JPS6354530B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a heat-resistant film, particularly to improving the uniformity of film thickness in the production of polyimide films. Currently, polyimide film is widely used as an electrical and electronic insulating material due to its excellent heat resistance and electrical insulation properties. requested. Regarding the manufacturing method of polyimide film, (A) a method of casting an organic solvent solution of a polyimide precursor material and then heating it to obtain a polyimide film; (B)
A method is known in which a composition comprising an organic solvent solution of a polyimide precursor material, a dehydrating agent and/or a catalyst is cast and gelled, and then heated to form a polyimide. Although method (B) has excellent productivity,
It requires a complicated process and is likely to cause many problems as a result. One example of this is the problem of non-uniform wall thickness. That is, after the composition is cast onto a carrier such as a heated endless belt or drum and gelled, it is peeled off and a polka dot or flow pattern appears when further heat treatment is performed. The thickness of the resulting film becomes significantly uneven. The inventors of the present invention conducted extensive research aimed at improving the non-uniformity of film thickness, and as a result, they found that the cause of the problem was liquid matter that adhered to the film surface as it gelled. I found out something.
As a result of further investigation, they discovered the surprising fact that a film with excellent thickness uniformity can be obtained by passing the liquid material through a subsequent heat treatment furnace under conditions below a certain limit, and arrived at the present invention. . That is, in the present invention, after casting and gelling a composition consisting of an organic solvent solution of a polyimide precursor material and a dehydrating agent and/or a catalyst, the composition is peeled off and then poured into a subsequent heat treatment furnace. production of a heat-resistant film, characterized in that the film is heat-treated in a state in which the amount of liquid matter adhering to the film surface is 8 mg/cm ² or less, and while maintaining an evaporation rate higher than the rate of generation of liquid matter during heat treatment. It is the law. After casting a composition consisting of an organic solvent solution of a polyimide precursor material and a dehydrating agent and/or a catalyst, when placed in a heating oven at approximately 50 to 150°C, it rapidly gels and forms a layer on the film surface. A large amount of liquid material is generated rapidly. This phenomenon is unique to method (B), and is not observed at all in method (A) described above as an example of the polyimide film manufacturing method. In method A, solidification is mainly carried out in conjunction with desolvation, whereas in method (B), solidification is mainly caused by the conversion reaction of the precursor substance to imide. It is presumed that this is due to the large difference in the That is, due to the rapid and drastic decrease in the solvency of the precursor material as a result of the conversion reaction into imide, and the extremely short time required for solidification, the initially existing liquid material becomes It is thought that the liquid substance that could no longer be contained overflows onto the surface of the film because it hardly evaporates. Peel off the obtained film from the carrier,
When the edge of the film is placed in a subsequent heat treatment furnace in a restrained state, the liquid begins to evaporate rapidly, but at this time, the evaporation is not uniform, but rather evaporation similar to the drying of a glass plate that has been washed with water. That is, in the middle of evaporation, the surface of the film is not entirely covered with liquid, but passes through a state where liquid is attached in the form of droplets. In the film thus obtained, numerous polka dot-like and flowing patterns are observed. When we examine the thickness of the film, we find that, for example, while the normal thickness is 30 microns, there is a thickness of 10 to 20 microns. Therefore, the appearance of uneven thickness of the film is probably due to the tension generated by drying being concentrated in the area to which the liquid substance is attached, causing the film to be significantly stretched locally. It is inferred. That is, in the process of evaporation of the liquid substance that is completely adhered to the surface of the film, the film changes from a uniformly wet state to a droplet-like wet state. Therefore, immediately after that, a state appears where the temperature of the film is slightly lower in the part where the liquid substance is attached than in other parts. This inevitably means that the portion of the film to which the liquid substance is attached is converted to imide more slowly than other portions, resulting in a softer film in which the former has a lower softening point than the latter. During this process, shrinkage force is simultaneously generated due to solvent removal, and tension is applied to the entire film under restraint conditions. This tension is likely to accumulate in the soft film portion, causing it to be significantly stretched and thinned. Therefore, this series of phenomena is unique to polyimide, in which a conversion reaction to imide is carried out via a precursor substance simultaneously with film forming. In addition, as a method for forming a film, when the composition is cast and gelated on a carrier and heat-treated as it is in a heat treatment furnace without peeling,
