JP7184563B2 - Nitrogen-containing aromatic polymer film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nitrogen-containing aromatic polymer film, and more particularly to a nitrogen-containing aromatic polymer film suitable as a material for electronic members.

Films made of high-molecular polymers are widely used as materials for various electronic members such as batteries, capacitors, and electric double layer capacitors. For example, a separator, which is a partition material between electrodes, is required to have electrical conductivity while retaining an electrolyte, high shielding between electrodes, low internal resistance, and the like. In particular, secondary batteries with a large electric capacity are required to suppress heat generation and ignition during a short circuit.

In order to meet the required characteristics of the separator described above, it is difficult to use only the porous polyolefin base material, which is widely used as a separator material, due to the thermal properties of the material. A method of applying a coating is applied. An inorganic particle layer, for example, is selected as the highly heat-resistant functional layer.

However, since it is difficult to form a layer with only inorganic fine particles, a high-molecular polymer is used as a binder between particles to coat a substrate with a particle-containing polymer film. In this case, the polymer used as the particle binder is naturally required to have high heat resistance, and therefore, for example, a nitrogen-containing aromatic polymer (hereinafter sometimes referred to as "aramid") is used.

Common nitrogen-containing aromatic polymers include, for example, polyparaphenylene terephthalamide. However, the polymer is difficult to dissolve in organic solvents, and it is very difficult to prepare a coating solution for coating. Moreover, even if the polymer can be dissolved, due to the liquid crystallinity of the polymer, the molecules tend to form domains with each other in the solution, resulting in a heterogeneous appearance that is difficult to redisperse, resulting in poor storage stability.

In contrast to the above, copolymerized polyparaphenylene terephthalamide having an oxydiphenylene component as a copolymer component actively introduces a bending component into the molecule, making it easier to dissolve in organic solvents and stabilizing the solution. It also has excellent sex. However, the solution in which the polymer is dissolved is highly viscous, making the coating process difficult. In order to lower the viscosity of the solution, it is conceivable to reduce the molecular weight of the polymer. Furthermore, it is generally difficult to control polymer molecular weights precisely and reproducibly. Therefore, it is difficult to appropriately manipulate the polymer molecular weight and provide a coating liquid having an appropriate viscosity according to the coating apparatus and process.

JP 2012-54230 A

The present invention achieves a sufficiently low viscosity of the coating liquid to exhibit good coating properties during film formation, while providing high mechanical properties. An object of the present invention is to provide a polymer film that can easily control the

The present invention provides a nitrogen-containing aromatic polymer film containing 55% by volume or more of particles per film volume, wherein the nitrogen-containing aromatic polymer comprises a polymer (A) having a number average molecular weight of 10,000 to 60,000 and a number A nitrogen-containing aromatic polymer film characterized by being a mixture with a polymer (B) having an average molecular weight of 100,000 to 400,000.

According to the present invention, while achieving a sufficiently low coating fluid viscosity to develop good coating properties during film formation, high mechanical properties are provided, and the coating fluid viscosity and film dynamics during film formation are improved. It is possible to provide a polymer film whose physical properties can be easily controlled.

It is a model diagram expressing a low-molecular-weight polymer portion as a low-elongation hard segment and a high-molecular-weight polymer portion as a high-elongation soft segment. 1 is a model diagram of a film using a single low-molecular-weight polymer. FIG. 1 is a model diagram of a film using a single high-molecular-weight polymer. FIG. 1 is a model diagram of a film system of a blend of a low molecular weight polymer and a high molecular weight polymer; FIG.

<Aromatic Polyamide>
In the present invention, nitrogen-containing aromatic polymers are used as polymer (A) and polymer (B). As the nitrogen-containing aromatic polymer, aromatic polyamide (hereinafter sometimes referred to as "aramid"), aromatic polyimide, and aromatic polyamideimide can be used. Among them, aromatic polyamides are preferred, and para-aromatic polyamides (hereinafter sometimes referred to as "para-aramid") are preferred from the viewpoint of physical properties, heat resistance and low heat shrinkage properties. Copolymerized poly-paraphenylene terephthalamide is preferred from the viewpoint of solubility in an organic solvent and stability of a solution. Preferred copolymerized polyparaphenylene terephthalamide is obtained by copolymerizing polyparaphenylene terephthalamide with 3,4'-oxydiphenylenediamine or 4,4'-oxydiphenylenediamine as a copolymerized diamine component. In this case, the ratio of 3,4'-oxydiphenylenediamine or 4,4'-oxydiphenylenediamine to the total diamine component is preferably 25 to 75 mol%, more preferably 30 to 70 mol%. By containing the above copolymerization component within this range, it is possible to ensure solubility in organic solvents while maintaining intermolecular interactions that contribute to the development of mechanical properties.

