JPH0230338B2 - HORIMETAFUENIRENISOFUTARUAMIDOKEIFUIRUMU - Google Patents

Description

[Detailed description of the invention]

The present invention relates to aromatic polyamide films with improved performance, particularly polymetaphenylene isophthalamide films. More specifically, the present invention relates to a polymetaphenylene isophthalamide film that has dramatically improved dimensional stability against humidity. Polymetaphenylene isophthalamide is a polymeric material that has excellent heat resistance and mechanical properties, and is used in various fields such as textiles and synthetic paper. However, polymetaphenylene isophthalamide has drawbacks due to its highly hygroscopic nature. Sheet-like materials (also called planar materials) such as films and synthetic papers made of conventionally known polymetaphenylene isophthalamide undergo large dimensional changes due to moisture absorption due to this hygroscopicity, and high dimensional accuracy is required. There is a restriction that it cannot be used for any purpose. Such applications include electronic board materials such as flexible printed circuit boards, which are currently demanding even higher wiring densities, and in fact, synthetic paper and film made of the above-mentioned polymetaphenylene isophthalamide are resistant to moisture absorption during processing and use. Because of the large dimensional changes caused by it, it is not used in electronic substrate materials with high wiring density. In view of the above-mentioned current situation, the inventors of the present invention have intensively investigated ways to improve the hygroscopicity of aromatic polyamides. The present invention was achieved by discovering the surprising fact that the stability is extremely excellent. That is, in the present invention, the film density d (g/cm ³ )
satisfies the formula, and the principal refractive indices n〓, n〓, and n〓 for the D-line (wavelength 589 nm) (however, the principal refractive indices are n〓, n〓, n〓 in descending order) satisfy the formula. This is a polymetaphenylene isophthalamide film. 1.35≦d≦1.41...() n〓+n〓/2-n〓≧0.05...() The present invention will be explained. The polymetaphenylene isophthalamide type polymer used in the polymetaphenylene isophthalamide type film of the present invention has at least 95 mol% of repeating units composed of m-phenylene diamine and isophthalic acid halide such as isophthalic acid chloride. Poly-m-phenylene isophthalamide is obtained by reacting P-phenylene isophthalamide by a method such as melt polymerization or interfacial polymerization, and the component to be copolymerized as necessary within a range of about 5 mol % is P- as an amine component. Examples include phenylene diamine, benzidine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, gysylylene diamine, toluene diamine, 4,4'-diaminodiphenyl sulfone, etc. Examples include dicarboxylic acid chloride such as terephthalic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, diphenylsulfone-4,4'-dicarboxylic acid chloride, and 4,4'-diphenyldicarboxylic acid chloride. A typical example is acid hydride. The polymetaphenylene isophthalamide polymer, which is the material of the film of the present invention, has a high affinity for water due to the polarity of the amide group, and has a water absorption of 10% or more in the form of an unoriented and amorphous solid. are doing. In response to this water absorption, molded products made of this polymer undergo large dimensional changes due to moisture absorption.
Under an environment where the humidity of the atmosphere changes, it could not be used for applications that require a high degree of dimensional stability. Generally, in a hygroscopic polymer system, when the degree of crystallinity increases due to heat treatment or the like, the hygroscopicity decreases. This is a property common to systems in which water cannot penetrate into the crystalline region of the polymer, and polymetaphenylene isophthalamide-based polymers also have similar properties.
