JP2022112170A - Fluorine resin multilayer tube - Google Patents

Abstract

To provide a fluorine resin multilayer tube that achieves both of resistance to elongation in a longitudinal direction and flexibility for bending and has excellent permeation resistance and airtightness.SOLUTION: A fluorine resin multilayer tube has an inner layer that contains a polytetrafluoroethylene resin and has a solid structure, and an outer layer that is in contact with the inner layer, wherein the outer layer contains a polytetrafluoroethylene resin and has a porous structure. The inner layer has the inner thickness that is smaller than the outer thickness of the outer layer. The inner thickness is 2 μm or more and 30 μm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fluororesin multilayer tube.

Polytetrafluoroethylene (PTFE) resin tubes are used in a wide range of fields due to their excellent lubricity, chemical resistance, heat resistance, and the like. In addition, PTFE has the advantage of having a low coefficient of friction, and is often used for sliding purposes. For example, in the case of catheter treatment, a PTFE resin tube is used as the inner material of the catheter so that the therapeutic jig can be smoothly passed through the catheter.

A soft tube is preferred for a catheter passed through a blood vessel so as not to damage the blood vessel. In particular, the tip portion of the catheter is required to be very flexible. However, when a soft tube is used and a treatment instrument is passed through the tube, the tube stretches in the longitudinal direction of the product, making it difficult for the treatment instrument to pass through. The elongation stress of the PTFE tube in the longitudinal direction of the product is largely due to the stress of the PTFE. Although it is possible to increase the thickness of the PTFE to increase the stress in order to suppress the deformation, there is a problem that the thicker the PTFE, the harder it becomes. In order to solve these problems, it is possible to use porous PTFE composed of fibers called fibrils, which is soft even when the thickness of the PTFE is increased. There was a concern that it could not withstand the pressure and that air bubbles would permeate into the holes or be entrapped from the holes.

A method using expanded PTFE has been reported to increase deformation stress. For example, Patent Document 1 (Japanese Patent Publication No. 2016-528966) discloses strengthening a microcatheter by including an expanded PTFE liner. However, since the strength is improved by stretching the PTFE, the orientation of the molecules in the longitudinal direction is strengthened, making it easy to tear. Contrast media may be introduced into the body via a catheter, but there is a risk of the expanded PTFE tube tearing due to the high pressure that is applied when the contrast media flows.

Multilayer PTFE tubes have also been reported that include a solid layer and a porous layer.

For example, Patent Document 2 (Japanese Patent Application Laid-Open No. 7-1630) describes a first layer made of polytetrafluoroethylene with a solid structure and a second layer made of polytetrafluoroethylene with a porous structure laminated on the outer peripheral surface. A flexible multi-layer tube is described which consists of a first layer and a second layer which are integrated by heat sealing. Since both the first layer and the second layer, that is, the solid layer and the porous layer are formed by winding and fixing the PTFE film, a step occurs. Therefore, even if it can be applied to applications using a relatively large tube such as an endoscope, it is not suitable for catheter applications that require precision in diameter size.

Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2001-46314) describes an endoscope in which a pipeline formed of a PTFE tube having a porous structure having an inner layer and an outer layer extends inside. Patent Document 3 describes forming a porous structure by extruding an inner layer and an outer layer at the same time and then stretching and expanding only the outer layer to make it porous. However, no specific means is described, and it is unclear how only the outer layer can be stretched and foamed.

Japanese Patent Publication No. 2016-528966 JP-A-7-1630 Japanese Patent Application Laid-Open No. 2001-46314

It is an object of the present invention to provide a fluororesin multilayer tube that has both resistance to elongation in the longitudinal direction and flexibility to bending, and is excellent in permeation resistance and airtightness.

The fluororesin multilayer tube includes an inner layer containing polytetrafluoroethylene resin and having a solid structure, and an outer layer in contact with the inner layer and containing polytetrafluoroethylene resin and having a porous structure. The inner layer thickness of the inner layer is thinner than the outer layer thickness of the outer layer. The inner layer thickness is in the range of 2 μm or more and 30 μm or less.

The fluororesin multilayer tube achieves both resistance to elongation in the longitudinal direction and flexibility to bending, and is excellent in permeation resistance and airtightness.

1 is a perspective view schematically showing an example of a fluororesin multilayer tube; FIG. FIG. 3 is a cross-sectional view along the imaginary plane II-II' shown in FIG. 2; FIG. 2 is a cross-sectional view schematically showing an example of forming an inner layer of a fluororesin multilayer tube by an extrusion molding method. FIG. 4 is a cross-sectional view schematically showing an example of formation of an inner layer of a fluororesin multilayer tube by a dip coating method. Sectional drawing which shows roughly an example of extrusion molding which forms the outer layer of a fluororesin multilayer tube. FIG. 4 is a conceptual diagram for explaining a method for evaluating the flexibility of a fluororesin multilayer tube according to an example.

