 60 87 Example 2 60 85 Example 3 65 86 Example 4 70 85 Example 5 55 84 Example 6 80 81 Example 7 60 85 Comparative Example 1 20 85 Comparative Example 2 160 50 Comparative Example 3 70 60

As shown in Table 2, in the case of the polyamic acids of Examples 1 to 7 in which the equivalence ratios were controlled within the range of the present invention, the polyamic acid compositions of Comparative Examples 1 and 2 in which the equivalence ratio was less than or more than the range of the present invention, The polyamic acid composition of Comparative Example 3 in which dianhydride monomers or diamine monomers were not added in portions was found to have a viscosity range of 30 to 150 poise suitable for coating with electric wire coating and superior in storage stability to 80% or more.

Preparation of polyimide coating

&Lt; Example 8 >

The polyamic acid composition prepared in Example 1 was coated on a copper wire having a diameter of 1 mm eight times, dried and cured to produce a wire including a polyimide coating having a thickness of 25 탆.

&Lt; Examples 9 to 14 and Comparative Examples 4 to 6 >

Except that the polyamic acid compositions prepared in Examples 2 to 7 and Comparative Examples 1 to 3 were used instead of the polyamic acid compositions of Example 1 in Example 8, wires containing polyimide coatings were prepared in the same manner as in Example 8 .

Experimental Example 2: Evaluation of defect

With respect to the coatings of the wires manufactured in each of Examples 8 to 14 and Comparative Examples 4 to 6, a wire having a length of 10 m was run in a winder provided with a defect detector, The number of pinholes was measured and the results are shown in Table 3 below.

The electric wire coatings prepared in each of Examples 8 to 14 and Comparative Examples 4 to 6 were evaluated for cracking of the polyimide coating and the copper wire at the time of 20% And the results are shown in Table 3 below.

Experimental Example 3: Evaluation of heat resistance - tan? Value

Using the Dynamic Mechanical Analysis (DMA Q800) manufactured by TA Instruments Co., Ltd., the sheathing of each of the wires prepared in Examples 8 to 14 and Comparative Examples 4 to 6 was measured, and the loss elastic modulus and storage The elastic modulus was measured and the value of tan? Was calculated. The results are shown in Table 3 below.

Pinhole
(Count) 20%
Tensile
crack flaw
(Count) tanδ
(° C) Example 8 0 none 0 300 Example 9 0 none 0 300 Example 10 0 none 0 300 Example 11 0 none 0 300 Example 12 0 none 0 290 Example 13 0 none 0 310 Example 14 0 none 0 300 Comparative Example 4 10 Occur 3 260 Comparative Example 5 0 none 10 300 Comparative Example 6 3 Occur 0 270

First, it can be confirmed that the number of pinholes and the number of defects generated on the coated surface of the wires of Examples 8 to 14 were significantly smaller than those of the wires of Comparative Examples 4 to 6. In the case of 20% It can be confirmed that no crack was generated at the time of pulling.

On the other hand, in the case of the wires of Examples 8 to 14, since the tan? Value is higher than those of Comparative Examples 4 and 6, it can be confirmed that the heat resistance is excellent.

In the case of Comparative Example 5 using the polyamic acid composition adjusted to have an equivalent ratio of the diamine monomer to the dianhydride monomer of 0.993, it was confirmed that the tan δ value was high, but more defects were found compared with Examples 8 to 14 Can be confirmed.

In the case of Comparative Example 6 in which the dianhydride monomer was not added and the polyamic acid composition containing 12.7% of the low molecular weight polymer having a molecular weight of 6,000 g / mole or less and the molecular weight distribution of 2.54 was used, And cracks were observed at 20% tensile strength.

Production of polyimide film

&Lt; Example 15 >

The polyamic acid composition prepared in Example 1 was bubbled through a high-speed rotation of 1,500 rpm or more. Thereafter, the defoamed polyamic acid composition was applied to the glass substrate using a spin coater. Thereafter, the resultant was dried in a nitrogen atmosphere at 120 ° C. for 30 minutes, heated to 450 ° C. at a rate of 2 ° C./min, heat-treated at 450 ° C. for 60 minutes, cooled to 30 ° C. at a rate of 2 ° C./min A polyimide film was obtained. Thereafter, the polyimide film was peeled off from the glass substrate by dipping in distilled water. The thickness of the produced polyimide film was 25 탆.