The problem of non-uniformity in film thickness does not occur. Based on the above series of results, the inventors of the present invention continued their intensive research in order to completely remove the problematic liquid, and found that, surprisingly, it is not always necessary to completely remove the liquid. It has been found that this problem can be solved by achieving a condition in which the amount of liquid matter adhering to the film surface is 8 mg/cm ² or less at the time of entering the subsequent heat treatment furnace. Factors that control the amount of liquid deposited on the film surface include the type and amount of the organic solvent of the polyimide precursor material, the type and amount of the dehydrating agent and/or catalyst, coating thickness, gelling conditions, and subsequent The conditions before entering the heat treatment furnace can be considered. However, among these, the part before the peeling process has many restrictions mainly from economic efficiency, workability, safety, quality, etc. Therefore, the part where freedom can be expected is from peeling to the subsequent heat treatment furnace. This is the process. On the other hand, according to the studies of the present inventors, a liquid substance is suddenly generated on the film surface at the same time as gelation begins, and therefore, the part that should be viewed as a problem is the process from peeling to the subsequent heat treatment furnace. Therefore, this process requires some ingenuity. The key point of the present invention is that the amount of liquid matter adhering to the film surface is 8 mg/cm ² or less, preferably 5 mg/cm 2 or less at the time of entering the subsequent heat treatment furnace after peeling.
The point is that the heat treatment is carried out at a concentration of mg/cm ² or less, most preferably 3.5 mg/cm ² or less, and while maintaining an evaporation rate higher than the new liquid generation rate during the heat treatment. The amount of liquid deposited on the film surface is affected by the coating thickness. That is, the thicker the coating, the more conspicuous the occurrence. however,
Because of the thickness, even if the amount of adhered liquid is relatively large, it does not tend to cause problems due to non-uniformity of the thickness, but it is determined by the amount relative to the surface area of one side of the film. In the heat treatment referred to in the present invention, it is necessary to maintain an evaporation rate higher than the liquid generation rate during the heat treatment.
This condition limits the amount of liquid that newly adheres during heat treatment even if the amount of liquid that adheres at the inlet is well controlled. However, in the case of a film that has already been endowed with self-supporting properties, the conversion rate to imide is significantly reduced, so the rate of generation of new liquid matter in the heat treatment furnace is substantially low, and in practice, Heat treatment can be carried out under conditions that ensure a temperature of 50°C or higher and the required air volume and speed for safety. That is, the reason why only the amount of liquid matter adhering to the film surface at one transit point in the film manufacturing process becomes dominant can be inferred as follows. When processing a film that has become self-supporting with the subsequent heat treatment furnace set at a temperature of 50°C or higher and the required airflow volume and speed for safety, the results at this point are compared to gelatinization. The conversion reaction to the corresponding imide slows down, and it becomes impossible to expect the rate of liquid product generation to be as fast as at the gelation stage. Therefore, it is considered that the amount of newly deposited liquid matter in the subsequent heat treatment furnace becomes substantially non-existent. On the other hand, in the method of the present invention, heat treatment is performed under restraint at both ends with a width that is approximately the same as or greater than the width of the gel film at the time of peeling. restrain,