A fluororesin multilayer tube according to an embodiment of the invention includes an inner layer having a solid structure and an outer layer having a porous structure in contact with the inner layer. The inner layer and the outer layer each contain polytetrafluoroethylene resin. The inner layer thickness of the inner layer is thinner than the outer layer thickness of the outer layer, and is in the range of 2 μm or more and 30 μm or less.

Since the fluororesin multilayer tube has a multilayer structure including an inner layer and an outer layer, it is thicker than each single layer, and deformation in the longitudinal direction is suppressed. In addition, since the outer layer has a porous structure, the multilayer tube as a whole is thicker, but has excellent lateral bending flexibility. That is, since the multilayer tube is soft, it has a small bending radius and is less prone to kinking (bending). In addition, since the fluororesin multilayer tube has a solid structure, that is, an inner layer with a non-porous structure, there is no concern about the generation of air bubbles or permeation of the chemical solution.

An example of a fluororesin multilayer tube is shown in FIGS. 1 and 2. FIG.

FIG. 1 is a perspective view schematically showing an example of a fluororesin multilayer tube, and FIG. 2 is a cross-sectional view along the imaginary plane II-II' shown in FIG. FIG. 2 shows a cross section orthogonal to the longitudinal direction of the fluororesin multilayer tube, that is, the axial direction of the tube.

The multilayer tube 1 shown in FIGS. 1 and 2 has a circular tubular shape. The multilayer tube 1 has a two-layer structure in which an inner layer 2 and an outer layer 3 are laminated in the radial direction of the circular tube. Both the inner layer 2 and the outer layer 3 preferably have a circular cross-section.

The inner layer 2 consists of a solid PTFE tube. That is, the inner layer 2 is an inner layer tube containing PTFE. The inner layer thickness TIN of the inner layer 2 is _thinner than the outer layer thickness _TEX of the outer layer 3 . The inner layer thickness _TIN is in the range of 2 μm or more and 30 μm or less.

The outer layer 3 consists of a PTFE tube with a porous structure consisting of fibrils. That is, the outer layer 3 is an outer layer tube containing PTFE. The outer layer thickness T _EX of the outer layer 3 can be, for example, within the range of 10 μm or more and 100 μm or less. The outer layer thickness T _EX is thicker than the inner layer thickness T _IN of the inner layer 2 . Moreover, it is desirable that the outer layer thickness _TEX is more than twice the inner layer thickness _TIN and not more than 9 times the inner layer thickness TIN.

The multi-layer tube 1 can have an outer diameter D _EX of 0.5 mm or more and 3 mm or less, for example. The outer diameter D _EX of the multilayer tube 1 may correspond to the outer diameter of the outer layer 3 . The multi-layer tube 1 can have an inner diameter D _IN of, for example, 0.4 mm or more and 2.8 mm or less. The inner diameter D _IN of the multi-layer tube 1 may correspond to the inner diameter of the inner layer 2 .

Such a multilayer tube can be obtained, for example, by the manufacturing method described below. Specifically, the method for producing a multilayer tube includes obtaining a tubular first extruded product by first extrusion using a first mixture containing polytetrafluoroethylene fine powder; subjecting the article to a first firing to obtain a first tubular precursor having a solid structure; forming a second extrusion to obtain a second tubular precursor; and subjecting the second tubular precursor to a second firing to include a solid inner layer and a porous outer layer. obtaining a fluororesin multilayer tube. Another method of manufacturing a multilayer tube is to apply a polytetrafluoroethylene dispersion to the outer surface of the core wire to obtain a first coating, and to perform a first baking on the polytetrafluoroethylene coating to form a solid structure first. obtaining a tubular precursor; and forming a second coating on the outer surface of the first tubular precursor by extruding an admixture containing polytetrafluoroethylene fine powder to obtain a second tubular precursor. and subjecting the second tubular precursor to a second firing to obtain a fluororesin multilayer tube comprising an inner layer of solid structure and an outer layer of porous structure.

That is, the method for producing a multilayer tube includes extruding and baking a tubular extruded product or applying and baking a PTFE dispersion such as a dip coating method to form a thin solid PTFE tube, and the outer surface of the obtained thin tube is coating by extrusion and firing to form a porous PTFE layer.

First, a method of obtaining a solid PTFE tube, which will be the inner layer, by extrusion molding (first extrusion molding) will be described.

As the PTFE fine powder, materials commonly used for extrusion molding of PTFE molded articles can be used. A fine powder is obtained by coagulating and drying an aqueous dispersion obtained by emulsion polymerization. The fine powder can be mainly composed of, for example, aggregated primary particles produced by polymerization to have a particle size of 500 μm.