Therefore, it is possible in principle to improve the dimensional stability against moisture absorption of this polymer molded product by promoting crystallization to a high degree. however,
Regarding polymers, no industrial technology has yet been established that can arbitrarily increase the degree of crystallinity. In addition, in the case of a film made of a polymer, unnecessarily increasing the degree of crystallinity will result in a loss of film integrity and practical value as a film. Therefore, it is not possible to obtain a practical polymetaphenylene isophthalamide film simply by increasing the degree of crystallinity. Therefore, the present inventor focused on the following two points. (b) Assuming that deformation due to moisture absorption is basically the expansion and expansion process of water, the amount of deformation due to moisture absorption is determined by the balance between the increment of free energy due to water adsorption and the elastic energy due to film deformation. . Therefore, by highly tensing the amorphous chains on which water is thought to be selectively sorbed and increasing the elastic modulus of the amorphous, the absolute amount of deformation decreases when the chemical potential of water in the atmosphere is the same. . (b) The sorption sites for water on polymers are distributed on the sides of the molecular chain. Therefore, when the molecular chains are oriented in a preferred manner, swelling by water causes anisotropy. In the case of a film, by orienting the molecular chains in the plane, in-plane dimensional changes can be reduced with respect to thickness changes due to moisture absorption. In this way, in polymetaphenylene isophthalamide films, the density d, which is an index of crystallinity, is within a specific range, and is also a measure of the tension of amorphous chains and the in-plane orientation of molecular chains ( When the value (n〓+n〓/2 -n〓) exceeds a specific value, it is possible to obtain a polymetaphenylene isophthalamide film whose dimensional stability has been improved to a practically satisfactory degree. The above specific range of density means that the film is 1.35
g/cm ³ to 1.41 g/cm ³ , and the specific value of the principal refractive index is expressed as n〓+n〓/2−n〓≧0.05 (). A polymetaphenylene isophthalamide film that satisfies this density and refractive index exhibits excellent dimensional stability due to moisture absorption, and can be applied to fields of application that require heat resistance and dimensional stability. When used as an electronic board material such as a flexible printed circuit board, it is practically necessary that the moisture absorption dimensional change rate at 65% RH is 1% or less, preferably 0.6% or less. Here, the 65%RH moisture absorption dimensional change rate is defined as the following formula. 65%RH moisture absorption dimensional change rate (%) = (Dimension of film when humidity conditioned at 25°C and 65%RH/Dimension of film at 25°C in pure dry state - 1) × 100 The density d is ()
It is necessary to satisfy the formula: 1.35≦d≦1.41 (). This formula indicates the range using density, which is a substitute characteristic for crystallinity. If the density of the film is less than 1.35 g/cm ³ , crystallization will be insufficient, and even if it is given a pseudoplane orientation, the 65% RH moisture absorption dimensional change rate will exceed the practically required 0.6%, making it flexible. Not suitable for printed circuit board applications. Also, the density is 1.41
When it exceeds g/cm ³ , the flexibility of the film is impaired and it is not practical. Note that the density of the film can be measured by a carbon tetrachloride-heptane density gradient tube method. The film of the present invention has sodium D-ray (wavelength
589nm) is n〓, n〓, n〓 (however, n〓,
Suppose that the order of magnitude is n〓, n〓. The principal refractive index is (n〓+n〓/2−n〓) of 0.05 or more when the three axes are mutually orthogonal. Preferably, the anisotropic film also satisfies the condition of n〓−n〓≦0.08 (). The refractive index of the film is measured using an Atsube refractometer or a polarizing microscope equipped with a universal stage. The film of the present invention can be obtained by adjusting stretching conditions (stretching bath or stretching atmosphere, stretching temperature, stretching ratio, etc.) so as to satisfy formula (). Equation () is a quantity that indicates the plane orientation of the film, and indicates the degree of anisotropy of the film and tension of molecular chains. In the present invention, the (n〓+n〓/2-n〓) value must be 0.05 or more. More preferably, the (n〓+n〓/2-n〓) value is 0.07 or more. (n〓＋n〓/2−n〓) value is 0.05
If it is less than that, the moisture absorption dimensional stability is low and it is not suitable for the present invention. Regarding the plane containing the optical elastic axes corresponding to n〓 and n〓, 65%RH moisture absorption dimensional change rate is 0.6% for practical performance.
