JP3286984B2 - Polytetrafluoroethylene porous body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an expanded polytetrafluoroethylene porous material and a method for producing the same.

[0002]

2. Description of the Related Art Polytetrafluoroethylene (hereinafter referred to as P)
The porous body is excellent in heat resistance of PTFE,
Utilizing features such as chemical resistance, electrical insulation, non-adhesion, lubricity, and flame retardancy, it is used in various fields. Above all, the PTFE porous body produced by the drawing method has a fine fibrous structure composed of very thin fibers and nodules connected to each other by the fibers, and by utilizing this porous structure, It is used in a wide range of fields such as filtration materials such as membrane filters, diaphragms, electric insulating materials, and artificial organ materials.

[0003] The expanded PTFE porous body can be freely set in its pore size by changing the stretching conditions such as the stretching ratio, so that it can be used for a wide range of applications requiring various pore sizes. However, as the fiber length is increased by increasing the draw ratio, the strength is reduced, and particularly, the strength in the direction perpendicular to the drawing direction is significantly reduced, so that it becomes impossible to finally maintain a structure having practical strength. Therefore, in the prior art, there was a limit in mechanically increasing the length of the PTFE porous body into a long fiber, and the limit of the length was very short.

[0004] That is, in the expanded porous PTFE, since the fine fibrous structure of the PTFE formed by the stretching is strongly oriented in the stretching direction, the tensile strength is strong in the stretching direction, but in a direction perpendicular to the stretching direction. Is weak and easily tears in the stretching direction. For this reason, the draw ratio of the porous PTFE body is improved,
When the fibers are lengthened, the strength is remarkably reduced, and particularly, the strength in the direction perpendicular to the drawing direction is remarkably reduced, and the structure cannot be maintained.

As a method for solving such a problem,
(1) a method of increasing the thickness of a porous PTFE body to improve strength, (2) a method of reinforcing with a reinforcing material such as a mesh,
And so on. However, the method (1) not only increases the volume, but also impairs the basic performance of a membrane filter, for example, because the permeation flow rate of the filtrate decreases. The method (2) has a problem that the reinforcing material is peeled off and the manufacturing process becomes complicated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a stretched PTF having a long structure and excellent strength characteristics.
An object of the present invention is to provide an E porous body. It is another object of the present invention to provide a method for easily producing an integrated porous PTFE body having a long fiber and excellent strength properties.

The inventor of the present invention has conducted intensive studies to overcome the problems of the prior art, and as a result, both sides of the front and back surfaces of the expanded porous PTFE body were heated at a temperature of 327 ° C. or higher, which is a sintering temperature. By heating one surface at a higher temperature in a specific range than the other surface to give a temperature gradient between the front and back surfaces of the porous body, the fiber-knot structure in the fine fibrous structure is The fiber is substantially composed of two parts, a long part of the fiber and a short part of the fiber, from the front to the back of the fiber. It has been found that a porous PTFE body which is continuous in a mesh shape in the thickness direction can be obtained.

[0008] The PTFE porous body produced by this method is
There are short portions of fibers that are three-dimensionally continuous in a network, with portions of fibers longer than those according to the prior art. The long fiber portion has a fiber length necessary to fulfill the function as a porous body, and the short fiber portion plays a role in maintaining the strength as a structure. Thereby, it becomes a expanded PTFE porous body which has a function as an expanded PTFE porous body of a long fiber, and is excellent in strength characteristics. The present invention has been completed based on these findings.

[0009]

Thus SUMMARY OF THE INVENTION According to the present invention, the polytetrafluoroethylene porous body having a fine fibrous structure consisting of nodules which are connected to each other by the fibers and the fibers, (1) fibers - A long fiber portion having an average fiber length of 60 to 1000 μm from the surface of the porous body to the back surface of the nodule structure
And two substantially short fiber portions having an average fiber length of 20 μm or less , and (2) the fiber-knot structure of the short fiber portion is a fiber of a porous body.
Orientation direction, direction perpendicular to fiber orientation direction, and porous
A polytetrafluoroethylene porous body characterized by being present in a network structure in three directions in the thickness direction of the body.

