KR20170092935A - Polyimide film with improved thermal stability - Google Patents

Abstract

The present invention relates to a transparent polyimide film. To this end, metal catalysts such as Grubbs and azobisisobutyronitrile (AIBN) are inserted into polyamic acid having low coefficient of thermal expansion (CTE), and then the obtained product is treated with heat for imidization. According to the present invention, the transmittance of the transparent polyimide film is greater than or equal to 86.5%, the coefficient of thermal expansion is less than 15, and the strength is greater than or equal to 160 MPa. The maximum cycle number of undamaged transparent polyimide films after repetitively bent for an elasticity test is greater than or equal to 10,000.

Description

TECHNICAL FIELD [0001] The present invention relates to a polyimide film having excellent thermal properties,

The present invention relates to a transparent polyimide film having improved flexibility, which comprises introducing an ether group into a side chain to improve transparency and colorlessness, minimizing deterioration of heat resistance and mechanical properties, and a transparent polyimide film having excellent physical properties and a method for producing the same will be.

Aromatic polyimides are widely used as electrical / electronic materials in aerospace / space fields, circuit boards, liquid crystal alignment films and the like due to their excellent heat resistance, chemical resistance, mechanical properties, electrical properties and dimensional stability. However, despite its many advantages, it has limited use in the field of transparent displays due to its unique dark brown color.

 Polyimide's properties to be applied to transparent flexible displays include YI, transparency, heat resistance, flexibility, and low CTE. In general, the reason why the aromatic polyimide is dark brown is that the π electrons of benzene present in the imide main chain absorb visible light due to the charge transfer complex (CTC) generated by the interchain bonds Because.

The colorless transparent polyimide film is prepared by thermally and chemically imidizing polyamic acid, which is synthesized in an organic solvent, by casting it on a glass substrate using various dianhydrides and diamines as raw materials. In order to replace the glass substrate, the transparent polyimide film should be colorless and transparent, exhibiting high heat resistance, chemical resistance and low thermal expansion coefficient.

Korean Patent Publication No. 102004-0108808

The conventional technique is colorless and transparent, has good heat resistance and chemical resistance, but has a high thermal expansion coefficient and can not be used in a high temperature process. Increasing the crystallinity of the polymer can lower the coefficient of thermal expansion. However, in general, when such a method is used, a charge transfer complex of π electrons in the imide chain occurs, There is a problem in producing a polyimide film having a low coefficient of thermal expansion.

The present invention relates to a colorless transparent polyimide film having a low thermal expansion coefficient by lowering a high thermal expansion coefficient, which is a problem of conventional colorless transparent polyimide film production technology through a crosslinking reaction, and a process for producing the same.

The solvent of the polyimide film was dimethylacetamide (DMAc), n-methylpyrrolidone (NMP), bicyclo (2.2.2) octo-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTDA) and diamine, and metal catalysts such as Grubbs and AIBN are used as catalysts. BTDA and diamine are added to DMAc to prepare polyamic acid, and the metal catalyst is added to the prepared polyamic acid, followed by heat treatment to imidize the polyamic acid. As the imidization proceeds, BTDA double bonds are broken by heat, and the metathesis reaction causes polyimide intergranular crosslinking.

Grubbs, AIBN is used as a catalyst to increase the degree of crosslinking because crosslinking does not generally occur when only solvent, dianhydride and diamine are added.

The crosslinked polyimide film exhibits a colorless transparent characteristic with a low coefficient of thermal expansion because the bonding strength between chains is strengthened.

According to a preferred embodiment of the present invention, a diamine (0.019 mole) is placed in a 100 ml three-necked flask and thoroughly dissolved in 50 g (53.56 ml) of solvent DMAc for 1 hour to completely dissolve. Then, 4.7156 g (0.0190 mol) Lt; / RTI > The inside of the reactor was replaced with nitrogen and reacted at 0 ° C for 1 hour and at room temperature for 24 hours to prepare a polyamic acid solution having a solid content of 20 wt%

After the metal catalyst such as Grubbs or AIBN is added to the prepared polyamic acid , the polyamic acid solution is cast on a glass plate, and then the solvent is slowly removed in a vacuum oven at 50 ° C for 1 hour and at 80 ° C for 1 hour. And heat treatment is performed for 30 minutes at 120, 150, 180, 220, and 250 캜 in a nitrogen atmosphere for a reversed imidization reaction, thereby providing a thermally and mechanically enhanced polyimide film.