<Mixture>
Polymer (A) has a number average molecular weight of 10,000 to 60,000, and polymer (B) has a number average molecular weight of 100,000 to 400,000. In the present invention, a mixture of these polymer (A) and polymer (B) is used.

When only the polymer (A) is used, the viscosity of the coating solution can be lowered and the coatability is excellent, but the entanglement points between polymer chains are reduced, resulting in a brittle film with low tensile strength and low elongation. becomes. On the other hand, when only the polymer (B) is used, sufficient entanglement points between polymer chains can be secured, so that the mechanical properties of the film are at a high level, but the viscosity of the coating solution increases and the coatability is poor.

The mixing ratio of polymer (A) and polymer (B) is preferably A/B=10 wt %/90 wt % to 90 wt %/10 wt %. By using within this range, the polymer blend effect of the polymer (A) and the polymer (B) can be sufficiently exhibited, and both coatability and mechanical properties can be achieved.

<Low molecular weight>
As a method of lowering the molecular weight of the polymer, a method of changing the polymerization conditions or a method of immersion in an acidic solution may be used. However, the former is a change that has a great influence on the polymer production process and requires fine control of the molecular weight, which is difficult to control. Moreover, the latter is not desirable because the decomposition reaction of the polymer is less likely to occur in an acidic environment, and it is necessary to set an excessive temperature and time.

In the present invention, polymer (A) and polymer (B) are preferably those obtained by subjecting a nitrogen-containing aromatic polymer having a higher molecular weight to alkali immersion treatment to adjust the molecular weight. Alkaline immersion treatment is a treatment for reducing the molecular weight of the nitrogen-containing aromatic polymer by immersing the polymer in an alkaline solution. Polymers having various molecular weights can be obtained from the same nitrogen-containing aromatic polymer by appropriately setting the conditions of the alkali immersion treatment by reducing the molecular weight in this treatment.

When using the method of reducing the molecular weight by alkali immersion treatment, the temperature of the immersion treatment is, for example, 80 to 140° C., the alkali concentration is, for example, 1 to 10% by weight when NaOH is used as the alkali, and the immersion time is, for example, 30. Minutes to 2 hours. If the alkali concentration is higher, the temperature is higher, or the time is longer than these conditions, the decomposition of the polymer by the alkali will proceed excessively, and in addition to the deterioration of the polymer after treatment and the deterioration of its mechanical properties, it will be more likely to occur. It is not preferable because the process and the neutralization step after the treatment require a large process cost. On the other hand, if the alkali concentration is lower, the temperature is lower, or the time is longer than these conditions, the polymer cannot be effectively reduced in molecular weight by alkali decomposition, and the viscosity of the coating solution cannot be reduced.

<Particle>
The polymer film of the present invention contains 55% by volume or more of particles, preferably 55 to 99% by volume. If the content is less than 55% by volume, it is not possible to obtain good heat resistance and low shrinkage when used as a separator while imparting sufficient porosity. If the volume exceeds 99%, when used as a separator, the movement of ions necessary for the application tends to be hindered, which is not preferable.

As the particles, both organic particles and inorganic particles can be used. Inorganic particles are preferred from the viewpoint of obtaining good heat resistance. Examples of substances constituting inorganic particles include metals, oxide compounds, semiconductor elements, and semiconductor compounds. Specifically, semiconductor materials such as silicon, silicon carbide, and germanium, compounds such as boron nitride, and carbon materials such as carbon nanofibers and graphite can be exemplified. Mineral fine particles such as kaolin, talc, clay, hydrotalcite, and diatomaceous earth can also be exemplified. Further examples include calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, mica, zeolite, and glass. Inorganic particles are excellent in terms of heat resistance and chemical stability, and silica, kaolin, carbon black, and alumina are particularly preferred.

The particle size is, for example, an average particle size of 10 μm or less, preferably 5 μm or less, more preferably 0.01 to 2 μm. A plurality of types of particles may be used in combination.