It can be: In the polymetaphenylene isophthalamide film obtained by the production method described below, n〓 and n〓
The optical elastic axis corresponding to , exists almost in the plane of the film without exception, and when the equations 1 and 2 are satisfied at the same time, the dimensional change in the film plane is also
The 65%RH moisture absorption dimensional change rate can exhibit performance of 0.6% or less. The film of the present invention preferably has a small and well-balanced anisotropy in the dimensional change rate due to humidity in the plane as a practical property.
65% RH moisture absorption dimensional change rate when taken in any in-plane direction by satisfying the condition 0.08≧(n〓−n〓) for a polymetaphenylene isophthalamide film defined by the above formula () The difference between the maximum value and the minimum value can be set to 0.5 or less. n〓
The value of -n〓 can be arbitrarily adjusted depending on the balance of stretching. Typical methods for producing the polymetaphenylene isophthalamide film of the present invention include (1) dry-wet film forming method and (2) wet film forming method. Regarding the method for producing the aromatic polyamide film of the present invention by the dry-wet film forming method, an aromatic polyamide-amide solvent composition is cast and heated at 150 to 250°C.
After removing the solvent under an atmosphere of 100 ml, water-soluble residual compounds are extracted by washing with water to obtain a water-containing film. The polymetaphenylene isophthalamide film of the present invention can be obtained by subjecting this water-containing film to stretching orientation and heat treatment described below. Regarding the production of polymetaphenylene isophthalamide film, the dry-wet method described above is
Since the solvent used is a highly polar, high boiling point solvent such as an amide solvent, high temperature and long periods of time are required to remove the solvent. Since there is a strong interaction between the polymetaphenylene isophthalamide polymer and the amide solvent, such as forming a complex, it is impossible to completely remove the solvent using only a dry process. Therefore, it is unavoidable to combine the dry method with the wet method, which inevitably poses the problem of complicating the process. On the other hand, the wet method involves a single step and is considered to be an advantageous method, but the wet coagulation properties of a composition made of a polymetaphenylene isophthalamide polymer and an amide solvent are not necessarily good.
Obtaining a strong polymer film is not easy.
This problem has been one of the reasons why polymetaphenylene isophthalamide films have not been successfully commercially produced. Wet film forming technology for aromatic polyamides that can eliminate these technical obstacles is already known (Special Application
54-116153, 55-67052). The compositional formula of the polymetaphenylene isophthalamide polymer composition is the following formula, 0.5≧a/a+b≧0.05...() c/a≧0.1...() [In the above formulas () and (), a is Parts by weight of the polymetaphenylene isophthalamide polymer, b represents parts by weight of the amide solvent, and c represents parts by weight of the solubilizing aid. ] A wet film forming method in which a polymer composition represented by the following formula is introduced into an aqueous coagulation bath is particularly preferred for obtaining the film of the present invention. Furthermore, the following conditions are preferable for the composition ratio of the polymetaphenylene isophthalamide polymer composition. When 0.25≦a/a+b≦0.336, 0.1≦c/a, when 0.336<a/a+b≦0.5, 2.8×a/a+b−0.84<c/a, by introducing such a composition into an aqueous coagulation bath. An unstretched film can be obtained by a film forming method. The amide solvents used here include tetramethylurea, hexamethylphosphoramide, N,
N-dimethylacetamide, N-methylpyrrolidone-2, N-methylpiperidone-2, N,N-dimethylethyleneurea, N,N,N',N'-tetramethylmalonic acid amide, N-methylcaprolactam, N-acetyl Pyrrolidine, N,N-diethylacetamide, N-ethylpyrrolidone-2, N,
Examples include N-dimethylpropionic acid amide, N,N-dimethylisobutyramide, N,N-dimethylpropylene urea, N,N-dimethylformamide, and mixtures thereof. Preferred amide solvents include N-methylpyrrolidone-2 (hereinafter abbreviated as NMP), N,N-dimethylacetamide, and mixtures thereof. As solubilizing aids which can preferably be used, mention may be made of metal salts of groups of the periodic table and/or groups of the periodic table and ammonium halides. Such salts are dissolved in the polymer solution and serve to enhance the stability of the solution, as described in, for example, Japanese Patent Publication No. 35-16027. Preferred solubilizing aids include lithium chloride, calcium chloride, and magnesium chloride, with calcium chloride being particularly preferred. In a polymetaphenylene isophthalamide polymer composition used for forming a polymetaphenylene isophthalamide film, a polymetaphenylene isophthalamide polymer (a), an amide solvent (b), and solubilization are used. As mentioned above, it is generally preferable that the auxiliary agent (c) has the following structure. 