JPH0773857B2 - Method for manufacturing polyimide film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyimide film having excellent heat resistance. More specifically, it relates to a method for producing a polyimide film having excellent heat resistance and mechanical properties by a casting method from a solution of polyamic acid that is a polycondensation product of aromatic tetracarboxylic dianhydride and aromatic diamine. .

[Prior art]

The wholly aromatic polyimide film has excellent heat resistance and mechanical properties, among which pyromellitic dianhydride (1,2,4,5
- benzene tetracarboxylic dianhydride) and diaminodiphenyl ether (4-aminophenyl ether) an aprotic polar solvent polycondensing a polyamic acid obtained by cyclodehydration to the poly -N obtained, N ^- - bis Phenoxyphenyl-pyromellitimide (1) is well known.

Polypyromellitimide does not melt even when heated to 400 ° C. or higher, and there is no solvent that dissolves it. For this reason, a method for producing a polypyromellitimide film is a method in which a solution of a precursor polyamic acid is molded into a film by a casting method and a polyimide film is formed by dehydration cyclization (imidization).

This polyimide film is manufactured by the following steps.

That is, the polyamic acid solution is applied to the surface of a smooth support such as metal or glass, the solvent is removed by heating, and the film is peeled from the support to obtain a self-supporting film. At this stage, the self-supporting film is not completely imidized yet, so that the self-supporting film is subsequently heat-treated at a high temperature or chemically treated to obtain a polyimide film.

By the way, the physical properties of a polymer largely depend not only on its chemical structure but also on its physical state, that is, the state of aggregation of molecules. This can be remarkably observed in crystalline polymers such as nylon, polyethylene terephthalate and polypropylene.

In the case of a film, being crystalline has an advantage in mechanical properties and thermal properties. Polyimide film is no exception,
Many researchers have already investigated the relationship between the crystallinity, mechanical properties, and thermal properties of polyimide films. Poly -N consisting of pyromellitic anhydride and diaminodiphenyl diphenyl ether, N ^- - Bis-phenoxyphenyl - presence of pyro for film benefits imide (1), clear regular molecular aggregation structure of the crystal structure is not observed things Has been suggested. (Isoda et al. J. Polym. Sci. Poly
m.Phys.Ed., 19 1293 (1981), TPRussel ibid 22 110
5 (1983)) According to these studies, formation of a regular molecular aggregate structure is largely dependent on thermal imidization conditions. For example, it is said that a polyamic acid solution is applied to a glass plate, dried under reduced pressure for a long time to form a polyamic acid film, and a regular molecular aggregation structure is generated by a method of further rapidly heating and imidizing at high temperature. However, it must be said that it is extremely difficult and impossible to industrially satisfy these conditions. Because it is very difficult to realize long-term drying under low temperature and reduced pressure in a continuous process. Furthermore, if the solvent contained in the self-supporting film is large at the stage of obtaining the self-supporting film, the solvent abruptly evaporates at the time of thermal imidization in the next step, and the surface property of the film is impaired, so that the temperature is inevitably high. This is because it must be dried. The manufacture of crystalline polyimide films has been extremely difficult to achieve, even though the principles have been demonstrated.

[Object of the Invention]

The present invention is a method for producing a polyimide film by a casting method from a polyamic acid solution, which was obtained as a result of research for industrially obtaining a film having excellent crystallinity and mechanical properties. Composition of the
Polyimide film having a self-supporting film production condition, a regular molecular aggregation structure by a specific combination of thermal imidization conditions, hereinafter referred to as a crystal in the present invention, that is, a crystalline and excellent mechanical property The inventors of the present invention have found that the following can be obtained and have reached the present invention.