<Film manufacturing method>
The nitrogen-containing aromatic polymer film of the present invention can be produced by dissolving the mixture of the polymer (A) and the polymer (B) in an organic solvent to prepare a coating liquid, applying the coating liquid to a substrate and drying. Obtainable.

Dissolution in an organic solvent is preferably carried out so that the polymer concentration in the solution is 1.5 to 4% by weight and the viscosity of the solution is 400 to 5000 mPa·S at room temperature. If the polymer concentration is less than 1.5% by weight, the shrinkage of the film increases during drying after forming, which is undesirable. On the other hand, if it exceeds 4% by weight, the amount of particles to be added becomes excessive, and it becomes difficult to prepare a solution capable of securing the volume of particles necessary for forming a film, which is not preferable. Further, if the viscosity of the solution is less than 400 mPa·S or more than 5000 mPa·S, the process of coating the substrate becomes difficult, which is not preferable.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples. Measurement was performed by the following method.
(1) Dope viscosity A sample for dope viscosity measurement was allowed to stand in a temperature and humidity control room controlled at room temperature of 25°C and humidity of 60% for 24 hours, and then measured under the following conditions.
B-type viscometer: BROOKFIELD Viscometer DV-I Prime
Rotor: SC4-18, SC4-29
Temperature: 20°C
(2) number average molecular weight (Mn) and weight average molecular weight (Mw)
It was measured by gel permeation chromatography (GPC) under the following conditions.
Device name: High performance liquid chromatograph LC-20A series Column oven: CTO-20A
Mobile phase: NMP
Autosampler: SIL-20AHT
LC workstation: LC solution
Flow rate: 0.3 ml/min Differential refractometer detector: RID-10A
Oven temperature: 60°C
Molecular weight standard sample: Polystyrene Ave Mn in the table was calculated by the following formula.
Ave Mn=Mn(A)×W(A)/100+Mn(B)×W(B)/100
Mn (A): Number average molecular weight of polymer A (lower molecular weight polymer) W (A): Mixing ratio (% by weight) of polymer A (lower molecular weight polymer)
Mn (B): Number average molecular weight of polymer B (high molecular weight polymer) W (B): Mixing ratio (% by weight) of polymer B (high molecular weight polymer)
(3) Film thickness Measured with a thickness meter.
(4) Film basis weight A sample was cut into 5 cm squares, and the weight was measured to calculate the basis weight.
(5) Tensile Strength, Elongation at Break, and Elastic Modulus A sample was cut into strips of 10 mm width×50 mm length, and subjected to a tensile test using a Tensilon universal testing machine (RTF-1210) for measurement. The tensile speed was set to 20 mm/min.

Example 1
(Polymer alkali treatment)
The following copolymerized polyparaphenylene terephthalamide was used as the nitrogen-containing aromatic polymer. That is, it is polymerized from paraphenylenediamine, a copolymerized diamine component and paraterephthalic acid dichloride, the copolymerized diamine component is 3,4'-oxydiphenylenediamine, and the ratio of the copolymerized diamine component to the total diamine component is 50. mol % nitrogen-containing aromatic polymer was used.

This polymer was placed in an aqueous solution of sodium hydroxide having a concentration of 5% by weight, and subjected to alkaline immersion treatment at 130° C. for 1 hour using an infrared heating type mini-color dyeing machine (manufactured by Texam Giken Co., Ltd.). The treated polymer was neutralized by washing with water to obtain a polymer sample. The weight average molecular weight (Mw) and number average molecular weight (Mn) of this polymer sample were measured. A nitrogen-containing aromatic polymer having a number average molecular weight (Mn) of 56,000 was obtained.

Furthermore, two types of nitrogen-containing aromatic polymers having number average molecular weights (Mn) of 178,000 and 318,000 were obtained by changing the alkali treatment conditions. Specifically, it is placed in an aqueous sodium hydroxide solution having a concentration of 3% by weight, and is subjected to alkali immersion treatment at 130° C. for 1 hour with an infrared heating type mini-color dyeing machine (manufactured by Texam Giken Co., Ltd.), resulting in a number average molecular weight. A nitrogen-containing aromatic polymer having a (Mn) of 178,000 and a nitrogen-containing aromatic polymer having a number average molecular weight (Mn) of 318,000 were prepared under the condition that no alkali immersion treatment was performed.