0.5≧a/a+b≧0.05 ...() c/a≧0.1 ...() More preferably, when 0.25≦a/a+b≦0.336 0.1≦c/a ...() 0.336<a/a+b≦0.5 A composition defined by the following formula is preferable: 2.8×a/a+b−0.84<c/a (). In the above formula (), when a/a+b<0.05, sufficient moldability may not be obtained for the purpose of film molding, and the amount of amide solvent used is undesirable. On the other hand, when a/a+b > 0.5 in formula (), the viscosity of the resulting composition solution becomes extremely high, often making it difficult to handle. In the above formula (), it is necessary that c/a≧0.1. Furthermore, it is desirable to use a solubilizing aid within the range of formula (). When c/a<0.1, it is difficult to obtain sufficient solution stability. Typical methods for producing such polymetaphenylene isophthalamide-based polymer compositions include (a) reliquid dissolution method, and (b) solution polymerization-neutralization method. The redissolution method is a method in which a pre-isolated polymetaphenylene isophthalamide polymer amide solvent and a solubilization aid are prepared in a predetermined ratio and redissolved. A typical method is to dissolve the solubilization aid in an amide solvent and then mix the polymer with the mixture, preferably while cooling. Depending on the type and amount of solubilization aid used, the entire amount may not be dissolved in the amide solvent alone.
Further mixing of the polymer often results in uniform dissolution. Alternatively, the solubilization aid powder and polymer powder may be further mixed and pulverized as required, and after thorough mixing, the amide solvent may be mixed under cooling. This composition can also be prepared by a solution polymerization-neutralization method (for example, Japanese Patent Publication No. 35-14399
(see publication). The polymetaphenylene isophthalamide polymer composition may also contain additives, modifiers, etc. as exemplified below, if necessary. For example, light stabilizers, heat stabilizers, antioxidants, crosslinking agents, flame retardants, UV blockers, antistatic agents, matting agents, dyes, etc.
These include coloring agents such as pigments, various organic and inorganic fillers or reinforcing materials, various other plasticizers, and solution viscosity regulators. The polymetaphenylene isophthalamide polymer composition can be molded into a film by a wet method or an air discharge wet method. In general, when using an aromatic polyamide composition with a low solution viscosity, a wet molding method is applied, and when the solution viscosity is relatively high, an air discharge-wet molding method is often applied, but the above method is not always necessary. It is not limited to means. As a coagulation solution, at least one of the baths having the following compositions is preferably used for forming polymetaphenylene isophthalamide films. (i) Inorganic salt aqueous solution, (ii) Organic solvent aqueous solution, or (iii) Mixed aqueous solution of (i) and (ii). Typical compounds contained in inorganic salt aqueous solution are CaCl ₂ , BaCl ₂ , ZnCl ₂ , MgCl ₂ , NaCl,
KCl, AlCl ₃ , SnCl ₂ , NiCl ₂ , SrCl ₂ , LiCl,
CaBr ₂ , LiBr, Ca(NO ₃ ) ₂ , Zn(NO ₃ ) ₂ , Al
Examples include (NO ₃ ) ₃ , Ca(SCN) ₂ , KSCN, and NaSCN. Preferably as an inorganic salt
Examples include CaCl ₂ , MgCl ₂ and ZnCl ₂ , with LiCl ₂ and CaCl ₂ being particularly preferred. It is also generally advantageous for the solubilization aid in the aromatic polyamide composition and the inorganic salt in the coagulation bath to be the same compound. The preferred concentration of the inorganic salt varies depending on the type of inorganic salt, the composition or composition ratio of the aromatic polyamide composition, molding conditions, etc., but an aqueous solution containing 20% by weight or more of the above-mentioned inorganic salt is preferable. When such a coagulation bath is used, it is possible to produce a film with excellent mechanical performance and transparency. Furthermore, although the coagulation bath composition, temperature, and immersion time are not constant depending on the desired thickness and transparency of the film, the preferred coagulation bath temperature when using an aqueous inorganic salt solution is 40 to 110°C. An aqueous organic solvent solution can also be used as a coagulation bath. Various alcohols and amide solvents can also be used as the organic solvent. Among various alcohols, alkylene glycol is one of the organic solvents that can be preferably selected. As typical alkylene glycols, ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, etc. can be used.
