JPH06263904A - Production of porous film - Google Patents

Abstract

PURPOSE:To provide a producing method of preparing a porous film uniformly dispersing a dispersing resin in a matrix resin consisting of a polyamide and excellent in permeability by a drawing method. CONSTITUTION:In a porous film dispersing particles consisting of a dispersing resin in a matrix resin and prepared by drawing a film in at least monoaxial direction, the matrix resin contains an aliphatic polyamide or semi-aromatic polyamide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous film, and more particularly to a method for producing a porous film produced by a stretching method using polyamide as a matrix.

[0002]

2. Description of the Related Art Although many porous films and methods for producing them are known, research and development have been actively conducted on porous films having a polyolefin such as polyethylene or polypropylene as a matrix. For example, Japanese Patent Publication Sho 49-8
Japanese Patent No. 6458 describes a method for producing a thermoplastic resin porous body in which a sheet made of a polar thermoplastic resin and a nonpolar thermoplastic resin is rolled and then stretched. The interface between these two kinds of resins is separated by stretching the sheet to generate pores, which is used to form a porous film. As the thermoplastic resin, polyethylene, vinyl chloride, styrene resin or the like is used.

The method for producing a porous film having a polyolefin as a matrix by such a stretching method is useful as a method for producing a porous film, and this production method is further described in JP-A-58-198536. Sho 6
It is also described in JP-A-3-270748 and JP-A-64-26655. For example, JP-A-58-198
No. 536 discloses a thermoplastic resin A such as polypropylene.
And a thermoplastic resin B having a low compatibility with the resin A and a melting point higher by at least 20 ° C., a method for producing a porous film by a stretching method is described.

[0004]

However, in these publications, a polyolefin having a small polarity is used as a thermoplastic resin for a matrix, and a dispersion material is a polar thermoplastic resin such as polystyrene, polycarbonate, polyester, or polyether. With that in mind. None of them describes using polyamide as a matrix.

Further, in these methods in which the matrix resin and the dispersion resin are kneaded, the film is formed, and the film is stretched, the pores are formed not in the thickness direction of the film but in the stretching direction. It is generally difficult to obtain a film having excellent air permeability by communicating pores. After film formation and before stretching, the matrix resin and the dispersion resin are
In these conventional examples, since the compatibility is poor, it is difficult to disperse the dispersed resin satisfactorily, and when stretched from such a state, the pore shape is not arranged even after stretching, and in the thickness direction of the film. It was difficult to form through holes, and the air permeability of the film was limited. Furthermore, the conventional combination of the matrix and the dispersant is reversed, and a matrix of polyamide having a functional group having a large polarity such as an amide group and a dispersant of a thermoplastic resin having a small polarity are combined and subjected to a stretching method, To produce a porous film, polyamide is
It has a lower degree of crystallinity than polyolefin and is more difficult to produce a uniform laminated lamella, which makes it technically more difficult than the production of a conventional porous film in which a conventional polyolefin is a matrix.

A porous film using polyamide as a matrix is proposed in Japanese Patent Application Laid-Open No. 60-65040. In this porous film, a polyolefin resin is used as the dispersed phase, and a separate resin having compatibility with the matrix or the dispersed phase is used in order to enhance the compatibility between the dispersed phase and the matrix. However, even if such a compatible resin is newly added, it is difficult to disperse the dispersed phase well in the matrix in the film after film formation and before stretching, and therefore, in the film direction. It has not been easy to obtain a porous film having excellent air permeability, which has pores penetrating therethrough. Incidentally, it is disclosed in Japanese Patent Laid-Open No. 53-153 that the voids are formed by subjecting a polyamide film to a stretching method.
It is described in Japanese Patent No. 43571. However, there is no description of using a dispersion resin in this porous polyamide film.