During heat treatment, the shrinkage force generated as a result of solvent removal peaks when the film temperature is around 120°C in the very early part of the subsequent heat treatment furnace. Once it rises, it drops sharply again. For these reasons, it is undesirable for the liquid matter adhering to the film surface to show wetting in the form of water beads under conditions of significant shrinkage due to desolvation, and for this reason, it is undesirable for the liquid matter adhering to the film surface to show wetting in the form of water droplets when it enters the subsequent heat treatment furnace. It is thought that the amount of adhered liquid matter is limited. Peeling in the present invention means physically peeling off the composition in a self-supporting solid state from a carrier. The film properties at the time of peeling can be expressed, for example, by the amount of residual solvent or the imidization rate. In this case, the amount of residual solvent is usually 1900 to 100 parts by weight based on 100 parts by weight of the resin consisting of the polyimide precursor material and polyimide. The imidization rate is usually 30% or more. The liquid substance adhering to the film surface in the present invention is composed of at least one of the organic solvent, dehydrating agent, catalyst, hydrolysis product of the dehydrating agent, and decomposition products thereof. be. The polyimide precursor used in the present invention is represented by the following structural formula (). One of the starting materials giving this structural formula is ()
It is an aromatic diamine represented by the structural formula. H ₂ N-R'-NH ₂ () Here, R' is a divalent aromatic group selected from a phenylene group, a naphthalene group, a biphenylene group, and a group represented by the structural formula (). Here, _R1 is selected from an alkylene group having 1 to 4 carbon atoms, -O-, -S-, _-SO2- , and a group represented by () below. However, here R ₂ , R ₃
is an aliphatic group or an aromatic group. Examples of diamines specifically used in the present invention include metaphenylene diamine, paraphenylene diamine, 4,4'-diaminodiphenylpropane, 4,4'-diaminophenylmethane, benzidine, 4,4' -diaminodiphenyl sulfide,
4,4'-diaminodiphenylsulfone, 3,3'-
Diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 2,6-diaminopyridine, bis(4-aminophenyl)diethylsilane, bis(4-aminophenyl)diphenylsilane, 3,3'-dichlorobenzidine, bis( 4-Aminophenyl)ethylphosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, bis(4-aminophenyl)-N-phenylamine, bis(4-aminophenyl)-N
-Methylamine, 1,5-diaminonaphthalene,
Examples include 3,3'-dimethyl-4,4'-diaminodiphenyl, 3,3'-dimethoxybenzidine, and mixtures of two or more thereof. Preferred among these diamines are 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, and mixtures of two or more of these, most preferably. is 4,4'-diaminodiphenyl ether. The other starting material is an aromatic tetracarboxylic dianhydride, such as pyromellitic dianhydride,
2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-diphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride , 2,2',3,3'-diphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl) ) Sulfone dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, naphthalene-
1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride substance, 1,1-bis(2,
3-dicarboxyphenyl)ethane dianhydride,
1,1-bis(3,4-dicarboxyphenyl)
Ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(3,4
-dicarboxyphenyl) sulfone dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, 3,4,3',4'-benzophenone tetracarboxylic dianhydride, etc. is pyromellitic dianhydride, 3,3',4,4'-diphenyltetracarboxylic dianhydride, benzene-1,2,3,4-
Tetracarboxylic dianhydride or a mixture of two or more thereof is preferred, and pyromellitic dianhydride is most preferred. In view of the gist of the present invention, the polyimide precursor material does not need to be 100% polyamic acid, and may partially have an imide structure as long as it is in a uniform solution state in an organic solvent. Examples of the organic solvent used in the present invention include N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, dimethylsulfoxide, Commonly known compounds such as hexamethylphosphoramide, N-methyl-2-pyrrolidone, dimethylsulfone, and tetramethylenesulfone can be used alone or in a mixture of two or more. Furthermore, it can be used in appropriate combination with a non-solvent such as benzene, toluene, xylene, benzonitrile, dioxane, cyclohexane and the like. The dehydrating agent referred to in the present invention includes, for example, aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride; aromatic acid anhydrides such as benzoic anhydride;
N,N'-disubstituted carbodiimide; lower fatty acid halide, etc., or a mixture of two or more thereof. Among these, at least one acid anhydride selected from aliphatic acid anhydrides and aromatic acid anhydrides is particularly preferred. The catalyst used in the present invention includes aliphatic tertiary amines such as trimethylamine and triethylenediamine.
and aromatic tertiary amines such as dimethylaniline; and heterocyclic tertiary amines such as pyridine and isoquinoline. At least one selected from among these heterocyclic tertiary amines