The cross-linking between the polyimide chains occurs through the metathesis reaction described below.

The obtained polyimide film has a transparency of 86.5% or more, a coefficient of thermal expansion (CTE) of less than 15, a strength of 160 MPa or more, and a maximum number of cycles of 10,000 or more after repeated bending, .

The present invention is characterized in that the film has a permeability of at least 86.5%, a coefficient of thermal expansion (CTE) of less than 15, a strength of at least 160 MPa, and a maximum number of cycles of not less than 10,000, And the film is excellent in transparency and is suitable for use as a film applicable to a transparent display.

When the film has a transmittance of less than 86.5%, a coefficient of thermal expansion (CTE) of 15 or more, a strength of less than 160 MPa, and a maximum number of cycles less than 10,000 after repeated bending under the flexibility standard, transparency is poor and thermal / mechanical stability is poor. .

Hereinafter, the present invention will be described in detail.

Basically polyimide is prepared by reacting dianhydride and diamine in a molar ratio of 1: 1 in a solvent of a polar solvent (DMAc, DMF, NMP, etc.).

The solvent of the polyimide film was dimethylacetamide (DMAc), n-methylpyrrolidone (NMP), bicyclo (2.2.2) octo-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTDA) and diamine, and metal catalysts such as Grubbs and AIBN are used as catalysts. BTDA and diamine are added to DMAc to prepare polyamic acid, and the metal catalyst is added to the prepared polyamic acid, followed by heat treatment to imidize the polyamic acid. As the imidization proceeds, BTDA double bonds are broken by heat, and the metathesis reaction causes polyimide intergranular crosslinking.

Grubbs, AIBN is used as a catalyst to increase the degree of crosslinking because crosslinking does not generally occur when only solvent, dianhydride and diamine are added.

The crosslinked polyimide film exhibits a colorless transparent characteristic with a low coefficient of thermal expansion because the bonding strength between chains is strengthened.

The cross-linking between the polyimide chains occurs through the metathesis reaction described below.

The above polyimide can be obtained by a dehydration condensation reaction between an aromatic tetracarboxylic acid dianhydride and an aromatic diamine.

The aromatic tetracarboxylic acid dianhydride used to obtain the polyimide may be selected from the group consisting of butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 2,3 , 6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 3,4,9,10-phefilenetetra 2, 3, 4, 4-biphenyltetracarboxylic dianhydride, 2, 3, 6, 7-anthracenetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, , 2 ', 3' -biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2', 3,3'-benzophenonetracarboxylic acid 2 (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane, Bis (3, 4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis Bis (3,4-dicarboxyphenyl) 1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) Dicarboxyphenyl) ethane dianhydride, bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1,1,1,3,3,3-hexachloropropane dianhydride, 1,1- Phenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 4,4'- (p- phenylenedioxy) diphthalic dianhydride, 4,4'- Phthalic acid dianhydride, 4,4'-diphenylsulfododoxybis (4-phthalic acid) dianhydride, 4,4'-diphenylsulfododoxybis (4-phthalic acid) dianhydride, methylenebis- (4-phenyleneoxy-4-phthalic acid) dianhydride, isopropylidenebis- (4-phenyleneoxy-4- Phthalic acid) dianhydride, hexafluoroisopropylidene bis- (4-phenyleneoxy-4-phthalic acid) dianhydride, and the like.

The aromatic diamine used for obtaining the polyimide is preferably at least one selected from the group consisting of bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- 2-bis [4- (3-aminophenoxy) phenyl] propane, 2,4-bis - (3-aminophenoxy) phenyl] -1,1,3,3-hexafluoropropane, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenyl ether , 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 1,1-di (p-aminophenyl) Di (p-aminophenyl) propane, and 2, 2-di (p-aminophenyl) -1,1,3,3,3-hexafluoropropane.

In the method of the present invention, it is preferable that the melt viscosity of the polyimide used is in the range of 500 to 100,000 poises at the molding temperature.

