JPS647856B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a porous tetrafluoroethylene resin tube, and in particular, a porous polyethylene resin tube characterized in that the fiber structure of the tube has a different composite structure on the outer surface and inner surface. The present invention relates to a tetrafluoroethylene resin tube and a method for manufacturing the same.

Regarding the manufacturing method of porous tetrafluoroethylene resin tubes, please refer to Japanese Patent Publication No. 13560/1973 and Japanese Patent Application Laid-open No. 1973-13560.
7284 etc. are publicly known. These methods are as follows: An unsintered tetrafluoroethylene resin mixture containing a liquid lubricant is formed into a sheet, rod, tube, etc. by extrusion rolling or a method including both, and then at least Approximately when stretched in one direction
It is characterized by heating to over 327℃. Although the porous structures obtained by these methods vary somewhat depending on the stretching ratio, temperature and speed during stretching, they have a micron composite structure consisting of nodules interconnected by small fibers. However, the spaces surrounded by these fibers and nodules correspond to porous pores. Generally, by increasing the degree of stretching, the length of the fibers is increased, the size of the nodules is decreased, and the percent porosity is increased.

As a result, it is known that porous structures such as sheets, rods and tubes can be obtained using these known methods.

The present invention relates to improvements in these methods, and in particular, the fiber structure including the thickness and length of the fibers of the tube-like porous structure, the direction thereof, and the shape of the nodules connected to the fibers is The present invention provides a porous tetrafluoroethylene resin tube having different high-order composite structures on its outer and inner surfaces.

Furthermore, the present invention involves heating the tube so that at least the outer surface of the tube is at a temperature of 327° C. or higher and the inner surface of the tube is lower than the outer surface of the tube when the tube is formed into a tube shape and then stretched in the length direction of the tube. Therefore, the present invention relates to a method for manufacturing a porous tetrafluoroethylene resin tube, which is characterized in that the fiber structure of the tube-like porous structure has a different composite structure on the outer surface and the inner surface. This is achieved by sintering while supplying cooling air to the inner cavity of the tube when heated above 327°C, which is the melting point of ethylene resin.

Therefore, the purpose of the present invention is to provide applications in which it is preferable that the outer and inner surfaces of the tube have different fibrous structures, specifically, artificial blood vessels, artificial tracheas, artificial esophagus,
For substitute prostheses such as artificial bile ducts, or for industrial purposes, it is a material that reduces excessive resistance and prevents clogging when gases, liquids, etc. permeate the porous tube wall, and also for seals. Our goal is to provide economical products for gasket packing, etc.

The requirements for artificial devices made of plastic are (1) not to be denatured by biological tissue fluids, (2) to be chemically inert, (3) to be non-inflammatory and free from foreign body reactions.
It is known that (4) it is not carcinogenic, (5) it does not swell within tissues, and (6) its mechanical properties such as tensile strength do not change over time. It satisfies all the conditions and is one of the most promising plastics. However, since molding and processing are quite difficult, it has not been possible to fully demonstrate its functions in the past.

For industrial applications, reverse osmosis membranes, excess membranes, etc. have recently been developed. The ultra-thin surface layer of these membranes has microscopic pores,
The support layer that maintains mechanical strength has a composite structure consisting of large pores, and not only planar shapes but also tube-like shapes are known. However, the material of this membrane is cellulose or polyamide, and no such structure is known for tetrafluoroethylene resin. Further, as a tube-shaped gasket, it is necessary that the outer surface is hard and the inner cavity surface is flexible and has good compressibility.

In the present invention, unsintered tetrafluoroethylene resin powder is uniformly mixed with a liquid lubricant, pre-compression molded, and then molded into a tube shape using a ram extruder. Then, after removing the liquid lubricant by evaporation or extraction, the tube is stretched in at least one direction, or in the case of a long or narrow direction, the length of the tube. Up to this step, the process is the same or similar to the above-mentioned known method, but the temperature in the next step is 327°C.
The heating to the above temperature is different from known methods and is the most important aspect of the present invention.

When heating a stretched tube, it is not impossible to supply heat only from inside the tube, but it is economical to heat it from outside the tube. At this time, by supplying heat from the outside while cooling the inside of the tube by flowing air, it becomes possible to change the porous fibrous structure of the inner surface and outer surface of the tube.

Porous fibrous tissues have a microstructure consisting of small fibers and nodules interconnected with the fibers. In the present invention, for example, the fiber diameter is small on the inner surface of the tube, and the outer surface has a high-order microstructure that is at least twice as thick as the inner surface of the tube. The first target is a structure whose outer surface remains almost unchanged. Although the size of the nodule and the fiber length vary depending on the drawing conditions, the fiber diameter does not change significantly as long as the fiber is drawn in one direction. On the other hand, it is known that the fiber diameter decreases rapidly when stretched in two or more directions, but even in such a porous fiber structure, the tube according to the present invention has different fiber thicknesses on the inner surface and outer surface. It is characterized by having a cross-sectional structure consisting of fiber length and nodular shape.