As the PTFE fine powder, a PTFE-only powder, for example, a virgin PTFE powder, which does not contain fillers or additives can be used. Such PTFE fine powder consists of PTFE. It is desirable to use virgin PTFE powder for forming the inner layer.

Alternatively, a filled PTFE fine powder including a composite material containing PTFE powder and filler may be used. As a filler, for example, imide resin powder can be mixed with PTFE powder. By forming the outer layer using a mixed powder of PTFE powder and imide resin powder, the abrasion resistance of the outer surface of the tube can be improved. In addition, by including a conductive material such as a carbon material as a filler, electrical properties can be imparted to the tube.

For example, a paste-like mixture (first mixture) can be obtained by mixing an extrusion aid such as a lubricant with the PTFE fine powder. By extruding the mixture containing the PTFE fine powder into a tubular shape (first extrusion molding), a tubular first extruded product can be obtained. For example, the first coating can be formed by extruding a blend of PTFE onto the outer surface of the core wire. By firing (first firing) the obtained first extruded product, a PTFE tube with a solid structure is obtained as the first tubular precursor.

Extrusion aids include, for example, commonly used solvent naphtha (e.g., registered trademark: Isoper E, Exxon Chemical Co., Ltd.), white oil, liquid paraffin having 6 to 12 carbon atoms (e.g., registered trademark: Cactus Normal Paraffin N -10, manufactured by Japan Energy Co., Ltd.).

The mixture obtained by mixing the PTFE fine powder and the extrusion aid may be aged before being subjected to extrusion molding. Alternatively, the aged admixture may be compressed to produce a compression molded body (billet). Compression can remove air in the PTFE fine powder and improve the uniformity of the extrudate. The shape of the compression-molded body is not particularly limited, but may be, for example, a columnar shape. The compression-molded body is put into an extruder and extruded.

At the time of extrusion molding of the first extruded product (first extrusion molding), for example, it is desirable to make the extrusion speed of the mixture containing the PTFE fine powder or the compression molded product approximately the same as the take-up speed of the core wire. By uniforming the speed, it becomes easier to keep the thickness of the first extruded product (first film) covering the core wire uniform along the longitudinal direction.

Heating may be performed during the extrusion molding. For example, extrusion molding may be performed while heating by setting the temperature of the mold (eg, die or dice) of the extruder to 40° C. or higher and 120° C. or lower. It is preferable to heat the mold to 50°C or higher and 60°C or lower.

A core wire may be used in the first extrusion molding. By carrying out extrusion molding so as to cover the outer periphery of the core wire with the mixture containing the PTFE fine powder, a tubular first extruded product, that is, the first coating can be formed on the core wire. Further, by subjecting the first extruded product (first film) on the core wire to firing (first firing) as it is, it is possible to obtain the first tubular precursor in the form of covering the core wire. Employing the core wire improves handling during and after manufacturing.

As the core wire, for example, a metal wire made of metal such as copper or aluminum, or a core material made of resin can be used. The diameter of the core wire can be appropriately changed according to the desired inner diameter of the tube.

The first extruded product, for example, the first film coated on the core wire is baked (first baked). Thus, a first tubular precursor is obtained which will be the inner layer of the fluororesin multilayer tube.

The sintering temperature in the sintering (first sintering) of the first extruded product (for example, the first coating on the core wire) is not particularly limited. It is desirable to bake at a temperature higher than the melting point of PTFE, 345° C., for example, at a temperature of 400° C. or higher.

Prior to firing, the extrudate may be dried, for example to remove extrusion aids. On the other hand, typical extrusion aids volatilize at about 200° C., so they volatilize during firing without prior removal. Therefore, drying may be omitted.

It is desirable that the first extrusion is not stretched. In order to improve permeation resistance and airtightness by making the inner layer of the multilayer tube a solid structure, it is desirable not to stretch the first extruded product, which is the precursor of the inner layer.

Next, a method of forming a solid PTFE tube, which will be the inner layer, by applying a PTFE dispersion will be described.

A PTFE dispersion includes a dispersion medium and PTFE powder in the dispersion medium. As the PTFE dispersion, it is possible to use a material that is widely used in a method of molding a resin tube by coating, such as a dip coating method. For example, PTFE dispersion is an aqueous dispersion obtained by dispersing PTFE powder in an aqueous dispersion medium by emulsion polymerization. A PTFE dispersion can be a suspension containing PTFE powder.

The dispersion medium can be, for example, water or the like. The composition of the PTFE dispersion is not particularly limited, and for example, a dispersion or suspension having a composition commonly used in techniques such as dip coating can be used.