The concentration of the polyalkylene glycol or glycerin aqueous solution varies depending on the composition or composition ratio of the polymetaphenylene isophthalamide polymer composition, molding method, or conditions, but generally an aqueous solution of 30% by weight or more can be used. . Suitable temperature conditions vary depending on other factors, but are selected from a range of 30° C. to the boiling point of the coagulation bath. In preferred embodiments of the present invention, multi-stage coagulation baths are often used. As a multi-stage coagulation bath, it is possible to use systems with different inorganic salt aqueous solutions at different concentrations and temperatures, systems with completely different coagulation compositions, etc., depending on the needs, but from an industrial standpoint, it is possible to use a combination of coagulation systems of the same type. A multi-stage coagulation bath is preferred. After the organic solvent or inorganic salt is removed in a water washing process, the film thus obtained has a water content of 40% by weight or more and usually 80% by weight.
A homogeneous transparent film of ~200% by weight can be obtained. The film of the present invention is characterized by a high degree of plane orientation and a high crystallinity defined within a certain range of density d and principal refractive index n〓, n〓, n〓 for the D line. This can be achieved by stretching and heat-treating a film or the like. Dry stretching or wet stretching is used as a stretching method for polymetaphenylene isophthalamide film.
This can be cited as a representative example. For stretching, the above-mentioned water-containing film or an absolutely dried film can be used. It is appropriate to use a dry film for dry stretching, and a hydrous film or a dry film for wet stretching. The polymetaphenylene isophthalamide film is produced by selecting either uniaxial stretching, sequential biaxial stretching, or simultaneous biaxial stretching. As dry stretching, roll stretching or tenter stretching can also be performed at a temperature of 260°C or higher. Next, wet stretching, which is considered to be an advantageous method for industrial production, will be described. When producing a polymetaphenylene isophthalamide film, the dry stretching described above has limitations on temperature control, stretching speed, sequential stretching ratio, etc. because the polymetaphenylene isophthalamide polymer has a strong cohesive force and a fast crystallization speed. There are many. On the other hand, in wet stretching, the molecular cohesive force is weakened by plasticity or low-molecular components, so moldability is high, and various stretching forms are possible by adjusting the type and content of plasticity and low-molecular components. , the condition setting is advantageous. Wet stretching involves immersing a film in a solvent such as water, alcohol, alkylene glycol, or glycerin, and stretching the film in the solvent or in a solvent vapor atmosphere. At this time, it is preferable that the solvent contains 0.1 to 80% by weight of an amide solvent in order to obtain a high stretching ratio. However, if it exceeds 80%, the mechanical strength of the film during stretching is lost, resulting in plasticized flow stretching, and no effective orientation can be achieved. Amide solvents include tetramethylurea, hexamethylphosphoramide, N,N-dimethylacetamide, N-methylpyrrolidone-2,
N-methylpiperidone-2, N,N-dimethylethyleneurea, N,N,N',N'-tetramethylmalonic acid amide, N-methylcaprolactam, N-