Furthermore, in the second structure to which the present invention is directed, the length and diameter of the fibers are the same between the inner and outer surfaces of the tube, but the shape of the nodule is an elongated spheroid on the outer surface of the tube. On the other hand, on the surface of the lumen, the spheroid is cut short in the longitudinal direction, and the long axis of the spheroid becomes extremely short, resulting in a shape close to that of a sphere. This second structure is characterized in that the long axis of the nodular shape forming the spheroid is small on the inner surface of the tube, and has a length at least twice as long as the inner surface on the outer surface.

The third structure of the present invention is directed to a structure in which not only the fiber length but also the nodule shape differs between the inner and outer surfaces of the tube. At this time, the fiber length is short on the inner surface of the tube, and on the outer surface it is at least 1.5 times longer than the inner surface, and the nodule shape is a spheroid whose long axis is somewhat shortened on the outer surface. On the other hand, the inner cavity surface has a substantially flat shape and at the same time does not have a structure as a rotating body.

The fiber structures in these three structures are not independent from each other, and the tube inner surface fiber structure of the first target structure matches the tube outer surface structure of the second target structure.

Further, the tube inner surface fibrous structure of the second target structure matches the tube outer surface structure of the third target structure.

The effect of a structure with different fiber diameters on the tube outer surface and inner lumen surface will be explained in detail. Among artificial organs, tubular organ prostheses, specifically blood vessels, trachea, esophagus,
When a bile duct is transplanted into a living body, the pore size must be so small that blood, body fluids, or bile will not leak from the duct wall. However, during the patient's recovery process, the canal wall must be quite large in order to be wrapped in connective tissue around the outer periphery of the implanted prosthesis, and then replaced by fibrous tissue that invades from the outer periphery to firmly communicate with the intima that forms on the inner canal wall. It must have a pore size.

The pore diameter necessary for this fibrous tissue to penetrate is at least 2 μm or more, and if it becomes smaller than that, the organization will not progress and will stagnate. Unless the canal wall of the prosthesis becomes organized, the intima cannot continue to grow on the lumen surface of the canal wall.
For this reason, the outer surface of the tube wall is often 5μ or more, and in most cases, woven and knitted fabrics such as polyethylene mesh, nylon mesh, and Dacron mesh have been tried, but the results are still not satisfactory. is not obtained.

Under these circumstances, as an organ prosthesis, the outer surface has a pore diameter of, for example, 10μ, and the inner surface has a pore diameter of, for example, 10μ.
The superiority of the composite structure with a pore size of 3μ can be understood.

In industrial applications, it is required to have functions such as separation and concentration division of different components, as well as the ability to process large quantities at the same time. The smaller the pore size distribution, the clearer the separation and division, but in order to increase the throughput in a given time, it is necessary to increase the number of pores or make the tube wall thickness as thin as possible. . It is extremely difficult to significantly increase the number of holes within the framework of specific manufacturing conditions, and a rapid decrease in thickness also impairs mechanical strength, which has the disadvantage that it cannot be a practical means. Even in this field, a composite pore structure in which the pore diameters of the inner and outer surfaces are different can claim its superiority.

Another characteristic is the relationship between flexibility and tear resistance.

The flexibility of a porous tube increases in proportion to its porosity, while its tear resistance decreases in inverse proportion. A decrease in tear strength will limit its usable range.

It is not impossible to improve only the tear strength by reducing the porosity or increasing the thickness of the tube wall. However, this approach greatly reduces flexibility. It is a major objective of the present invention to improve tear strength without reducing flexibility, and it has been found that this can be achieved by varying the fiber structure of the inner and outer surfaces of the tube.

In particular, in order to improve the tear strength, the direction in which the small fibers forming the tube wall of the tetrafluoroethylene resin tube are arranged is important. Since the direction in which the fibrils are arranged coincides with the stretching direction of the tube, if the tube is stretched only in its length direction, the direction of the fibrils also coincides with that direction.

If the tube is expanded only in the radial direction, the direction in which the fibrils are arranged also coincides with that direction. Therefore, the purpose of increasing the tear strength can also be achieved by expanding the tube in the radial direction as much as possible. However, when a mixture of tetrafluoroethylene resin powder and liquid lubricant is molded into a tube shape using an extruder, shearing force is generated at the contact surface with the mold, and the tetrafluoroethylene resin becomes fibrous in the tube extrusion direction. Arrange in.

This fibrous arrangement progresses sufficiently in the length direction of the tube and has considerable strength, but almost no fibrous arrangement progresses in the radial direction of the tube, so the strength is lower than that in the length direction. then 1/3
I only have ~1/5 of it. As a result, although it is not impossible to obtain a porous tube by expanding only in the radial direction of the tube, one must be prepared for the occurrence of a considerable number of defective products that may be cracked.