[Structure of Invention]

The present invention is a method for producing a polyimide film by a casting method from a solution of polyamic acid which is a polycondensation product of aromatic tetracarboxylic dianhydride and aromatic diamine,
A mixture of the aprotic polar solvent (A) and the aprotic polar solvent in which the solvent of the polyamic acid solution that is the precursor of the polyimide is compatible, and the vapor pressure at 140 ° C. is 550 mmHg or more (B). And (A):
(B) a step of uniformly coating a polyamic acid solution consisting of 70:30 to 97: 3 on a support and drying at a temperature of 140 ° C. or lower to a solvent content of 5 to 40% by weight to obtain a self-supporting film. (1) and the step (2) of peeling the self-supporting film obtained in the step (1) from the support and heating the film at a rate of 30 ° C / min or more to imidize at a temperature of 200 ° C or more. And a method for producing a polyimide film.

The aromatic tetracarboxylic dianhydride used in the present invention is
Examples thereof include pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, 2.2 ', 3,3'-diphenyltetracarboxylic dianhydride, and aromatic diamines such as diaminodiphenyl ether and p-phenylenediamine. A particularly preferred combination in the present invention is a combination of pyromellitic dianhydride and diaminodiphenyl ether from the viewpoint of heat resistance and mechanical strength.

The polycondensation reaction is carried out in an aprotic polar solvent. The aprotic polar solvent is N, N-dimethylformamide (D
MF), N, N-dimethylamide (DMAC), N-methyl-2
-Such as pyrrolidone (NMP). The aprotic polar solvent may be used alone or in combination of two or more.

The non-polar solvent used as a mixture with the aprotic polar solvent is compatible with the above-mentioned aprotic polar solvent at 140 ° C.
The solvent has a vapor pressure of 550 mmHg or more. Particularly preferred are aromatic hydrocarbons such as toluene and xylene. This solvent is added for the purpose of promoting evaporation of the solvent and reducing the solvent content in the step of obtaining a self-supporting film. If the vapor pressure at 140 ° C. is 550 mmHg or less, the evaporation of the solvent does not proceed, and the drying temperature must be raised after all, which is not preferable.

The proportion of the aprotic polar solvent in the mixed solvent is 70% by weight or more and 97% by weight or less. Except for the aprotic polar solvent, there is no other good solvent for the polyamic acid, and if the aprotic polar solvent is less than 70% by weight, the solvent power is reduced and the polyamic acid precipitates, which is not preferable. Further, if the aprotic polar solvent exceeds 97% by weight, the effect of the mixed solvent is not exhibited, which is not preferable. In the step of applying the polyamic acid solution to a support and drying it to obtain a self-supporting film, the drying must be performed at 140 ° C. or lower, more preferably 120 ° C. or lower. The dehydration cyclization reaction from polyamic acid to polyimide proceeds remarkably at about 130 ° C. 150
When imidized at a low temperature of about ℃, because the glass transition temperature of the already imidized portion becomes extremely high at 400 ℃ or more, from the structure of bulky polyamic acid, regular molecular aggregation structure of dense polyimide, that is, crystal Cannot move to structure. Therefore, the drying must be within the range of the above conditions so that the imidization does not proceed at low temperature.

The solvent content of the self-supporting film is 40% by weight or less, 5
Must be at least wt%. If the solvent content of the self-supporting film exceeds 40% by weight, the film strength will decrease and the adhesion to the support will be large, making peeling difficult. To solve this problem, a large amount of a release agent may be added, but the release agent bleeding on the surface often becomes an obstacle depending on the use of the film, and this method is not suitable. Further, if the solvent content is high, the mobility of the molecular chain is increased, which is advantageous for the dehydration cyclization reaction, but the molecular chain flows and is strongly oriented even with a small force. The molecular orientation at this stage is
It is not preferable because the film characteristics are inferior. The solvent content of the self-supporting film should be 40% by weight or less, 5% by weight or more, and more preferably 30% by weight or less and 10% by weight or more in order to promote the dehydration cyclization reaction and prevent molecular orientation. I have to.

Then, the self-supporting film is treated at a high temperature to dehydrate cyclize and imidize. At this time, the heat treatment must be performed at a temperature of 30 ° C./min or more and at an temperature of 200 ° C. or more. As described above, the reason why it has to be imidized at a high temperature is that the glass transition temperature of the imidized portion becomes extremely high.
This is because it takes a high temperature to move to a regular molecular aggregation structure of a dense polyimide, that is, a crystal structure.