(Preparation of polymer solution)
The above nitrogen-containing aromatic polymer with Mn = 56,000 is used as polymer (A), the above nitrogen-containing aromatic polymer with Mn = 318,000 is used as polymer (B), and the mixture ratio of both is polymer (A )/polymer (B) = 50% by weight/50% by weight, and the polymer concentration (total of polymer (A) and polymer (B)) in N-methyl-2-pyrrolidone (NMP) is 3. % by weight and stirred at a temperature of 80.degree.

At this time, it was confirmed that the polymer mixture was swollen by NMP, lithium chloride was added to 0.8% by weight of the total solution, and a solution in which the polymer was dissolved in NMP (hereinafter, this solution is referred to as "dope ”) was produced. The dope viscosity of this dope was measured.

(Production of film)
Based on the solid weight of the polymer contained in the polymer dope prepared above and the densities of the polymer and alumina, alumina fine particles were prepared with a weight that would give a polymer/alumina fine particle volume fraction of 40/60 in the dope. These fine alumina particles were added to N-methyl-2-pyrrolidone (NMP) to prepare a dispersion having a fine alumina particle concentration of 50% by weight. A polymer dope containing fine alumina particles was prepared by adding this dispersion while heating and stirring the previously prepared polymer dope at 80°C.

The resulting polymer dope is applied onto a smooth glass substrate using a stainless steel coating bar, dried at 100° C. for 15 minutes to volatilize NMP to some extent, and placed in a water bath at room temperature. The coated film was immersed for 30 minutes to solidify. After that, water was wiped off and dried again at 80° C. for 10 minutes to obtain a film sample. The particle content of this film sample was 60% by volume. The tensile strength, elongation at break and elastic modulus of the film samples were measured.

Example 2
Same as Example 1, except that the same polymer as in Example 1 was used, and the mixing ratio of the polymer was polymer (A) (low molecular weight side)/polymer (B) (high molecular weight side) = 75% by weight/25% by weight. and implemented.

Comparative example 1
The dope was prepared with a single polymer with Mn=318,000. Dope and film samples were prepared and their physical properties were evaluated in the same manner as in Example 1.

Comparative example 2
The dope was prepared with a single polymer with Mn=178,000. Dope and film samples were prepared and their physical properties were evaluated in the same manner as in Example 1.

Comparative example 3
The dope was prepared with a single polymer with Mn=56,000. Dope and film samples were prepared and their physical properties were evaluated in the same manner as in Example 1.
Table 1 shows the evaluation results.

Considering the high-molecular-weight polymer, the dope viscosity can be effectively reduced by blending a polymer with a relatively low number-average molecular weight (comparison between Example 1 and Comparative Example 1). Also, the degree of viscosity-lowering effect is generally consistent with a single polymer doped system with a molecular weight similar to the average molecular weight (Ave Mn) (compare Example 1 and Comparative Example 2).

However, the physical properties of the film of Comparative Example 2 are lower than those of the film of Comparative Example 1 in terms of both strength and elongation. In the film of Comparative Example 3, deterioration in physical properties is more pronounced.

On the other hand, the physical properties of the film of Example 1, which is a polymer blend system, maintain high strength and high elongation. It is compatible with high mechanical properties.

In addition, in Example 2 in which the blend ratio was changed, the dope viscosity was further reduced compared to Example 1 due to the increase in the ratio of the low-molecular-weight polymer. On the other hand, the physical properties of the film are lower than those of Example 1 because the proportion of the high-molecular-weight polymer is relatively reduced.

In the present invention, the coatability and physical properties of the film can be controlled by the easily modifiable factor of using two types of molecular weight polymers and changing their mixing ratio.

The polymer blend effect described above is considered as follows.
A low-molecular-weight polymer is considered to have a generally elongated shape because of its short polymer chain length and low flexibility. Therefore, it is considered that the polymer chain is completely stretched when it is pulled, and the original tensile elastic modulus of the polymer chain is exhibited at an early stage. On the other hand, high-molecular-weight polymers are considered to have a high flexibility due to their long polymer chain length, and take a tangled form like a string. Therefore, the polymer chain undergoes low-rigidity behavior in which the entangled polymer chains are loosened when pulled, so it is considered that there is a time gap before the stretched polymer chain reaches its original tensile modulus.

