JP2015098573A - High crystal polyimide fine particle and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polyimide fine particles in which crystallinity and the orientation of crystals are controlled as well as form and grain sizes.SOLUTION: Provided is high crystalinity polyimide fine particles being high crystalinity planar crystals, produced by subjecting monomer salt crystals obtained by mixing an aqueous solution of aromatic tetracarboxylic acid and an aqueous solution of aromatic diamine or an aqueous solution to solid phase polymerization under ordinary pressure. Then, as the raw material for making the high crystalinity polyimide fine particles, pyromellitic acid and p-phenylenediamine are suitable.

Description

  The present invention relates to highly crystalline polyimide fine particles and a method for producing the same.

  The material in which polyimide is made into fine particles combines the characteristics of polyimide with its excellent heat resistance, wear resistance, chemical resistance, electrical insulation, mechanical properties, etc., and the shape of the powder toner for image formation. It is used in various applications such as additives, additives that improve screen printability, and precursors of carbonaceous fine particles.

  On the other hand, in recent years, research has been conducted on polymer crystals aimed at high functionality such as non-linear optical materials, conductive materials, heat conductive materials, and the like. Control of crystallinity and higher order structure is required.

Here, as a method for producing these polyimide fine particles, several methods have been proposed so far, for example, by reacting tetracarboxylic dianhydride and diamine in a solvent such as dimethylformamide, After preparing the precursor polyamic acid varnish, the polyamic acid fine particles are prepared from this varnish by the precipitation method, and then the polyamic acid fine particles are imidized to produce polyimide fine particles whose particle shape and particle size distribution are controlled. A method to do this has been proposed (Patent Document 1).

  In addition, after preparing a polyamic acid solution dissolved in a good solvent, the polyamic acid solution is subjected to heat treatment at a temperature of 100 to 400 ° C. under pressure to imidize polyimide fine particles having high crystallinity in the solvent. A method for precipitation is also proposed (Patent Document 2).

  In addition, as other prior art, fine particles made of a polyimide precursor that can be converted into a polyimide having a high degree of polymerization, and as a method for producing the polyimide precursor fine particles, an aromatic diamine is used in a poor solvent for the polyimide precursor to be produced. And 3,3 ′, 4,4′-biphenyltetracarboxylic acid are mixed to obtain fully aromatic polyimide precursor fine particles (Patent Document 3).

  Furthermore, as another prior art, pyromellitic anhydride and p-phenylenediamine are reacted at a high temperature in a solvent such as liquid paraffin in which the monomer is dissolved but the oligomer is not dissolved, and high crystallinity is obtained. A method of preparing polyimide fine particles has been proposed (Non-patent Document 1).

  Thus, various proposals regarding polyimide fine particles and their production techniques have been made as conventional techniques, but the shape of polyimide fine particles obtained by conventional methods is mostly spherical, and most of them are in the form of It is difficult to control higher order structures such as crystallinity and crystal orientation. Moreover, although there is an example in which the control of the higher-order structure is achieved partially as in Non-Patent Document 1, only a single form has not been completely prepared and practicality is poor. In addition, in the conventional method, a large amount of organic solvent is used in the production process, and the environmental load is large.

Patent Publication 2000-248063 Patent Publication H07-33875 Patent Publication H11-14185

Kunio Kimura et al. Macromolecules, 36, 6292-6294 (2003)

  The present invention has been made in order to solve the above-described conventional problems, and a first object of the present invention is to provide polyimide fine particles in which crystallinity and crystal orientation are controlled as well as morphology and particle size. is there. A second object is to provide a manufacturing method that is inexpensive and has a low environmental impact by using water or an aqueous solvent in the preparation of the polyimide fine particles.

  The inventors of the present invention have completed the present invention as a result of intensive studies in order to develop polyimide fine particles whose shape and size, crystallinity and crystal orientation are controlled.

  That is, the present invention is characterized by having the following configuration.