Further, according to the present invention, the polytetrafluoroethylene blends unsintered containing liquid lubricant is formed into a desired shape, a porous body obtained by stretching a molded product in at least one direction , In a fixed state so that it does not shrink,
The front and both sides of the rear surface of its heating at 3 27 ° C. or higher,
At this time, one surface is set at 50 ° C. to 30 ° C.
By heating in the range of high temperatures of up to 0 ° C., the production method of the polytetrafluoroethylene porous body according to claim sintering to Rukoto is provided giving the temperature gradient between the front and back sides of the porous body .

Hereinafter, the present invention will be described in detail. The PTFE porous body targeted by the present invention is basically a
Manufactured by the method described in No. 13560,
The shape can be selected arbitrarily, such as a sheet, a tube, and a rod.

In the method for producing a porous PTFE body of the present invention, first, a liquid lubricant is mixed with the unsintered PTFE powder, and the mixture is extruded, rolled, and formed into a desired shape. With or without removing the liquid lubricant from the obtained molded body,
When stretched in at least one axial direction, a porous PTFE body having a fine fibrous structure composed of fibers and nodes connected to each other by the fibers is formed. The PTFE porous body usually has both a front surface and a rear surface (or an inner surface and an outer surface) such as a tube or a sheet. When the porous body is heated to 327 ° C. or more and fixed to prevent shrinkage, and the stretched structure is sintered, a PTFE porous body having improved strength can be obtained. It is characterized in that

That is, in a state where the porous body is fixed so as not to shrink, both the front surface and the back surface (or the inner surface and the outer surface) are heated at a temperature of 327 ° C. or more of the sintering temperature. Is heated at a temperature higher than the other surface by 50 ° C. to 300 ° C., preferably 100 ° C. to 250 ° C., to provide a temperature gradient between the front surface and the back surface of the porous body. As a result, rearrangement of the fiber-knot structure occurs from the front surface to the back surface of the porous body, and a portion which is further stretched to have a longer fiber than before the treatment and a portion which has a shorter fiber than before the treatment are obtained. In addition, a PTFE porous body having a structure in which the short fiber portion is continuous in a mesh shape in three directions of a stretching direction, a direction perpendicular to the stretching direction, and a thickness direction of the structure is obtained.

When the porous PTFE body is tubular, the heating temperature of the outer surface is preferably higher than the heating temperature of the inner surface.
It is desirable to control the temperature to 500 ° C. or lower so that PTFE is not decomposed.

As a method for heating both surfaces of the PTFE porous body to 327 ° C. or more and providing a temperature difference between the both sides, for example, in the case of a sheet-like PTFE porous body, the porous PTFE body is not shrunk. 327 ° C on each side
As described above, there are a method of blowing hot air having different temperatures or a method of contacting with heating belts having different temperatures. In the case of a tubular PTFE porous body, a stainless steel rod is inserted into the inner cavity, the inner surface is heated by the stainless steel rod, and hot air is blown on the outer surface, thereby heating the inner surface and causing a temperature difference. Can be provided.

The heating time depends on the heating temperature, but is usually
It is about 10 to 200 seconds. In addition, when the both surfaces of the PTFE porous body are not heated at a temperature of 327 ° C. or more, or when the temperature difference is not controlled within a range of 50 to 300 ° C., the specific fiber-knot structure cannot be formed. .

FIG. 1 is a schematic view of the microstructure on the inner surface of the tubular porous PTFE body of the present invention. FIG. 2 is a schematic diagram of a microstructure of a cross section in a stretching direction of the tubular PTFE porous body of the present invention. All of these figures show PTF
It was created based on the result of observing a micrograph of the E porous body. In each figure, 1 indicates a long fiber portion, 2 indicates a short fiber portion, and 3 indicates a nodule. The longitudinal direction of the fiber indicates the direction of uniaxial stretching.