In the present invention, the tube is first stretched at a constant rate in the length direction of the tube to create small fibers in the length direction of the tube, and then expanded in the radial direction to generate small fibers in the radial direction of the tube, thereby improving flexibility. A porous tube with excellent tear strength is obtained.
Of course, the same structure can be obtained by expanding in the radial direction first and then stretching in the length direction, but a product with more stable quality can be obtained by stretching in the length direction first.

Radial expansion can be achieved continuously by creating a vacuum around the tube.

It is natural that the number, length, thickness, etc. of fibrils produced in the longitudinal and radial directions change depending on the degree of stretching/expansion in that direction, and the desired porosity, pore diameter, etc.
It can be appropriately selected depending on the values of flexibility and tear resistance. When the rates of stretching and expansion are balanced, the direction of the fibrils is uniformly distributed radially around the spherical nodule. Nevertheless, the orientation of the fibers will be different on the inner and outer surfaces of the tube.

When one of the stretching and expansion is larger than the other, the fibrils in the larger direction are longer and more numerous, but conversely the fibrils in the right direction are shorter and fewer in number.

Observation using an electron microscope shows that the size of nodules and the thickness of fibers treated in two directions (stretching and expansion) are significantly different compared to those treated in one direction only by stretching or expansion. Can be confirmed. In particular, it can be seen that the fiber direction is more strongly distributed radially on the inner surface than on the outer surface.

The size of the nodule gradually decreases depending on the rate of stretching, but when it is stretched in only one direction, it is an elongated spheroid, but when it is stretched in two directions, the size of the nodule becomes uniform. 1/3 of the direction
It often becomes smaller by 1/10 and at the same time takes a nearly spherical shape.

When the fibers are stretched in one direction, they exhibit a constant value of 0.5 to 1μ regardless of the stretching ratio, but by processing the fibers in two directions, the thickness can be reduced to 1/3 to 1/5 of that value. Therefore, there will be a correspondingly large number of fibers.

As described above, the first target structure of the present invention has extremely excellent properties in terms of flexibility and tear resistance, and is a structure completely unknown heretofore.

The second and third target structures also showed excellent flexibility, and a tube with an outer diameter of 6.0 mm and an inner diameter of 5.0 mm completely deformed into a compressed body under a load of 20 g or less, and in most cases under a load of 10 g. I end up. The sealing properties of this compressed product against gas and liquid are sufficient to withstand the use of conventional heat-resistant and chemical-resistant gaskets and packing, and it is useful as a sealing material for large-diameter flange surfaces.
Metal packing made of copper or aluminum has excellent heat resistance, but in order to achieve sealing properties, it is necessary to tighten it with a load of several kilograms or more, and this load causes plastic flow, so it may be necessary to use it several times. If the material is tight, the sealing performance will be extremely poor.

A string-shaped sealing material made of tetrafluoroethylene resin is used, but as it has not undergone any heat treatment, it must be considered a disposable product that can only be used once for sealing purposes.

Since the second and third target structures of the present invention have undergone heat treatment on the outer surface of the tube at a temperature of at least 327°C, there is little change in the structure even after they are used for sealing purposes, and even with a small tightening force. It has the characteristic that a perfect seal can be achieved.

Here, it is necessary to mention the temperatures during stretching, expansion, and sintering.

In stretching or expanding, the tube becomes at least in a different size and shape than before the treatment, and at least an external force must be applied to cause this deformation. This external force decreases as the temperature of the tube increases, and increases as the tube temperature decreases, as in general thermoplastic plastics. The external force required for this deformation is compared to the strength that the tube itself possesses due to its fibrous orientation when extruded.

The strength accumulated through extrusion molding largely depends on the conditions of extrusion molding, but it does not depend much on the temperature and atmosphere after molding.

When the temperature at which the tube undergoes deformation such as stretching or expansion is below a certain value, the external force required for deformation is greater than the strength of the tube, and as a result, more parts break during deformation. On the other hand, when the temperature exceeds a certain point, the external force for deformation becomes smaller than the strength of the tube, and the rate of breakage rapidly decreases.

Therefore, there is a lower temperature limit for deforming the tube depending on the extrusion molding conditions.

The same tendency exists for deformation rates such as stretching and expansion. As the deformation rate increases, the external force required for deformation increases, and therefore it is necessary to heat the tube to a higher temperature in order to prevent it from being damaged.

Since the retained strength of the tube changes depending on the extrusion molding conditions of the tube, the minimum temperature at which deformation occurs cannot be clearly specified, but it can be easily determined by experts in the industry.