However, in the actual process, the rate of temperature rise is a problem, and it has to be brought to a high temperature before the low-temperature imidization proceeds. A crystal structure will not be generated unless the temperature is raised to 200 ° C. or higher in a short time to imidize. For that purpose, the temperature must be raised at a rate of 30 ° C./min or more, and if the temperature is raised at a rate of 30 ° C./min or less, it becomes almost an amorphous structure, which is not preferable.
Further, imidization at a temperature of 200 ° C. or lower is not preferable because no crystal structure is generated and the cyclization rate is insufficient.

Regarding the heat treatment conditions, the temperature must be raised at a rate of 30 ° C./min or more and imidization must be performed at a temperature of 200 ° C. or more. More preferably, the temperature must be raised at a rate of 40 ° C./min or more and imidization should be performed at a temperature of 250 ° C. or more. Although the upper limit of the heat treatment temperature is not limited, it is preferably 450 ° C. or lower in consideration of oxidative deterioration due to oxygen.

〔The invention's effect〕

According to the polyamic acid solution composition of the present invention, the solvent can be removed at a temperature at which the imidization reaction does not proceed. Furthermore, a dense and excellent polyimide film can be produced under the thermal imidization conditions of the present invention.

That is, according to the method of the present invention, a crystalline polyimide film having excellent mechanical properties can be produced by an industrially possible method.

The present invention will be described in detail below with reference to examples. The density is 25 ℃ measured by the density gradient tube method using sodium iodide.
Is the value at. The crystallinity was calculated from the density value by the following formula.

The X-ray diffraction was measured by injecting X-rays perpendicularly to the film surface. The temperature rising rate was calculated based on the data measured by the thermocouple attached to the film.

Example 1 2,000 g of dehydrated and purified DMAC was placed in a 5-liter three-necked flask, and the mixture was vigorously stirred for 10 minutes while flowing nitrogen gas. Next, add 200.24 g (1.000 mol) of diaminodiphenyl ether and stir until a uniform solution is obtained. Then 218.00 g (0.999 mol) of pyromellitic dianhydride are added.
During this time, keep the flask at 20 ° C. When the viscosity of the solution became sufficiently high, DMAC454g and xylene 613g were added to obtain a polyamic acid solution having a resin content of 12.3% by weight and a solvent composition of DMAC / xylene = 80/20.

This polyamic acid solution is applied to a mirror-polished stainless steel plate (300 x 300 x 3t), 90 ° C for 10 minutes, 110 ° C for 10 minutes.
Dry with a hot air circulation dryer for 2 minutes, solvent content 22.7% by weight
I got a self-supporting film.

The self-supporting film was heated from 20 ° C to 250 ° C in 4 minutes and kept at 250 ° C for 3 minutes. The heating rate at this time is 57.5 ° C
/ Min. Further, the temperature was raised to 360 ° C. in about 2 minutes and kept for 25 minutes, and then gradually cooled to 80 ° C. to obtain a polyimide film.
The performance of this polyimide film is shown in Table 2 and the X-ray diffraction pattern is shown in FIG. From the density and the X-ray diffraction pattern, this polyimide film has crystallinity. Xylene 140
The vapor pressure at 0 ° C is about the same for o-xylene, which has the highest boiling point.
It is 675 mmHg.

Comparative Example 1 The polyamic acid solution of Example 1 was used and applied to a stainless steel plate as in Example 1, and the temperature was 110 ° C. for 10 minutes and 150 ° C. for 10 minutes.
After drying for a minute, a self-supporting film having a solvent content of 21.0% by weight was obtained.

The thermal imidization conditions of the film are the same as in Example 1. It can be seen from the X-ray diffraction pattern and the density value of FIG. 2 that this polyimide film is amorphous. Further, as seen from the stress-strain curve in FIG. 4, the elastic modulus and tensile strength are inferior to those of the polyimide film of Example 1.

Comparative Example 2 A polyamic acid solution having a resin content of 11.9% was prepared in the same manner as in Example 1, but the solvent composition was NMP 100%. This polyamic acid solution was applied to a stainless steel plate as in Example 1 and dried at 90 ° C for 60 minutes to obtain a self-supporting film. The solvent content of this self-supporting film was 46.8% by weight.

