JPH0625269B2 - 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, the present invention 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 which is a polycondensation product of aromatic tetracarboxylic dianhydride and aromatic diamine.

[Prior Art] A wholly aromatic polyimide film has excellent heat resistance and mechanical properties, among which 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride) and 4-amino Poly-N, N'-bisphenoxyphenyl-pyromellitimide (1), which is obtained by cyclocondensation of polyamic acid obtained by polycondensing phenyl ether (diaminodiphenyl ether) in an aprotic polar solvent, is well known. ing.

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 of producing a polypyromellitimide film has adopted a method in which a solution of a precursor polyamic acid is formed into a film by a casting method, and dehydration cyclization (imidization) is performed to obtain a polyimide film.

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 high temperature or chemically treated to form 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 favors mechanical properties and thermal properties. Polyimide films are no exception, and many researchers have already studied the relationship between crystallinity, mechanical properties, and thermal properties of polyimide films. Regarding the poly-N, N'-bisphenoxyphenyl-pyromellitimide (1) film consisting of pyromellitic dianhydride and 4-aminophenyl ether, the presence of a regular molecular aggregation structure, although no clear crystal structure was observed Have been suggested (Isoda et al. J.Polym.Sci.Poly
m.Phys.Ed., 19 1293 (1981), TPRussel ibid 22 1105 (1
983)).

According to these studies, the formation of a regular molecular aggregate structure depends largely on the thermal imidization conditions. For example, applying a polyamic acid solution to a glass plate, drying it under reduced pressure for a long time at a low temperature to form a polyamic acid film, and further increasing the temperature rapidly and imidizing at a high temperature to form a regular molecular aggregation structure There is. Further, it is stated that if a polyamic acid solution is applied to a glass plate, slowly dried at a high temperature, and thermally imidized, a regular agglomerated structure is not formed.

However, it must be said that a method of drying under reduced pressure at a low temperature for a long time, further raising the temperature rapidly and imidizing at a high temperature is extremely difficult and impossible industrially. Because it is very difficult to realize long-term drying under low temperature and reduced pressure in a continuous process.

If a large amount of solvent is contained in the self-supporting film at the stage of obtaining the self-supporting film, the solvent abruptly evaporates at the time of thermal imidization in the next step and foams to impair the surface property of the film.
Therefore, in order to evaporate the aprotic polar solvent having a high boiling point, it must be dried slowly at a high temperature to obtain a self-supporting film. Further, the agglomeration structure of the polyimide film is determined not only by the temperature condition but also by the external force applied to the film. Stretch orientation is also an important factor.

As described above, it is extremely difficult to produce a crystalline polyimide film having excellent mechanical properties.

[Object of the Invention] The present invention is a method for producing a polyimide film from a polyamic acid solution by a casting method, which is obtained as a result of research for industrially obtaining a film having excellent crystallinity and mechanical properties. So, the composition of the polyamic acid solution,
It has been found that a polyimide film having a regular molecular aggregation structure, that is, crystalline and excellent mechanical properties can be obtained by a specific combination of conditions for producing a self-supporting film and thermal imidization conditions, and has reached the present invention. It was done.

[Structure of the Invention] The present invention relates to a polyimide film prepared by casting from a solution of polyamic acid which is a polycondensation product of 1,2,4,5-benzenetetracarboxylic dianhydride and 4-aminophenyl ether. In the method for producing (A), the polyamic acid solution is a mixed solvent of an aprotic polar solvent, and a non-polar solvent having a vapor pressure at 140 ° C. that is compatible with the aprotic polar solvent of 550 mmHg or more, and Aprotic polar solvent is over 70% by weight of all solvents, 97%
A polyamic acid solution of the following mixed solvent, wherein (B) the polyamic acid solution is applied to a support and dried at a temperature of 140 ° C. or less to have a solvent content of 5% by weight or more and 40% by weight or less. A step of obtaining a supporting film, and (C) subsequently to 150-300 of the self-supporting film.
In the temperature range of ℃, the temperature is raised at a rate of 18 ℃ / min or more and 50 ℃ / min or less, and at the same time, in the temperature range of 200 ℃ or more and 370 ℃ or less, 10% in the film take-up direction and the direction perpendicular to it.
As described above, the method for producing a polyimide film is characterized in that it is produced by a step of stretching at 70% or less and imidizing at a temperature of 300 ° C. or more and 500 ° C. or less.