The process of sintering means heating the stretched or stretched and expanded tube to a temperature of at least 327° C. while fixing it so that it does not shrink. At this time, the porous fiber structure of the inner surface and outer surface of the tube can be changed by externally heating the inner surface while cooling the inner surface by flowing air into the inner surface of the tube. By increasing the amount of air flowing over the tube lumen surface or lowering the temperature of the air, the outer surface of the tube can be heated above 327°C, but the lumen surface can be heated to 327°C or higher.
It can also be heated to temperatures below ℃. Although only the outer surface of such a tube is sintered, the inner surface is unsintered, and the shape and size of the fibers and nodules differ greatly between the inner and outer surfaces.

On the other hand, by reducing the amount of air flowing over the surface of the tube lumen or increasing the temperature of the air (specifically, by increasing the length of the furnace or increasing the temperature of the furnace), it is possible to It is also possible to heat the resin fibers on the outer surface to 327
As it is exposed to temperatures above ℃ for a long period of time, at least two or more fibers that have the same fiber structure as the inner surface, especially the thickness, coalesce and gradually become thicker.

By changing the amount of cooling air flowing through the inner cavity and the amount of heat supplied from the outside, the thicknesses of the inner and outer surface structures of the tube can be varied.

As mentioned above, the thickness of the fibers and the shape of the nodules vary greatly depending on the temperature of the tube. Figure 1 shows a state where the temperature of the tube undergoing stretching and expansion is below 327°C. Many small cracks 1 have occurred over the entire surface of the tube wall. A large number of fibers 2 are seen in the crack 1 parallel to the direction of stretching and expansion. Figure 1 and subsequent electron micrographs correspond to a magnification of 400x.

Nodules 3 which are not subjected to heat treatment at 327° C. or higher have a complex shape with many protrusions, as if their interfaces are partitioned by cracks 1.

Figure 2 shows the tube that has been stretched and expanded at 327°C.
This shows a state in which the tetrafluoroethylene resin has not been completely melted even though it has been heated to the above level. In this state, below 327°C, the nodule 3 has a complex shape and is considerably melted and has a rounded appearance, but the bonding surface with the fiber 2 has not yet been welded and is only in a crimped state. do not have. However, the length of the fiber 2 has grown much longer than in FIG.

Therefore, the state in which "a crack 1 has occurred" in FIG. 1 changes to the state in which "fibers 2 are interconnected by knots 3."

Figure 3 shows that nodule 3 has completely dissolved and therefore fibers 2
The adhesive portions are also welded, and the fibers 2 are arranged in an orderly manner in the direction in which they are stretched or expanded.

Although the length and thickness of the fibers are almost the same between Figures 2 and 3, there is a considerable difference in the shape of the nodule.

Figure 4 shows a state where the heat treatment was performed at 327°C or higher for an even longer period of time, and the knot 3 is almost the same as in Figure 3, but the thickness of the fiber 2 is thicker than in Figure 3, and the fiber The number of 2 is also decreasing.

The tubular porous structure that is the subject of the present invention has its outer surface and inner cavity surface in the states shown in FIGS. 2 and 1, FIG. 3 and 2, and FIG. 4 and 3, respectively. Includes all composite fiber structures.

FIG. 5 shows the same heat treatment as in FIG. 3, but because the fibers 2 have been stretched and expanded, the directions of the fibers 2 stretched between the nodules 3 are distributed radially around the nodules 3.

[Brief explanation of drawings]

1 to 5 are electron micrographs of porous tetrafluoroethylene resin tubes of the present invention. 1 is a crack, 2 is a fiber, and 3 is a nodule.

Claims (1)

[Scope of Claims] 1. A tube made of porous tetrafluoroethylene resin, wherein the porous tetrafluoroethylene resin has a microstructure consisting of nodes interconnected by fibers, and A porous tetrafluoroethylene resin tube characterized in that the fiber direction on the inner surface is distributed more radially than the fiber direction on the outer surface. 2. The long axis of the nodules on the outer surface of the porous tetrafluoroethylene resin tube is at least twice as long as the long axis of the nodules on the inner surface. Porous tetrafluoroethylene resin tube. 3. After molding an unsintered tetrafluoroethylene resin mixture containing a liquid lubricant into a tube shape, at least the outside surface of the tube is at least 327°C when stretched in the length direction of the tube, and the temperature of the tube is A method for producing a porous tetrafluoroethylene resin tube, the method comprising heating the inner surface to a lower temperature than the outer surface of the tube. 4. The porous tube according to claim 3, characterized in that when at least the outer surface of the tube is heated to 327° C. or higher while the tube is stretched in the longitudinal direction, the outside of the tube is depressurized. A method for producing polytetrafluoroethylene resin tubes. 5. The method for producing a porous tetrafluoroethylene resin tube according to claim 3, which comprises heating from the outer surface of the tube and supplying cooling air to the inner cavity of the tube.