JP2003080590A - Fluoroplastic porous body and manufacturing method thereof, tetrafluoroethylene resin fine powder, or extruded article using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problem that, although porosity is increased as a percentage of stretch is increased, the diameters of pores are also enlarged and a filtering performance lessens when a method of opening the pores by stretching is adopted as a manufacturing method of a fluoroplastic porous body and that, when the porosity is increased for enlarging a flow rate of permeation as to the porous body having small pore diameters and a high filtering performance, but having a small flow rate of penetration consequently, the pore diameters are enlarged accordingly, while the filtering performance lessens, and thereby to obtain the fluoroplastic porous body which has high processing efficiency and also has a high filtering performance. SOLUTION: In a manufacturing process of the fluoroplastic porous body, PTFE fine powder exposed to a radiation such as electron rays or gamma rays is extruded, or it is exposed to the radiation after it is extruded. Then, the material is stretched to manufacture the porous body.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is used for a gas separation membrane, a liquid separation membrane, a gas-liquid separation membrane for the purpose of degassing a liquid or dissolving a gas in a liquid, a medical material such as an artificial blood vessel, and the like. The present invention relates to a fluororesin porous body and a method for producing the same, and a tetrafluoroethylene resin fine powder, or an extrusion molded product thereof.

[0002]

2. Description of the Related Art A porous body (hereinafter referred to as fluororesin porous body) made of tetrafluoroethylene resin (hereinafter abbreviated as PTFE) has excellent characteristics such as chemical resistance and heat resistance. , Which has a uniform and fine porous structure, and has traditionally been
It is used in many applications such as separation membranes, artificial blood vessels, catheters and incubators. In addition, utilizing the fact that it is water repellent,
It is also used for degassing an aqueous liquid, or conversely, as a gas dissolution membrane for an aqueous liquid.

This fluororesin porous material is usually prepared by mixing PTFE fine powder as a raw material with a liquid lubricant (auxiliary agent), pressing it into a cylindrical shape by preforming, and then extruding the paste into a predetermined shape. This extruded product is manufactured by a method in which the extruded product is stretched in the major axis direction to make it porous, and then fired. In addition to the stretching method, the porosification includes extraction of the pore-forming agent after mixing the pore-forming agent, foaming with a foaming agent, and the like.
The above stretching method is superior in terms of porosity indicating the degree of porosity, filter performance, or performance such as strength.

The fluororesin porous material is required to have desired properties such as average pore diameter, transmittance, permeation flow rate and strength according to various uses. Among these characteristics, the performance of the filter is mainly determined by the permeation flow rate of the gas or liquid that permeates the inside of the porous material and the limit value of the size of the particles to be separated by filtration, that is, the pore size. These two characteristics are often substituted by the porosity, which is the ratio of air to the pores, and the bubble point, which is the pressure at which air permeates in alcohol. The bubble point is a method utilizing the capillary phenomenon, and the smaller the pore diameter, the larger the capillary phenomenon. Therefore, the higher the bubble point, the smaller the pore.

Generally, it is desirable that the porosity indicating the treatment efficiency of filtration is higher if the pore diameter and bubble point, which are the separation ability of filtration, are the same. However, as a method for producing a fluororesin porous body, if a method of forming holes by stretching is adopted, the porosity increases as the stretching rate increases, but at the same time, the pore size also increases, Filtration performance becomes smaller. As described above, there is a correlation between the porosity and the bubble point, and normally, when the porosity is determined, the bubble point is also determined. Therefore, a filter having a small pore size and high filtration performance has a small permeation flow rate, and when the porosity is increased in order to increase the permeation flow rate, the pore size also becomes large and the filtration performance becomes small. Therefore, for example, when it is attempted to be used as a filter having a small pore size, which has higher filtration performance due to the higher integration of semiconductors, only a filter having an extremely small filtration treatment capacity can be obtained, which is difficult to put into practical use.