When the melt viscosity is less than 500 poise, there is no tensile force due to the elasticity in the molten state, and it is difficult to make uniform contact with the cooling roll. When the melt viscosity exceeds 100,000 poises, the flowability in the molten state is markedly deteriorated , There is a problem that the film is broken when it is extended by the cooling roll.

Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to these examples.

In the present invention, the physical properties of the film were measured by the following method.

1) Colorlessness (YI)

- using a spectrophotometer, the value measured according to ASTM E313

2) Transmittance

- The value measured at 550 nm with a UV spectrometer.

3) Tg

- Tg represents the value at 20 ° C temperature rise rate using Dsc.

4) CTE

- The thermal expansion coefficient at 50 ~ 200 ℃ was measured twice with TMA method according to TMA-Method. The rate of temperature increase was 10 ℃ / min, load of 100mN.

5) Strength, elongation

- Test 10 times using Instron according to ASTM 882D and take the average value.

6) Flexibility

- A film type substrate specimen of 25 mm (width) and 150 mm (length) as a measure of flexibility was mounted on an MIT type Folding Endurance Tester (TMI), and a flexural angle of 135 degrees, Flexibility evaluation criteria were established based on the maximum number of cycles without bending even after flexing at a flexing repetition rate of 50 mm / min. The results are shown in [Table 1].

[Example 1]

A diamine (0.019 mol) was added to a 100 mL three-necked flask, and 50 g (53.56 mL) of the solvent DMAc was thoroughly stirred for 1 hour to completely dissolve. Then, 4.7156 g (0.0190 mol) of BTDA was added in a solid state. The inside of the reactor was replaced with nitrogen and reacted at 0 ° C for 1 hour and at room temperature for 24 hours to prepare a polyamic acid solution having a solid content of 20 wt%

After the metal catalyst such as Grubbs or AIBN is added to the prepared polyamic acid , the polyamic acid solution is cast on a glass plate, and then the solvent is slowly removed in a vacuum oven at 50 ° C for 1 hour and at 80 ° C for 1 hour. Heat treatment was performed for 30 minutes at 120, 150, 180, 220, and 250 ℃ in a nitrogen atmosphere for the reversed imidization reaction. The polyimide film thus prepared was immersed in distilled water and slowly peeled off from the glass plate.

.

[Comparative Example 1]

The diamine (0.019 mol) was added to a 100 mL three-necked flask and thoroughly stirred in 50 g (53.56 mL) of the solvent DMAc for 1 hour to completely dissolve. Then, 5.6029 g (0.0190 mol) of BTDA was added in a solid state. The inside of the reactor was replaced with nitrogen and reacted at 0 ° C for 1 hour and at room temperature for 24 hours to prepare a polyamic acid solution having a solid content of 20 wt%

At this time, only a common solvent, dianhydride and diamine are added without using a metal catalyst, and the polyimide film thereafter is prepared in the same manner as in Example 1.

The measurement results are shown in [Table 1] as follows.

Film type Permeability (%) CTE (ppm) Strength (MPa) flexibility Example 88.8 12 175 ○ Comparative Example 83.4 28 75 △

As shown in Table 1, the film according to the present invention has a film permeability of at least 86.5%, a coefficient of thermal expansion (CTE) of less than 15, a strength of at least 160 MPa, a maximum number of cycles of 10,000 cycles Or more.

Claims (4)

A metal catalyst is prepared by reacting dianhydride and diamine in a molar ratio of 1: 1 in a polar solvent and having a low coefficient of thermal expansion of the polyimide. The metal catalyst is then added to the polyamic acid, Wherein the polyimide film has a low thermal expansion coefficient by imidizing and cross-linking, and comprises polyimide.
The method according to claim 1,
Wherein the cross-linking between chains has a low thermal expansion coefficient represented by the following reaction formula (1) and contains polyimide.

Reaction formula (1)
The method according to claim 1,
Wherein the film has a coefficient of transparency of at least 86.5%, a coefficient of thermal expansion (CTE) of less than 15, a strength of at least 160 MPa, and a maximum number of cycles of 10,000 or more after repeated bending, ≪ / RTI >
A polyimide film produced by the method according to any one of claims 1 to 3.