[1] A highly crystalline polyimide fine particle, which is a polyimide represented by the following formula (1) and is a highly crystalline plate crystal.
[2] The highly crystalline polyimide fine particles as described in [1] above, wherein the plate crystal has a thickness of 0.05 μm or more and 20 μm or less, and the length of the longest straight line on the plane is 1 μm or more and 100 μm or less. [3] The highly crystalline polyimide fine particles according to [1] or [2], wherein polyimide molecular chains are oriented in the thickness direction of the plate crystals.
[4] The highly crystalline polyimide fine particles according to any one of [1] to [3], wherein the plate-like crystals overlap each other in an inclined state. The highly crystalline polyimide fine particles according to any one of [1] to [4], which are (p-phenylenepyromellitimide).
[6] A monomer salt crystal obtained by mixing an aqueous solution or an aqueous solution of an aromatic tetracarboxylic acid represented by the following formula (2) and an aqueous solution or an aqueous solution of an aromatic diamine represented by the following formula (3) under normal pressure: A method for producing highly crystalline polyimide fine particles, characterized by solid-phase polymerization.
[7] The aromatic tetracarboxylic acid of the formula (2) is pyromellitic acid, and the aromatic diamine of the formula (3) is p-phenylenediamine, A method for producing highly crystalline polyimide fine particles.

  The polyimide fine particles obtained by the present invention are expected to have high mechanical strength, gas barrier properties, thermal conductivity, and the like because of their very high crystallinity. In particular, the plate-like crystal not only has high crystallinity but also the molecular chain of polyimide is oriented in the thickness direction of the plate-like crystal, so that the thermal conductivity is in the direction of this molecular chain, that is, the thickness direction of the plate-like crystal. It is expected to have thermal conductivity anisotropy that cannot be achieved with existing thermal conductive fillers. Further, since it is a plate-like crystal or a plate-like crystal aggregate in which the plate-like crystals are aggregated (hereinafter, sometimes collectively referred to as “plate-like crystal”), the flow direction in a molded body such as injection molding. Therefore, the filler when mixed in the resin is expected to exhibit the above characteristics more effectively.

  Further, from the orientation direction, crystallinity, and morphological characteristics of the plate-like crystal, when used as a carbon material precursor, it is difficult to produce a graphite sheet having an orientation structure, that is, in the thickness direction of the sheet. It is possible to produce a graphite sheet having a developed graphite structure. Further, since water or an aqueous solvent is used as a solvent in the production of polyimide fine particles, the cost and environmental burden required for the production of polyimide fine particles can be greatly reduced.

Electron microscope observation result of the monomer salt crystal obtained in Production Example 1 Electron microscope observation results of monomer salt crystals obtained in Production Example 2 Electron microscope observation results of monomer salt crystals obtained in Production Example 3 Electron microscope observation result of the monomer salt crystal obtained in Production Example 3 (enlarge) Electron microscope observation results of monomer salt crystals obtained in Production Example 4 Electron microscope observation result of the polyimide crystal obtained in Example 1 Powder X-ray diffraction measurement result of the polyimide crystal obtained in Example 1 Transmission electron microscope observation results and electron beam diffraction images of the polyimide crystal flakes obtained in Example 1 Electron microscope observation result of the polyimide crystal obtained in Example 2 Powder X-ray diffraction measurement result of the polyimide crystal obtained in Example 2 Electron microscope observation result of the polyimide crystal obtained in Example 3 Electron microscope observation result (enlarged) of the polyimide crystal obtained in Example 3 Electron microscope observation result of the polyimide crystal obtained in Example 4 Powder X-ray diffraction measurement result of the polyimide crystal obtained in Example 4