The PTFE powder contained in the PTFE dispersion is desirably a PTFE-only powder that does not contain fillers, additives, or the like. That is, the PTFE dispersion is preferably a dispersion medium in which PTFE powder is dispersed. Preferably, the PTFE dispersion is a virgin PTFE dispersion.

The PTFE dispersion is applied to the outer surface of the core wire to obtain the first coating, ie the dispersed PTFE coating. To apply the PTFE dispersion, for example, the core wire can be immersed in the PTFE dispersion. Specifically, it is preferable to employ a dip coating method. In the dip coating method, a uniform coating thickness can be formed by passing the core wire through the PTFE dispersion and pulling it up at a constant speed.

As the core wire, the same core wire that can be used in the first extrusion molding described above can be used.

A first coating obtained by coating the PTFE dispersion on the core wire is baked (first baking). Thus, a first tubular precursor is obtained which will be the inner layer of the fluororesin multilayer tube.

After the PTFE dispersion is applied once and then baked, the outer surface of the obtained tube may be further coated with the PTFE dispersion and baked. By alternately repeating application and baking of the dispersion, the thickness of the tube can be adjusted to a desired thickness.

Alternatively, after the PTFE dispersion is applied and baked, the filler-containing dispersion containing the composite material containing the PTFE powder and the filler may be applied and baked. Electrical properties can be imparted to the tube by including, for example, a conductive material such as a carbon material as a filler. However, the dispersion applied directly to the outer surface of the core wire is preferably a PTFE dispersion containing no filler.

The firing temperature in firing the first coating on the core wire (first firing) is not particularly limited. It is desirable to bake at a temperature higher than the melting point of PTFE, 345° C., for example, at a temperature of 400° C. or higher.

Next, a method of forming a porous outer layer on a solid PTFE tube by extrusion molding to obtain a multi-layer tube will be described.

As the PTFE fine powder, the same material as the PTFE fine powder that can be used in the first extrusion molding described above can be used. The PTFE fine powder can be either virgin PTFE powder or filled PTFE fine powder.

Similar to the preparation of the mixture (first mixture) used for the first extrusion molding, for example, by mixing an extrusion aid such as a lubricant with PTFE fine powder, a paste-like mixture (second mixture) can be obtained. A second coating can be formed by extruding an admixture containing PTFE fine powder onto the outer surface of the first tubular precursor. By firing (second firing) the second tubular precursor containing the first tubular precursor and the second coating thus obtained, a PTFE tube with a multilayer structure, that is, a fluororesin multilayer tube is obtained.

That is, extrusion molding is performed using the first tubular precursor, which is the precursor of the inner layer of the multilayer tube, as the core wire, and the first tubular precursor is coated with the second coating of PTFE resin to form the second tubular shape. obtain precursors. By baking the second tubular precursor to convert the second coating into a tubular PTFE layer, a fluororesin multilayer tube in which a tubular inner layer and a tubular outer layer are overlapped can be obtained.

The first tubular precursor as a core wire used for extrusion molding of the second coating (second extrusion molding) may be a solid PTFE tube obtained by the first extrusion molding described above, or may be the PTFE dispersion described above. It may be a solid PTFE tube obtained by a method of applying a liquid.

Similar to the admixture used for the first extrusion (first admixture), the admixture (second admixture) used for extrusion of the second coating (second extrusion) is aged prior to extrusion. Alternatively, a compression molded body (billet) may be produced.

During the extrusion molding of the second coating (second extrusion molding), for example, the first tubular precursor as the core wire is drawn at a speed higher than the extrusion speed of the mixture containing the PTFE fine powder or the compression molding. By setting the take-up speed higher than the extrusion speed, it is possible to obtain a second coating having a porous structure, and thus an outer layer having a porous structure. Since the take-up speed of the first tubular precursor is faster, the PTFE resin adhering to its surface is stretched in the longitudinal direction, so that the second coating is not dense and a porous layer is formed.

Heating may be performed during the extrusion molding. For example, extrusion molding may be performed while heating by setting the temperature of the mold (eg, die or dice) of the extruder to 40° C. or higher and 120° C. or lower. It is preferable to heat the mold to 50°C or higher and 60°C or lower.

The firing temperature in firing the second tubular precursor (second firing) is not particularly limited. It is desirable to bake at a temperature higher than the melting point of PTFE, 345° C., for example, at a temperature of 400° C. or higher.

Prior to firing, the aid may be removed by drying. As mentioned above, typical extrusion aids volatilize at around 200° C., so they volatilize during firing without prior removal. Therefore, drying may be omitted.