The polycondensation reaction is carried out in an aprotic polar solvent. The aprotic polar solvent is N, N-dimethylformamide (D
MF), N, N-dimethylacetamide (DMAC), N-
Methyl-2-pyrrolidone (NMP) and the like. 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 aprotic polar solvent and has a temperature of 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 lowering 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 order to obtain practical strength as a film, it is necessary to have a high molecular weight. It is difficult to know the absolute value of the molecular weight of the polyamic acid, but in the case of the same composition, the molecular weight can be known from the intrinsic viscosity. In practice, instead of obtaining the intrinsic viscosity, the molecular weight is often expressed by the inherent viscosity (ηinh) at a polymer concentration of 0.5 g / dl. In the polycondensation reaction, the molecular weight can be controlled by the monomer molar ratio. After all, the molecular weight of the polymer can be evaluated by the inherent viscosity, and the molecular weight can be controlled by the monomer molar ratio. In the present invention, as a result of examining the relationship between the inherent viscosity and the monomer molar ratio, and further the relationship with the film strength, the monomer molar ratio r is in the range of 0.960 ≦ r ≦ 1.000, more preferably 0.980 ≦ r ≦ 1.000. Preferred (but Is).

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.

When imidized at a low temperature of about 150 ° C., the glass transition temperature of the already imidized portion becomes extremely high at 400 ° C. or higher, so that from the bulky polyamic acid structure, a regular polyimide molecular aggregation structure, That is, it is not possible to shift to a crystal structure. Therefore, the drying must be performed within the temperature range of the above conditions so that the imidization does not proceed at a low temperature.

The solvent content of the self-supporting film is 5 wt% or more, 40
Must be below 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. Further, since a large amount of solvent is vaporized in the subsequent thermal imidization step, bubbles are easily generated in the film, which is not preferable. On the other hand, when the content of the solvent is low and it is 5% by weight or less, the mobility of the molecular chain is low and the cyclodehydration reaction is prevented. The solvent content of the self-supporting film is 5% by weight or more and 40% by weight or less, more preferably 15% in order to promote the dehydration cyclization reaction and prevent molecular orientation at low temperature.
It must be in the range of not less than 30% by weight and not more than 30% by weight.

Then, the self-supporting film is treated at a high temperature to dehydrate cyclize and imidize.
The temperature must be raised at a rate of ℃ / min or less to imidize in the temperature range of 300 ℃ or more and 500 ℃ or less. 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, so that the structure of the bulky polyamic acid causes a regular molecular aggregation structure of a dense polyimide, that is, This is because a high temperature is required to shift to the 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 imidization proceeds at a low temperature. A crystal structure will not be formed unless the temperature is raised to 300 ° C or higher in a short time to imidize. For that, 150-300
In the temperature range of ° C, the temperature must be raised at a rate of 18 ° C / min or more and 50 ° C / min or less. If the temperature is raised at a rate of 18 ° C./minute or less, the structure becomes almost amorphous, which is not preferable. On the other hand, if the heating rate exceeds 50 ° C./min, the solvent and condensed water remaining in the film will evaporate abruptly, resulting in holes in the film and roughening of the surface, which is not preferable. Final imidization temperature is 30
When the temperature is 0 ° C or lower, a crystal structure is not formed and the cyclization rate is insufficient, which is not preferable. Further, considering the oxidative deterioration of oxygen, the final imidization temperature is preferably 300 ° C. or higher and 500 ° C. or lower.

As for the heat treatment conditions, the temperature must be raised in the temperature range of 150 to 300 ° C. at a rate of 18 ° C./min or more and 50 ° C./min or less to imidize at a temperature of 300 ° C. or more and 500 ° C. or less. More preferably, the temperature is raised at a rate of 20 ° C / min or more and 40 ° C / min or less and 320 ° C.
As described above, it must be imidized at a temperature of 450 ° C. or lower.

In order to improve the mechanical properties of the polyimide film, it is extremely effective to orient the aggregate structure in a certain direction. Anisotropy appears when oriented in a uniaxial direction, so biaxial orientation is preferred. In case of polyimide film,
The temperature range for stretching is important and the reason is unknown, but no improvement in properties is observed even when stretching at a temperature of 200 ° C or lower. 200 ° C
It has been found that the tensile strength and the tensile elastic modulus are remarkably improved when the film is stretched biaxially by 10% or more at the above temperatures. The stretching temperature needs to be 200 ° C or higher, more preferably 250 ° C or higher and 370 ° C or lower. If the draw ratio is 10% or less, the effect of draw orientation is not observed and it is not suitable. The upper limit of the draw ratio is preferably 70% or less because defects such as pinholes and film breakage become problems. The biaxial stretching may be simultaneous or sequential.

[Effects of the Invention] 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, and the thermal imidization conditions and the stretching of the present invention make the composition dense and strong. An excellent polyimide film can be manufactured.

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 wide-angle scattering measurement was performed by a transmission method in which X-rays were incident perpendicularly to the film surface.