Acetylpyrrolidine, N,N-diethylacetamide, N-ethylpyrrolidone-2, N,N-dimethylpropionic acid amide, N,N-dimethylisobutyramide, N,N-dimethylpropylene urea, N,N-dimethylformamide and mixtures thereof. The stretching temperature is not particularly limited, but it is preferably carried out at 0° C. or higher and lower than the boiling point of the solvent. The stretching ratio can be adjusted within the range of 1 to 15 using the above-mentioned stretching method. In order to produce the highly planarly oriented and highly crystallized polymetaphenylene isophthalamide film of the present invention, the lower limit of the stretching ratio is at least 1.5 or more, more preferably 2.5 or more. By washing the stretched film with water and drying it at a constant length, it can be confirmed whether the film satisfies the orientation conditions (formula) of the present invention. The degree of crystallinity of the film after stretching varies depending on the stretching temperature and the composition of the stretching bath, but if the density of the film after washing and drying is 1.35 g/cm ³ or less, heat treatment is required. After drying, the stretched and oriented polymetaphenylene isophthalamide film can be crystallized by a dry heat treatment method in which it is heat-treated at a temperature of 300° C. or higher for 30 seconds or more under constant length or tension. As a heat treatment method for polymetaphenylene isophthalamide films, the conventional dry heat treatment required extremely high temperatures. Moreover, since the thermal decomposition temperature of the polymetaphenylene isophthalamide-based polymer and the heat treatment temperature are close to each other, there have been problems such as the polymer being susceptible to decomposition and deterioration. As a heat treatment method improved in this respect, the heat treatment method using a plasticizer addition system described below is mentioned as a preferable heat treatment method. 1 to 200% by weight, preferably 3 to 150% by weight in polymetaphenylene isophthalamide film
Containing an amide solvent of
100℃ or more and 450℃ or less, preferably 100℃ or more and 360℃
The following can be heat treated. The amide solvents used here include tetramethylurea, hexamethylphosphoramide, N,N
-Dimethylacetamide, N-methylpyrrolidone-2, N-methylpiperidone-2, N,N-dimethylethyleneurea, N,N,N',N'-tetramethylmalonic acid amide, N-methylcaprolactam, N-acetylpyrrolidine , N,N-diethylacetamide, N-ethylpyrrolidone-2, N,
Examples include N-dimethylpropionic acid amide, N,N-dimethylisobutylamide, N,N-dimethylpropylene urea, N,N-dimethylformamide, and mixtures thereof. This improved heat treatment method requires that the polymetaphenylene isophthalamide film contains at least 1% by weight of an amide solvent, but solvents other than the amide solvent, such as water, alcohol, alkylene glycol, etc. A halogenated hydrocarbon or the like may be included if necessary. This heat treatment method requires at least
It is necessary to conduct the test at a temperature of 100°C or higher and 450°C or lower. If the heat treatment temperature is less than 100°C, the crystallization and heat fixation of the film will not be sufficient, while if it exceeds 450°C, the mechanical properties of the film will be markedly deteriorated, which is undesirable. By appropriately adjusting the heat treatment temperature and heat treatment time within the above range, the film density d
A polymetaphenylene isophthalamide film having (g/cm ³ ) of 1.35 to 1.42 can be obtained. By selecting the stretching orientation and heat treatment crystallization conditions of polymetaphenylene isophthalamide,
The requirements of the configurations () and () of the present invention can be satisfied. The in-plane moisture absorption dimensional change rate (0%→65%RH.) of the thus obtained film satisfies the practical performance of 0.6% or less. In addition, the film has not only high moisture absorption dimensional stability, but also Young's modulus, F-5
Another feature is that it has excellent mechanical properties such as strength and breaking strength. Therefore, the film of the present invention has practical utility as an electronic component material for high-density wiring. The present invention will be explained in detail with reference to Examples below. Examples 1 to 5 Compositions having the following compositions were prepared using polymetaphenylene isophthalamide, N-methylpyrrolidone-2 as an amide solvent, and calcium chloride as a solubilization aid. a/a+b=0.33, c/a=0.20 The above composition was heated to 0.1 mm using a 30 m/m extruder.