By the way, in Japanese Patent Publication No. 58-1656,
A method for producing a PTFE porous body having excellent strength characteristics in a direction perpendicular to the stretching direction is disclosed. In the invention described in the publication, a part of the PTFE porous body, for example, P
By heating the outside of the TFE porous body tube,
The fibers that connect between the nodes are cut, and some nodes are gathered together, and the heating surface eventually forms a network-like uneven structure having a pore diameter of several tens of μm to several mm, and as a result, a fine fibrous This is to provide a PTFE porous body having a part where the orientation of the tissue is strong in one direction and a part which is strong in a direction perpendicular to the direction.

However, in the method described in the publication,
In order to heat a part of the expanded PTFE porous body, one surface of the porous body is heated to 327 ° C. or higher, while the other surface is lower than 327 ° C., so that the PTFE porous body as in the present invention is used. The rearrangement of the fiber-knot structure from the front surface to the back surface does not occur, and furthermore, it is divided into a long fiber portion and a short fiber portion, and the short fiber portion extends in the stretching direction, the direction perpendicular to the stretching direction and the structure. An expanded PTFE porous body having a structure that is continuous in a network in three directions in the thickness direction cannot be obtained.

In the expanded porous PTFE material according to the present invention, the average fiber length of the long fiber portion is 60 to 1000 μm.
It can be optionally formed in a range of, the good Mashiku 1
It is at least 00 μm, more preferably at least 150 μm.
On the other hand, the average fiber length of the short fiber portion is 20 μm or less. Section, consisting of the short fibers has a high density of the nodule is excellent in strength properties, further, by short fiber sections takes three directions of the mesh structure, the strength of the porous body is increased I do. Therefore, it is an expanded porous PTFE having a large pore diameter and a high porosity, and can maintain the mechanical properties as a structure.

Therefore, according to the manufacturing method of the present invention,
A large pore diameter having a fiber length of substantially up to 1000 μm,
Moreover, it is possible to provide an expanded porous PTFE body having excellent strength characteristics.

[0022]

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

[0023]

Comparative Example 1 PTFE powder (Polyflon F
-104) To 100 parts by weight, 27 parts by weight of a liquid lubricant was added and mixed, and after pressurized preforming, extruded into a tube having an inner diameter of 3 mm and an outer diameter of 4 mm using an extruder. After drying and removing the liquid lubricant from the tube, the tube was heated to 400 ° C. and uniaxially stretched at a stretching ratio of 1000%. The entire tube was sintered by heating it to about 390 ° C. in a stretched state. Table 1 shows the measurement results of the physical properties.

Comparative Example 2 PTFE powder (Polyflon F
-104) To 100 parts by weight, 27 parts by weight of a liquid lubricant was added and mixed, and after pressurized preforming, extruded into a tube having an inner diameter of 3 mm and an outer diameter of 4 mm using an extruder. After drying and removing the liquid lubricant from the tube, the tube was heated to 400 ° C. and uniaxially stretched at a stretching ratio of 1000%. A stainless steel rod having an outer diameter of 3 mm was inserted into the lumen of the stretched tube, and the outer surface side was heated at 680 ° C. and the inner surface side at 280 ° C. for 70 seconds. Table 1 shows the measurement results of the physical properties.

[0026]

[Table 1]

The method for measuring physical properties is as follows. <Average fiber length> The average value of the internodal distance measured with a scanning electron microscope. <Bubble point> After the expanded PTFE tube is impregnated with isopropyl alcohol, the inside of the tube wall is filled with isopropyl alcohol, and when the air pressure is gradually applied from the inside of the tube, the pressure at which bubbles come out for the first time is reduced. Measure. <Water leak pressure> When the water pressure is gradually applied from the inside of the expanded PTFE tube, the water pressure when water first comes out from the tube wall is measured. <Circumferential tensile strength> The strength at which a tube is cut open in the circumferential direction and breaks when pulled at a tensile speed of 100 mm / min. <Tear strength> 0.2 mm at 3 mm from the tube end
The load that causes tearing when pulled through a mmφ wire.