[0006]

As described above, the PTFE stretched porous body has a problem that the speed at the time of stretch
Although it is possible to change the pore diameter and the porosity to some extent by changing the temperature conditions, basically there is little freedom in the relationship between the pore diameter and the porosity. Of course, as a mechanism for generating pores in the porous body, in addition to stretching, PTF due to the pressure during extrusion will be described later.
The degree of connection between the E particles and the degree of firing depending on the heating conditions during firing also affect. However, the former has a limit value as described later, and the latter has high performance as a filter when firing is weak, but strength and durability are impaired, so in many cases it is necessary to completely fire even if the performance decreases. is there. Therefore, PTFE made from PTFE fine powder
In the case of the E porous body, it was not possible to realize a porous body having better filtration performance and higher treatment efficiency.

It is an object of the present invention to provide a fluororesin porous material which improves the characteristics of PTFE fine powder during stretching, has good filtration performance and high processing efficiency, and a method for producing the same. .

[0008]

As a result of intensive studies on this problem, the present inventor has found that PT at the raw material powder stage before the stretching step in the manufacturing process of the fluororesin porous material.
By irradiating the FE fine powder or the extrusion-molded product in the extrusion molding step with radiation, there is a correlation between the bubble point and the porosity, and the bubble point becomes smaller when the porosity is increased. By modifying the inherent drawbacks of fine powder, a porous fluororesin having good filtration performance and high processing efficiency was obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The fluororesin porous material of the present invention comprises
For example, it can be manufactured by the following technique. First, in the extrusion step, a mixed paste of PTFE fine powder and a lubricant is extruded into a sheet shape or a tube shape, rolled if necessary, and then stretched. In this step, fibers are formed in the drawing direction so that a thread is drawn between the crack-like holes formed so that the resin powders press-bonded by extrusion separate from each other by drawing and are torn. After or at least PT
A fluororesin porous body can be obtained by heating the FE to a melting point of 327 ° C. or higher and sintering.

In the present invention, in the above process, the PTFE fine powder is obtained at any stage before the stretching process,
Irradiation with heavy ion rays, alpha rays, beta rays, that is, electron rays, gamma rays, X rays, ultraviolet rays, and the like. About this line type, PTFE is used for large particle beams such as heavy ions.
It is not suitable because the effect on the molecule is uneven, and the energy given to the PTFE molecule is small with X-rays and ultraviolet rays. From the viewpoint of versatility, it is desirable to use an electron beam or gamma ray, which is uniform for powder and extrusion molding. Gamma rays, which have high transparency, are most desirable because they can be irradiated.

The radiation dose before stretching in the present invention is
It is necessary to make the irradiation dose extremely small as compared with the irradiation dose of general polymer treatment. Specifically, it is preferably 10 Gy or more and less than 1000 Gy, and more preferably 100 Gy to 500 Gy from the viewpoint of controlling the stretchability described later.

The function of the present invention will be described below. PT
Secondary particles of several hundred μm of FE fine powder have a particle size of about 0.
It is made up of primary particles with a size of about 2 μm.
In this primary particle, band-shaped crystals exist in a folded state. The connection between the primary particles formed by rubbing the particles by the flow in the extrusion process connects both particles, and when the particles are stretched during stretching, the band of folded crystals in the primary particles unwinds and becomes fibrous. It becomes a structure. That is, the porous structure by stretching is determined by two factors, the amount of this connection formation and the degree to which the crystal bands from the folded structure start to squeeze out.

Since the porosity correlates with the draw ratio, the size of the pores at the same porosity depends on how many pores are generated per unit length of the extruded product before stretching, that is, the generation density of the holes. Inversely correlate. That is, if the number of holes generated by stretching is large, many small holes are open, and if the number of generated holes is small, each hole becomes large. Generally, the higher the extrusion pressure, the more shear stress is applied to the particles, the more the amount of connections formed, and the higher the open hole density.

In the prior art, as a method of increasing the extrusion pressure, a method of reducing the amount of oil as an extrusion aid has been used. However, according to the results of the study conducted by the inventors, the number of connections is two per particle, that is, the state where adjacent particles hold hands is limited, and the number of connections does not increase even if the extrusion pressure is further increased. know.

As mentioned above, the porous structure due to stretching is determined by the amount of connection formation and the degree of squeezing out the crystal bands from the folded structure. As a result of intensive studies on the method of controlling the porous structure in addition to the limited amount of connection formation, the present inventors have found that the length of fibers that can be generated from PTFE fine powder particles can be changed by irradiation with radiation. did. That is, when the PTFE fine powder is irradiated with radiation, the folded structure of the crystal bands in the primary particles is partially destroyed, and the amount of thread tipped is shortened.