[0007]

Therefore, the present invention eliminates the defects of the conventional porous membrane as described above, and uses a polyamide-containing matrix to provide a porous membrane film having fine and uniform pores. As a result of various studies to obtain the above, a combination of a matrix resin having a specific physical property and a dispersion resin was found to be a production method capable of obtaining such a porous film, and the present invention has been completed. That is,
According to the present invention, a mixture of a matrix resin and a dispersion resin having a melting point that is at least 20 ° C. higher than the melting point of the matrix resin is kneaded at a temperature equal to or higher than the melting point of the dispersion resin and dispersed higher than the melting point of the matrix resin. At a temperature lower than the melting point of the resin, the kneaded melt is molded into a sheet, and then, in the method for producing a porous film which is stretched in at least one direction at a temperature lower than the melting point of the matrix resin, the matrix resin and the above An interfacial tension with a dispersion resin is 8 mN / m or less, and a matrix resin contains an aliphatic polyamide or an aromatic polyamide.

Further, in the present invention, it is preferable that the matrix resin contains an aliphatic polyamide as a main component. Further, in the present invention, it is preferable that the dispersion resin mainly contains a polymer having as a repeating unit at least one functional group of the group consisting of an ester group, an amide group, a sulfone group, an ether group and an arylate group.

[0009]

The matrix resin of the present invention contains an aliphatic polyamide or a semiaromatic polyamide. It is preferred that the matrix resin consists essentially of aliphatic or semi-aromatic polyamide. Examples of the aliphatic polyamide include nylon-4,6, nylon-6,6, nylon-6,9, nylon-6,10, nylon-6.
12, Nylon-6, Nylon-3, Nylon-4, Nylon-8, Nylon-9, Nylon-10, Nylon-11, Nylon-12, etc., or copolymers thereof can be used. In addition, so-called semi-aromatic polyamide such as MXD6 nylon can be used. Also, a mixture of these can be used. However, Kevlar and Nomex are not preferable because their melting points are too high.

The dispersion resin, which is a thermoplastic resin, has a melting point that is at least 20 ° C. higher than the melting point of the matrix resin. This is because, under this condition, as described below, the dispersed resin is well dispersed in the film after film formation and before stretching. In the method of kneading the matrix resin and the dispersion resin, forming a film, and stretching, the pores are communicated in the thickness direction of the film, and in order to obtain a film having excellent air permeability, the dispersion resin in the mixture after kneading is It is necessary to be dispersed in the matrix resin in a spherical shape or a shape close to it, and it is also necessary that the dispersion state is maintained even when this mixture is formed into a film.

However, in this film forming step, the dispersed resin is easily deformed into a layer or a fiber due to shear stress or withdrawal immediately after die slip. When the dispersed resin has a layered or fibrous shape after the film formation and before the stretching as described above, the stretching causes the interface between the two polymers to peel off and generate a certain number of pores. However, such voids have a low porosity, and the voids do not communicate with each other. Moreover, holes are unlikely to occur in the thickness direction of the film. As a result of these, the air permeability of the porous film is limited.

Therefore, in order to prevent such deformation of the dispersed resin in the film forming step, the matrix resin has plasticity to the extent that it can be formed into a film at the temperature of the film forming step, while the dispersed resin is solid. It is preferably present in a form that does not readily flow. Therefore, in the present invention, since the matrix resin and the dispersion resin are determined to have such physical properties, the interfacial tension between the matrix resin and the dispersion resin is 8 mN / m or less. This allows the dispersed resin to be uniformly and finely dispersed in the matrix resin in the film after film formation and before stretching. By stretching this film, the dispersed resin particles can be uniformly and finely dispersed in the matrix even after stretching. Further, the porous film thus obtained has pores also in the thickness direction of the film, and has excellent air permeability. The value of the interfacial tension is also a parameter indicating the compatibility between the matrix resin and the dispersion resin. That is, the larger this value, the more easily the dispersed resin in the dispersed phase aggregates.

In order to obtain this interfacial tension, first, for each of the matrix resin and the dispersion resin, the Properti
es of Polymers (DW Van Krevelen, Elsevier)
The solubility parameter δ of the constitutional unit and the dispersion component δ ^d of the solubility parameter are determined by the method described on pages 212 to 213. From this value, the surface tension γ (t) of each resin at the kneading temperature t is obtained by the equation (1).