More than one species is particularly preferred. In the present invention, it is not essential that the dehydrating agent and the catalyst coexist, and the aim is to consciously enhance the conversion to imide by the presence of at least the dehydrating agent and/or the catalyst. It is also a priority. In a preferred example of the present invention, a dehydrating agent and a catalyst are used together. In this case, the ratios of the precursor substance, organic solvent, dehydrating agent, and catalyst are not particularly limited. Examples of preferred ratio ranges of the present invention are as follows. Precursor substance/organic solvent = 0.08 to 0.3 (weight ratio) Dehydrating agent/precursor substance = 0.5 to 8 (mole ratio) Catalyst/precursor substance = 0.01 to 2 (mole ratio) The composition referred to in the present invention is: It does not mean only that a dehydrating agent and/or a catalyst is added to a solution of a precursor substance in an organic solvent to form a homogeneous solution. Therefore, in cases where only an organic solvent solution of a precursor material is cast and brought into contact with a dehydrating agent and/or a catalyst before the stripping process,
This method also includes modifications such as a case where a uniform mixture of the organic solvent solution and a dehydrating agent or catalyst is cast, and the insufficient dehydrating agent or catalyst is brought into contact before the stripping step. In addition, when an organic solvent solution and a dehydrating agent are uniformly mixed (), the organic solvent solution and a catalyst are uniformly mixed (), and both are instantaneously mixed and cast, or when both are layered separately. It also includes modifications such as casting. In short, before the peeling process,
This means that a composition consisting of the organic solvent and a dehydrating agent and/or a catalyst is formed in some form. It is convenient to quantify the liquid substance as referred to in the present invention by a gravimetric method using paper or the like. That is, paper of known weight, which has been sufficiently preliminarily dried, is brought into contact with both surfaces of the film at the point where it enters the subsequent heat treatment furnace to absorb the liquid material, and the weight increase is measured. The amount of adhesion is determined by dividing the weight increase at this time by the area of one side of the film. In cases where a liquid other than the liquid substance is mixed, gas chromatography or the like can be used in combination to quantify the liquid substance. The condition of reducing the amount of liquid matter adhering to the film surface at the time of entering the heat treatment furnace to 8 mg/cm ² or less, which is a feature of the present invention, can be achieved, for example, by the following method. A first example is a method in which contact is made with a solvent between the time of stripping and the entrance of the subsequent heat treatment furnace. In this case, the effect will be significant if it is connected for 0.1 to 10 seconds to a compound that is liquid at room temperature and has a boiling point of 150°C or less, which has low affinity with the precursor substance but has an affinity with the liquid substance. The second example is a method in which the adhering liquid material is blown away using a gas flow between the time of peeling and the entrance of the subsequent heat treatment furnace. Ten~
A remarkable effect can be obtained by blowing 200°C air almost parallel to the film surface using a nozzle.
A third example is a method in which at least one set of nip rolls is placed between the peeling and the entrance of the subsequent heat treatment furnace, and the material is passed through the gap while being slightly pressurized. According to the present invention, by devising the process from the peeling process to the heat treatment process, it is possible to achieve a state in which the amount of liquid matter adhering to the film surface is 8 mg/cm ² or less, and as a result, the film It is possible to ensure a high level of wall thickness uniformity,
This makes it possible to produce high-quality heat-resistant films. Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Example 1 4,
4'-diaminodiphenyl ether 6.06g (0.0303
6.605 g of high purity pyromellitic dianhydride powder was added little by little to this.
(0.0303 mol). The reaction was carried out while carefully cooling the outside of the flask with ice water, and stirring was continued for an additional 5 hours. The resulting precursor solution had a viscosity of 4000 poise at 23°C. Next, take 50 g of this solution in a beaker, add 6.29 g of acetic anhydride and 0.86 g of isoquinoline.
g was added, quickly mixed, and cast onto a 30 μm thick aluminum foil to a thickness of 300 μm. This cast product was immediately heated in an oven at 100°C for 1 minute, and the amount of remaining solvent and imide ratio were immediately measured. The amount of remaining solvent was 843 parts by weight, and the imidization rate was 50%.
It was hot. This coating film was immediately peeled off from the aluminum foil, and the amount of liquid material adhering to the surface of the gel film was measured. On the other hand, the film obtained in the same manner was fixed on all sides to a frame and heat-treated at 300°C for 30 minutes. Table 1 shows the properties of the obtained film. Furthermore, as a result of analyzing the liquid by chromatography, it was found that mainly N-methyl-2-pyrrolidone,
It turned out to be a mixture consisting of acetic anhydride, isoquinoline, and acetic acid.