The self-supporting film was placed in a hot air circulation dryer at 360 ° C, heated to 360 ° C in 15 minutes and kept for 30 minutes. The density of this film is almost the same as that of the film of Example 1, but X in FIG.
As seen in the line diffraction pattern, there is a peak at 2θ = 5.8 ° which seems to be due to the orientation. As shown in the stress-strain curve of FIG. 4, the modulus of elasticity is slightly higher than that of the polyimide film of Example 1, but the tensile strength and elongation are inferior.

Comparative Example 3 A polyamic acid solution was prepared in the same manner as in Example 1, but the solvent composition was NMP 100%. This polyamic acid solution was applied to a stainless steel plate as in Example 1, and the temperature was 100 ° C.
It was dried with a hot air circulation dryer for 10 minutes and tried to peel it off, but the drying was still insufficient. Therefore, it was further dried at 150 ° C. for 10 minutes to obtain a self-supporting film having a solvent content of 38.3% by weight.

The thermal imidization of the film was carried out by raising the temperature from room temperature to 150 ° C. in 10 minutes and holding it for 15 minutes. The heating rate at this time is 13 ° C./minute. Raise the temperature to 250 ° C for another 10 minutes and hold for 15 minutes.
The temperature was raised to 350 ° C. in 0 minutes and kept for 15 minutes. It can be seen from the density value that this polyimide film is amorphous. Further, as seen from the stress-strain curve in FIG. 4, the elastic modulus and tensile strength are inferior to those of the polyimide film of Example 1.

Example 2 A polyamic acid solution was prepared in the same manner as in Example 1, but the solvent composition was NMP / xylene = 90/10, and the resin content was 12.
It was 6% by weight. This polyamic acid solution was used in Example 1.
Similarly to the above, it was coated on a stainless plate and dried at 120 ° C. for 20 minutes in a heat cycle dryer to obtain a self-supporting film having a solvent content of 26.0% by weight. Thermal imidization of film is from room temperature to 2
The temperature was raised to 200 ° C. for 3 minutes and kept for 3 minutes.

The heating rate at this time is 90 ° C./min. 30 in another 2 minutes
The temperature was raised to 0 ° C. and kept for 15 minutes, and then the temperature was raised to 350 ° C. and kept for 15 minutes to obtain a polyimide film.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of the polyimide film prepared in Example 1. FIG. 2 is an X-ray diffraction diagram of the polyimide film prepared in Comparative Example 1. FIG. 3 is an X-ray diffraction diagram of the polyimide film prepared in Comparative Example 2. FIG. 4 shows the results of the tensile test of the polyimide films prepared in Examples 1 and 2 and Comparative Examples 1 to 3 as a stress-strain curve, where 1 is Example 1 and 2 to 4 are Comparative Example 1. ~
3 and 5 are stress-strain curves of Example 2, respectively.

Claims (2)

[Claims] 1. A method for producing a polyimide film from a solution of polyamic acid, which is a polycondensation product of aromatic tetracarboxylic dianhydride and aromatic diamine, by a casting method, wherein a polyamic acid which is a precursor of polyimide is used. The solvent of the acid solution is compatible with the aprotic polar solvent (A) and the aprotic polar solvent, and the vapor pressure at 140 ° C is 5
A mixture of a non-polar solvent (B) of 50 mmHg or more and (A) :( B) of 70:30 to 97: 3 is uniformly applied on the support, and the temperature is 140 ° C or lower. The step (1) of obtaining a self-supporting film by drying to a solvent content of 5 to 40% by weight, and the self-supporting film obtained in the continuous step (1) are peeled off from the support at 30 ° C / min or more. A method for producing a polyimide film, which comprises the step (2) of heating at a speed and imidizing at a temperature of 200 ° C. or higher. 2. The method for producing a polyimide film according to claim 1, wherein the polyamic acid comprises pyromellitic dianhydride and diaminophenyl ether.