[0014]

[Equation 1]

Further, the solubility parameter δ, the dispersion component δ ^d of the solubility parameter, and the surface tension γ (t) at the kneading temperature t of the resin are substituted into the equation (2) to obtain the dispersion component γ ^{d of the} surface tension. Further, the surface tension γ (t) and the dispersion component γ ^d of the surface tension are substituted into the equation (3) to obtain the polar component γ ^{p of the} surface tension. Finally, substituting these values in the matrix resin A and the dispersion resin B into the equation (4),
The interfacial tension γ _AB can be obtained.

[0016]

[Equation 2]

As a specific example of the dispersion resin which can be used in the present invention, a monomer unit contains at least one polar functional group such as an ester group, an amide group, a sulfone group, an ether group and an arylate group. It is a dispersion resin containing a polymer. It is preferred that the dispersing resin consists essentially of these polymers. Further, a copolymer of these functional groups or a mixture of these polymers can be used as the dispersion resin.

It is also possible to use copolymers or mixtures of these which contain small amounts of polyolefins. This is because the surface tension can be controlled by such modification, and when the resin is melted and kneaded with the polyamide, the dispersed resin is finely and uniformly dispersed without agglomeration. It is preferable to add an antioxidant, an ultraviolet absorber, a heat stabilizer, a plasticizer, a pigment, a dye or the like to these resins, if necessary.

The method for producing the porous film according to the present invention will be described below. It is preferable that the matrix resin and the dispersion resin are melt-kneaded to form uniform pellets or the like.
The temperature when kneading is higher than the melting temperature of the dispersed resin.

The above mixture is formed into a film by a conventional method, for example, by extrusion molding in which an extruder is equipped with a T die or the like, or by hot pressing. The melting point of the dispersed resin is higher than that of the matrix resin, and the molding temperature is
It is preferably between the melting point of the matrix resin and the melting point of the dispersion resin. The thickness of the film before stretching is 10 to
The thickness is preferably 300 μm, more preferably 20 to 200 μm.

Then, a stretching process is performed to make the film porous. It may be uniaxially stretched or biaxially stretched, and a simultaneous biaxially stretched method may be used.

The stretching temperature is preferably 70 to 250 ° C.,
Furthermore, 100-180 degreeC is preferable. The draw ratio is 1.2 to 4 times in each direction. The stretching speed is 10 to
2000% / min is preferable, and 10 to 500% is more preferable.

[0023]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples.

(Example 1) 52% by volume of nylon-6 (UBE nylon 1024B, Ube Industries, Ltd.) and 48% by volume of polyethylene terephthalate resin (Unitika, NEH2050)
And were extruded into a cylindrical shape while kneading at 280 ° C. using a co-rotating biaxial kneader. After cooling it with water, cut it,
Dry, both resins mixed, diameter 3mm, length 4-5m
m pellets were obtained. In addition, the temperature at the time of kneading is hereinafter referred to as a kneading temperature.

An extruder having a diameter of 30 mm and a T having a width of 300 mm are used.
Using a film forming machine equipped with a die, the pellets were molded into a film having a width of 280 mm and a thickness of 40 μm at a molding temperature of 240 ° C., and the film was 150 mm in width and 60 mm in length.
Was cut into strips of film. This film was stretched 300% in the longitudinal direction at a strain rate of 50% / min using a test uniaxial stretching machine to obtain a white opaque porous film having a width of 150 mm and a length of 240 mm.

Using a gas permeability tester, a pressure difference of 1 k
When the nitrogen gas permeability of this film was measured at gf / cm ² , it was 300 l / m ² · min · (kgf / cm ² )
Met. Note that 1 kgf corresponds to 9.80665N.

The cross section of this film was observed with a scanning electron microscope, and three regions randomly extracted from it were photographed at a magnification of 3
I took a picture at 000 times. From these three photographs, the major axis and minor axis of each particle of the polysulfone resin were measured, and the average particle diameter and the ratio of major axis to minor axis, that is, the aspect ratio was determined.
The average particle size of the dispersed phase of this porous film was 8.2 μm.
m, the average aspect ratio of the particles was 1.6.