Polyimide fine particles The polyimide fine particles obtained by the present invention are plate crystals and aggregates of the plate crystals. The length (L) in the plane direction of the plate crystal is 1 to 100 μm, the thickness (D) is 0.05 to 20 μm, and in the case of an aggregate of plate crystals, the size of one side is usually It is about 50-1000 micrometers. The polyimide fine particles are highly crystalline polyimide fine particles characterized in that almost no amorphous peak is observed in X-ray diffraction measurement. The polyimide fine particles are highly crystalline polyimide fine particles in which molecular chains of polyimide are aligned and aligned in the thickness direction. The fact that the molecular chains of polyimide are aligned in the thickness direction can be confirmed by cutting out an ultrathin section of a specific surface of the obtained highly crystalline polyimide fine particles, taking an electron diffraction pattern, and analyzing it. In addition, it can be confirmed by performing X-ray diffraction measurement from directions parallel and perpendicular to the plane direction of the plate crystals arranged in a specific direction. Further, the aggregate of plate crystals is formed by laminating and laminating plate-like polyimide fine particles.

Production method of polyimide fine particles The production method of the present invention comprises monomer salt crystals obtained by mixing an aqueous solution or an aqueous solution of an aromatic tetracarboxylic acid and an aromatic diamine represented by the following formulas (2) and (3). , A method for producing a polyimide crystal characterized by solid-phase polymerization under normal pressure,
(A) a first step of preparing and separating a polyimide precursor by generating and crystallizing a monomer salt in water or an aqueous solvent from an equivalent equivalent of an aromatic tetracarboxylic acid and an aromatic diamine; and (b) ) A second step of solid-phase polymerization of the obtained polyimide precursor under normal pressure,
It is characterized by including.

The first step aromatic tetracarboxylic acid is not particularly limited as long as it is water-soluble or soluble in an aqueous solvent, and a general one can be used. For example, pyromellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 Examples include '4,4'-benzophenone tetracarboxylic acid, 3,3', 4,4'-diphenylsulfone tetracarboxylic acid, and the like. These can use 1 type (s) or 2 or more types. In the present invention, pyromellitic acid is particularly preferable from the viewpoint of the crystallinity of the monomer salt to be produced, and the aromatic tetracarboxylic acid is preferably limited to one type.

  The aromatic diamine is not particularly limited as long as it is water-soluble or soluble in an aqueous solvent, and a general one can be used. For example, p-phenylenediamine, m-phenylenediamine, 4-4′-diaminodiphenyl ether, 4-4′-diaminodiphenylmethane, 4-4′-diaminodiphenylsulfide, 4-4′diaminodiphenylsulfone, 4-4′- Examples include diaminodiphenyl ether and 4-4′-diaminobenzophenone. These can be used alone or in a mixture of two or more. In the present invention, p-phenylenediamine is preferred from the viewpoint of crystallinity of the monomer salt to be produced, and the aromatic diamine is preferably limited to one kind.

  The aqueous solvent is not particularly limited as long as it is a solution composed of water and a water-soluble solvent, and general water-soluble solvents can be used. Examples thereof include alcohols such as methanol and ethanol, polyhydric alcohols such as diethylene glycol and glycerin, pyrrolidone solvents such as N-methylpyrrolidone, and ketone solvents such as acetone. These can be used alone or in a mixture of two or more. The mixing ratio of water and the water-soluble solvent is 0.1 to 99.9 wt% for water, and preferably 20 to 99.9 wt%, more preferably 50 to 99.9 wt% from the viewpoint of reducing the environmental load. It is.

  The conditions for producing a monomer salt that is a polyimide precursor from an aqueous solution or an aqueous solution of an aromatic tetracarboxylic acid and an aromatic diamine may be any condition / mode as long as a predetermined polyimide precursor is produced. Although the form and size of the finally obtained polyimide fine particles are determined by the form and size of the present monomer salt, it is necessary to appropriately adjust the conditions and methods according to the purpose.

  As a method for adjusting the monomer salt, for example, a method of adding and dissolving an aromatic diamine as a solid in an aqueous solution of an aromatic tetracarboxylic acid to obtain a monomer salt crystal, or an aqueous solution of an aromatic tetracarboxylic acid and an aromatic diamine However, this is not a limitation.