A specific example of a method for manufacturing a fluororesin tube will be described with reference to the drawings. FIG. 3 is a cross-sectional view schematically showing an example of a method of forming a first tubular precursor, which will be the inner layer of the fluororesin multilayer tube, by an extrusion molding method. That is, FIG. 3 shows an example of the first extrusion molding. FIG. 4 is a cross-sectional view schematically showing an example of a method of forming a first tubular precursor, which will be the inner layer of the fluororesin multilayer tube, by a dip coating method. FIG. 5 is a cross-sectional view schematically showing an example of a method of manufacturing a fluororesin tube by forming a second tubular precursor, which will be the outer layer of the fluororesin multilayer tube, by extrusion molding. The example shown in FIG. 5 can be an example of a second extrusion.

First, referring to FIG. 3, a method of forming a precursor of the inner layer by extrusion molding, that is, an example of the first extrusion molding will be described.

An extrusion die 51 provided in an extruder 50 is filled with a mixture 20 containing PTFE fine powder. The admixture 20 is a mixture of PTFE fine powder and other materials such as extrusion aids. The admixture 20 can be, for example, a paste containing PTFE fine powder. Alternatively, the admixture 20 may be a compression molded body (billet) containing PTFE fine powder.

The core wire 40 unwound from the supply roll 90 is supplied inside the extrusion die 51 . The core wire 40 passes through the inside of the extrusion die 51 and is pulled out from the ejection port 52 of the extrusion die 51 to the outside.

When the extrusion ram 53 is moved toward the discharge port 52 , the mixture 20 is compressed and adheres to the outer surface of the core wire 40 and is extruded from the discharge port 52 together with the core wire 40 as the first coating 21 . Here, it is desirable to synchronize the movement of the extrusion ram 53 and the take-up of the core wire 40 so that the speed at which the first coating 21 is extruded from the discharge port 52 is approximately the same as the take-up speed of the core wire 40 . Thus, the outer circumference of the core wire 40 is covered with the tubular first coating 21 (first extruded product).

The first coating 21 on the core wire 40 is supplied to the drying furnace 61 and dried there (first drying). Subsequently, the first coating 21 is supplied to the heating furnace 62 and subjected to the first firing there. By the first firing, the first tubular precursor 22 having a solid structure in which the core wire 40 is covered is obtained.

The first tubular precursor 22 on the core wire 40 is supplied to the winding roll 93 via the cooling device 63 . The means of cooling by the cooling device 63 is not particularly limited, and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of the guide rollers 92 may be set so that the distance from the heating furnace 62 to the take-up roll 93 is long, thereby gaining heat radiation time. Also, the arrangement and number of guide rollers 92 are not limited to those illustrated. The first tubular precursor 22 is wound around the winding roll 93 while including the core wire 40 .

It is desirable to apply tension to the core wire 40 and its coating by tension pulleys 91 and guide rollers 92 arranged before and after the extruder 50 to prevent slack. The number and positions of the tension pulleys 91 are not limited to the illustrated example, and may be increased or decreased. Also, the tension pulley 91 may be omitted.

Next, with reference to FIG. 4, an example of a method of forming the inner layer precursor by dip coating will be described.

The core wire 40 is unwound from the supply roll 90 and supplied to the dispersion liquid 23 in the bath 70 . Dispersion 23 is a PTFE dispersion. The core wire 40 is pulled up after being immersed in the dispersion liquid 23 . The dispersion liquid 23 is applied to the outer surface of the core wire 40 via the dip coating to obtain the first coating 21 .

The core wire 40 and the first coating 21 covering the outer periphery thereof are supplied to a drying furnace 61 and dried there (first drying). Subsequently, the core wire 40 and the first coating 21 are supplied to the heating furnace 62 and subjected to the first firing there. By the first firing, the first tubular precursor 22 having a solid structure in which the core wire 40 is covered is obtained.

The first tubular precursor 22 on the core wire 40 is supplied to the winding roll 93 via the cooling device 63 . The means of cooling by the cooling device 63 is not particularly limited, and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of the guide rollers 92 may be set so that the distance from the heating furnace 62 to the take-up roll 93 is long, thereby gaining heat radiation time. Also, the arrangement and number of guide rollers 92 are not limited to those illustrated.

Further, before the first tubular precursor 22 is fed to the take-up roll 93 , it may be re-fed sequentially through the bath 70 , the drying oven 61 , the heating oven 62 and optionally the cooling device 63 . The re-feeding of the first tubular precursor 22 to the bath 70, the drying oven 61, the heating oven 62 and optionally the cooling device 63 may be repeated multiple times depending on the desired inner layer 2 thickness.

It is desirable to apply tension to the core wire 40 and its coating by tension pulleys 91 and guide rollers 92 arranged in front of and behind the tub 70 to prevent slack. The number and positions of the tension pulleys 91 are not limited to the illustrated example, and may be increased or decreased. Also, the tension pulley 91 may be omitted. The first tubular precursor 22 is wound around the winding roll 93 while including the core wire 40 .