This phenomenon can be shown by the relationship between the irradiation amount and the elongation in the tensile test of the extruded product after irradiation.
The elongation of the extruded product depends on the irradiation dose of radiation, and the phenomenon of elongation begins to be detected at an irradiation dose of about 10 Gy,
Irradiation of more than Gy causes almost no elongation. That is, the fiber-forming ability is lost and the film cannot be substantially stretched. This decrease in elongation does not differ between irradiation of the raw material powder before extrusion and irradiation after extrusion molding. The tensile strength correlates with the extrusion pressure but does not correlate with the irradiation dose. In other words, irradiation does not affect the connection formation during extrusion, but it does not prevent the thread from the particles, that is, the twitching of the thread, that is, the extension of the folded structure of the crystal band.

The present inventors have also discovered that these phenomena can be caught by observing the endothermic curve of PTFE with a differential scanning calorimeter. The PTFE fine powder produced by emulsion polymerization has an endothermic peak at 347 ° C., which is 20 ° C. higher than 327 ° C. which is obtained by molding powder made by another polymerization method or PTFE once heated. Irradiation causes this melting point peak at 347 ° C to reach 335 ° C.
It turned out to change to the neighborhood.

It is known that the PTFE fine powder has a peak at 347 ° C. and a shoulder near 335 ° C. When the PTFE fine powder is irradiated with radiation, an endothermic peak begins to appear on the shoulder at around 335 ° C from about 10 Gy, and when the irradiation amount is further increased, the peak at 347 ° C decreases and conversely the peak at 335 ° C. Is getting bigger. With irradiation of about 1 kGy or more, the peak at 347 ° C. can no longer be detected.
(See FIG. 2) As shown in FIG.
When a tensile test is conducted, an extruded product made of PTFE in a state where the peak at 0 ° C cannot be detected breaks with almost no elongation, and stretching is actually impossible.

That is, when the present invention is realized, in order to control the stretching well, the PTFE irradiated with the radiation is used.
In addition, it is necessary to have both a peak of 347 ° C. indicating that the elongation increases and a peak of 335 ° C. indicating that the elongation decreases. Incidentally, in the radiation irradiation of at least the above range, the amount of heat necessary for melting the crystal that is an index of the amount of crystals, that is, the latent heat of fusion, is not different from that in the case of no irradiation, and the phenomenon such as the decrease in elongation described above It is suggested that this is not due to the crystal breakdown of PTFE.

As a conventional technique for changing the melting point peak of this type, for example, the PTFE disclosed in Japanese Patent Publication No. Sho 58-145735 and Japanese Patent No. 2533329 is disclosed.
There is fine powder heat treatment. The former is 34 without the melting point shoulder of 338 ° C that fine powder has.
This is a method of making a single peak at 7 ° C, and the latter is characterized by making a single peak at 335 ° C. The biggest difference between these methods and the present invention is that the method of the present invention does not involve the change of the latent heat of fusion as described in the previous section. Ie PT
In the conventional method in which FE fine powder is heat-treated, it is unavoidable that the amount of crystals changes because the crystals melt to some extent by heating and change the melting point. In the method of the present invention, there is almost no change in the latent heat of fusion, that is, the amount of crystals, even if irradiation is performed until a single peak at 335 ° C. similar to the fusion heat peak obtained by the method disclosed in Japanese Patent No. 2533329 is irradiated. , The mechanism affecting the crystal is considered to be different from these heating methods.

An application example of the technique of the present invention will be specifically described in the case of reducing the pore diameter without changing the porosity. Ordinary extruded products are generally 1
Stretching of 000% or more is possible. When it is desired to reduce the pore size, the stretching rate is lowered, but for example, for a uniaxially stretched tube having a pore size of 0.1 μm, the stretching rate must be suppressed to 100 to 150%. When unirradiated, it is possible to deal with stretching of 1000% or more, and therefore the pores initially generated are reasonably large to some extent and do not lead to the generation of the next pore. That is, the density of the openings does not increase so much.