(Examples 2 to 11) The same as Example 1 except that the combination of the matrix resin A and the dispersion resin B, and the volume fraction, kneading temperature, molding temperature, stretching temperature and stretching ratio of both were changed. A porous film was obtained. The stretching direction and the stretching speed are the same as in Example 1. 1 and 2, a polysulfone that may be contained in the dispersion resin of the present invention,
Examples of the monomer units of polyether sulfone and polyarylate are shown in formulas (1) to (18). The dispersion resin may be a mixture or copolymer of these. For example, as the polymer of the formula (1), a brand name of Umco Co., UDE
L can be used. Formula (2) is a trade name VICTREX-PES of ICI, formula (3) is a U-polymer U100 trade name of Unitika, formula (4) is a brand name RADEL-R of Amoco, and formula (5) is ICI. Company name VIC
TREX-HTA can be used. Further, as the copolymer of the formulas (2) and (6), the brand name RADEL-A of Amoco Co. can be used. The polysulfone of Example 3 used the formula (1) of FIG. 1, the polyether sulfone of Example 4 used the formula (2) of FIG. 1, and the polyarylate of Example 5 used the formula (3) of FIG.

From the obtained porous film, the nitrogen gas permeability, the average particle size, and the average aspect ratio were determined in the same manner as in Example 1. The scanning magnification of the scanning electron microscope was changed in the range of 600 to 3000 times according to the size of the particles in the dispersed phase. The results are summarized in Table 1.

[0030]

[Table 1]

(Comparative Examples 1 to 5) A combination of the matrix resin A and the dispersion resin B, the volume fraction of both, the kneading temperature,
A porous film was obtained in the same manner as in Example 1 except that the molding temperature, the stretching temperature and the stretching ratio were changed. The stretching direction and the stretching speed are the same as in Example 1. From the obtained porous film, the nitrogen gas permeability, the average particle size, and the average aspect ratio were determined in the same manner as in Example 1. Note that the scanning magnification of the scanning electron microscope is 60 depending on the size of the particles in the dispersed phase.
The value was changed in the range of 0 to 3000 times. These results are shown in Table 2.
Put together.

[0032]

[Table 2]

It can be seen that in the porous film obtained by the production method of the present invention, the dispersed resin is more uniformly dispersed than in the porous film of the comparative example. Further, in the porous film obtained by the production method of the present invention, the porosity and the nitrogen gas permeability are larger than those of the porous films of Comparative Examples,
It can be seen that it has excellent breathability.

[0034]

According to the present invention, since the interfacial tension between the matrix resin and the dispersion resin is 8 mN / m or less, the matrix resin contains polyamide, and the dispersion resin is uniformly and finely dispersed in the matrix resin, It is possible to obtain a porous film having excellent air permeability.

The polyamide film produced by the present invention is, for example, a filter, a packaging sheet, a membrane for batteries, an oil-impregnated insulator, a gas separation membrane, a filtration membrane, a porcelain tape, a photographic film, a microfilm, a pressure-sensitive film. It can be applied to various uses such as tapes, artificial leather and sterilized paper.

[Brief description of drawings]

FIG. 1 is an explanatory view showing monomer units of polysulfone, polyether sulfone and polyarylate which can be used in the present invention.

FIG. 2 is an explanatory view showing monomer units of polysulfone, polyether sulfone and polyarylate which can be used in the present invention.

Claims (1)

[Claims] 1. A mixture of a matrix resin and a dispersion resin having a melting point at least 20 ° C. higher than the melting point of the matrix resin is kneaded at a temperature equal to or higher than the melting point of the dispersion resin, In a method for producing a porous film in which a kneaded melt is molded into a sheet at a temperature higher than the melting point of the dispersion resin, and then stretched in at least one direction at a temperature lower than the melting point of the matrix resin, The interfacial tension between the matrix resin and the dispersion resin is 8
mN / m or less, and the matrix resin contains an aliphatic polyamide or a semi-aromatic polyamide.