Next, an example of a method of forming an outer layer by extrusion molding will be described with reference to FIG. The example shown in FIG. 5 can be a second extrusion.

An extrusion die 51 provided in an extruder 50 is filled with a mixture 30 containing PTFE fine powder. The admixture 30 is a mixture of PTFE fine powder and other materials such as extrusion aids. The admixture 30 can be, for example, a paste containing PTFE fine powder. Alternatively, the mixture 30 may be a compression molding (billet) containing PTFE fine powder.

The first tubular precursor 22 sent out from the supply roll 90 is supplied to the inside of the extrusion die 51 . The first tubular precursor 22 covers the outer periphery of the core wire 40 , and the first tubular precursor 22 is supplied together with the core wire 40 . The first tubular precursor 22 on the core wire 40 passes through the inside of the extrusion die 51 and is pulled out from the ejection port 52 of the extrusion die 51 .

The first tubular precursor 22 can be obtained by the first extrusion molding illustrated in FIG. Alternatively, the first tubular precursor 22 can be obtained by the dip coating method illustrated in FIG.

As the extrusion ram 53 is moved toward the discharge port 52 , the admixture 30 is compressed and adheres to the outer surface of the first tubular precursor, and the first tubular precursor 22 and the core wire 40 form the second coating 31 . are extruded from the discharge port 52 together. The first tubular precursor 22 and the core wire 40 are taken up at a speed faster than the speed at which the second coating 31 is extruded from the discharge port 52 . In this way, the outer circumference of the first tubular precursor 22 is covered with the tubular second film 31, and the second tubular precursor 10 is obtained.

The second tubular precursor 10 is supplied to the drying furnace 61 and dried there (second drying). Subsequently, the second coating 31 is supplied to the heating furnace 62 and subjected to a second firing there. Through the second firing, a multilayer tube 1 having a two-layer structure including an inner layer 2 that is a solid layer and an outer layer 3 that is a porous layer is obtained. Note that the inner layer 2 corresponds to the first tubular precursor 22 that is reheated by the second firing.

The multilayer tube 1 on the core wire 40 is supplied to the winding roll 93 via the cooling device 63 . The means of cooling by the cooling device 63 is not particularly limited, and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of the guide rollers 92 may be set so that the distance from the heating furnace 62 to the take-up roll 93 is long, thereby gaining heat radiation time. Also, the arrangement and number of guide rollers 92 are not limited to those illustrated. The multilayer tube 1 is wound around the winding roll 93 while including the core wire 40 .

It is desirable to apply tension to the core wire 40 and its coating by tension pulleys 91 and guide rollers 92 arranged before and after the extruder 50 to prevent slack. The number and positions of the tension pulleys 91 are not limited to the illustrated example, and may be increased or decreased. Also, the tension pulley 91 may be omitted.

By removing the core wire 40 at the time of use, the multilayer tube 1 having a hollow structure can be used. For example, when manufacturing a catheter, the core wire 40 is removed and the multilayer tube 1 is used as a member of the catheter.

The above example is an example of manufacturing such a fluororesin multilayer tube, but the manufacturing method is not limited to the above example. For example, after performing the first baking, the core wire 40 and the first tubular precursor 22 are directly supplied to the extruder 50 without being wound on the winding roll 93, and the core wire 40 is supplied to the multilayer tube 1. Completion and winding may be performed continuously.

As described below, it can be confirmed that a fluororesin multilayer tube including an inner layer and an outer layer is obtained. A section is exposed by cutting the tube at a cutting plane that intersects the main axis of the fluororesin multilayer tube. The obtained cross section is observed with an optical microscope. A visual difference can be seen between the inner layer of solid structure and the outer layer of porous structure. In that case, the inner layer and the outer layer can be distinguished by cross-sectional observation. Also, the dimensions of each of the inner and outer layers can be measured in cross section.

The resin material forming each portion of the fluororesin multilayer tube can be confirmed as follows. It is possible to confirm that the resin material is PTFE by measuring the melting point using a differential scanning calorimeter (DSC).

[Example]
(Example 1)
A PTFE resin tube was manufactured by a method similar to the manufacturing method described with reference to FIGS. That is, the inner layer was formed by the first extrusion molding, and the outer layer was formed by the second extrusion molding to manufacture the PTFE multilayer tube. Details are as follows.

As the PTFE fine powder for extrusion molding of the inner layer, Teflon (registered trademark) PTFE fine powder 641-J manufactured by Mitsui Chemours Fluoro Products Co., Ltd. was used. As the PTFE fine powder for extrusion molding of the outer layer, PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. was used.