On the other hand, in the case of the irradiated product in which the stretchable amount is limited, even if the stretching ratio is low, the fibers in the apertured portion do not extend further, and other apertured portions can be generated. As a result, the open pore density is increased, and it becomes possible to obtain one having a smaller pore diameter with the same draw ratio, that is, porosity.

The technique of the present invention is not limited to the tube in the above example, but can be applied to a sheet-shaped porous body or a rod-shaped porous body having a high degree of freedom in molding by biaxial stretching or the like. is there. Further, in addition to this example, for example, the irradiation of only the surface of the extrusion-molded product after irradiation is performed by using an electron beam having a low accelerating voltage that affects only the surface layer, rather than a highly permeable radiation such as gamma rays. By doing so, it is possible to create a porous body in which the irradiation portion and the non-irradiation portion inside or on the back side have different pore sizes. It is also possible to obtain a porous body having a non-uniform porous structure in the plane direction rather than in the thickness direction described above by irradiating the extruded body with a metal net, a pattern, a mask such as pictograms, etc. It is possible and can be used for marking a PTFE porous body without using a dye. Since the technique of the present invention reduces only the elongation of PTFE and does not affect the strength, various applications are possible.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

As the PTFE fine powder, tetrafluoroethylene resin fine powder CD-123 manufactured by Asahi IC Polymer Co., Ltd. was used. Gamma rays with Co60 as the radiation source are applied to the powder at doses of 100, 300,
Irradiation was performed with five doses of 500, 1000, and 1500 Gy. 22 parts by weight of solvent naphtha was mixed with each powder, and the mixture was extruded into a tube having an inner diameter of 1.5 mm and an outer diameter of 2.7 mm. Further, naphtha was removed in a 60 ° C. drying oven to obtain a dry extruded product. These were made into Examples 1-5.
Further, a dry extruded product obtained in the same manner as the unirradiated powder was set as Comparative Example 1.

Further, the unexposed dry extruded product of Comparative Example 1 was irradiated with gamma rays having Co60 as a radiation source at doses of 300 and 5, respectively.
Irradiation with a dose of 00 Gy was set as Examples 6 and 7. A tensile test was conducted on the above Examples 1 to 7 and Comparative Example 1 at a tensile temperature of 200 ° C., a tensile speed of 100 mm / min, and a chuck gap of 2.5 cm. The results are shown in Table 1.

In Examples 1 to 7, reduction in elongation at break was observed in comparison with Comparative Example 1 depending on the irradiation amount of gamma rays. Regarding the yield point strength, since the extrusion resistance of the powder is lowered by irradiation and the fluidity is increased, the extrusion pressure is lowered when the powder is extruded into the same shape with the same number of parts of the auxiliary agent. The yield strength depends on the amount of connections formed between the powder particles, and thus on the shear stress forming the connections, that is, the extrusion pressure. On the contrary, in Examples 6 and 7 in which irradiation is performed after extrusion, there is not much reduction.

Further, the melting point peaks of Examples 1 to 7 and Comparative Example 1 were observed with a differential scanning calorimeter. In Comparative Example 1, one peak at 347 ° C. was observed, whereas in Example 1, it was observed that the peak at 335 ° C. gradually increased as the irradiation amount increased. 335 ° C peak and 34
The peak height at 7 ° C. was reversed between Examples 1 and 2, 34
Absorption at around 7 ° C. remained slightly in Example 4, but was hardly seen in Example 5.

Dry extrudates were obtained in the same manner as in Examples 1 to 5 except that the amount of the auxiliary agent was 16.5 parts and the gamma ray irradiation amount was 500 Gy. This was drawn in a furnace with a furnace length of 1 m and a furnace temperature of 550 ° C. at a draw ratio of 75% and a winding wire speed of 5.5 m / min.
Firing was performed in the same heating furnace at a furnace temperature of 600 ° C. and a winding wire speed of 5 m / min. This stretched porous tube was designated as Example 8.

Example 9 was obtained in the same manner as in Example 8 except that the dry extruded product of Example 6 was used and the stretching ratio was 100%. Further, Comparative Example 2 was prepared in the same manner as in Example 8 except that the dry extruded product obtained in the same manner as in Comparative Example 1 was used except that the number of assistants was 21. Further, Comparative Example 3 was prepared in the same manner as in Example 6 except that the dry extruded product of Comparative Example 1 was used.