  In controlling the form and size of the monomer salt, the mixing method of the raw material aqueous solution such as aromatic tetracarboxylic acid and aromatic diamine and the concentration at the time of mixing are important factors. The higher the raw material concentration, the more the raw material. The faster the mixing speed, the larger the size of the monomer salt crystals obtained. For example, in a method of mixing an aqueous solution of an aromatic tetracarboxylic acid or an aqueous solution and an aqueous solution or an aqueous solution of an aromatic diamine, when the raw material concentration is 30 mmol / L or more, the resulting salt crystals of the monomer salt are formed. While forming large monomer salt crystals, single plate crystals are obtained at concentrations below 30 mmol / L. In addition, when the monomer salt is obtained by adding and mixing the whole amount of an aqueous solution in which an equivalent equivalent aromatic diamine is dissolved into the aqueous solution of the aromatic tetracarboxylic acid under strong stirring, the thickness is 1 to 10 μm, While large monomer salt crystals of about 50 to 1000 μm are obtained in the in-plane direction of the crystal, an aqueous solution in which an equivalent equivalent of aromatic diamine is dissolved is slowly added dropwise to an aqueous solution of aromatic tetracarboxylic acid while stirring. In this case, a small monomer salt crystal having a thickness of 0.1 to 3 μm and about 3 to 10 μm in the in-plane direction of the crystal is obtained.

  The obtained monomer salt crystals are recovered from the liquid by a separation method such as filtration and centrifugation, and then dried to obtain a polyimide precursor. At this time, the drying temperature is 20 to 170 ° C., preferably 30 to 140 ° C., more preferably 50 to 100 ° C., in order to prevent re-dissolution by water or an aqueous solvent attached to the surface and the progress of polymerization. It is preferable to dry under conditions.

In the second step, the second step, solid phase polymerization of the polyimide precursor obtained in the first step is performed. The solid phase polymerization in the present invention is not particularly limited as long as highly crystalline polyimide fine particles can be obtained without changing the form as it is from the polyimide precursor, but in the present invention, from the viewpoint of productivity, at 200 ° C. under normal pressure. It is preferable to carry out the polymerization by appropriately heating up to ˜400 ° C.

  In the above method, for example, a polyimide precursor is placed in a glass container, and heated and dehydrated at a temperature of about 200 ° C. to 250 ° C., preferably about 210 ° C. to 230 ° C. for about 2 hours under an inert gas flow, and then 240 to 400 What is necessary is just to heat up suitably between degrees C and to implement an imidation process. Since water is generated by this heating, it is preferable to carry out the reaction while removing water from the reaction system in the second step.

  In the present invention, a plate-like monomer salt crystal can be prepared by using the above-described method, and the change in the form of the particles is suppressed by solid-phase polymerization as a polyimide precursor. Plate-like polyimide crystal fine particles having high crystallinity can be obtained while maintaining the morphological characteristics. In the present invention, it is possible to obtain polyimide crystal fine particles having different crystal forms and sizes by controlling the conditions for generating the polyimide precursor. Specifically, the size of the polyimide crystal fine particles obtained by the present invention is such that, in the case of an independent plate crystal, the length (L) in the plane direction is 1 to 100 μm and the thickness (D) is 0.05 to In the case of a plate-like aggregate, the size of one side is usually about 50 to 1000 μm.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

[Production Example 1]
When 150 g of an aqueous solution in which an equivalent amount of paraphenylenediamine (hereinafter referred to as PPDA) was dissolved in 150 g of an aqueous solution in which 3.4 mmol of pyromellitic acid (hereinafter referred to as PMA) was dissolved, it was added and mixed all at once. Precipitation occurred. The slurry was filtered to collect white crystals. The yield was 94.7 wt%. From the FT-IR measurement result of the obtained white crystals, a broad salt-derived characteristic absorber is observed from 2500 to 3500 cm-1, and it is a monomer salt consisting of PMA and PPDA (hereinafter PMA-PPDA-1). Was confirmed. Further, from the observation result of the obtained white crystal with a scanning electron microscope, it was confirmed that the white crystal was a tapered plate-like crystal having a length of 20 to 40 μm, a center width of 5 to 7 μm, and a thickness of 0.5 to 2 μm. (FIG. 1).