An inner layer tube (first tubular precursor) was obtained by the following procedure. After adding 21 parts by mass of naphtha (extrusion aid) to 100 parts by mass of PTFE fine powder (641-J) for the inner layer, the mixture was mixed at room temperature using a Turbula mixer to prepare a mixture. Subsequently, the obtained mixture was formed into a cylindrical shape by a preforming machine. The obtained preform was put into an extruder equipped with a die having a thickness of 20 μm and a guide tube. Next, a silver-plated copper wire with an outer diameter of φ0.49 (mm) as a core wire was placed in the paste extruder so as to pass through the cylindrical hollow portion of the preform and the guide tube. Extrusion molding (first extrusion molding) is performed while pulling the core wire synchronously with the extrusion, and the obtained first extruded product is first dried at 180 ° C. to 200 ° C. and first dried at 380 ° C. to 400 ° C. subjected to firing. The solid-structured polytetrafluoroethylene resin tube (first tubular precursor) thus obtained was cooled and wound up on a roll.

By the following procedure, an outer layer having a porous structure was formed on the outer surface of the inner layer tube to obtain a PTFE tube having a two-layer structure.

After adding 21 parts by mass of naphtha (extrusion aid) to 100 parts by mass of PTFE fine powder (F201) for the outer layer, they were mixed at room temperature using a Turbula mixer to prepare a mixture. Subsequently, the obtained mixture was formed into a cylindrical shape by a preforming machine. The obtained preform was put into an extruder equipped with a die and a guide tube having a size of 100 μm in thickness of two layers of PTFE. Then, the inner layer tube on the copper wire obtained as described above as the core wire was placed in the paste extruder so as to pass through the cylindrical hollow portion of the preform and the guide tube. Extrusion molding (second extrusion molding) is performed while pulling the core wire at a speed higher than the extrusion speed, and the resulting extruded product (second tubular precursor) is subjected to second drying at 180 ° C. to 200 ° C. and 380 ° C. C. to 400.degree. C. for a second calcination. The obtained two-layered polytetrafluoroethylene resin tube was cooled and wound up on a roll.

(Example 2)
A polytetrafluoroethylene resin tube having a two-layer structure was produced in the same manner as in Example 1, except for the following changes. The PTFE fine powder for the inner layer was changed to PTFE fine powder Polyflon (registered trademark) F208 manufactured by Daikin Industries, Ltd. The die used for the first extrusion molding was changed to a die having a thickness of 30 µm.

(Comparative example 1)
A polytetrafluoroethylene resin tube having a two-layer structure was produced in the same manner as in Example 1, except for the following changes. The PTFE fine powder for the inner layer was changed to PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. The die used for the first extrusion molding was changed to a die having a thickness of 50 µm.

(Comparative example 2)
Only one extrusion was performed to form a solid monolayer tube, as described below.

A solid PTFE tube was manufactured by the same procedure as the first extrusion molding in Example 1, except for the following changes. The PTFE fine powder was changed to PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. The die used for the extrusion molding (corresponding to the first extrusion molding) was changed to a size with a wall thickness of 100 μm.

No outer layer was formed on the resulting PTFE tube. A monolayer tube having a solid structure was thus obtained.

(Comparative Example 3)
As described below, only one extrusion process was employed to form a single-layer tube with a porous structure.

A PTFE tube with a porous structure was manufactured by the same procedure as the second extrusion molding in Example 1, except for the following changes. The PTFE fine powder was changed to PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. As a core wire, instead of an inner layer tube, a silver-plated copper wire with an outer diameter of 0.49 (mm) was used alone.

A monolayer tube with a wall thickness of 100 μm with a porous structure was thus obtained.

<Evaluation>
(Confirmation of tube wall thickness)
The dimensions of each tube manufactured in Example 1-2 and Comparative Example 1-3 were measured by the method described above, and the wall thicknesses of the inner layer and the outer layer were determined. The measurement results are shown in Table 1 below.

(Measurement of 10% strain stress)
The strength against elongation for each tube was evaluated as follows.

Each tube section of a certain length cut out from each tube obtained in Example 1-2 and Comparative Example 1-3 was fixed at both ends in the longitudinal direction with a chuck of a universal testing machine, and a tensile test was performed. rice field. The tensile strength was gradually increased and the stress at which the strain of the tube increased the length by 10% was recorded as the 10% strain stress.

(Evaluation of tube flexibility)
Flexibility for each tube was evaluated as follows.

One end and the other end of each tube were held and held vertically so that the longitudinal direction of the tube was parallel to the direction of gravity. Gradually lower the part held on the upper side, and the line connecting the hanging upper end part and the upper holding position was held vertically with the upper holding position as the intersection. The length of the bent tube was measured when the angle formed with the rest of the tube from the upper holding position to the lower holding position was 90 degrees.