Table 2 and FIG. 1 show the manufacturing conditions of Examples 8 and 9 and Comparative Examples 2 and 3 and the characteristics of their porosity.

In Example 8 and Comparative Example 2, the number of auxiliary agents was adjusted to match the extrusion pressure, and in Example 9 and Comparative Example 3, the same dry extruded product was used. It can be seen from FIG. 1 that the examples have characteristics that the porosity is substantially the same as the corresponding comparative examples and the pore size is small.

It is considered that this is because the dry extruded products used in the examples have their stretchability limited by irradiation with radiation, and the stretchability is close to the limit at which they can be stretched. Table 1
With reference to, the unirradiated product can be stretched by nearly 800%. In the case of 75 to 100% stretching as in Comparative Examples 2 and 3, it was not possible to generate all the holes. On the other hand, in Examples, the stretching of 75 to 100% was close to the limit of the stretchable range, and numerous small holes were opened.

In each of Examples 8 and 9 and Comparative Examples 2 and 3 described above, as a result of analysis by a differential scanning calorimeter, the melting point peak was in the range of 327 to 329 ° C., and the latent heat of fusion was 25 J / g or less. It was considered that the difference between the example and the comparative example was not due to the difference in the degree of baking.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

Industrial Applicability As described above, according to the method of the present invention, it is possible to control the stretchability of PTFE fine powder, and by selecting an appropriate radiation dose, even if the same permeability is obtained, It is possible to obtain a fluororesin porous body having high filtration performance. Further, its performance can be known in advance by analysis of a melting peak by a differential scanning calorimeter, and industrially well-controlled production becomes possible. The use of these invention products is not particularly limited, but they can be preferably used for separation membrane applications and the like.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between bubble point and porosity in Examples 8 and 9 of the present invention and Comparative Examples 2 and 3.

FIG. 2 is a diagram showing a change in melting point peak due to radiation irradiation on a differential scanning calorimeter chart of PTFE fine powder.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B29K 27:18 B29K 27:18 105: 04 105: 04 B29L 31:14 B29L 31:14 C08L 27: 18 C08L 27:18 (72) Inventor Akihiro Oshima 2710-1, Shinmachi, Tano-gun, Gunma Heights Persimmon No. 202 (72) Inventor Shigetoshi Ikeda 210 Gunma Prefecture Fujioka Tateshinarita 210 Pure Heights 101 F term (reference) 4D006 GA02 GA32 GA41 MB10 MB11 MB15 MC30X NA34 NA54 PB09 4F074 AA39 BB25 CA01 CC12Z CC48 DA43 DA53 DA59 4F207 AA17 AC04 AG20 AH03 KA01 KA11 KE30 KW26 KW33 4F210 AA17 AC04 AG20 AH03 QA10 QC01 QD10 QG04

Claims (4)

[Claims] 1. A method for producing a fluororesin porous body which comprises extruding tetrafluoroethylene resin fine powder into a desired shape and then stretching it, wherein the tetrafluoroethylene resin fine powder or its extruded product is: A method for producing a fluororesin porous body, which comprises irradiating with radiation before stretching. 2. A tetrafluoroethylene resin fine powder after irradiation with radiation, or an extrusion-molded product of the powder has a heat absorption curve in a differential scanning calorimeter analysis that appears due to the radiation peak and the 347 ° C. absorption peak that the powder originally has. The method for producing a fluororesin porous material according to claim 1, which has both absorption peaks near 335 ° C. 3. A tetrafluoroethylene resin fine powder irradiated with radiation or an extrusion molded article using the same, wherein the heat absorption curve in differential scanning calorimeter analysis is
34 originally possessed by tetrafluoroethylene resin fine powder
7 ° C absorption peak and 335 ° C appearing by irradiation
A tetrafluoride ethylene resin fine powder characterized by having both absorption peaks in the vicinity, or an extrusion molded product thereof. 4. An extruded product using a tetrafluoroethylene resin fine powder irradiated with radiation, or an extruded product using a tetrafluoroethylene resin fine powder irradiated with radiation is stretched. A fluororesin porous material characterized by being obtained.