Example 1 To 100 parts by weight of PTFE powder (Polyflon F-104), 27 parts of a liquid lubricant was added and mixed. After preforming under pressure, a sheet having a thickness of 0.5 mm was formed by rolling. did. After drying and removing the liquid lubricant from the sheet, the sheet was uniaxially stretched at a stretching ratio of 1000%, and then sintered at 390 ° C. in a stretched state.

[0029] One surface of the stretched sheet was heated at 650 ° C.
The other surface was heat-treated at 450 ° C. for 60 seconds. The average fiber length of the obtained expanded PTFE sheet is 1 in the long fiber portion.
It was 80 μm, and the average was 15 μm in the short fiber part.

The stretched sheet was looped through a stainless steel rod of 0.4 mm diameter at a position 5 mm from one end of one end of the stretched sheet, and the load at which tearing occurred when the sheet was stretched at a rate of 50 mm / min in the stretching direction and the direction perpendicular thereto was measured. However, the weight was 180 g in the stretching direction and 160 g in the vertical direction.

Comparative Example 3 PTFE powder (Polyflon F
-104) To 100 parts by weight, add and mix 27 parts of a liquid lubricant, press-form preform, and then roll 0.5 m
m thick sheet. After the liquid lubricant was removed from the sheet by drying, it was uniaxially stretched at a stretching ratio of 1000%. Approximately 39 with this sheet fixed so as not to shrink
Sintering was performed by heating to 0 ° C.

The average fiber length of the expanded PTFE sheet is 1
It was 50 μm. When the tear strength of this sheet was evaluated in the same manner as in Example 2, the stretching direction was 195 g,
The vertical direction was 100 g or less.

[0033]

The strength of the porous PTFE body of the present invention is increased by the short fiber portion even if the length of the fiber in the fiber-knot structure is too long to maintain the strength of the conventional expanded PTFE porous body. Since it is maintained, it can be put to practical use. Moreover, since the fiber-knot structure including these long fibers and short fibers is integrally formed,
There is no problem as in the case where a reinforcing material is used. Therefore, the porous PTFE of the present invention is particularly suitable for the conventional expanded PTFE.
It can be used as a porous body having a large pore size that could not be used in E and requiring chemical resistance and heat resistance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram created based on a scanning electron micrograph of the inner surface of a tubular porous PTFE body of the present invention.

FIG. 2 is a schematic diagram created based on a scanning electron micrograph of a cross section in the stretching direction of the tubular PTFE porous body of the present invention.

[Explanation of symbols]

 1 long part of fiber 2 short part of fiber 3 nodule

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) C08J 9/00-9/42 B01D 71/36 B29C 55/04-55/08

Claims (2)

(57) [Claims] 1. A polytetrafluoroethylene porous body having a fine fibrous structure composed of fibers and nodules connected to each other by the fibers, wherein (1) a fiber-knot structure is formed from the front surface to the back surface of the porous body. Until , the long fiber portion of average fiber length 60-1000μm
And two substantially short fiber portions having an average fiber length of 20 μm or less , and (2) the fiber-knot structure of the short fiber portion is a fiber of a porous body.
Orientation direction, direction perpendicular to fiber orientation direction, and porous
A porous polytetrafluoroethylene, which is present in a network structure in three directions in the thickness direction of the body. Wherein the polytetrafluoroethylene blends unsintered containing liquid lubricant is formed into a desired shape, a porous body obtained by stretching a molded product in at least one direction, Osamu
While it fixed so as not to shrink, its surface and the rear surface on both sides
Was heated at 3 27 ° C. or higher, this time, by heating the one surface at a high temperature of ranging 300 ° C. from 50 ° C. than the other surface, the temperature gradient between the front and back sides of the porous body method for producing a polytetrafluoroethylene porous body, wherein a sintered to isosamples given.