[Production Example 2]
White crystals were obtained in the same manner as in Production Example 1 except that 100 g of an aqueous solution in which an equivalent equivalent of PPDA was dissolved was dropped into 150 g of an aqueous solution in which 3.4 mmol of PMA had been dissolved at a dropping rate of 10 ml / min. It was. The obtained white crystals were confirmed to be a monomer salt composed of PMA and PPDA (hereinafter referred to as PMA-PPDA-2) from the FT-IR measurement results as in Production Example 1. Further, from the observation result of the obtained white crystal with a scanning electron microscope, it was confirmed that it was a rhomboid plate-like crystal having a width of 2 to 10 μm, a length of 2 to 10 μm, and a thickness of 0.3 to 2 μm (FIG. 2).

[Production Example 3]
White crystals were obtained in the same manner as in Production Example 1, except that 100 g of an aqueous solution in which an equivalent equivalent of PPDA was dissolved was added and mixed all at once with stirring into 150 g of an aqueous solution in which 34 mmol of PMA had been dissolved. The obtained white crystals were confirmed to be a monomer salt composed of PMA and PPDA (hereinafter referred to as PMA-PPDA-3) from the FT-IR measurement results as in Production Example 1. Further, from the observation result of the obtained white crystal with a scanning electron microscope, it is a crystal of a tapered plate crystal having a center width of 20 to 50 μm, a length of 130 to 300 μm, and a thickness of 1 to 10 μm. (FIG. 3). When the surface of the plate was enlarged and observed, it was confirmed that it was an aggregate in which plate crystals were inclined and stacked (FIG. 4).

[Production Example 4]
To 100 g of an aqueous solution in which 3.9 mmol of PMA was heated to 80 ° C., 40 g of ethanol in which 4 equivalents of 4-4′-diaminodiphenyl ether (ODA) was dissolved was added and mixed, and then at room temperature overnight. When allowed to stand, a large amount of white crystals precipitated. The solution containing the crystals was filtered to collect white crystals. The yield was 92.8 wt%. From the result of FT-IR measurement of the obtained white crystals, a broad salt-derived characteristic absorber is observed from 2500 to 3500 cm-1, and it is a monomer salt composed of PMA and ODA (hereinafter PMA-ODA-1). Was confirmed. Moreover, it was confirmed from the scanning electron microscope observation result of the obtained white crystal that it is a plate crystal having a length of 20 to 100 μm, a width of 5 to 30 μm, and a thickness of 0.5 to 3 μm (FIG. 5).

[Example 1]
The PMA-PPDA-1 obtained in Production Example 1 was reacted at 220 ° C. for 2 h, and then heated to 400 ° C. to obtain brown crystals. When FT-IR measurement of the obtained crystal was carried out, characteristic absorbers of imide groups were observed at 1780 cm −1 and 1720 cm −1, and it was confirmed to be polyimide. When this polyimide crystal was observed with a scanning electron microscope, it was a tapered plate-like crystal having a center width of 5 to 7 μm, a length of 20 to 40 μm, and a thickness of 0.5 to 2 μm. -It was confirmed that it was the same form as PPDA-1 (FIG. 6). Moreover, when the powder X-ray-diffraction measurement of this crystal was performed, it turned out that the amorphous | non-crystalline origin halo is not detected but shows very high crystallinity (FIG. 7). Moreover, from the result of cutting out the thin slice in the thickness direction of the obtained plate crystal with a focused ion processing apparatus and performing transmission electron diffraction measurement, polyimide molecules are highly oriented in the thickness direction of the plate crystal. This was confirmed (FIG. 8).