Based on the above, the low-molecular-weight polymer portion is modeled as a low-elongation hard segment, and the high-molecular-weight polymer portion is modeled as a high-elongation soft segment (Fig. 1). In this model, the physical properties of the film can be described by (i) the structure of the segment itself (primary structure) and (ii) the entanglement structure between the segments (secondary structure).

A model diagram of a film system consisting of a single low-molecular-weight polymer is shown in FIG. In this system, hard segments are mainly present, and soft segments (high-molecular-weight polymer chains) minor in molecular weight distribution form entanglements (2.1 in FIG. 2). Since there are many rigid hard segments, the initial elastic modulus is expected to be high. 2.2). As a result, fracture occurs in the hard segment portion where stress is concentrated (2.3 in FIG. 2), or in the soft segment portion where there is locally less entanglement (2.4 in FIG. 2).

A model diagram of a film system consisting of a single high-molecular-weight polymer is shown in FIG. In this system, the soft segments are mainly present, and therefore the tensile properties are considered to be dominated by the entanglement formed by the soft segments (3.1 in Fig. 3). Therefore, elongation increases. However, the entanglement is not uniformly formed, and there are many and few entanglement points. Therefore, the stress concentrates on a less entangled portion corresponding to a mechanically weak portion (3.2 in FIG. 3), and only this portion reaches breaking elongation and breaks (3.3 in FIG. 3).

A model diagram of a blend film system of a low molecular weight polymer and a high molecular weight polymer is shown in FIG. In this system, both soft segments and hard segments are present (4.1 in FIG. 4), so in contrast to the model in FIG. there is As in Fig. 3, the entanglement unevenness formed by the soft segments also exists in this system, but the presence of the rigid hard segments increases the initial elastic modulus and suppresses the intensive elongation of areas with less entanglement. (4.2 in FIG. 4). As a result, the entire system is stretched relatively uniformly while preventing stress concentration, and high elasticity and high elongation are considered to be compatible (4.3 in FIG. 4).

The nitrogen-containing aromatic film of the present invention can be suitably used, for example, as a separator for secondary batteries.

2.1 Hard segments are mainly present in the film, and minor soft segments (high molecular weight chains) form entanglement in the molecular weight distribution. 2.3 Fracture occurs in hard segment where stress is concentrated 2.4 Soft segment where entanglement is locally low 3.1 Soft segments are mainly present, and entanglement formed by soft segments is dominant in tensile properties 3.2 Although the elongation of the film increases, the entanglement is formed uniformly 3.3 Only the places where the stress is concentrated reach the breaking elongation and the film is broken. 4.1 Fracture state 4.1 Since both soft segments and hard segments exist, there are many entanglements due to soft segments compared to the model in Fig. 2, and high elongation is secured 4.2 Soft segment formation Although entanglement unevenness exists, the initial elastic modulus of the film increases due to the presence of rigid hard segments, and the intensive elongation of areas with less entanglement is suppressed 4.3 Overall film while preventing stress concentration is stretched relatively uniformly, achieving both high elasticity and high elongation

Claims (2)

A method for producing a nitrogen-containing aromatic polymer film containing 55% by volume or more of particles per film volume, wherein the nitrogen-containing aromatic polymer comprises a polymer (A) having a number average molecular weight of 10,000 to 60,000 and a number average It is a mixture with a polymer (B) having a molecular weight of 100,000 to 400,000. 10% by weight, the polymer (A) and the polymer (B) are polyparaphenylene terephthalamide and 3,4'-oxydiphenylenediamine or 4,4'-oxydiphenylenediamine as a copolymerized diamine component. It is a copolymerized poly-paraphenylene terephthalamide, and in the production method, the polymer (A) and the polymer (B) are mixed in an organic solvent at a mixing ratio of A/B = 10 wt%/90 wt% to 90 wt%/10 wt%. A method for producing a nitrogen-containing aromatic polymer film, comprising dissolving a coating solution to form a coating solution, applying the coating solution to a substrate, and drying the coating solution to produce a nitrogen-containing aromatic polymer film. The polymer (A) is a nitrogen-containing aromatic polymer having a number average molecular weight in the range of 10,000 to 60,000 by immersion treatment in an alkaline solution, and the polymer (B) is a nitrogen-containing 2. The method for producing a film according to claim 1 , wherein the aromatic polymer is immersed in an alkaline solution to have a number average molecular weight in the range of 100,000 to 400,000.

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