A state in which the tube is bent by its own weight and the angle is 90 degrees will be described with reference to FIG. Although the multi-layer tube 1 is shown as an example in FIG. 6, single-layer tubes such as the tubes obtained in Comparative Examples 2 and 3 can also be evaluated in the same manner.

The multi-layer tube 1 shown in FIG. 6 is held vertically at two points, one end and the middle of the tube. The other end of the tube hangs down. The portion of the tube held vertically is supported vertically with the lower end positioned at a lower holding position 11 and the portion held in the middle of the tube at an upper holding position 12. not bent. An imaginary line connecting the upper holding position 12 and the upper end 13 corresponding to the end of the hanging portion (the other end) is indicated by a dashed line 14 . The portion held vertically between the upper holding position 12 and the lower holding position 11 and the dashed line 14 intersect at the upper holding position 12, and the angle θ between them is 90 degrees. In this state, the length along the multilayer tube 1 from the upper end 13 to the upper holding position 12 was measured. The larger the value of this length, the stronger the force supporting its own weight and the more rigid it is. In other words, the smaller the value of this length, the softer it is.

The measurement results for each tube are summarized in Table 1 below. Specifically, Table 1 shows the thickness of the inner layer having a solid structure (inner layer thickness), the thickness of the outer layer having a porous structure (outer layer thickness), and the outermost diameter of the tube (outer diameter D _EX ), the 10% strain stress, and the length to bend to the 90 degree position under its own weight. In Comparative Examples 2 and 3, although single-layer tubes were manufactured, they are referred to as "inner layer" or "outer layer" for convenience, depending on whether the corresponding single layer had a solid structure or a porous structure.

As shown in Table 1, for both the tubes of Example 1-2 and Comparative Example 1-3, which have a total thickness of 100 μm including the inner layer and the outer layer, regardless of the ratio and presence or absence of solid structure and porous structure, The strain stress for longitudinal elongation was comparable. On the other hand, in Example 1-2 and Comparative Example 3, a more flexible tube was obtained as compared with Comparative Example 1-2. As described above, in Example 1-2 and Comparative Example 3, it was possible to obtain a soft tube while maintaining the difficulty of elongation. However, since the tube of Comparative Example 3 had a single-layer porous structure, it was unsuitable for applications to avoid permeation and applications requiring airtightness.

According to the embodiments described above, a fluororesin multilayer tube including an inner layer containing polytetrafluoroethylene resin and an outer layer containing polytetrafluoroethylene resin is provided. The inner layer has a solid structure. The outer layer is in contact with the inner layer and has a porous structure. The inner layer thickness of the inner layer is thinner than the outer layer thickness of the outer layer. The inner layer thickness is in the range of 2 μm or more and 30 μm or less. The fluororesin multilayer tube has both resistance to elongation in the longitudinal direction and flexibility to bending, and is excellent in permeation resistance and airtightness.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the scope of the invention. Further, each embodiment may be implemented in combination as appropriate, in which case the combined effect can be obtained. Furthermore, various inventions are included in the above embodiments, and various inventions can be extracted by combinations selected from a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiments, if the problem can be solved and effects can be obtained, the configuration with the constituent elements deleted can be extracted as an invention.

REFERENCE SIGNS LIST 1 multi-layer tube 2 inner layer 3 outer layer 10 second tubular precursor 11 lower holding position 12 upper holding position 13 upper end 20 mixture 21 second 1 Coating 22 First Tubular Precursor 23 Dispersion Liquid 30 Mixture 31 Second Coating 40 Core Wire 50 Extruder 51 Extrusion Mold 52 Discharge Port 53 Extrusion ram 61 Drying furnace 62 Heating furnace 63 Cooling device 70 Bathtub 90 Supply roll 91 Tension pulley 92 Guide roller 93 Winding roll.

Claims (4)

an inner layer containing a polytetrafluoroethylene resin and having a solid structure;
An outer layer that is in contact with the inner layer and contains a polytetrafluoroethylene resin and has a porous structure, wherein the inner layer thickness of the inner layer is thinner than the outer layer thickness of the outer layer, and the inner layer thickness is in the range of 2 μm or more and 30 μm or less. There is a fluororesin multilayer tube. 2. The fluororesin multilayer tube according to claim 1, wherein said outer layer thickness is in the range of 10 [mu]m to 100 [mu]m. 3. The fluororesin multilayer tube according to claim 1, wherein the thickness of the outer layer is more than twice the thickness of the inner layer and less than or equal to 9 times the thickness of the inner layer. The fluororesin multilayer tube according to any one of claims 1 to 3, having an outer diameter of 0.5 mm or more and 3 mm or less.

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