[Example 2]
Brown crystals were obtained in the same manner as in Example 1 except that PMA-PPDA-2 obtained in Production Example 2 was used. When FT-IR measurement of the obtained crystal was carried out, characteristic absorbers of imide groups were observed at 1780 cm −1 and 1720 cm −1, and it was confirmed to be polyimide. This polyimide crystal is a rhomboid plate-like crystal having a width of 2 to 10 μm, a length direction of 2 to 10 μm, and a thickness of 0.3 to 2 μm, and is confirmed to have the same form as PMA-PPDA-2 in Production Example 2. (FIG. 9). Moreover, when the powder X-ray-diffraction measurement of this crystal | crystallization was performed, it turned out that the amorphous | non-crystalline origin halo is not detected but shows very high crystallinity (FIG. 10).

[Example 3]
Brown crystals were obtained in the same manner as in Example 1 except that PMA-PPDA-3 obtained in Production Example 3 was used. When FT-IR measurement of the obtained crystal was carried out, characteristic absorbers of imide groups were observed at 1780 cm −1 and 1720 cm −1, and it was confirmed to be polyimide. This polyimide crystal was confirmed to be a tapered plate crystal having a central width of 20 to 50 μm, a length of 130 to 300 μm, and a thickness of 1 to 10 μm (FIG. 11). When the plate surface was enlarged and observed, it was confirmed that it was an aggregate in which plate crystals were inclined and laminated (FIG. 12), and it was the same form as PMA-PPDA-3 in Production Example 3 Was confirmed. Moreover, when the powder X-ray diffraction measurement of this crystal was performed, it turned out that the amorphous | non-crystalline origin halo is not detected but shows very high crystallinity.

[Example 4]
PMA-ODA-1 obtained in Production Example 4 was reacted at 180 ° C. for 1 h, then heated to 320 ° C. and polymerized for 2 hours to obtain brown crystals. When FT-IR measurement of the obtained crystal was carried out, characteristic absorbers of imide groups were observed at 1780 cm −1 and 1720 cm −1, and it was confirmed to be polyimide. When this polyimide crystal was observed with a scanning electron microscope, it was a plate-like crystal having a width of 5 to 30 μm, a length of 20 to 100 μm, and a thickness of 0.5 to 3 μm, and PMA-ODA-1 in Production Example 4 It was confirmed that it was the same form (FIG. 13). Moreover, when the powder X-ray-diffraction measurement of this crystal | crystallization was performed, it turned out that the amorphous | non-crystalline origin halo is not detected but shows very high crystallinity (FIG. 14).

The polyimide fine particles obtained by the present invention can be used as a filler for improving the mechanical strength due to its high crystallinity, and as a filler for improving gas barrier properties and the like as a heat conductive filler due to its morphological characteristics. The application of can be expected. Also, due to its crystallinity, molecular chain orientation, and its morphological characteristics of plate crystals, it becomes possible to produce a graphite sheet having an orientation structure that has been difficult until now when used as a carbon material precursor. .

Claims (7)

Highly crystalline polyimide fine particles, which are polyimides represented by the following formula (1) and are highly crystalline plate crystals.
  2. The highly crystalline polyimide fine particle according to claim 1, wherein the plate crystal has a thickness of 0.05 μm to 20 μm, and the length of the longest straight line on the plane is 1 μm to 100 μm.   The highly crystalline polyimide fine particle according to claim 1, wherein molecular chains of polyimide are oriented in a thickness direction of the plate crystal. The highly crystalline polyimide fine particles according to any one of claims 1 to 3, wherein the plate-like crystals are aggregates that are stacked in an inclined state.   The highly crystalline polyimide fine particle according to any one of claims 1 to 4, wherein the polyimide is poly (p-phenylenepyromellitimide). A monomer salt crystal obtained by mixing an aqueous solution or an aqueous solution of an aromatic tetracarboxylic acid of the following formula (2) and an aqueous solution or an aqueous solution of an aromatic diamine of the following formula (3) is subjected to solid phase polymerization under normal pressure. A method for producing highly crystalline polyimide fine particles, characterized by comprising:
The highly crystalline polyimide according to claim 6, wherein the aromatic tetracarboxylic acid of the formula (2) is pyromellitic acid, and the aromatic diamine of the formula (3) is p-phenylenediamine. A method for producing fine particles.