An unstretched hydrous film was obtained by extruding it from a T-die with a width of 400 mm onto a casting roller at 110°C, introducing it into a 43% calcium chloride aqueous solution at 100°C, and then washing it in cold water below 10°C. Ta.
This unstretched hydrous film was heated 1.9 times in the machine direction (MD) and 1.9 times in the vertical direction (TD) in hot water at 95°C.
Biaxial stretching was carried out successively at a stretching ratio of 100%. This water-containing biaxially stretched film was immersed in a 30% by weight aqueous solution of N-methylpyrrolidone-2 at room temperature for 10 minutes, and then dried at a constant length for 10 minutes in a hot air dryer at 60°C. A film containing 20% of This film is then heated to 230-310℃.
Heat treatments were carried out at various temperatures. The physical properties of the obtained film are shown in Table 1. The 65%RH moisture absorption dimensional change rate of each film was clearly smaller than that of the films of Comparative Examples 1 to 3, which will be described below, and had excellent mechanical properties, indicating that the films of the present invention have excellent performance. I understand. Comparative Examples 1 to 5 The unstretched hydrous films used in Examples 1 to 3 were
It was sequentially biaxially stretched at various areal magnifications of 1.3 to 3.6 in boiling water at a temperature of 250°C to 350°C, and dried for 10 minutes in a hot air dryer at 120°C without being immersed in an aqueous N-methylpyrrolidone-2 solution. Heat treated at various temperatures of ℃. The physical properties of the obtained film are shown in Table 2, and all of the dimensional changes due to moisture absorption showed extremely large values. Examples 6 to 10 The same procedure as in Examples 1 to 5 was carried out except for the stretching conditions, and for stretching, N-methylpyrrolidone-2 was used.
Sequential biaxial stretching was carried out at various area magnifications in an aqueous solution containing 30% at 60°C. The results are shown in Table 3. As the surface magnification increases, the value of (n〓+n〓/2-n〓) increases monotonically, indicating an improvement in the surface orientation of the film. Correspondingly, the 65%RH moisture absorption dimensional change rate decreased, and the mechanical properties such as Young's modulus, F-S value, and tensile strength improved significantly. The performance was clearly observed. Examples 11 to 12 The same procedure as Examples 6 to 10 was carried out except for the stretching ratio, and the stretching was performed sequentially by setting various ratios of the stretching ratio in the machine direction (MD) and the vertical direction (TD). .
As shown in Table 4, the (n〓−n〓) value of the obtained film was within 0.08 in all cases, and compared to Comparative Example 6 described below, the in-plane RH was 65%.
The anisotropy of the moisture absorption sizing rate is small, and the effects of the present invention are clear. Comparative Example 6 The same procedure as Examples 1 to 5 was performed except for the stretching ratio, and stretching was performed only in the MD direction. The physical property value is the fourth
Shown in the table.

【table】

【table】

【table】

[Table] Example 13 The biaxially stretched film used in Example 1 (NMP content was essentially 0% by weight) was added to a 30% by weight N,N'-dimethylacetamide aqueous solution instead of the NMP aqueous solution. After being immersed for 10 minutes at room temperature, it was dried for 10 minutes in a hot air dryer at 60°C, and then heat treated for 10 minutes at various temperatures shown in Table 5. All of the obtained heat-treated films had small dimensional changes upon moisture absorption and had excellent mechanical properties.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A polymetaphenylene isophthalamide film made of an aromatic polyamide containing metaphenylene isophthalamide as a main repeating unit, the film having a density d (g/cm ³ ) of 1.35 to 1.35.
1.41, and the principal birefringence n〓, n〓, and n〓 for the D line (wavelength 589 nm) (however, n〓, n〓, n〓 are taken in order of increasing principal birefringence value), A polymetaphenylene isophthalamide film that satisfies the following formula n〓+n〓/2-n〓≧0.05. 2. The polymetaphenylene isophthalamide film according to claim 1, wherein the principal birefringence n〓 and n〓 satisfy the relationship n〓−n〓≦0.08.