The peak near 2θ = 5.8 ° is the reflection peak due to the poly-N, N′-bisphenoxyphenyl-pyromellitimide (1) molecular aggregation structure.

The temperature was measured with a thermocouple attached to the film, and the heating rate was calculated based on this data.

The draw ratio was calculated from the following formula by writing a rating on the polyamic acid self-supporting film before heat treatment and measuring the length, then heat treating the film and again measuring the distance between the marks. .

L _O : Gauge distance before heat treatment L: Gauge distance after heat treatment The linear expansion coefficient was measured with a thermomechanical tester (TMA).

Example 1 2,000 g of dehydrated and purified NMP in a 5-liter three-necked flask
And stir vigorously for 10 minutes while flowing Chisso gas. Next, 200.24 g (1.000 mol) of 4-amine phenyl ether was added and stirred until a uniform solution was obtained. Then 217.68 g (0.988 mol) of pyromellitic dianhydride are added.
During this time, the flask is kept at 5 ° C. When the viscosity of the solution became sufficiently high, 454 g of NMP and 613 g of xylene were added to obtain a polyamic acid solution having a resin content of 12.0% by weight and a solvent composition of NMP / 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 1 minute.
It was dried by a hot air circulation dryer for 0 minutes to obtain a self-supporting film having a solvent content of 22.7% by weight.

This self-supporting film was placed in a heat treatment dryer at 150 ° C. and heated to 360 ° C.

Average heating rate from 150 to 300 ℃ is 24.5 ℃ / min, 300 to 350
The average heating rate up to ° C was 18.9 ° C / min. The film was kept at 360 ° C for 10 minutes. During this period, the film was stretched from 270 ° C in the biaxial directions orthogonal to each other and stopped at 335 ° C. Then, it was gradually cooled to 150 ° C. to obtain a polyimide film. The average stretch ratio was 28%. The performance of this polyimide film is shown in Table 1, and the X-ray diffraction pattern is shown in FIG. From the density and X-ray diffraction pattern, it can be seen that this polyimide film has high crystallinity. The vapor pressure of xylene at 140 ° C. is about 675 mmHg for o-xylene, which has the highest boiling point.

Comparative Example 1 The same polyamic acid self-supporting film as in Example 1 was used, and the thermal imidization of the film was the same as in Example 1, but it was not stretched at all. This polyimide film is
The crystallinity is low from the X-ray diffraction pattern and the value of density in FIG.
It can be seen that it is almost amorphous. Further, the elastic modulus and tensile strength are inferior to those of the polyimide film of Example 1.

Comparative Example 2 The same polyamic acid self-supporting film as in Example 1 was used. This self-supporting film was heated at an average temperature rising rate of 150 to 300 ° C. of 10 ° C./minute and kept at 360 ° C. for 10 minutes. During this time, stretching was performed in the same manner as in Example 1. As seen in the X-ray diffraction pattern of Fig. 3, the peak at 2θ = 5.8 ° is small,
It can be seen that the crystallinity is low. Although the elastic modulus is slightly higher than that of the polyimide film of Example 1, tensile strength and elongation are inferior.

[Brief description of drawings]

FIG. 1 is an X-ray (wide-angle scattering) diffraction pattern of the polyimide film prepared in Example 1. FIG. 2 is an X-ray (wide-angle scattering) diffraction diagram of the polyimide film prepared in Comparative Example 1. FIG. 3 is an X-ray (wide-angle scattering) diffraction diagram of the polyimide film prepared in Comparative Example 2.

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Claims (1)

[Claims] 1. A method for producing a polyimide film from a solution of polyamic acid which is a polycondensation product of 1,2,4,5-benzenetetracarboxylic dianhydride and 4-aminophenyl ether by a casting method. In (A) the polyamic acid solution is a mixture of an aprotic polar solvent and a non-polar solvent having a vapor pressure at 140 ° C. that is compatible with the aprotic polar solvent of 550 mmHg or more, and is an aprotic polar solvent. Solvent is 70% by weight or more of the total solvent, 97
% Or less of a mixed solvent polyamic acid solution, wherein (B) the polyamic acid solution is applied to a support and dried at a temperature of 140 ° C. or lower to have a solvent content of 5% by weight or more and 40% by weight or less. A step of obtaining a self-supporting film, and (C) subsequently to 150-300
In the temperature range of ℃, the temperature is raised at a rate of 18 ℃ / min or more and 50 ℃ / min or less, and at the same time, in the temperature range of 200 ℃ or more and 370 ℃ or less, 10% in the film take-up direction and the direction perpendicular to it.
As described above, the process for stretching a film to 70% or less and imidizing at a temperature of 300 ° C. or more and 500 ° C. or less, and a method for producing a polyimide film.