&Lt; Examples 16 to 21, Comparative Examples 7 to 9 >

A polyimide film was prepared in the same manner as in Example 15, except that the polyamic acid compositions prepared in Examples 2 to 7 and Comparative Examples 1 to 3 were used instead of the polyamic acid compositions of Example 1, respectively.

Experimental Example 4: Evaluation of mechanical properties

The elongation of each of the polyimide films prepared in Examples 16 to 21 and Comparative Examples 7 to 9 was measured according to ASTM D882 and the results are shown in Table 4 Respectively.

Experimental Example 5: Evaluation of heat resistance-Glass transition temperature

The polyimide films prepared in Examples 16 to 21 and Comparative Examples 7 to 9 were subjected to Dynamic Mechanical Analysis (TA Instruments, Inc.) for measuring glass transition temperature (Tg) DMA Q800). The results are shown in Table 4 below.

Shinto (%) Tg
(° C) Example 15 50 400 Example 16 57 390 Example 17 58 380 Example 18 60 360 Example 19 45 400 Example 20 80 410 Example 21 70 370 Comparative Example 7 30 290 Comparative Example 8 35 410 Comparative Example 9 30 400

First, as shown in Table 4, in the case of the polyimide films of Examples 16 to 21, the elongation is higher than that of the polyimide films of Comparative Examples 7 to 9.

In addition, in the case of the polyimide films of Examples 16 to 21, since the glass transition temperature is higher than that of the polyimide films of Comparative Examples 7 and 9, it can be confirmed that the heat resistance is excellent.

From these results, it can be confirmed that the coating according to the present invention has excellent elongation and glass transition temperature, and furthermore, excellent mechanical properties and heat resistance.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention.

Claims (14)

An insulating composition for covering a conductor comprising a polyamic acid and an organic solvent,
The polyamic acid is formed by the reaction of a dianhydride monomer with a dianhydride monomer,
And less than 10% by weight of a low molecular weight polymer having a molecular weight of 6,000 g / mole or less based on the entire polyamic acid,
Wherein the equivalent ratio of the diamine monomer to the dianhydride monomer is 0.960 to 0.990 or 1.040 to 1.075. The method according to claim 1,
And at least 80 mol% of a soft diamine monomer containing two or more benzene rings in a molecular structure with respect to the entire diamine monomer. 3. The method of claim 2,
The soft diamine monomer may be at least one selected from the group consisting of 4,4'-oxydianiline (ODA) and 4,4'-methylenedianiline (MDA) Polyamic acid composition. The method according to claim 1,
The dianhydride monomer is selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride (BTDA), and Wherein the polyamic acid composition comprises at least one monomer selected from the group consisting of oxydiphthalic anhydride (ODPA). The method according to claim 1,
Wherein the polyamic acid has a molecular weight distribution index (Polydispersity Index) of from 1.57 to 1.82. The method according to claim 1,
Wherein the polyamic acid composition has a viscosity of 30 to 150 poise. The method according to claim 1,
Wherein the content of the polyamic acid is 10 to 40% by weight based on the entire polyamic acid composition. A process for preparing a polyamic acid composition according to claim 1,
An organic solvent is added,
Adding at least one of a dianhydride monomer and a diamine monomer to the organic solvent to dissolve the organic solvent,
At least one of a dianhydride monomer and a diamine monomer is added to the organic solvent at least twice,
Wherein the composition comprising the organic solvent, the dianhydride monomer, and the diamine monomer is stirred to polymerize the polyamic acid composition. 9. The method of claim 8,
Wherein at least one of the dianhydride monomer and the diamine monomer is added at least twice to 10 times or less. A polyimide coating formed by coating and imidizing the polyamic acid composition according to claim 1 on a conductor surface. 11. The method of claim 10,
Wherein the coating has a coefficient of thermal expansion (CTE) of 20 to 40 ppm / 占 폚. 11. The method of claim 10,
Wherein the coating has a tan? Of 280 to 420 占 폚. A wire comprising a polyimide coating prepared by applying and imidizing a polyamic acid composition according to claim 1 on a wire surface. An electronic device comprising a wire according to claim 13.