【table】

[Table] (Measurement method) 1. Amount of residual solvent: Calculated from the weight change before and after heat treatment at 300°C for 30 minutes. Weight loss due to dehydration reaction was ignored. 2 Imidization rate: Calculated based on the absorbance ratio of 730 cm ^-1 to 870 cm ^-1 . 3. Frequency of thin film parts: Displayed as the number of thin parts present when a 10 cm square sample was arranged in a grid of 5 mm. 4. Amount of liquid adhered: The weight of the liquid adhered to both surfaces of the film was measured, and the weight was divided by the area of one side of the film and expressed as a value. The above results show that the thickness uniformity of the film is significantly improved by controlling the amount of liquid matter deposited on the gel film to be 8 mg/cm ² or less. Example 2 Casting with different wall thicknesses was carried out in the same manner as in Example 1. The results are shown in Table 2.

【table】

[Table] The above results show that the thickness uniformity of the film can be greatly improved by controlling the amount of liquid matter to be 8 mg/cm ² or less over a coating thickness of 50 to 1500 μm. Example 3 Table 3 shows the results of an investigation using the same starting materials as in Example 1 and varying the solid content concentration, type and amount of dehydrating agent, type and amount of catalyst, gelation temperature and time, etc. show.

【table】

[Table] *Resin concentration in organic solvent solution of precursor material.
This result shows that, regardless of various conditions, uniformity in film thickness can be ensured by keeping the amount of liquid matter adhering to the surface of the gel film at the time of peeling to 8 mg/cm ² or less. Example 4 Example 1 with various starting materials
Table 4 shows the results of the same study.

[Table] Example 5 0.86 g of isoquinoline was added to 50 g of the solution of the precursor material obtained in Example 1, and mixed quickly to create a wall thickness of approx.
It was cast to a thickness of 100μ. The cast product was immediately immersed in an acetic anhydride dehydration bath heated to 70° C. for 3 minutes, and then the gelled film surface was wiped with paper to remove the liquid material. This film was fixed on a four-sided frame and heat treated in an oven at 300°C for 30 minutes. The amount of liquid matter adhering to the film before heat treatment was 0.3 mg/cm ² . No polka dot or flowing patterns were observed in the obtained film, and the thickness was extremely uniform. Example 6 The following table shows the results of examining the uniformity of wall thickness by changing the conditions of the subsequent heat treatment furnace in the same manner as in Example 1. For comparison, the amount of liquid attached is 6.2mg/
cm ² was left at 20℃ for 5 minutes (liquid adhesion amount 12.3
mg/cm ² ) and then heat-treated at 300° C. for 20 minutes, the film had a markedly uneven thickness.

【table】

[Table] From this result, it can be seen that the temperature of the subsequent heat treatment furnace is 50℃ or higher.
It can be seen that a film with excellent thickness uniformity can be obtained if the amount of liquid deposited (at the time of entering the subsequent heat treatment furnace) is 8 mg/cm ² or less under the exhaust air volume and wind speed required for safety.

Claims (1)

[Claims] 1 an organic solvent solution of a polyimide precursor substance;
After the composition consisting of a dehydrating agent and/or a catalyst is cast and gelled, it is peeled off, and the peeled gel film adheres to the surface of the gel film when it enters a subsequent heat treatment furnace. 8mg/liquid
cm ² or less, and while maintaining an evaporation rate higher than the generation rate of liquid newly generated during heat treatment, heat treatment is performed with both ends restrained to a width that is approximately the same as or greater than the width of the gel film at the time of peeling. A method for producing a heat-resistant film characterized by: